1
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Bruijning M, Metcalf CJE, Visser MD. Closing the gap in the Janzen-Connell hypothesis: What determines pathogen diversity? Ecol Lett 2024; 27:e14316. [PMID: 37787147 DOI: 10.1111/ele.14316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Revised: 09/11/2023] [Accepted: 09/17/2023] [Indexed: 10/04/2023]
Abstract
The high tree diversity in tropical forests has long been a puzzle to ecologists. In the 1970s, Janzen and Connell proposed that tree species (hosts) coexist due to the stabilizing actions of specialized enemies. This Janzen-Connell hypothesis was subsequently supported by theoretical studies. Yet, such studies have taken the presence of specialized pathogens for granted, overlooking that pathogen coexistence also requires an explanation. Moreover, stable ecological coexistence does not necessarily imply evolutionary stability. What are the conditions that allow Janzen-Connell effects to evolve? We link theory from community ecology, evolutionary biology and epidemiology to tackle this question, structuring our approach around five theoretical frameworks. Phenomenological Lotka-Volterra competition models provide the most basic framework, which can be restructured to include (single- or multi-)pathogen dynamics. This ecological foundation can be extended to include pathogen evolution. Hosts, of course, may also evolve, and we introduce a coevolutionary model, showing that host-pathogen coevolution can lead to highly diverse systems. Our work unpacks the assumptions underpinning Janzen-Connell and places theoretical bounds on pathogen and host ecology and evolution. The five theoretical frameworks taken together provide a stronger theoretical basis for Janzen-Connell, delivering a wider lens that can yield important insights into the maintenance of diversity in these increasingly threatened systems.
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Affiliation(s)
- Marjolein Bruijning
- Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
| | - C Jessica E Metcalf
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
| | - Marco D Visser
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
- Institute of Environmental Sciences, Leiden University, Leiden, The Netherlands
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2
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Ramage BS, Johnson DJ, Chan DM. Effects of drought, disturbance, and biotic neighborhood on experimental tree seedling performance. Ecol Evol 2023; 13:e10413. [PMID: 37593754 PMCID: PMC10427772 DOI: 10.1002/ece3.10413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 07/24/2023] [Accepted: 07/26/2023] [Indexed: 08/19/2023] Open
Abstract
Forest biodiversity is likely maintained by a complex suite of interacting drivers that vary in importance across both space and time. Contributing factors include disturbance, interannual variation in abiotic variables, and biotic neighborhood effects. To probe ongoing uncertainties and potential interactions, we investigated tree seedling performance in a temperate mid-Atlantic forest ecosystem. We planted seedlings of five native tree species in mapped study plots, half of which were subjected to disturbance, and then monitored seedling survival, height growth, and foliar condition. The final year of data collection encompassed a drought, enabling comparison between intervals varying in water availability. Seedling performance was analyzed as a function of canopy cover and biotic neighborhood (conspecific and heterospecific abundance), including interactions, with separate generalized linear mixed models fit for each interval. All species exhibited: (a) pronounced declines in height growth during the drought year, (b) detrimental effects of adult conspecifics, and (c) beneficial effects of canopy openness. However, despite these consistencies, there was considerable variation across species in terms of the relevant predictors for each response variable in each interval. Our results suggest that drought may strengthen or reveal conspecific inhibition in some instances while weakening it or obscuring it in others, and that some forms of conspecific inhibition may manifest only under particular canopy conditions (although given the inconsistency of our findings, we are not convinced that conspecific inhibition is critical for diversity maintenance in our study system). Overall, our work reveals a complex forest ecosystem that appears simultaneously and interactively governed by biotic neighborhood structure (e.g., conspecific and/or heterospecific abundance), local habitat conditions (e.g., canopy cover), and interannual variability (e.g., drought).
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Affiliation(s)
| | - Daniel J. Johnson
- School of Forest, Fisheries, & Geomatics sciencesUniversity of FloridaGainesvilleFloridaUSA
| | - David M. Chan
- Department of Mathematics and Applied MathematicsVirginia Commonwealth UniversityRichmondVirginiaUSA
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3
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Chen Y, McConkey KR, Fan P. Sympatric primate seed dispersers and predators jointly contribute to plant diversity in a subtropical forest. Oecologia 2023; 202:715-727. [PMID: 37553533 DOI: 10.1007/s00442-023-05430-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2023] [Accepted: 07/27/2023] [Indexed: 08/10/2023]
Abstract
Mutualistic and antagonistic plant-animal interactions differentially contribute to the maintenance of species diversity in ecological communities. Although both seed dispersal and predation by fruit-eating animals are recognized as important drivers of plant population dynamics, the mechanisms underlying how seed dispersers and predators jointly affect plant diversity remain largely unexplored. Based on mediating roles of seed size and species abundance, we investigated the effects of seed dispersal and predation by two sympatric primates (Nomascus concolor and Trachypithecus crepusculus) on local plant recruitment in a subtropical forest of China. Over a 26 month period, we confirmed that these primates were functionally distinct: gibbons were legitimate seed dispersers who dispersed seeds of 44 plant species, while langurs were primarily seed predators who destroyed seeds of 48 plant species. Gibbons dispersed medium-seeded species more effectively than small- and large-seeded species, and dispersed more seeds of rare species than common and dominant species. Langurs showed a similar predation rate across different sizes of seeds, but destroyed a large number of seeds from common species. Due to gut passage effects, gibbons significantly shortened the duration of seed germination for 58% of the dispersed species; however, for 54% of species, seed germination rates were reduced significantly. Our study underlined the contrasting contributions of two primate species to local plant recruitment processes. By dispersing rare species and destroying the seeds of common species, both primates might jointly maintain plant species diversity. To maintain healthy ecosystems, the conservation of mammals that play critical functional roles needs to receive further attention.
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Affiliation(s)
- Yuan Chen
- School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China
- School of Tropical Agriculture and Forestry, Hainan University, Haikou, 570228, China
| | - Kim R McConkey
- School of Environmental and Geographical Sciences, University of Nottingham Malaysia, 43500, Semenyih, Selangor, Malaysia
| | - Pengfei Fan
- School of Life Sciences, Sun Yat-Sen University, Guangzhou, 510275, China.
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4
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Lebrija-Trejos E, Hernández A, Wright SJ. Effects of moisture and density-dependent interactions on tropical tree diversity. Nature 2023; 615:100-104. [PMID: 36792827 DOI: 10.1038/s41586-023-05717-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Accepted: 01/08/2023] [Indexed: 02/17/2023]
Abstract
Tropical tree diversity increases with rainfall1,2. Direct physiological effects of moisture availability and indirect effects mediated by biotic interactions are hypothesized to contribute to this pantropical increase in diversity with rainfall2-6. Previous studies have demonstrated direct physiological effects of variation in moisture availability on tree survival and diversity5,7-10, but the indirect effects of variation in moisture availability on diversity mediated by biotic interactions have not been shown11. Here we evaluate the relationships between interannual variation in moisture availability, the strength of density-dependent interactions, and seedling diversity in central Panama. Diversity increased with soil moisture over the first year of life across 20 annual cohorts. These first-year changes in diversity persisted for at least 15 years. Differential survival of moisture-sensitive species did not contribute to the observed changes in diversity. Rather, negative density-dependent interactions among conspecifics were stronger and increased diversity in wetter years. This suggests that moisture availability enhances diversity indirectly through moisture-sensitive, density-dependent conspecific interactions. Pathogens and phytophagous insects mediate interactions among seedlings in tropical forests12-18, and many of these plant enemies are themselves moisture-sensitive19-27. Changes in moisture availability caused by climate change and habitat degradation may alter these interactions and tropical tree diversity.
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Affiliation(s)
- Edwin Lebrija-Trejos
- Department of Biology and Environment, University of Haifa-Oranim, Kiryat Tiv'on, Israel.
| | | | - S Joseph Wright
- Smithsonian Tropical Research Institute, Balboa Ancón, Panama
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5
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Idbella M, Abd‐ElGawad AM, Mazzoleni S, Bonanomi G. Microclimate, soil chemistry, and microbiota fail to explain
Euphorbia dendroides
Janzen‐Connell
pattern in a shrubland. Ecosphere 2022. [DOI: 10.1002/ecs2.4296] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Affiliation(s)
- Mohamed Idbella
- Department of Agricultural Sciences University of Naples Federico II Naples Italy
- Laboratory of Biosciences, Faculty of Sciences and Techniques Hassan II University Casablanca Morocco
| | - Ahmed M. Abd‐ElGawad
- Department of Botany, Faculty of Sciences Mansoura University Mansoura Egypt
- Plant Production Department, College of Food and Agriculture Sciences King Saud University Riyadh Saudi Arabia
| | - Stefano Mazzoleni
- Department of Agricultural Sciences University of Naples Federico II Naples Italy
- Task Force on Microbiome Studies University of Naples Federico II Naples Italy
| | - Giuliano Bonanomi
- Department of Agricultural Sciences University of Naples Federico II Naples Italy
- Task Force on Microbiome Studies University of Naples Federico II Naples Italy
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Holík J, Janík D. Seed and seedling predation by vertebrates mediates the effects of adult trees in two temperate tree species. Oecologia 2022; 199:625-636. [PMID: 35661249 DOI: 10.1007/s00442-022-05203-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Accepted: 05/24/2022] [Indexed: 11/25/2022]
Abstract
Specialised natural enemies can locally suppress seeds and seedlings near conspecific adults more than far from them. Whilst this is thought to facilitate species coexistence, the relative contribution of multiple enemies to whether heterospecific seeds and seedlings rather than conspecifics perform better beneath a particular adult species remains less clear, especially in regions with spatially extensive monodominant stands. We designed a field exclusion experiment to separate the effects of fungi, insects and vertebrates on the seedling establishment and early survival of two temperate tree species, Fagus sylvatica and Picea abies, in the adult tree monocultures of these species. Our experiment demonstrates the key role of vertebrates in mediating the effects of adult trees on seeds and seedlings. Due to vertebrates and partly insects, Fagus sylvatica seedlings survived worse beneath conspecific than heterospecific adults and were also outperformed by Picea abies seedlings beneath their own adults. Picea abies seedling establishment was higher beneath conspecific than heterospecific adults, but Fagus sylvatica seedlings outperformed them beneath their own adults. The impact of enemies on Picea abies establishment beneath conspecific adults was less clear. Fungi did not influence seedling establishment and survival. Our findings highlight the need to compare enemy impacts on each seedling species beneath conspecific and heterospecific adults with their impacts on conspecific and heterospecific seedlings beneath a particular adult species. Such evaluations can shed more light on the role of enemies in tree communities by identifying the plant-enemy interactions that facilitate species coexistence and those that promote species monodominance.
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Affiliation(s)
- Jan Holík
- Department of Forest Ecology, The Silva Tarouca Research Institute for Landscape and Ornamental Gardening, Lidická 25/27, 602 00, Brno, Czech Republic.
- Department of Silviculture, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemědělská 3, 613 00, Brno, Czech Republic.
| | - David Janík
- Department of Forest Ecology, The Silva Tarouca Research Institute for Landscape and Ornamental Gardening, Lidická 25/27, 602 00, Brno, Czech Republic
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7
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He Y, Liu H, Yang Q, Cao Y, Yin H, Zhou Z, Yu Q, Wang X. Neighborhood Effects on Tree Mortality Depend on Life Stage of Neighbors. FRONTIERS IN PLANT SCIENCE 2022; 13:838046. [PMID: 35273630 PMCID: PMC8902350 DOI: 10.3389/fpls.2022.838046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 01/31/2022] [Indexed: 06/14/2023]
Abstract
Neighborhood effects are a crucial ecological processes that allow species to coexist in a forest. Conspecific and heterospecific neighbors, as major group classifications, affect tree mortality through various mechanisms associated with neighbor life stages. However, the influence of neighbor life stages on neighborhood effects and by what mechanisms remains a knowledge gap. Here we censused the mortality of 82,202 trees belonging to 30 species in a 20-ha subtropical forest and classified their neighbors into the following life stages: earlier, same and later. Next, we implemented generalized linear mixed models to estimate the effect of neighbors at different life stages on tree mortality. Our results showed that conspecific later stage neighbors had a positive effect on tree mortality overall, while conspecific earlier stage neighbors had a negative effect on tree mortality. Furthermore, these opposing effects appear to offset each other so that the overall effect of conspecific neighbors on tree mortality is weakened. In contrast, heterospecific neighbors had a decreasing effect on tree mortality overall. These effects are consistent with those of later stage heterospecific neighbors. Our findings demonstrate that neighbors strongly impact tree mortality, and their specific effects are closely related to neighbor life stages. Further, any single effect from one neighbor life stage may disturb or dominate the total effects of the neighbors. Therefore, the neighbors must be divided into different life stages to best explain the neighborhood effect on forest dynamics.
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Affiliation(s)
| | - Heming Liu
- Zhejiang Tiantong Forest Ecosystem National Observation and Research Station, School of Ecological and Environmental Sciences, East China Normal University, Shanghai, China
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8
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Song X, Corlett RT. Do natural enemies mediate conspecific negative distance‐ and density‐dependence of trees? A meta‐analysis of exclusion experiments. OIKOS 2021. [DOI: 10.1111/oik.08509] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Xiaoyang Song
- CAS Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences Mengla China
- Center of Conservation Biology, Core Botanical Gardens, Chinese Academy of Sciences Mengla China
| | - Richard T. Corlett
- Center of Conservation Biology, Core Botanical Gardens, Chinese Academy of Sciences Mengla China
- Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences Mengla China
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9
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Jevon F, Lang A, Ayres M, Matthes JH. Limited evidence that larger acorns buffer Quercus rubra seedlings from density-dependent biotic stressors. AMERICAN JOURNAL OF BOTANY 2021; 108:1861-1872. [PMID: 34596895 DOI: 10.1002/ajb2.1740] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 05/21/2021] [Accepted: 05/24/2021] [Indexed: 06/13/2023]
Abstract
PREMISE Plant performance and functional traits vary considerably within species, particularly in response to environmental variation. Plant responses may reflect life-history trade-offs, such as between resource acquisition and resource conservation. Larger seeds may buffer young plants from the negative effects of environmental variation, such as limitations in nutrients or water. However, whether seed size plays a similar role in how plants respond to variation in their biotic environment, including competition and soil microbial communities, remains poorly understood. METHODS We used a greenhouse experiment to test the interactive effects of intraspecific competition, the origin of the soil microbial community, and seed size on performance and functional traits in Quercus rubra L. seedlings. RESULTS Intraspecific variation in seedling traits weakly aligned with a resource acquisition-conservation trade-off. Across the wide range of initial acorn mass, competition decreased seedling biomass by about 35%. Competition directly decreased the root mass ratio and indirectly increased specific leaf area and specific root length, via the negative effects on total biomass. In contrast, soil microbial communities had minor effects on seedlings, and we found no differences between plants receiving soil originating from a conspecific adult and plants receiving soil originating from a heterospecific adult. CONCLUSIONS Competition is a more important driver of intraspecific variation in young Quercus rubra seedling performance and traits, both directly and by delaying ontogenetic development, than soil microbial communities. Seed size is an important predictor of seedling biomass, but a larger seed does not necessarily buffer seedlings from the effects of competition.
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Affiliation(s)
- Fiona Jevon
- Department of Biological Sciences, Dartmouth College, Hanover, NH, 03755, USA
| | - Ashley Lang
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
| | - Matthew Ayres
- Department of Biological Sciences, Dartmouth College, Hanover, NH, 03755, USA
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10
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Domínguez-Begines J, Ávila JM, García LV, Gómez-Aparicio L. Disentangling the role of oomycete soil pathogens as drivers of plant-soil feedbacks. Ecology 2021; 102:e03430. [PMID: 34105778 DOI: 10.1002/ecy.3430] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Accepted: 03/16/2021] [Indexed: 02/03/2023]
Abstract
Interactions among plant species and their soil biota drive plant-soil feedbacks (PSFs) that play a major role in the dynamics and diversity of plant communities. Among the different components of the soil community, pathogens are considered to be the main drivers of negative PSFs. Despite this, the number of studies that have experimentally quantified the contribution of soil pathogens to PSFs remains considerably low. Here we conducted a greenhouse experiment with oomycete-specific fungicide to quantify the contribution of soil pathogens, and particularly oomycete pathogens, to individual and pairwise PSFs in forest communities. We used as a case study Mediterranean mixed forests dominated by Quercus suber and invaded by the oomycete pathogen Phytophthora cinnamomi. The fungicide treatment was crossed with a competition treatment to explore how conspecific neighbors might modify pathogen effects. To place the results of the experiment in a wider context, we also conducted a systematic review of published papers that explicitly used fungicide to explore the role of pathogens in PSF experiments. Our experimental results showed that oomycete pathogens were the main drivers of individual PSFs in the study forests. Oomycete effects varied among tree species according to their susceptibility to P. cinnamomi, driving negative PSFs in the highly susceptible Q. suber but not in the coexistent Olea europaea. Oomycete-driven PSFs were not modified by intraspecific competition. Oomycete pathogens were also major contributors to negative pairwise PSFs assumed to promote species coexistence. Results from the systematic review supported the novelty of our experimental results, since only three studies had previously used oomycete-specific fungicide in a PSF context and none in systems invaded by exotic oomycetes. Overall, our results provide novel evidence of oomycete pathogens (including the exotic P. cinnamomi) as fundamental drivers of negative individual and pairwise PSFs with implications for species coexistence in invaded communities. Although in the short-term invasive pathogens might contribute to species coexistence by causing self-limitation in dominant species, strong inter-specific variation in self-limitation might undermine coexistence in the long-term. Because of the increasing number of exotic oomycetes worldwide, further attention should be given to oomycetes as drivers of PSFs in plant communities.
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Affiliation(s)
- Jara Domínguez-Begines
- Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes, 10, Sevilla, 41012, Spain
| | - José M Ávila
- Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes, 10, Sevilla, 41012, Spain
| | - Luis V García
- Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes, 10, Sevilla, 41012, Spain
| | - Lorena Gómez-Aparicio
- Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes, 10, Sevilla, 41012, Spain
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11
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Luskin MS, Johnson DJ, Ickes K, Yao TL, Davies SJ. Wildlife disturbances as a source of conspecific negative density-dependent mortality in tropical trees. Proc Biol Sci 2021; 288:20210001. [PMID: 33653133 DOI: 10.1098/rspb.2021.0001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Large vertebrates are rarely considered important drivers of conspecific negative density-dependent mortality (CNDD) in plants because they are generalist consumers. However, disturbances like trampling and nesting also cause plant mortality, and their impact on plant diversity depends on the spatial overlap between wildlife habitat preferences and plant species composition. We studied the impact of native wildlife on a hyperdiverse tree community in Malaysia. Pigs (Sus scrofa) are abnormally abundant at the site due to food subsidies in nearby farmland and they construct birthing nests using hundreds of tree saplings. We tagged 34 950 tree saplings in a 25 ha plot during an initial census and assessed the source mortality by recovering tree tags from pig nests (n = 1672 pig-induced deaths). At the stand scale, pigs nested in flat dry habitats, and at the local neighbourhood scale, they nested within clumps of saplings, both of which are intuitive for safe and efficient nest building. At the stand scale, flat dry habitats contained higher sapling densities and higher proportions of common species, so pig nesting increased the weighted average species evenness across habitats. At the neighbourhood scale, pig-induced sapling mortality was associated with higher heterospecific and especially conspecific sapling densities. Tree species have clumped distributions due to dispersal limitation and habitat filtering, so pig disturbances in sapling clumps indirectly caused CNDD. As a result, Pielou species evenness in 400 m2 quadrats increased 105% more in areas with pig-induced deaths than areas without disturbances. Wildlife induced CNDD and this supported tree species evenness, but they also drove a 62% decline in sapling densities from 1996 to 2010, which is unsustainable. We suspect pig nesting is an important feature shaping tree composition throughout the region.
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Affiliation(s)
- Matthew Scott Luskin
- School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia.,Forest Global Earth Observatory, Smithsonian Tropical Research Institute, Washington, DC, USA.,Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
| | - Daniel J Johnson
- School of Forest Resources and Conservation, University of Florida, Gainesville, FL, USA
| | - Kalan Ickes
- Department of Biological Sciences, Clemson University, Clemson, SC, USA
| | - Tze Leong Yao
- Forest Research Institute Malaysia (FRIM), Kepong, Selangor Darul Ehsan, Malaysia
| | - Stuart J Davies
- Forest Global Earth Observatory, Smithsonian Tropical Research Institute, Washington, DC, USA
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12
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Song X, Corlett RT. Enemies mediate distance- and density-dependent mortality of tree seeds and seedlings: a meta-analysis of fungicide, insecticide and exclosure studies. Proc Biol Sci 2021; 288:20202352. [PMID: 33468003 DOI: 10.1098/rspb.2020.2352] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Conspecific negative distance- and density-dependence is often assumed to be one of the most important mechanisms controlling forest community assembly and species diversity globally. Plant pathogens, and insect and mammalian herbivores, are the most common natural enemy types that have been implicated in this phenomenon, but their general effects at different plant life stages are still unclear. Here, we conduct a meta-analysis of studies that involved robust manipulative experiments, using fungicides, insecticides and exclosures, to assess the contributions of different natural enemy types to distance- and density-dependent effects at seed and seedling stages. We found that distance- and density-dependent mortality caused by natural enemies was most likely at the seedling stage and was greater at higher mean annual temperatures. Conspecific negative distance- and density-dependence at the seedling stage is significantly weakened when fungicides were applied. By contrast, negative conspecific distance- and density-dependence is not a general pattern at the seed stage. High seed mass reduced distance- and density-dependent mortality at the seed stage. Seed studies excluding only large mammals found significant negative conspecific distance-dependent mortality, but exclusion of all mammals resulted in a non-significant effect of conspecifics. Our study suggests that plant pathogens are a major cause of distance- and density-dependent mortality at the seedling stage, while the impacts of herbivores on seedlings have been understudied. At the seed stage, large and small mammals, respectively, weaken and enhance negative conspecific distance-dependent mortality. Future research should identify specific agents of mortality, investigate the interactions among different enemy types and assess how global change may affect natural enemies and thus influence the strength of conspecific distance- and density-dependence.
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Affiliation(s)
- Xiaoyang Song
- CAS Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, People's Republic of China.,Center of Conservation Biology, Core Botanical Gardens, Chinese Academy of Sciences, Mengla 666303, People's Republic of China
| | - Richard T Corlett
- Center of Conservation Biology, Core Botanical Gardens, Chinese Academy of Sciences, Mengla 666303, People's Republic of China.,Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, People's Republic of China
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13
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Song X, Lim JY, Yang J, Luskin MS. When do Janzen-Connell effects matter? A phylogenetic meta-analysis of conspecific negative distance and density dependence experiments. Ecol Lett 2020; 24:608-620. [PMID: 33382527 DOI: 10.1111/ele.13665] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 08/18/2020] [Accepted: 11/25/2020] [Indexed: 12/24/2022]
Abstract
The Janzen-Connell (J-C) hypothesis suggests that specialised natural enemies cause distance- or density-dependent mortality among host plants and is regarded as an important mechanism for species coexistence. However, there remains debate about whether this phenomenon is widespread and how variation is structured across taxa and life stages. We performed the largest meta-analysis of experimental studies conducted under natural settings to date. We found little evidence of distance-dependent or density-dependent mortality when grouping all types of manipulations. Our analysis also reveals very large variation in response among species, with 38.5% of species even showing positive responses to manipulations. However, we found a strong signal of distance-dependent mortality among seedlings but not seed experiments, which we attribute to (a) seedlings sharing susceptible tissues with adults (leaves, wood, roots), (b) seedling enemies having worse dispersal than seed enemies and (c) seedlings having fewer physical and chemical defences than seeds. Both density- and distance-dependent mortality showed large variation within genera and families, suggesting that J-C effects are not strongly phylogenetically conserved. There were no clear trends with latitude, rainfall or study duration. We conclude that J-C effects may not be as pervasive as widely thought. Understanding the variation in J-C effects provides opportunities for new discoveries that will refine our understanding of J-C effects and its role in species coexistence.
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Affiliation(s)
- Xiaoyang Song
- Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Yunnan, 666303, China.,Center of Plant Ecology, Core Botanical Gardens, Chinese Academy of Sciences, Mengla, 666303, China
| | - Jun Ying Lim
- School of Biological Sciences, Nanyang Technological University, Singapore
| | - Jie Yang
- Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Yunnan, 666303, China.,Center of Plant Ecology, Core Botanical Gardens, Chinese Academy of Sciences, Mengla, 666303, China
| | - Matthew Scott Luskin
- School of Biological Sciences, University of Queensland, Brisbane, Qld., 4072, Australia
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14
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Hülsmann L, Chisholm RA, Hartig F. Is Variation in Conspecific Negative Density Dependence Driving Tree Diversity Patterns at Large Scales? Trends Ecol Evol 2020; 36:151-163. [PMID: 33589047 DOI: 10.1016/j.tree.2020.10.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 09/28/2020] [Accepted: 10/01/2020] [Indexed: 02/06/2023]
Abstract
Half a century ago, Janzen and Connell hypothesized that the high tree species diversity in tropical forests is maintained by specialized natural enemies. Along with other mechanisms, these can cause conspecific negative density dependence (CNDD) and thus maintain species diversity. Numerous studies have measured proxies of CNDD worldwide, but doubt about its relative importance remains. We find ample evidence for CNDD in local populations, but methodological limitations make it difficult to assess if CNDD scales up to control community diversity and thereby local and global biodiversity patterns. A combination of more robust statistical methods, new study designs, and eco-evolutionary models are needed to provide a more definite evaluation of the importance of CNDD for geographic variation in plant species diversity.
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Affiliation(s)
- Lisa Hülsmann
- Theoretical Ecology, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
| | - Ryan A Chisholm
- Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore
| | - Florian Hartig
- Theoretical Ecology, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany
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15
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Differences among species in seed dispersal and conspecific neighbor effects can interact to influence coexistence. THEOR ECOL-NETH 2020. [DOI: 10.1007/s12080-020-00468-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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16
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Greenspoon P, Wadhawan K. Colonization limitation of specialized enemies reduces species richness. THEOR ECOL-NETH 2020. [DOI: 10.1007/s12080-020-00474-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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17
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Xi X, Yang Y, Tylianakis JM, Yang S, Dong Y, Sun S. Asymmetric interactions of seed-predation network contribute to rare-species advantage. Ecology 2020; 101:e03050. [PMID: 32233082 DOI: 10.1002/ecy.3050] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Accepted: 02/25/2020] [Indexed: 01/11/2023]
Abstract
Although the asymmetry of species linkage within ecological networks is now well recognized, its effect on communities has scarcely been empirically investigated. Based on theory, we predicted that an asymmetric architecture of antagonistic plant-herbivore networks would emerge at the community level and that this asymmetry would negatively affect community-common plants more than rare ones. We tested this prediction by analyzing the architectural properties of an alpine plant and pre-dispersal seed-predator network and its effect on seed loss rate of plants in the Tibetan Plateau. This network showed an asymmetric architecture, where the common plant species (with a larger aboveground biomass per area) were infested by a higher number of predator species. Moreover, they asymmetrically interacted with specialized herbivores, presumably because of greater seed resource abundance. In turn, the asymmetric interactions led to a higher proportion of seed loss in the common plants at the species level. Our results suggest that asymmetric antagonistic networks may improve species coexistence by contributing to a mechanism of rare-species advantage.
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Affiliation(s)
- Xinqiang Xi
- Department of Ecology, School of Life Science, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, China
| | - Yangheshan Yang
- Department of Ecology, School of Life Science, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, China
| | - Jason M Tylianakis
- Bioprotection Research Centre and Centre for Integrative Ecology, School of Biological Sciences, University of Canterbury, Christchurch, 8140, New Zealand
| | - Sihai Yang
- Department of Ecology, School of Life Science, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, China
| | - Yuran Dong
- Department of Ecology, School of Life Science, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, China
| | - Shucun Sun
- Department of Ecology, School of Life Science, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, China.,Chengdu Institute of Biology, Chinese Academy of Sciences, 9 Section 4, Renminnan Rd, Chengdu, 610041, China
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18
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Schlägel UE, Grimm V, Blaum N, Colangeli P, Dammhahn M, Eccard JA, Hausmann SL, Herde A, Hofer H, Joshi J, Kramer-Schadt S, Litwin M, Lozada-Gobilard SD, Müller MEH, Müller T, Nathan R, Petermann JS, Pirhofer-Walzl K, Radchuk V, Rillig MC, Roeleke M, Schäfer M, Scherer C, Schiro G, Scholz C, Teckentrup L, Tiedemann R, Ullmann W, Voigt CC, Weithoff G, Jeltsch F. Movement-mediated community assembly and coexistence. Biol Rev Camb Philos Soc 2020; 95:1073-1096. [PMID: 32627362 DOI: 10.1111/brv.12600] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2019] [Revised: 03/20/2020] [Accepted: 03/23/2020] [Indexed: 01/11/2023]
Abstract
Organismal movement is ubiquitous and facilitates important ecological mechanisms that drive community and metacommunity composition and hence biodiversity. In most existing ecological theories and models in biodiversity research, movement is represented simplistically, ignoring the behavioural basis of movement and consequently the variation in behaviour at species and individual levels. However, as human endeavours modify climate and land use, the behavioural processes of organisms in response to these changes, including movement, become critical to understanding the resulting biodiversity loss. Here, we draw together research from different subdisciplines in ecology to understand the impact of individual-level movement processes on community-level patterns in species composition and coexistence. We join the movement ecology framework with the key concepts from metacommunity theory, community assembly and modern coexistence theory using the idea of micro-macro links, where various aspects of emergent movement behaviour scale up to local and regional patterns in species mobility and mobile-link-generated patterns in abiotic and biotic environmental conditions. These in turn influence both individual movement and, at ecological timescales, mechanisms such as dispersal limitation, environmental filtering, and niche partitioning. We conclude by highlighting challenges to and promising future avenues for data generation, data analysis and complementary modelling approaches and provide a brief outlook on how a new behaviour-based view on movement becomes important in understanding the responses of communities under ongoing environmental change.
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Affiliation(s)
- Ulrike E Schlägel
- Plant Ecology and Nature Conservation, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.,Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany
| | - Volker Grimm
- Plant Ecology and Nature Conservation, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.,Department of Ecological Modelling, Helmholtz Centre for Environmental Research-UFZ, Permoserstr. 15, 04318, Leipzig, Germany.,German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, 04103, Leipzig, Germany
| | - Niels Blaum
- Plant Ecology and Nature Conservation, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.,Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany
| | - Pierluigi Colangeli
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Department of Ecology and Ecosystem Modelling, University of Potsdam, Maulbeerallee 2, 14469, Potsdam, Germany
| | - Melanie Dammhahn
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Animal Ecology, University of Potsdam, Maulbeerallee 1, 14469, Potsdam, Germany
| | - Jana A Eccard
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Animal Ecology, University of Potsdam, Maulbeerallee 1, 14469, Potsdam, Germany
| | - Sebastian L Hausmann
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Plant Ecology, Institute of Biology, Freie Universität Berlin, 14195, Berlin, Germany
| | - Antje Herde
- Plant Ecology and Nature Conservation, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.,Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Department of Animal Behaviour, Bielefeld University, Morgenbreede 45, 33615, Bielefeld, Germany
| | - Heribert Hofer
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany.,Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.,Department of Biology, Chemistry, Pharmacy, Freie Universität Berlin, Berlin, Germany
| | - Jasmin Joshi
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Biodiversity Research and Systematic Botany, University of Potsdam, Maulbeerallee 2, 14469, Potsdam, Germany.,Institute for Landscape and Open Space, Hochschule für Technik HSR Rapperswil, Seestrasse 10, 8640 Rapperswil, Switzerland
| | - Stephanie Kramer-Schadt
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany.,Department of Ecology, Technische Universität Berlin, Rothenburgstr. 12, 12165, Berlin, Germany
| | - Magdalena Litwin
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Evolutionary Biology/Systematic Zoology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam, Germany
| | - Sissi D Lozada-Gobilard
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Biodiversity Research and Systematic Botany, University of Potsdam, Maulbeerallee 2, 14469, Potsdam, Germany
| | - Marina E H Müller
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz-Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, 15374, Müncheberg, Germany
| | - Thomas Müller
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz-Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, 15374, Müncheberg, Germany
| | - Ran Nathan
- Department of Ecology, Evolution and Behavior, Movement Ecology Laboratory, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Jana S Petermann
- Department of Biosciences, University of Salzburg, Hellbrunner Straße 34, 5020, Salzburg, Austria
| | - Karin Pirhofer-Walzl
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Plant Ecology, Institute of Biology, Freie Universität Berlin, 14195, Berlin, Germany.,Leibniz-Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, 15374, Müncheberg, Germany
| | - Viktoriia Radchuk
- Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany
| | - Matthias C Rillig
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Plant Ecology, Institute of Biology, Freie Universität Berlin, 14195, Berlin, Germany
| | - Manuel Roeleke
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany
| | - Merlin Schäfer
- Plant Ecology and Nature Conservation, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.,Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz-Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, 15374, Müncheberg, Germany
| | - Cédric Scherer
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany
| | - Gabriele Schiro
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz-Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, 15374, Müncheberg, Germany
| | - Carolin Scholz
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany
| | - Lisa Teckentrup
- Plant Ecology and Nature Conservation, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.,Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany
| | - Ralph Tiedemann
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Evolutionary Biology/Systematic Zoology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam, Germany
| | - Wiebke Ullmann
- Plant Ecology and Nature Conservation, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.,Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz-Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, 15374, Müncheberg, Germany
| | - Christian C Voigt
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany.,Behavioral Biology, Institute of Biology, Freie Universität Berlin, Takustr. 6, 14195, Berlin, Germany
| | - Guntram Weithoff
- Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany.,Department of Ecology and Ecosystem Modelling, University of Potsdam, Maulbeerallee 2, 14469, Potsdam, Germany
| | - Florian Jeltsch
- Plant Ecology and Nature Conservation, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam, Germany.,Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195, Berlin, Germany
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19
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Downey H, Lewis OT, Bonsall MB, Ward A, Gripenberg S. Assessing the potential for indirect interactions between tropical tree species via shared insect seed predators. Biotropica 2020. [DOI: 10.1111/btp.12759] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Harriet Downey
- Department of Zoology University of Cambridge Cambridge UK
- Department of Zoology University of Oxford Oxford UK
| | - Owen T. Lewis
- Department of Zoology University of Oxford Oxford UK
| | | | - Alan Ward
- Department of Zoology University of Oxford Oxford UK
| | - Sofia Gripenberg
- Department of Zoology University of Oxford Oxford UK
- School of Biological Sciences University of Reading Reading UK
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20
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Gap creation alters the mode of conspecific distance-dependent seedling establishment via changes in the relative influence of pathogens and mycorrhizae. Oecologia 2020; 192:449-462. [PMID: 31960145 DOI: 10.1007/s00442-020-04596-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Accepted: 01/07/2020] [Indexed: 12/22/2022]
Abstract
In forest communities, conspecific density/distance dependence (CDD) is an important factor regulating diversity. It remains unknown how and the extent to which gap creation alters the mode and strength of CDD via changes in the relative importance of pathogens and mycorrhizae. Seeds of two hardwoods (i.e., Acer mono associated with arbuscular mycorrhizae [AM] and Quercus serrata associated with ectomycorrhizae [EM]) were sown reciprocally at four distances from the boundary between Acer- and Quercus-dominated forests towards forest interior in each of forest understories (FUs) and gaps. The causes of seed and seedling mortality, seedling growth and colonization of mycorrhizal fungi were investigated. In Acer, seed and seedling mortality were highest in Acer forests and gradually decreased towards the interior of Quercus forests in FU, mainly due to severe attack of soil pathogens, invertebrates, and leaf diseases. The reverse was true in gaps, due to reduction of damping-off damage caused by distance-dependent colonization of AM. In Quercus, most seeds and seedlings were eaten by vertebrates in FUs. The seedling mortality caused by leaf diseases was not high, even beneath conspecific forests with higher colonization of EM in gaps, suggesting a positive EM influence. In both species, seedling mass was greatest in conspecific forests and gradually decreased towards the interior of heterospecific forests in gaps, due to higher colonization of mycorrhizae near conspecifics. In conclusion, light conditions strongly altered the mode of CDD via changes in relative influence of pathogens and mycorrhizae, suggesting that gap creation may regulate species diversity via changes in the mode of CDD.
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21
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Rehm E, Fricke E, Bender J, Savidge J, Rogers H. Animal movement drives variation in seed dispersal distance in a plant-animal network. Proc Biol Sci 2020; 286:20182007. [PMID: 30963874 DOI: 10.1098/rspb.2018.2007] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Frugivores play differing roles in shaping dispersal patterns yet seed dispersal distance is rarely quantified across entire communities. We model seed dispersal distance using gut passage times and bird movement for the majority (39 interactions) of known bird-tree interactions on the island of Saipan to highlight differences in seed dispersal distances provided by the five avian frugivores. One bird species was found to be a seed predator rather than a disperser. The remaining four avian species dispersed seeds but differences in seed dispersal distance were largely driven by interspecific variation in bird movement rather than intraspecific variation in gut passage times. The median dispersal distance was at least 56 m for all species-specific combinations, indicating all species play a role in reducing high seed mortality under the parent tree. However, one species-the Micronesian Starling-performed 94% of dispersal events greater than 500 m, suggesting this species could be a key driver of long-distance dispersal services (e.g. linking populations, colonizing new areas). Assessing variation in dispersal patterns across this network highlights key sources of variation in seed dispersal distances and suggests which empirical approaches are sufficient for modelling how seed dispersal mutualisms affect populations and communities.
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Affiliation(s)
- E Rehm
- 1 Department of Ecology, Evolution, and Marine Biology, University of California at Santa Barbara , Santa Barbara, CA , USA
| | - E Fricke
- 2 Department of Ecology, Evolution, and Organismal Biology, Iowa State University , Ames, IA , USA
| | - J Bender
- 3 Lincoln Park Zoo , Chicago, IL , USA
| | - J Savidge
- 4 Department of Fish, Wildlife and Conservation Biology, Colorado State University , Fort Collins, CO , USA
| | - H Rogers
- 2 Department of Ecology, Evolution, and Organismal Biology, Iowa State University , Ames, IA , USA
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22
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Tree species traits affect which natural enemies drive the Janzen-Connell effect in a temperate forest. Nat Commun 2020; 11:286. [PMID: 31941904 PMCID: PMC6962457 DOI: 10.1038/s41467-019-14140-y] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2019] [Accepted: 12/14/2019] [Indexed: 01/25/2023] Open
Abstract
A prominent tree species coexistence mechanism suggests host-specific natural enemies inhibit seedling recruitment at high conspecific density (negative conspecific density dependence). Natural-enemy-mediated conspecific density dependence affects numerous tree populations, but its strength varies substantially among species. Understanding how conspecific density dependence varies with species’ traits and influences the dynamics of whole communities remains a challenge. Using a three-year manipulative community-scale experiment in a temperate forest, we show that plant-associated fungi, and to a lesser extent insect herbivores, reduce seedling recruitment and survival at high adult conspecific density. Plant-associated fungi are primarily responsible for reducing seedling recruitment near conspecific adults in ectomycorrhizal and shade-tolerant species. Insects, in contrast, primarily inhibit seedling recruitment of shade-intolerant species near conspecific adults. Our results suggest that natural enemies drive conspecific density dependence in this temperate forest and that which natural enemies are responsible depends on the mycorrhizal association and shade tolerance of tree species. The Janzen-Connell hypothesis posits that seedlings may be less likely to establish near conspecifics due to shared natural enemies. Here, Jia et al. show that tree species traits determine whether fungal pathogens or insect herbivores inhibit seedling recruitment and survival in a temperate forest.
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23
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Martini F, Zou C, Goodale UM. Intrinsic biotic factors and microsite conditions drive seedling survival in a species with masting reproduction. Ecol Evol 2019; 9:14261-14272. [PMID: 31938517 PMCID: PMC6953690 DOI: 10.1002/ece3.5861] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 10/23/2019] [Accepted: 11/04/2019] [Indexed: 11/08/2022] Open
Abstract
Seedling recruitment following a masting event, where more fruits are produced in synchrony and intermittently compared with other species, plays a crucial role in determining species diversity and community structure. Such seedling recruitment can be superabundant, but followed by high mortality shortly thereafter. Differences in biotic factors such as seedling characteristics, competition, and herbivory, and microsite-specific abiotic factors could determine seedling fate in space and time.In a subtropical forest in south China, for 2 years using censuses conducted every 1-2 months, we monitored 40 seed traps and 120, 1 m2 quadrats in five 1-ha plots located from 1,400 to 1,850 m asl for the masting maple species, Acer campbellii subsp. sinense (Pax) P.C.DeJong. We measured biotic-conspecific and heterospecific seedling density, species richness, herbivory, seedling height, and leaf number-and abiotic-canopy openness, slope, and aspect-factors to assess drivers of seedling survival and evaluated A. campbellii subsp. sinense presence in the soil seed bank (SSB).The masting seed dispersal peak and seedling emergence peak occurred between October 2017 and January 2018, and May 2018, respectively. Of 688 selected seedlings, mortality was 92.7% within one year. No seeds were observed in the SSB. Seedling height and leaf number positively affected seedling survival, while seed placement as measured by aspect also showed effects on survival. Conspecific and heterospecific density and herbivory did not show any clear effect. Higher probabilities of seedling survival were found in areas with larger canopy openness (≥12% canopy gap size) and in steeper microsites (≥35°). Synthesis. Masting is mainly studied as a population-level phenomenon from the fruiting tree perspective. Our study of individual seedling fate revealed that intrinsic biotic factors and seed placement were key drivers of survival. Although biotic determinants such as competition from conspecifics or heterospecifics or herbivory did not determine survival, their ubiquitous presence may be an underlying equalizer in community dynamics where seedlings that overcome biotic pressures, if placed at the right microsite, are at better odds at being recruited to the next life history stages.
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Affiliation(s)
- Francesco Martini
- Guangxi Key Laboratory of Forest Ecology and ConservationCollege of ForestryGuangxi UniversityNanningChina
- State Key Laboratory of Conservation and Utilization of Subtropical Agro‐bioresourcesCollege of ForestryGuangxi UniversityNanningChina
| | - Chaobo Zou
- Guangxi Key Laboratory of Forest Ecology and ConservationCollege of ForestryGuangxi UniversityNanningChina
- State Key Laboratory of Conservation and Utilization of Subtropical Agro‐bioresourcesCollege of ForestryGuangxi UniversityNanningChina
| | - Uromi Manage Goodale
- Guangxi Key Laboratory of Forest Ecology and ConservationCollege of ForestryGuangxi UniversityNanningChina
- State Key Laboratory of Conservation and Utilization of Subtropical Agro‐bioresourcesCollege of ForestryGuangxi UniversityNanningChina
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24
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Calderón‐Sanou I, Ríos LD, Cascante‐Marín A, Barrantes G, Fuchs EJ. The effect of conspecific density, herbivory, and bamboo on seedling dynamics of a dominant oak in a Neotropical highland forest. Biotropica 2019. [DOI: 10.1111/btp.12714] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
| | - Luis Diego Ríos
- Escuela de Biología Universidad de Costa Rica San José Costa Rica
| | | | | | - Eric J. Fuchs
- Escuela de Biología Universidad de Costa Rica San José Costa Rica
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25
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Enríquez S, Olivé I, Cayabyab N, Hedley JD. Structural complexity governs seagrass acclimatization to depth with relevant consequences for meadow production, macrophyte diversity and habitat carbon storage capacity. Sci Rep 2019; 9:14657. [PMID: 31601973 PMCID: PMC6787196 DOI: 10.1038/s41598-019-51248-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 09/18/2019] [Indexed: 11/29/2022] Open
Abstract
Analyses of the integrated seagrass response to depth support the previously documented low plasticity and consistent shade-adapted leaf physiology of a habitat-builder that dominates well-illuminated reef environments. Two structural responses, “canopy-opening” and “below-ground-mass-depletion”, govern the photoacclimatory response and facilitate, respectively, light penetration within the canopy and functional adjustments in whole-plant carbon balances. Conversely, “canopy-closing” may also explain dense canopies formed close to the waterline, as they provide shade and photoprotection to a susceptible leaf physiology under high-light. Canopy light attenuation is primarily regulated by the leaf area index (LAI), which is governed by changes in shoot size and density. Shoot density diminishes non-linearly with depth, while shoot size increases to a maximum followed by a decline. The initial increase in shoot size, which resembles a self-thinning response, increases LAI and meadow production in shallow depths. These seagrass structural adjustments have relevant ecological implications. Canopy-thinning allows macrophyte diversity to increase with depth, while seagrass production and carbon storage diminish exponentially, and are maximal only in a shallow coastal fringe. The results support the universality of plant self-thinning, from phytoplankton to complex canopies, likely the consequence of simple physical laws related to light limitation and pigment self-shading within photosynthetic structures and communities.
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Affiliation(s)
- Susana Enríquez
- Laboratorio de Fotobiología, Unidad Académica de Sistemas Arrecifales Puerto Morelos, Universidad Nacional Autónoma de México, Apto. Postal 13, 77500-QR, Cancún, Mexico.
| | - Irene Olivé
- Laboratorio de Fotobiología, Unidad Académica de Sistemas Arrecifales Puerto Morelos, Universidad Nacional Autónoma de México, Apto. Postal 13, 77500-QR, Cancún, Mexico.,School of Geographical and Earth Sciences, Gregory Building Rm419, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Napo Cayabyab
- Laboratorio de Fotobiología, Unidad Académica de Sistemas Arrecifales Puerto Morelos, Universidad Nacional Autónoma de México, Apto. Postal 13, 77500-QR, Cancún, Mexico
| | - John D Hedley
- Numerical Optics Ltd., Belmont House, Witheridge, Tiverton, Devon, EX16 8AA, UK
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26
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Forrister DL, Endara MJ, Younkin GC, Coley PD, Kursar TA. Herbivores as drivers of negative density dependence in tropical forest saplings. Science 2019; 363:1213-1216. [PMID: 30872524 DOI: 10.1126/science.aau9460] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Accepted: 02/19/2019] [Indexed: 01/25/2023]
Abstract
Ecological theory predicts that the high local diversity observed in tropical forests is maintained by negative density-dependent interactions within and between closely related plant species. By using long-term data on tree growth and survival for coexisting Inga (Fabaceae, Mimosoideae) congeners, we tested two mechanisms thought to underlie negative density dependence (NDD): competition for resources and attack by herbivores. We quantified the similarity of neighbors in terms of key ecological traits that mediate these interactions, as well as the similarity of herbivore communities. We show that phytochemical similarity and shared herbivore communities are associated with decreased growth and survival at the sapling stage, a key bottleneck in the life cycle of tropical trees. None of the traits associated with resource acquisition affect plant performance, indicating that competition between neighbors may not shape local tree diversity. These results suggest that herbivore pressure is the primary mechanism driving NDD at the sapling stage.
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Affiliation(s)
- Dale L Forrister
- School of Biological Sciences, University of Utah, Salt Lake City, UT, USA.
| | - María-José Endara
- School of Biological Sciences, University of Utah, Salt Lake City, UT, USA.,Centro de Investigación de la Biodiversidad y Cambio Climático (BioCamb) e Ingeniería en Biodiversidad y Recursos Genéticos. Facultad de Ciencias de Medio Ambiente, Universidad Tecnológica Indoamérica, Quito, Ecuador
| | - Gordon C Younkin
- School of Biological Sciences, University of Utah, Salt Lake City, UT, USA
| | - Phyllis D Coley
- School of Biological Sciences, University of Utah, Salt Lake City, UT, USA.,Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panamá
| | - Thomas A Kursar
- School of Biological Sciences, University of Utah, Salt Lake City, UT, USA.,Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panamá
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27
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Fricke EC, Tewksbury JJ, Rogers HS. Linking intra‐specific trait variation and plant function: seed size mediates performance tradeoffs within species. OIKOS 2019. [DOI: 10.1111/oik.06494] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Evan C. Fricke
- National Socio‐Environmental Synthesis Center, Univ. of Maryland Annapolis MD 21401 USA
| | - Joshua J. Tewksbury
- Colorado Global Hub, Future Earth Boulder CO USA
- Sustainability, Energy and Environment Complex, Univ. of Colorado Boulder CO USA
| | - Haldre S. Rogers
- Dept of Ecology, Evolution, and Organismal Biology, Iowa State Univ Ames IA USA
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28
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Yang Q, Ding J, Siemann E. Biogeographic variation of distance‐dependent effects in an invasive tree species. Funct Ecol 2019. [DOI: 10.1111/1365-2435.13306] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Qiang Yang
- Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden Chinese Academy of Sciences Wuhan China
- State Key Laboratory of Grassland Agro‐ecosystems, School of Life Sciences Lanzhou University Lanzhou China
| | - Jianqing Ding
- School of Life Sciences Henan University Kaifeng China
| | - Evan Siemann
- Department of Biosciences Rice University Houston Texas
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29
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Solé R, Gripenberg S, Lewis OT, Markesteijn L, Barrios H, Ratz T, Ctvrtecka R, Butterill PT, Segar S, Metz MA, Dahl C, Rivera M, Viquez K, Ferguson W, Guevara M, Basset Y. The role of herbivorous insects and pathogens in the regeneration dynamics of Guazuma ulmifolia in Panama. NATURE CONSERVATION 2019. [DOI: 10.3897/natureconservation.32.30108] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A significant proportion of the mortality of rainforest trees occurs during early life stages (seeds and seedlings), but mortality agents are often elusive. Our study investigated the role of herbivorous insects and pathogens in the early regeneration dynamics of Guazumaulmifolia (Malvaceae), an important tree species in agroforestry in Central America. We reared pre-dispersal insect seed predators from G.ulmifolia seeds in Panama. We also carried out an experiment, controlling insects and pathogens using insecticide and/or fungicide treatments, as well as seed density, and compared survivorship of G.ulmifolia seeds and seedlings among treatments and relative to untreated control plots. We observed (1) high pre-dispersal attack (92%) of the fruits of G.ulmifolia, mostly by anobiine and bruchine beetles; (2) negligible post-dispersal attack of isolated seeds by insects and pathogens; (3) slow growth and high mortality (> 95%) of seedlings after 14 weeks; (4) low insect damage on seedlings; and (5) a strong positive correlation between seedling mortality and rainfall. We conclude that for G.ulmifolia at our study site the pre-dispersal seed stage is by far the most sensitive stage to insects and that their influence on seedling mortality appears to be slight as compared to that of inclement weather. Thus, the regeneration of this important tree species may depend on effective primary dispersal of seeds by vertebrates (before most of the seed crop is lost to insects), conditioned by suitable conditions in which the seedlings can grow.
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30
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Rosin C, Poulsen JR. Seed traits, not density or distance from parent, determine seed predation and establishment in an Afrotropical forest. Biotropica 2018. [DOI: 10.1111/btp.12601] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Cooper Rosin
- Nicholas School of the Environment; Duke University; 9 Circuit Dr. Durham NC U.S.A
- Nelson Institute for Environmental Studies; University of Wisconsin-Madison; 550 N. Park St. Madison WI U.S.A
| | - John R. Poulsen
- Nicholas School of the Environment; Duke University; 9 Circuit Dr. Durham NC U.S.A
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31
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Gripenberg S. Do pre-dispersal insect seed predators contribute to maintaining tropical forest plant diversity? Biotropica 2018. [DOI: 10.1111/btp.12602] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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32
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Nunes KA, Kotanen PM. Does local isolation allow an invasive thistle to escape enemy pressure? Oecologia 2018; 188:139-147. [PMID: 29869020 DOI: 10.1007/s00442-018-4175-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Accepted: 05/22/2018] [Indexed: 01/03/2023]
Abstract
Enemy release often is invoked to explain the success of invasive plants: an invader benefits from reduced attack as it escapes specialized enemies through the invasion process. Enemy release typically is thought of as occurring at large geographic scales, but local-scale interactions may also be important for invader establishment and success. Furthermore, most tests of local enemy release have been conducted over a single year even though release may be a transient phenomenon, especially at small scales. In this study, we used a multi-year field experiment to investigate whether locally isolated populations of the noxious non-native weed Cirsium arvense benefit from reduced levels of aboveground damage, and whether any initial advantage is lost over subsequent growing seasons. Populations of C. arvense were grown in plots at set distances from established source populations for 4 years. In the first year of the experiment, folivory significantly declined with host isolation, but damage from specialist stem gallers and seed predators did not. However, in subsequent years of observation, folivores began colonizing isolated C. arvense populations while stem gallers exhibited very slow colonization of more isolated plots; seed predation showed no pattern with distance in any year. Local enemy escape did not result in increased plant performance, which instead negatively correlated with degree of isolation. Nonetheless, our results stress the importance of multi-year observations in tests of enemy release, since the herbivory patterns initially observed often changed within subsequent years depending on the dispersal ability and biology of the causal organism involved.
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Affiliation(s)
- Krystal A Nunes
- Department of Ecology and Evolutionary Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada.
| | - Peter M Kotanen
- Department of Ecology and Evolutionary Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada
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33
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Urli M, Brown CD, Narváez Perez R, Chagnon PL, Vellend M. Increased seedling establishment via enemy release at the upper elevational range limit of sugar maple. Ecology 2017; 97:3058-3069. [PMID: 27870043 DOI: 10.1002/ecy.1566] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 07/08/2016] [Accepted: 07/13/2016] [Indexed: 11/10/2022]
Abstract
The enemy release hypothesis is frequently invoked to explain invasion by nonnative species, but studies focusing on the influence of enemies on natural plant range expansion due to climate change remain scarce. We combined multiple approaches to study the influence of plant-enemy interactions on the upper elevational range limit of sugar maple (Acer saccharum) in southeastern Québec, Canada, where a previous study had demonstrated intense seed predation just beyond the range limit. Consistent with the hypothesis of release from natural enemies at the range limit, data from both natural patterns of regeneration and from seed and seedling transplant experiments showed higher seedling densities at the range edge than in the core of the species' distribution. A growth chamber experiment manipulating soil origin and temperature indicated that this so-called "happy edge" was not likely caused by temperature (i.e., the possibility that climate warming has made high elevation temperatures optimal for sugar maple) or by abiotic soil factors that vary along the elevational gradient. Finally, an insect-herbivore-exclusion experiment showed that insect herbivory was a major cause of seedling mortality in the core of sugar maple's distribution, whereas seedlings transplanted at or beyond the range edge experienced minimal herbivory (i.e., enemy release). Insect herbivory did not completely explain the high levels of seedling mortality in the core of the species' distribution, suggesting that seedlings at or beyond the range edge may also experience release from pathogens. In sum, while some effects of enemies are magnified beyond range edges (e.g., seed predation), others are dampened at and beyond the range edge (e.g., insect herbivory), such that understanding the net outcome of different biotic interactions within, at and beyond the edge of distribution is critical to predicting species' responses to global change.
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Affiliation(s)
- Morgane Urli
- Département de Biologie, Université de Sherbrooke, 2500 Boulevard de l'Université, Sherbrooke, Québec, J1K 2R1, Canada.,Direction de la Recherche Forestière, Ministère des Forêts, de la Faune et des Parcs du Québec, 2700 Einstein, Québec, Québec, G1P 3W8, Canada.,Centre d'étude de la Forêt, Université du Québec à Montréal, Case Postale 8888, Succursale Centre-ville, Montréal, Québec, H3C 3P8, Canada
| | - Carissa D Brown
- Département de Biologie, Université de Sherbrooke, 2500 Boulevard de l'Université, Sherbrooke, Québec, J1K 2R1, Canada.,Department of Geography, Memorial University, 230 Elizabeth Avenue, St John's, Newfoundland and Labrador, A1B 3X9, Canada
| | - Rosela Narváez Perez
- Département de Biologie, Université de Sherbrooke, 2500 Boulevard de l'Université, Sherbrooke, Québec, J1K 2R1, Canada
| | - Pierre-Luc Chagnon
- Département de Biologie, Université de Sherbrooke, 2500 Boulevard de l'Université, Sherbrooke, Québec, J1K 2R1, Canada
| | - Mark Vellend
- Département de Biologie, Université de Sherbrooke, 2500 Boulevard de l'Université, Sherbrooke, Québec, J1K 2R1, Canada
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34
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Donoso I, Schleuning M, García D, Fründ J. Defaunation effects on plant recruitment depend on size matching and size trade-offs in seed-dispersal networks. Proc Biol Sci 2017; 284:20162664. [PMID: 28566481 PMCID: PMC5454253 DOI: 10.1098/rspb.2016.2664] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Accepted: 05/02/2017] [Indexed: 11/12/2022] Open
Abstract
Defaunation by humans causes a loss of large animals in many ecosystems globally. Recent work has emphasized the consequences of downsizing in animal communities for ecosystem functioning. However, no study so far has integrated network theory and life-history trade-offs to mechanistically evaluate the functional consequences of defaunation in plant-animal networks. Here, we simulated an avian seed-dispersal network and its derived ecosystem function seedling recruitment to assess the relative importance of different size-related mechanisms. Specifically, we considered size matching (between bird size and seed size) and size trade-offs, which are driven by differences in plant or animal species abundance (negative size-quantity relationship) as well as in recruitment probability and disperser quality (positive size-quality relationship). Defaunation led to impoverished seedling communities in terms of diversity and seed size, but only if models accounted for size matching. In addition, size trade-off in plants, in concert with size matching, provoked rapid decays in seedling abundance in response to defaunation. These results underscore a disproportional importance of large animals for ecosystem functions. Downsizing in ecological networks will have severe consequences for ecosystem functioning, especially in interaction networks that are structured by size matching between plants and animals.
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Affiliation(s)
- Isabel Donoso
- Departamento de Biología de Organismos y Sistemas and Unidad Mixta de Investigación en Biodiversidad (UMIB, CSIC-Uo-PA), University of Oviedo, Valentín Andrés Álvarez s/n, 33071 Oviedo, Spain
| | - Matthias Schleuning
- Senckenberg Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, 60325 Frankfurt (Main), Germany
| | - Daniel García
- Departamento de Biología de Organismos y Sistemas and Unidad Mixta de Investigación en Biodiversidad (UMIB, CSIC-Uo-PA), University of Oviedo, Valentín Andrés Álvarez s/n, 33071 Oviedo, Spain
| | - Jochen Fründ
- Biometry and Environmental System Analysis, University of Freiburg, Tennenbacher Strasse 4, 79106 Freiburg, Germany
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35
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Fricke EC, Tewksbury JJ, Wandrag EM, Rogers HS. Mutualistic strategies minimize coextinction in plant-disperser networks. Proc Biol Sci 2017; 284:20162302. [PMID: 28490622 PMCID: PMC5443928 DOI: 10.1098/rspb.2016.2302] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Accepted: 04/18/2017] [Indexed: 11/22/2022] Open
Abstract
The global decline of mutualists such as pollinators and seed dispersers may cause negative direct and indirect impacts on biodiversity. Mutualistic network models used to understand the stability of mutualistic systems indicate that species with low partner diversity are most vulnerable to coextinction following mutualism disruption. However, existing models have not considered how species vary in their dependence on mutualistic interactions for reproduction or survival, overlooking the potential influence of this variation on species' coextinction vulnerability and on network stability. Using global databases and field experiments focused on the seed dispersal mutualism, we found that plants and animals that depend heavily on mutualistic interactions have higher partner diversity. Under simulated network disruption, this empirical relationship strongly reduced coextinction because the species most likely to lose mutualists depend least on their mutualists. The pattern also reduced the importance of network structure for stability; nested network structure had little effect on coextinction after simulations incorporated the empirically derived relationship between partner diversity and mutualistic dependence. Our results highlight a previously unknown source of stability in mutualistic networks and suggest that differences among species in their mutualistic strategy, rather than network structure, primarily accounts for stability in mutualistic communities.
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Affiliation(s)
- Evan C Fricke
- Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA
| | - Joshua J Tewksbury
- Colorado Global Hub, Future Earth, Boulder, CO 80309, USA
- Sustainability, Energy and Environment Complex, University of Colorado, Boulder, CO 80309, USA
- School of Global Environmental Studies, Colorado State University, Fort Collins, CO 80523, USA
| | - Elizabeth M Wandrag
- Institute for Applied Ecology, University of Canberra, Canberra, Australian Capital Territory 2617, Australia
| | - Haldre S Rogers
- Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA
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36
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Fricke EC, Wright SJ. Measuring the demographic impact of conspecific negative density dependence. Oecologia 2017; 184:259-266. [DOI: 10.1007/s00442-017-3863-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 04/02/2017] [Indexed: 11/29/2022]
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37
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Effects of an invasive predator cascade to plants via mutualism disruption. Nat Commun 2017; 8:14557. [PMID: 28270682 PMCID: PMC5344968 DOI: 10.1038/ncomms14557] [Citation(s) in RCA: 76] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Accepted: 01/06/2017] [Indexed: 11/29/2022] Open
Abstract
Invasive vertebrate predators are directly responsible for the extinction or decline of many vertebrate species, but their indirect impacts often go unmeasured, potentially leading to an underestimation of their full impact. When invasives extirpate functionally important mutualists, dependent species are likely to be affected as well. Here, we show that the invasive brown treesnake, directly responsible for the extirpation of forest birds from the island of Guam, is also indirectly responsible for a severe decline in plant recruitment as a result of disrupting the fruit-frugivore mutualism. To assess the impact of frugivore loss on plants, we compare seed dispersal and recruitment of two fleshy-fruited tree species on Guam and three nearby islands with intact disperser communities. We conservatively estimate that the loss of frugivorous birds caused by the brown treesnake may have caused a 61–92% decline in seedling recruitment. This case study highlights the potential for predator invasions to cause indirect, pervasive and easily overlooked interaction cascades. Invasive brown treesnakes decimated the forest bird community on the island of Guam. Now, Rogers and colleagues document the indirect effects of the snake on trees, linking snake-initiated bird loss to reduced seed dispersal and plant recruitment on Guam compared to nearby uninvaded islands.
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38
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Piiroinen T, Valtonen A, Roininen H. Vertebrate herbivores are the main cause of seedling mortality in a logged African rainforest-implications for forest restoration. Restor Ecol 2016. [DOI: 10.1111/rec.12460] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Tiina Piiroinen
- Faculty of Science and Forestry, Department of Environmental and Biological Sciences; University of Eastern Finland; PO Box 111 FI-80101 Joensuu Finland
| | - Anu Valtonen
- Faculty of Science and Forestry, Department of Environmental and Biological Sciences; University of Eastern Finland; PO Box 111 FI-80101 Joensuu Finland
- Center for Ecological Research; Kyoto University; Hirano 2 Otsu Shiga 520-2113 Japan
| | - Heikki Roininen
- Faculty of Science and Forestry, Department of Environmental and Biological Sciences; University of Eastern Finland; PO Box 111 FI-80101 Joensuu Finland
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39
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Tree species effects on pathogen-suppressive capacities of soil bacteria across two tropical dry forests in Costa Rica. Oecologia 2016; 182:789-802. [PMID: 27573616 DOI: 10.1007/s00442-016-3702-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Accepted: 08/08/2016] [Indexed: 10/21/2022]
Abstract
Antibiotic-producing bacteria in the genus Streptomyces can inhibit soil-borne plant pathogens, and have the potential to mediate the impacts of disease on plant communities. Little is known about how antibiotic production varies among soil communities in tropical forests, despite a long history of interest in the role of soil-borne pathogens in these ecosystems. Our objective was to determine how tree species and soils influence variation in antibiotic-mediated pathogen suppression among Streptomyces communities in two tropical dry forest sites (Santa Rosa and Palo Verde). We targeted tree species that co-occur in both sites and used a culture-based functional assay to quantify pathogen-suppressive capacities of Streptomyces communities beneath 50 focal trees. We also measured host-associated litter and soil element concentrations as potential mechanisms by which trees may influence soil microbes. Pathogen-suppressive capacities of Streptomyces communities varied within and among tree species, and inhibitory phenotypes were significantly related to soil and litter element concentrations. Average proportions of inhibitory Streptomyces in soils from the same tree species varied between 1.6 and 3.3-fold between sites. Densities and proportions of pathogen-suppressive bacteria were always higher in Santa Rosa than Palo Verde. Our results suggest that spatial heterogeneity in the potential for antibiotic-mediated disease suppression is shaped by tree species, site, and soil characteristics, which could have significant implications for understanding plant community composition and diversity in tropical dry forests.
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Persistence of Neighborhood Demographic Influences over Long Phylogenetic Distances May Help Drive Post-Speciation Adaptation in Tropical Forests. PLoS One 2016; 11:e0156913. [PMID: 27305092 PMCID: PMC4909291 DOI: 10.1371/journal.pone.0156913] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 05/20/2016] [Indexed: 01/24/2023] Open
Abstract
Studies of forest dynamics plots (FDPs) have revealed a variety of negative density-dependent (NDD) demographic interactions, especially among conspecific trees. These interactions can affect growth rate, recruitment and mortality, and they play a central role in the maintenance of species diversity in these complex ecosystems. Here we use an equal area annulus (EAA) point-pattern method to comprehensively analyze data from two tropical FDPs, Barro Colorado Island in Panama and Sinharaja in Sri Lanka. We show that these NDD interactions also influence the continued evolutionary diversification of even distantly related tree species in these FDPs. We examine the details of a wide range of these interactions between individual trees and the trees that surround them. All these interactions, and their cumulative effects, are strongest among conspecific focal and surrounding tree species in both FDPs. They diminish in magnitude with increasing phylogenetic distance between heterospecific focal and surrounding trees, but do not disappear or change the pattern of their dependence on size, density, frequency or physical distance even among the most distantly related trees. The phylogenetic persistence of all these effects provides evidence that interactions between tree species that share an ecosystem may continue to promote adaptive divergence even after the species’ gene pools have become separated. Adaptive divergence among taxa would operate in stark contrast to an alternative possibility that has previously been suggested, that distantly related species with dispersal-limited distributions and confronted with unpredictable neighbors will tend to converge on common strategies of resource use. In addition, we have also uncovered a positive density-dependent effect: growth rates of large trees are boosted in the presence of a smaller basal area of surrounding trees. We also show that many of the NDD interactions switch sign rapidly as focal trees grow in size, and that their cumulative effect can strongly influence the distributions and species composition of the trees that surround the focal trees during the focal trees’ lifetimes.
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41
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Making dispersal syndromes and networks useful in tropical conservation and restoration. Glob Ecol Conserv 2016. [DOI: 10.1016/j.gecco.2016.03.002] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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42
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Gut passage and secondary metabolites alter the source of post-dispersal predation for bird-dispersed chili seeds. Oecologia 2016; 181:905-10. [PMID: 27016078 DOI: 10.1007/s00442-016-3612-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2015] [Accepted: 03/09/2016] [Indexed: 10/22/2022]
Abstract
Plants can influence the source and severity of seed predation through various mechanisms; the use of secondary metabolites for chemical defense, for example, is well documented. Gut passage by frugivores can also reduce mortality of animal-dispersed seeds, although this mechanism has gained far less attention than secondary metabolites. Apart from influencing the severity of seed predation, gut passage may also influence the source of seed predation. In Bolivia, we compared impacts of these two mechanisms, gut passage and secondary metabolites, on the source of seed predation in Capsicum chacoense, a wild chili species that is polymorphic for pungency (individual plants either produce fruits and seeds containing or lacking capsaicinoids). Using physical exclosures, we isolated seed removal by insects, mammals, and birds; seeds in the trials were from either pungent or non-pungent fruits and were either passed or not passed by seed-dispersing birds. Pungency had little influence on total short-term seed removal by animals, although prior work on this species indicates that capsaicin reduces mortality caused by fungi at longer time scales. Gut passage strongly reduced removal by insects, altering the relative impact of the three predator types. The weak impact of pungency on short-term predation contrasts with previous studies, highlighting the context dependence of secondary metabolites. The strong impact of gut passage demonstrates that this mechanism alone can influence which seed predators consume seeds, and that impacts of gut passage can be larger than those of secondary metabolites, which are more commonly acknowledged as a defense mechanism.
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43
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Plant-soil feedbacks: a comparative study on the relative importance of soil feedbacks in the greenhouse versus the field. Oecologia 2016; 181:559-69. [DOI: 10.1007/s00442-016-3591-8] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Accepted: 02/12/2016] [Indexed: 10/22/2022]
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44
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Norghauer JM, Free CM, Landis RM, Grogan J, Malcolm JR, Thomas SC. Herbivores limit the population size of big-leaf mahogany trees in an Amazonian forest. OIKOS 2016. [DOI: 10.1111/oik.02324] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Julian M. Norghauer
- Faculty of Forestry, Earth Sciences Centre, Univ. of Toronto; 33 Willcocks St. Toronto ON M5S 3B3 Canada
- Inst. of Plant Sciences, Univ. of Bern; Altenbergrain 21 BE 3013 Bern Switzerland
| | - Christopher M. Free
- Inst. of Marine and Coastal Sciences, Rutgers Univ.; 71 Dudley Road New Brunswick NJ 08901 USA
| | - R. Matthew Landis
- Dept of Biology; Middlebury College; Middlebury VT 05753 USA
- ISciences, LLC; Burlington VT 05401 USA
| | - James Grogan
- Dept of Biological Sciences; Mount Holyoke College; 50 College St South Hadley MA 01075 USA
- Inst. Floresta Tropical, Rua dos Mundurucus; 1613, Jurunas Belém Pará 66.025-660 Brazil
| | - Jay R. Malcolm
- Faculty of Forestry, Earth Sciences Centre, Univ. of Toronto; 33 Willcocks St. Toronto ON M5S 3B3 Canada
| | - Sean C. Thomas
- Faculty of Forestry, Earth Sciences Centre, Univ. of Toronto; 33 Willcocks St. Toronto ON M5S 3B3 Canada
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45
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Parent tree distance-dependent recruitment limitation of native and exotic invasive seedlings in urban forests. Urban Ecosyst 2015. [DOI: 10.1007/s11252-015-0507-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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46
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Bever JD, Mangan SA, Alexander HM. Maintenance of Plant Species Diversity by Pathogens. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2015. [DOI: 10.1146/annurev-ecolsys-112414-054306] [Citation(s) in RCA: 245] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- James D. Bever
- Department of Biology, Indiana University, Bloomington, Indiana 47405;
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045
| | - Scott A. Mangan
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri 63130
| | - Helen M. Alexander
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045
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47
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Distance-responsive predation is not necessary for the Janzen–Connell hypothesis. Theor Popul Biol 2015; 106:60-70. [DOI: 10.1016/j.tpb.2015.10.006] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Revised: 10/13/2015] [Accepted: 10/13/2015] [Indexed: 01/07/2023]
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Gibbs DA, Hay ME. Spatial patterns of coral survivorship: impacts of adult proximity versus other drivers of localized mortality. PeerJ 2015; 3:e1440. [PMID: 26623193 PMCID: PMC4662597 DOI: 10.7717/peerj.1440] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2015] [Accepted: 11/04/2015] [Indexed: 11/20/2022] Open
Abstract
Species-specific enemies may promote prey coexistence through negative distance- and density-dependent survival of juveniles near conspecific adults. We tested this mechanism by transplanting juvenile-sized fragments of the brooding corals Pocillopora damicornis and Seriatopora hystrix 3, 12, 24 and 182 cm up- and down-current of conspecific adults and monitoring their survival and condition over time. We also characterized the spatial distribution of P. damicornis and S. hystrix within replicate plots on three Fijian reef flats and measured the distribution of small colonies within 2 m of larger colonies of each species. Juvenile-sized transplants exhibited no differences in survivorship as a function of distance from adult P. damicornis or S. hystrix. Additionally, both P. damicornis and S. hystrix were aggregated rather than overdispersed on natural reefs. However, a pattern of juveniles being aggregated near adults while larger (and probably older) colonies were not suggests that greater mortality near large adults could occur over longer periods of time or that size-dependent mortality was occurring. While we found minimal evidence of greater mortality of small colonies near adult conspecifics in our transplant experiments, we did document hot-spots of species-specific corallivory. We detected spatially localized and temporally persistent predation on P. damicornis by the territorial triggerfish Balistapus undulatus. This patchy predation did not occur for S. hystrix. This variable selective regime in an otherwise more uniform environment could be one mechanism maintaining diversity of corals on Indo-Pacific reefs.
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Affiliation(s)
- David A Gibbs
- School of Biology, Georgia Institute of Technology , Atlanta, GA , United States ; Current affiliation: Tetra Tech, Inc. , Atlanta, GA , United States
| | - Mark E Hay
- School of Biology and Aquatic Chemical Ecology Center, Georgia Institute of Technology , Atlanta, GA , United States
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Yan Y, Zhang C, Wang Y, Zhao X, von Gadow K. Drivers of seedling survival in a temperate forest and their relative importance at three stages of succession. Ecol Evol 2015; 5:4287-99. [PMID: 26664679 PMCID: PMC4667830 DOI: 10.1002/ece3.1688] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Revised: 07/29/2015] [Accepted: 08/05/2015] [Indexed: 11/11/2022] Open
Abstract
Negative density dependence (NDD) and niche partitioning have been perceived as important mechanisms for the maintenance of species diversity. However, little is known about their relative contributions to seedling survival. We examined the effects of biotic and abiotic neighborhoods and the variations of biotic neighborhoods among species using survival data for 7503 seedlings belonging to 22 woody species over a period of 2 years in three different forest types, a half-mature forest (HF), a mature forest (MF), and an old-growth forest (OGF), each of these representing a specific successional stage in a temperate forest ecosystem in northeastern China. We found a convincing evidence for the existence of NDD in temperate forest ecosystems. The biotic and abiotic variables affecting seedlings survival change with successional stage, seedling size, and age. The strength of NDD for the smaller (<20 cm in height) and younger seedlings (1-2 years) as well as all seedlings combined varies significantly among species. We found no evidence that a community compensatory trend (CCT) existed in our study area. The results of this study demonstrate that the relative importance of NDD and habitat niche partitioning in driving seedling survival varies with seedling size and age and that the biotic and abiotic factors affecting seedlings survival change with successional stage.
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Affiliation(s)
- Yan Yan
- Key Laboratory for Forest Resources & Ecosystem Processes of Beijing Beijing Forestry University Beijing 100083 China
| | - Chunyu Zhang
- Key Laboratory for Forest Resources & Ecosystem Processes of Beijing Beijing Forestry University Beijing 100083 China
| | - Yuxi Wang
- Division of Forestry and Natural Resource West Virginia University Morgantown West Virginia
| | - Xiuhai Zhao
- Key Laboratory for Forest Resources & Ecosystem Processes of Beijing Beijing Forestry University Beijing 100083 China
| | - Klaus von Gadow
- Georg-August University Göttingen Germany ; Department of Forest and Wood Science University of Stellenbosch Stellenbosch South Africa
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