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Pomeranz J, Junker JR, Gjoni V, Wesner JS. Maximum likelihood outperforms binning methods for detecting differences in abundance size spectra across environmental gradients. J Anim Ecol 2024; 93:267-280. [PMID: 38167802 DOI: 10.1111/1365-2656.14044] [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: 08/17/2023] [Accepted: 11/21/2023] [Indexed: 01/05/2024]
Abstract
Individual body size distributions (ISD) within communities are remarkably consistent across habitats and spatiotemporal scales and can be represented by size spectra, which are described by a power law. The focus of size spectra analysis is to estimate the exponent (λ ) of the power law. A common application of size spectra studies is to detect anthropogenic pressures. Many methods have been proposed for estimatingλ most of which involve binning the data, counting the abundance within bins, and then fitting an ordinary least squares regression in log-log space. However, recent work has shown that binning procedures return biased estimates ofλ compared to procedures that directly estimateλ using maximum likelihood estimation (MLE). While it is clear that MLE produces less biased estimates of site-specific λ's, it is less clear how this bias affects the ability to test for changes in λ across space and time, a common question in the ecological literature. Here, we used simulation to compare the ability of two normalised binning methods (equal logarithmic and log2 bins) and MLE to (1) recapture known values ofλ , and (2) recapture parameters in a linear regression measuring the change inλ across a hypothetical environmental gradient. We also compared the methods using two previously published body size datasets across a natural temperature gradient and an anthropogenic pollution gradient. Maximum likelihood methods always performed better than common binning methods, which demonstrated consistent bias depending on the simulated values ofλ . This bias carried over to the regressions, which were more accurate whenλ was estimated using MLE compared to the binning procedures. Additionally, the variance in estimates using MLE methods is markedly reduced when compared to binning methods. The error induced by binning methods can be of similar magnitudes as the variation previously published in experimental and observational studies, bringing into question the effect sizes of previously published results. However, while the methods produced different regression slope estimates, they were in qualitative agreement on the sign of those slopes (i.e. all negative or all positive). Our results provide further support for the direct estimation ofλ and its relative variation across environmental gradients using MLE over the more common methods of binning.
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Affiliation(s)
| | - James R Junker
- Great Lakes Research Center, Michigan Technological University, Houghton, Michigan, USA
- Louisiana Universities Marine Consortium, Chauvin, Louisiana, USA
| | - Vojsava Gjoni
- Department of Biology, University of South Dakota, Vermillion, South Dakota, USA
| | - Jeff S Wesner
- Department of Biology, University of South Dakota, Vermillion, South Dakota, USA
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Portela AP, Gonçalves JF, Durance I, Vieira C, Honrado J. Riparian forest response to extreme drought is influenced by climatic context and canopy structure. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 881:163128. [PMID: 37030365 DOI: 10.1016/j.scitotenv.2023.163128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 02/26/2023] [Accepted: 03/24/2023] [Indexed: 06/01/2023]
Abstract
Droughts significantly impact forest ecosystems, reducing forest health and productivity, compromising ecosystem functioning, and nature-based solutions for climate change. The response and resilience of riparian forests to drought are poorly understood despite their key role in the functioning of aquatic and terrestrial ecosystems. Here we investigate riparian forest drought responses and resilience to an extreme drought event at a regional scale. We also examine how drought event characteristics, average climate conditions, topography, soil, vegetation structure, and functional diversity shape the resilience of riparian forests to drought. We used a time series of the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) to calculate the resistance to and recovery after an extreme drought (2017-2018) in 49 sites across an Atlantic-Mediterranean climate gradient in North Portugal. We used generalized additive models and multi-model inference to understand which factors best explained drought responses. We found a trade-off between drought resistance and recovery (maximum r = -0.5) and contrasting strategies across the climatic gradient of the study area. Riparian forests in the Atlantic regions showed comparatively higher resistance, while Mediterranean forests recovered more. Canopy structure and climate context were the most relevant predictors of resistance and recovery. However, median NDVI and NDWI had not returned to pre-drought levels (RcNDWI mean = 1.21, RcNDVI mean = 1.01) three years after the event. Our study shows that riparian forests have contrasting drought response strategies and may be susceptible to extended legacy effects associated with extreme and/or recurring droughts, similarly to upland forests. This work highlights the drought vulnerability of riparian ecosystems and emphasises the need for further studies on long-term resilience to droughts.
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Affiliation(s)
- Ana Paula Portela
- CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto, 4485-661 Vairão, Portugal; Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, 4099-002 Porto, Portugal; BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO, Campus de Vairão, 4485-661 Vairão, Portugal.
| | - João F Gonçalves
- CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto, 4485-661 Vairão, Portugal; BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO, Campus de Vairão, 4485-661 Vairão, Portugal; proMetheus-Research Unit in Materials, Energy and Environment for Sustainability, Instituto Politécnico de Viana do Castelo (IPVC), Avenida do Atlântico, No. 644, 4900-348 Viana do Castelo, Portugal.
| | - Isabelle Durance
- Water Research Institute and School of Biosciences, Cardiff University, The Sir Martin Evans Building, Museum Avenue, Cardiff CF10 3AX, United Kingdom.
| | - Cristiana Vieira
- Museu de História Natural e da Ciência da Universidade do Porto (MHNC-UP/UPorto/PRISC), Praça Gomes Teixeira, 4099-002 Porto, Portugal..
| | - João Honrado
- CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto, 4485-661 Vairão, Portugal; Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, 4099-002 Porto, Portugal; BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO, Campus de Vairão, 4485-661 Vairão, Portugal.
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Abstract
AbstractTrophic transfer efficiency (TTE) is usually calculated as the ratio of production rates between two consecutive trophic levels. Although seemingly simple, TTE estimates from lakes are rare. In our review, we explore the processes and structures that must be understood for a proper lake TTE estimate. We briefly discuss measurements of production rates and trophic positions and mention how ecological efficiencies, nutrients (N, P) and other compounds (fatty acids) affect energy transfer between trophic levels and hence TTE. Furthermore, we elucidate how TTE estimates are linked with size-based approaches according to the Metabolic Theory of Ecology, and how food-web models can be applied to study TTE in lakes. Subsequently, we explore temporal and spatial heterogeneity of production and TTE in lakes, with a particular focus on the links between benthic and pelagic habitats and between the lake and the terrestrial environment. We provide an overview of TTE estimates from lakes found in the published literature. Finally, we present two alternative approaches to estimating TTE. First, TTE can be seen as a mechanistic quantity informing about the energy and matter flow between producer and consumer groups. This approach is informative with respect to food-web structure, but requires enormous amounts of data. The greatest uncertainty comes from the proper consideration of basal production to estimate TTE of omnivorous organisms. An alternative approach is estimating food-chain and food-web efficiencies, by comparing the heterotrophic production of single consumer levels or the total sum of all heterotrophic production including that of heterotrophic bacteria to the total sum of primary production. We close the review by pointing to a few research questions that would benefit from more frequent and standardized estimates of TTE in lakes.
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Saboret G, Buckle DJ, King AJ, Douglas MM, Crook DA. Partial migration in diadromous fishes drives the allocation of subsidies across the freshwater-marine ecotone. ANIMAL MIGRATION 2021. [DOI: 10.1515/ami-2020-0108] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Abstract
Migratory animals can act as cross-boundary subsidies sustaining ecosystem functioning, such as diadromous fishes that migrate between fresh water and seawater and carry nutrients and energy across the freshwater-marine ecotone. Frequency and timing of migration are however highly variable within and among populations. We hypothesized that in catadromous fishes (i.e., diadromous fishes that grow in freshwater and spawn in the sea, such as eels), the import of subsidies by migratory juveniles could outweigh the export of subsidies by adults due to skipped spawning migration. We used the diamond mullet Planiliza ordensis, as a model species, and determined life-history traits using a combination of length-to-age data, acoustic telemetry and otolith (fish ear stone) microchemistry. We used a mass balance approach to model individual mass acquisition and allocation, and extended our model to other life-history strategies. Our results showed high intra-population variation of migratory behaviour in P. ordensis, with few individuals migrating every year to spawn. We estimated that an individual P. ordensis acted as a net 42.6g biomass subsidy in fresh water, representing a retention of more than 50% of the juvenile mass at freshwater entry. Our model predicts that skipped spawning is likely to alter the allocation of subsidies in diadromous species, highlighting the important effects of individual variation in migratory behaviour on fluxes of energy and nutrient at ecosystem scales. We encourage future studies to consider how variation in migratory behaviour is likely to affect the direction and magnitude of biomass fluxes across ecotone boundaries.
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Affiliation(s)
- Grégoire Saboret
- Research Institute for the Environment and Livelihoods , Charles Darwin University , Darwin , 0810, NT , Australia ; Master Biosciences, ENS de Lyon, Département de Biologie , 46 allée d’Italie, 69007 Lyon , France ; Department of Surface Waters, EAWAG, Center for Ecology, Evolution and Biogeochemistry , 6047 Kastanienbaum , Switzerland
| | - Duncan J. Buckle
- Research Institute for the Environment and Livelihoods , Charles Darwin University , Darwin , 0810, NT , Australia
| | - Alison J. King
- Research Institute for the Environment and Livelihoods , Charles Darwin University , Darwin , 0810, NT , Australia
- Centre for Freshwater Ecosystems , La Trobe University , Albury-Wodonga, 3690, New South Wales , Australia
| | - Michael M. Douglas
- Research Institute for the Environment and Livelihoods , Charles Darwin University , Darwin , 0810, NT , Australia
- School of Biological Sciences , The University of Western Australia , 6009, Western Australia , Australia
| | - David A. Crook
- Research Institute for the Environment and Livelihoods , Charles Darwin University , Darwin , 0810, NT , Australia
- Centre for Freshwater Ecosystems , La Trobe University , Albury-Wodonga, 3690, New South Wales , Australia
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Perkins DM, Durance I, Jackson M, Jones JI, Lauridsen RB, Layer-Dobra K, Reiss J, Thompson MSA, Woodward G. Systematic variation in food web body-size structure linked to external subsidies. Biol Lett 2021; 17:20200798. [PMID: 33726566 DOI: 10.1098/rsbl.2020.0798] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The relationship between body mass (M) and size class abundance (N) depicts patterns of community structure and energy flow through food webs. While the general assumption is that M and N scale linearly (on log-log axes), nonlinearity is regularly observed in natural systems, and is theorized to be driven by nonlinear scaling of trophic level (TL) with M resulting in the rapid transfer of energy to consumers in certain size classes. We tested this hypothesis with data from 31 stream food webs. We predicted that allochthonous subsidies higher in the web results in nonlinear M-TL relationships and systematic abundance peaks in macroinvertebrate and fish size classes (latter containing salmonids), that exploit terrestrial plant material and terrestrial invertebrates, respectively. Indeed, both M-N and M-TL significantly deviated from linear relationships and the observed curvature in M-TL scaling was inversely related to that observed in M-N relationships. Systemic peaks in M-N, and troughs in M-TL occurred in size classes dominated by generalist invertebrates, and brown trout. Our study reveals how allochthonous resources entering high in the web systematically shape community size structure and demonstrates the relevance of a generalized metabolic scaling model for understanding patterns of energy transfer in energetically 'open' food webs.
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Affiliation(s)
- Daniel M Perkins
- Department of Life Sciences, Whitelands College, University of Roehampton, London SW15 4JD, UK
| | - Isabelle Durance
- Cardiff Water Research Institute, Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
| | | | - J Iwan Jones
- School of Biological and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK.,Centre for Ecology and Hydrology, Wallingford OX10 8BB, UK
| | - Rasmus B Lauridsen
- School of Biological and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK.,Game and Wildlife Conservation Trust, Salmon and Trout Research Centre, Wareham, Dorset BH20 6BB, UK
| | - Katrin Layer-Dobra
- Grand Challenges in Ecosystems and the Environment, Department of Life Sciences, Imperial College London, Silwood Park Campus SL5 7PY, UK
| | - Julia Reiss
- Department of Life Sciences, Whitelands College, University of Roehampton, London SW15 4JD, UK
| | - Murray S A Thompson
- Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK
| | - Guy Woodward
- Grand Challenges in Ecosystems and the Environment, Department of Life Sciences, Imperial College London, Silwood Park Campus SL5 7PY, UK
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