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Sandal L, Sæther BE, Freckleton RP, Noble DG, Schwarz J, Leivits A, Grøtan V. Species richness and evenness of European bird communities show differentiated responses to measures of productivity. J Anim Ecol 2024. [PMID: 38979934 DOI: 10.1111/1365-2656.14136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Accepted: 05/14/2024] [Indexed: 07/10/2024]
Abstract
Understanding patterns of species diversity is crucial for ecological research and conservation, and this understanding may be improved by studying patterns in the two components of species diversity, species richness and evenness of abundance of species. Variation in species richness and evenness has previously been linked to variation in total abundance of communities as well as productivity gradients. Exploring both components of species diversity is essential because these components could be unrelated or driven by different mechanisms. The aim of this study was to investigate the relationship between species richness and evenness in European bird communities along an extensive latitudinal gradient. We examined their relationships with latitude and Net Primary Productivity, which determines energy and matter availability for heterotrophs, as well as their responses to territory densities (i.e. the number of territories per area) and community biomass (i.e. the bird biomass per area). We applied a multivariate Poisson log-normal distribution to unique long-term, high-quality time-series data, allowing us to estimate species richness of the community as well as the variance of this distribution, which acts as an inverse measure of evenness. Evenness in the distribution of abundance of species in the community was independent of species richness. Species richness increased with increasing community biomass, as well as with increasing density. Since both measures of abundance were explained by NPP, species richness was partially explained by energy-diversity theory (i.e. the more energy, the more species sustained by the ecosystem). However, species richness did not increase linearly with NPP but rather showed a unimodal relationship. Evenness was not explained either by productivity nor by any of the aspects of community abundance. This study highlights the importance of considering both richness and evenness to gain a better understanding of variation in species diversity. We encourage the study of both components of species diversity in future studies, as well as use of simulation studies to verify observed patterns between richness and evenness.
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Affiliation(s)
- Lisa Sandal
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
| | - Bernt-Erik Sæther
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
| | - Robert P Freckleton
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK
| | - David G Noble
- British Trust for Ornithology, Thetford, Norfolk, UK
| | | | - Agu Leivits
- Department of Nature Conservation, Environmental Board, Pärnu, Estonia
| | - Vidar Grøtan
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
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2
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Ruiz-Moreno A, Emslie MJ, Connolly SR. High response diversity and conspecific density-dependence, not species interactions, drive dynamics of coral reef fish communities. Ecol Lett 2024; 27:e14424. [PMID: 38634183 DOI: 10.1111/ele.14424] [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: 01/09/2024] [Revised: 03/11/2024] [Accepted: 03/14/2024] [Indexed: 04/19/2024]
Abstract
Species-to-species and species-to-environment interactions are key drivers of community dynamics. Disentangling these drivers in species-rich assemblages is challenging due to the high number of potentially interacting species (the 'curse of dimensionality'). We develop a process-based model that quantifies how intraspecific and interspecific interactions, and species' covarying responses to environmental fluctuations, jointly drive community dynamics. We fit the model to reef fish abundance time series from 41 reefs of Australia's Great Barrier Reef. We found that fluctuating relative abundances are driven by species' heterogenous responses to environmental fluctuations, whereas interspecific interactions are negligible. Species differences in long-term average abundances are driven by interspecific variation in the magnitudes of both conspecific density-dependence and density-independent growth rates. This study introduces a novel approach to overcoming the curse of dimensionality, which reveals highly individualistic dynamics in coral reef fish communities that imply a high level of niche structure.
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Affiliation(s)
- Alfonso Ruiz-Moreno
- College of Science and Engineering, James Cook University, Townsville, Queensland, Australia
- Australian Institute of Marine Science, Townsville, Queensland, Australia
- Smithsonian Tropical Research Institute, Panama City, Panama
| | - Michael J Emslie
- Australian Institute of Marine Science, Townsville, Queensland, Australia
| | - Sean R Connolly
- Smithsonian Tropical Research Institute, Panama City, Panama
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3
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Fung T, Pande J, Shnerb NM, O'Dwyer JP, Chisholm RA. Processes governing species richness in communities exposed to temporal environmental stochasticity: A review and synthesis of modelling approaches. Math Biosci 2024; 369:109131. [PMID: 38113973 DOI: 10.1016/j.mbs.2023.109131] [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: 06/30/2023] [Revised: 11/10/2023] [Accepted: 12/15/2023] [Indexed: 12/21/2023]
Abstract
Research into the processes governing species richness has often assumed that the environment is fixed, whereas realistic environments are often characterised by random fluctuations over time. This temporal environmental stochasticity (TES) changes the demographic rates of species populations, with cascading effects on community dynamics and species richness. Theoretical and applied studies have used process-based mathematical models to determine how TES affects species richness, but under a variety of frameworks. Here, we critically review such studies to synthesise their findings and draw general conclusions. We first provide a broad mathematical framework encompassing the different ways in which TES has been modelled. We then review studies that have analysed models with TES under the assumption of negligible interspecific interactions, such that a community is conceptualised as the sum of independent species populations. These analyses have highlighted how TES can reduce species richness by increasing the frequency at which a species becomes rare and therefore prone to extinction. Next, we review studies that have relaxed the assumption of negligible interspecific interactions. To simplify the corresponding models and make them analytically tractable, such studies have used mean-field theory to derive fixed parameters representing the typical strength of interspecific interactions under TES. The resulting analyses have highlighted community-level effects that determine how TES affects species richness, for species that compete for a common limiting resource. With short temporal correlations of environmental conditions, a non-linear averaging effect of interspecific competition strength over time gives an increase in species richness. In contrast, with long temporal correlations of environmental conditions, strong selection favouring the fittest species between changes in environmental conditions results in a decrease in species richness. We compare such results with those from invasion analysis, which examines invasion growth rates (IGRs) instead of species richness directly. Qualitative differences sometimes arise because the IGR is the expected growth rate of a species when it is rare, which does not capture the variation around this mean or the probability of the species becoming rare. Our review elucidates key processes that have been found to mediate the negative and positive effects of TES on species richness, and by doing so highlights key areas for future research.
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Affiliation(s)
- Tak Fung
- Department of Biological Sciences, National University of Singapore, 16 Science Drive 4, Singapore 117558, Singapore.
| | - Jayant Pande
- Department of Physical and Natural Sciences, FLAME University, Pune, Maharashtra 412115, India
| | - Nadav M Shnerb
- Department of Physics, Bar-Ilan University, Ramat Gan 52900, Israel
| | - James P O'Dwyer
- Department of Plant Biology, School of Integrative Biology, University of Illinois, 505, South Goodwin Avenue, Urbana, IL 61801, United States
| | - Ryan A Chisholm
- Department of Biological Sciences, National University of Singapore, 16 Science Drive 4, Singapore 117558, Singapore
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4
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Saether BE, Engen S, Solbu EB. Assessing the sensitivity and resistance of communities in a changing environment. J Anim Ecol 2024; 93:8-20. [PMID: 37740526 DOI: 10.1111/1365-2656.14003] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Accepted: 08/28/2023] [Indexed: 09/24/2023]
Abstract
We propose that the ecological resilience of communities to permanent changes of the environment can be based on how variation in the overall abundance of individuals affects the number of species. Community sensitivity is defined as the ratio between the rate of change in the log expected number of species and the rate of change in the log expected number of individuals in the community. High community sensitivity means that small changes in the total abundance strongly impact the number of species. Community resistance is the proportional reduction in expected number of individuals that the community can sustain before expecting to lose one species. A small value of community resistance means that the community can only endure a small reduction in abundance before it is expected to lose one species. Based on long-term studies of four bird communities in European deciduous forests at different latitudes large differences were found in the resilience to environmental perturbations. Estimating the variance components of the species abundance distribution revealed how different processes contributed to the community sensitivity and resistance. Species heterogeneity in the population dynamics was the largest component, but its proportion varied among communities. Species-specific response to environmental fluctuations was the second major component of the variation in abundance. Estimates of community sensitivity and resistance based on data only from a single year were in general larger than those based on estimates from longer time series. Thus, our approach can provide rapid and conservative assessment of the resilience of communities to environmental changes also including only short-term data. This study shows that a general ecological mechanism, caused by increased strength of density dependence due to reduction in resource availability, can provide an intuitive measure of community resilience to environmental variation. Our analyses also illustrate the importance of including specific assumptions about how different processes affect community dynamics. For example, if stochastic fluctuations in the environment affect all species in a similar way, the sensitivity and resistance of the community to environmental changes will be different from communities in which all species show independent responses.
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Affiliation(s)
- Bernt-Erik Saether
- Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Steinar Engen
- Department of Mathematical Sciences, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Erik Blystad Solbu
- Department of Landscape and Biodiversity, Norwegian Institute of Bioeconomy Research (NIBIO), Trondheim, Norway
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Bellier E, Engen S, Jensen TC. Seasonal diversity dynamics of a boreal zooplankton community under climate impact. Oecologia 2022; 199:139-152. [PMID: 35471618 PMCID: PMC9120095 DOI: 10.1007/s00442-022-05165-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 04/02/2022] [Indexed: 12/03/2022]
Abstract
Seasonality and long-term environmental variability affect species diversity through their effects on the dynamics of species. To investigate such effects, we fitted a dynamic and heterogeneous species abundance model generating the lognormal species abundance distribution to an assemblage of freshwater zooplankton sampled five times a year (June-October) during the ice-free period over 28 years (1990-2017) in Lake Atnsjøen (Norway). By applying a multivariate stochastic community dynamics model for describing the fluctuations in abundances, we show that the community dynamics was driven by environmental variability in spring (i.e., June). In contrast, community-level ecological heterogeneity is highest in autumn. The autumn months (i.e., September and October) that rearranged the community are most likely crucial months to monitor long-term changes in community structure. Indeed, noises from early summer are filtered away, making it easier to track long-term changes. The community returned faster towards equilibrium when ecological heterogeneity was the highest (i.e., in September and October). This occurred because of stronger density-regulation in months with highest ecological heterogeneity. The community responded to the long-term warming of water temperature with decreasing species diversity and increasing abundance. Unevenness associated with variabilities in abundances might affect species interactions within the community. These can have consequences for the stability and functioning of the ecosystem.
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Affiliation(s)
- Edwige Bellier
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, 9037, Tromsø, Norway.
- Department of Natural Resources Science, University of Rhode Island, Kingston, RI, 02881, USA.
| | - Steinar Engen
- Centre for Biodiversity Dynamics, Department of Mathematical Science, Norwegian University for Science and Technology, 7491, Trondheim, Norway
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Fung T, O'Dwyer JP, Chisholm RA. Effects of temporal environmental stochasticity on species richness: a mechanistic unification spanning weak to strong temporal correlations. OIKOS 2021. [DOI: 10.1111/oik.08667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Tak Fung
- National Univ. of Singapore, Dept of Biological Sciences Singapore Singapore
| | - James P. O'Dwyer
- Dept of Plant Biology, School of Integrative Biology, Univ. of Illinois Urbana IL USA
| | - Ryan A. Chisholm
- National Univ. of Singapore, Dept of Biological Sciences Singapore Singapore
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8
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Mechanism, Process, and Causation in Ecological Models: A Reply to McGill and Potochnik. Trends Ecol Evol 2017; 33:305-306. [PMID: 29279296 DOI: 10.1016/j.tree.2017.11.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 11/30/2017] [Indexed: 11/23/2022]
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Fung T, O'Dwyer JP, Rahman KA, Fletcher CD, Chisholm RA. Reproducing static and dynamic biodiversity patterns in tropical forests: the critical role of environmental variance. Ecology 2016; 97:1207-17. [PMID: 27349097 DOI: 10.1890/15-0984.1] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Ecological communities are subjected to stochasticity in the form of demographic and environmental variance. Stochastic models that contain only demographic variance (neutral models) provide close quantitative fits to observed species-abundance distributions (SADs) but substantially underestimate observed temporal species-abundance fluctuations. To provide a holistic assessment of whether models with demographic and environmental variance perform better than neutral models, the fit of both to SADs and temporal species-abundance fluctuations at the same time has to be tested quantitatively. In this study, we quantitatively test how closely a model with demographic and environmental variance reproduces total numbers of species, total abundances, SADs and temporal species-abundance fluctuations for two tropical forest tree communities, using decadal data from long-term monitoring plots and considering individuals larger than two size thresholds for each community. We find that the model can indeed closely reproduce these static and dynamic patterns of biodiversity in the two communities for the two size thresholds, with better overall fits than corresponding neutral models. Therefore, our results provide evidence that stochastic models incorporating demographic and environmental variance can simultaneously capture important static and dynamic biodiversity patterns arising in tropical forest communities.
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Solbu EB, Engen S, Diserud OH. Characteristics of temporal changes in communities where dynamics differ between species. Theor Popul Biol 2016; 111:65-74. [PMID: 27393240 DOI: 10.1016/j.tpb.2016.06.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Revised: 05/26/2016] [Accepted: 06/13/2016] [Indexed: 11/30/2022]
Abstract
Communities with different phenotypic variation among species can have identical species abundance distributions, although their temporal dynamics may be very different. By using stochastic species abundance models, both the lognormal and beta prime abundance distributions can be obtained with either homogeneous or heterogeneous dynamics among species. Assuming that anthropogenic activity disturbs the communities such that species' carrying capacities are decreasing deterministically, the structure of the communities are studied using simulations. In order to construct homogeneous communities with reasonable variation in abundance, the parameter values describing the dynamics of the species can be unrealistic in terms of long return times to equilibrium. Species in heterogeneous communities can have stronger density regulation, while maintaining the same variation in abundance, by assuming heterogeneity in one of the dynamical parameters. The heterogeneity generates variation in carrying capacity among species, while reducing the temporal stochasticity. If carrying capacity decreases, changes in community structure occur at a much slower rate for the homogeneous compared to the heterogeneous communities. Even over short time periods, the difference in response to deterministic changes in carrying capacity between homogeneous and heterogeneous community models can be substantial, making the heterogeneous model a recommended starting point for community analysis.
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Affiliation(s)
- Erik Blystad Solbu
- Centre for Biodiversity Dynamics, Department of Mathematical Sciences, Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
| | - Steinar Engen
- Centre for Biodiversity Dynamics, Department of Mathematical Sciences, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
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11
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Fung T, O'Dwyer JP, Chisholm RA. Species-abundance distributions under colored environmental noise. J Math Biol 2016; 74:289-311. [PMID: 27225431 DOI: 10.1007/s00285-016-1022-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2015] [Revised: 05/03/2016] [Indexed: 11/26/2022]
Abstract
Natural communities at all spatiotemporal scales are subjected to a wide variety of environmental pressures, resulting in random changes in the demographic rates of species populations. Previous analyses have examined the effects of such environmental variance on the long-term growth rate and time to extinction of single populations, but studies of its effects on the diversity of communities remain scarce. In this study, we construct a new master-equation model incorporating demographic and environmental variance and use it to examine how statistical patterns of diversity, as encapsulated by species-abundance distributions (SADs), are altered by environmental variance. Unlike previous diffusion models with environmental variance uncorrelated in time (white noise), our model allows environmental variance to be correlated at different timescales (colored noise), thus facilitating representation of phenomena such as yearly and decadal changes in climate. We derive an exact analytical expression for SADs predicted by our model together with a close approximation, and use them to show that the main effect of adding environmental variance is to increase the proportion of abundant species, thus flattening the SAD relative to the log-series form found in the neutral case. This flattening effect becomes more prominent when environmental variance is more correlated in time and has greater effects on species' demographic rates, holding all other factors constant. Furthermore, we show how our model SADs are consistent with those from diffusion models near the white noise limit. The mathematical techniques we develop are catalysts for further theoretical work exploring the consequences of environmental variance for biodiversity.
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Affiliation(s)
- Tak Fung
- Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, 117543, Singapore, Singapore.
| | - James P O'Dwyer
- Department of Plant Biology, School of Integrative Biology, University of Illinois, 505 S. Goodwin Avenue, Urbana, IL, 61801, USA
| | - Ryan A Chisholm
- Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, 117543, Singapore, Singapore
- Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panama
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Fung T, Villain L, Chisholm RA. Analytical formulae for computing dominance from species-abundance distributions. J Theor Biol 2015; 386:147-58. [PMID: 26409166 DOI: 10.1016/j.jtbi.2015.09.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Revised: 08/06/2015] [Accepted: 09/12/2015] [Indexed: 10/23/2022]
Abstract
The evenness of an ecological community affects ecosystem structure, functioning and stability, and has implications for biodiversity conservation. In uneven communities, most species are rare while a few dominant species drive ecosystem-level properties. In even communities, dominance is lower, with possibly many species playing key ecological roles. The dominance aspect of evenness can be measured as a decreasing function of the proportion of species required to make up a fixed fraction (e.g., half) of individuals in a community. Here we sought general rules about dominance in ecological communities by linking dominance mathematically to the parameters of common theoretical species-abundance distributions (SADs). We found that if a community's SAD was log-series or lognormal, then dominance was almost inevitably high, with fewer than 40% of species required to account for 90% of all individuals. Dominance for communities with an exponential SAD was lower but still typically high, with fewer than 40% of species required to account for 70% of all individuals. In contrast, communities with a gamma SAD only exhibited high dominance when the average species abundance was below a threshold of approximately 100. Furthermore, we showed that exact values of dominance were highly scale-dependent, exhibiting non-linear trends with changing average species abundance. We also applied our formulae to SADs derived from a mechanistic community model to demonstrate how dominance can increase with environmental variance. Overall, our study provides a rigorous basis for theoretical explorations of the dynamics of dominance in ecological communities, and how this affects ecosystem functioning and stability.
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Affiliation(s)
- Tak Fung
- National University of Singapore, Department of Biological Sciences, 14 Science Drive 4, 117543 Singapore.
| | - Laura Villain
- Institut National des Sciences Appliquées de Lyon, 20 Avenue Albert Einstein, Villeurbanne cedex, 69621 Lyon, France.
| | - Ryan A Chisholm
- National University of Singapore, Department of Biological Sciences, 14 Science Drive 4, 117543 Singapore; Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panama.
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Sæther BE, Engen S, Grøtan V. Species diversity and community similarity in fluctuating environments: parametric approaches using species abundance distributions. J Anim Ecol 2013; 82:721-38. [PMID: 23578202 DOI: 10.1111/1365-2656.12068] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Accepted: 02/07/2013] [Indexed: 11/30/2022]
Abstract
Here we review recent advances in characterizing pattern of variation in community structure in space and time based on parametric approaches utilizing the full distribution of abundances of species rather than some summary indices. Assessment of biodiversity based on the structure of rank-abundance plots or simple species diversity indices, which describe properties of the sample of individuals, may reveal limited information about the underlying species abundance distribution of the community because the number of individuals counted are dependent on the sampling intensity. For instance, assuming Poisson sampling and an underlying lognormal species abundance distribution implies that observed abundances (counts) are a sample from a Poisson lognormal distribution. A convenient property of this distribution is that the estimate of σ(2) can be used as an inverse measure of species diversity in a community as well as the number of unobserved species can be estimated approximately without bias for unknown sampling intensities. If two communities can be described by a bivariate lognormal species abundance model, then the correlation between the log abundances of species in the two communities is an index of similarity that can be estimated without knowledge of sampling intensities using the bivariate Poisson lognormal distribution. This method is even applicable as an approximation when the abundance distribution deviates from the lognormal. An analysis of the interrelationship between the parameters of the lognormal species abundance distribution in communities of species from a wide variety of taxa shows that the canonical hypothesis of Preston in general, for a given number of species, gives far too large variances in the distribution of log abundances. A general feature in community dynamics is that a large component of the variance in the species abundance distribution is caused by heterogeneity among species in the population dynamics as well as environmental noise. This pattern is in contrast to the assumptions of the neutral theory of community dynamics. The choice of species abundance distribution should be a consequence of specific assumptions about the dynamics of the species. We suggest that such specific assumptions for the choice of species abundance model will facilitate more robust comparisons of changes in community structure in time and space.
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Affiliation(s)
- Bernt-Erik Sæther
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Realfagbygget NO 7491, Trondheim, Norway
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Combining counts and incidence data: an efficient approach for estimating the log-normal species abundance distribution and diversity indices. Oecologia 2012; 170:477-88. [DOI: 10.1007/s00442-012-2311-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2011] [Accepted: 03/15/2012] [Indexed: 10/28/2022]
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