Publications by authors named "David Storch"

34 Publications

A meta-analysis of global fungal distribution reveals climate-driven patterns.

Nat Commun 2019 11 13;10(1):5142. Epub 2019 Nov 13.

Laboratory of Environmental Microbiology, Institute of Microbiology of the Czech Academy of Sciences, Vídeňská 1083, 14220, Praha 4, Czech Republic.

The evolutionary and environmental factors that shape fungal biogeography are incompletely understood. Here, we assemble a large dataset consisting of previously generated mycobiome data linked to specific geographical locations across the world. We use this dataset to describe the distribution of fungal taxa and to look for correlations with different environmental factors such as climate, soil and vegetation variables. Our meta-study identifies climate as an important driver of different aspects of fungal biogeography, including the global distribution of common fungi as well as the composition and diversity of fungal communities. In our analysis, fungal diversity is concentrated at high latitudes, in contrast with the opposite pattern previously shown for plants and other organisms. Mycorrhizal fungi appear to have narrower climatic tolerances than pathogenic fungi. We speculate that climate change could affect ecosystem functioning because of the narrow climatic tolerances of key fungal taxa.
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http://dx.doi.org/10.1038/s41467-019-13164-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6853883PMC
November 2019

A Minimal Model for the Latitudinal Diversity Gradient Suggests a Dominant Role for Ecological Limits.

Am Nat 2019 11 23;194(5):E122-E133. Epub 2019 Aug 23.

The latitudinal diversity gradient (LDG) is one of Earth's most iconic biodiversity patterns and still one of the most debated. Explanations for the LDG are often categorized into three broad pathways in which the diversity gradient is created by (1) differential diversification rates, (2) differential carrying capacities (ecological limits), or (3) differential time to accumulate species across latitude. Support for these pathways has, however, been mostly verbally expressed. Here, we present a minimal model to clarify the essential assumptions of the three pathways and explore the sensitivity of diversity dynamics to these pathways. We find that an LDG arises most easily from a gradient in ecological limits compared with a gradient in the time for species accumulation or diversification rate in most modeled scenarios. Differential diversification rates create a stronger LDG than ecological limits only when speciation and dispersal rates are low, but then the predicted LDG seems weaker than the observed LDG. Moreover, range dynamics may reduce an LDG created by a gradient in diversification rates or time for species accumulation, but they cannot reduce an LDG induced by differential ecological limits. We conclude that our simple model provides a null prediction for the effectiveness of the three LDG pathways and can thus aid discussions about the causal mechanisms underlying the LDG or motivate more complex models to confirm or falsify our findings.
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http://dx.doi.org/10.1086/705243DOI Listing
November 2019

Linking scaling laws across eukaryotes.

Proc Natl Acad Sci U S A 2019 10 7;116(43):21616-21622. Epub 2019 Oct 7.

Centre for Biodiversity Theory and Modelling, Theoretical and Experimental Ecology Station, CNRS, 09200 Moulis, France.

Scaling laws relating body mass to species characteristics are among the most universal quantitative patterns in biology. Within major taxonomic groups, the 4 key ecological variables of metabolism, abundance, growth, and mortality are often well described by power laws with exponents near 3/4 or related to that value, a commonality often attributed to biophysical constraints on metabolism. However, metabolic scaling theories remain widely debated, and the links among the 4 variables have never been formally tested across the full domain of eukaryote life, to which prevailing theory applies. Here we present datasets of unprecedented scope to examine these 4 scaling laws across all eukaryotes and link them to test whether their combinations support theoretical expectations. We find that metabolism and abundance scale with body size in a remarkably reciprocal fashion, with exponents near ±3/4 within groups, as expected from metabolic theory, but with exponents near ±1 across all groups. This reciprocal scaling supports "energetic equivalence" across eukaryotes, which hypothesizes that the partitioning of energy in space across species does not vary significantly with body size. In contrast, growth and mortality rates scale similarly both within and across groups, with exponents of ±1/4. These findings are inconsistent with a metabolic basis for growth and mortality scaling across eukaryotes. We propose that rather than limiting growth, metabolism adjusts to the needs of growth within major groups, and that growth dynamics may offer a viable theoretical basis to biological scaling.
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http://dx.doi.org/10.1073/pnas.1900492116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6815163PMC
October 2019

The Latitudinal Diversity Gradient: Novel Understanding through Mechanistic Eco-evolutionary Models.

Trends Ecol Evol 2019 03 24;34(3):211-223. Epub 2018 Dec 24.

Department of Biology and Curriculum in Environment and Ecology, University of North Carolina, Chapel Hill, NC 27599, USA.

The latitudinal diversity gradient (LDG) is one of the most widely studied patterns in ecology, yet no consensus has been reached about its underlying causes. We argue that the reasons for this are the verbal nature of existing hypotheses, the failure to mechanistically link interacting ecological and evolutionary processes to the LDG, and the fact that empirical patterns are often consistent with multiple explanations. To address this issue, we synthesize current LDG hypotheses, uncovering their eco-evolutionary mechanisms, hidden assumptions, and commonalities. Furthermore, we propose mechanistic eco-evolutionary modeling and an inferential approach that makes use of geographic, phylogenetic, and trait-based patterns to assess the relative importance of different processes for generating the LDG.
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http://dx.doi.org/10.1016/j.tree.2018.11.009DOI Listing
March 2019

Direct and indirect effects of climate on richness drive the latitudinal diversity gradient in forest trees.

Ecol Lett 2019 Feb 12;22(2):245-255. Epub 2018 Dec 12.

Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, 650223, Kunming.

Climate is widely recognised as an important determinant of the latitudinal diversity gradient. However, most existing studies make no distinction between direct and indirect effects of climate, which substantially hinders our understanding of how climate constrains biodiversity globally. Using data from 35 large forest plots, we test hypothesised relationships amongst climate, topography, forest structural attributes (stem abundance, tree size variation and stand basal area) and tree species richness to better understand drivers of latitudinal tree diversity patterns. Climate influences tree richness both directly, with more species in warm, moist, aseasonal climates and indirectly, with more species at higher stem abundance. These results imply direct limitation of species diversity by climatic stress and more rapid (co-)evolution and narrower niche partitioning in warm climates. They also support the idea that increased numbers of individuals associated with high primary productivity are partitioned to support a greater number of species.
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http://dx.doi.org/10.1111/ele.13175DOI Listing
February 2019

Macroecology to Unite All Life, Large and Small.

Trends Ecol Evol 2018 10 9;33(10):731-744. Epub 2018 Sep 9.

German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, 04103 Leipzig, Germany; Department of Computer Science, Martin Luther University, Halle-Wittenberg, Saxony-Anhalt, Germany.

Macroecology is the study of the mechanisms underlying general patterns of ecology across scales. Research in microbial ecology and macroecology have long been detached. Here, we argue that it is time to bridge the gap, as they share a common currency of species and individuals, and a common goal of understanding the causes and consequences of changes in biodiversity. Microbial ecology and macroecology will mutually benefit from a unified research agenda and shared datasets that span the entirety of the biodiversity of life and the geographic expanse of the Earth.
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http://dx.doi.org/10.1016/j.tree.2018.08.005DOI Listing
October 2018

Carnivore distribution across habitats in a central-European landscape: a camera trap study.

Zookeys 2018 4(770):227-246. Epub 2018 Jul 4.

Department of Ecology, Faculty of Science, Charles University, Viničná 7, CZ-12844 Prague 2, Czech Republic.

Quantitative data on local variation in patterns of occurrence of common carnivore species, such as the red fox, European badger, or martens in central Europe are largely missing. We conducted a study focusing on carnivore ecology and distribution in a cultural landscape with the use of modern technology. We placed 73 automated infra-red camera traps into four different habitats differing in water availability and canopy cover (mixed forest, wetland, shrubby grassland and floodplain forest) in the Polabí region near Prague, Czech Republic. Each habitat was represented by three or four spatially isolated sites within which the camera traps were distributed. During the year of the study, we recorded nine carnivore species, including the non-native golden jackal. Habitats with the highest numbers of records pooled across all species were wetland (1279) and shrubby grassland (1014); fewer records were made in mixed (876) and floodplain forest (734). Habitat had a significant effect on the number of records of badger and marten, and a marginally significant effect on fox. In terms of seasonal dynamics, there were significant differences in the distribution of records among seasons in fox, marginally significant in least weasel, and the occurrence among seasons did not differ for badger and marten. In the summer, fox and marten were more active than expected by chance during the day, while the pattern was opposite in winter when they were more active during the night. Our findings on habitat preferences and circadian and seasonal activity provided the first quantitative data on patterns whose existence was assumed on the basis of conventional wisdom. Our study demonstrates the potential of a long-term monitoring approach based on infra-red camera traps. Generally, the rather frequent occurrence of recorded species indicates that most carnivore species are thriving in current central-European landscapes characterized by human-driven disturbances and urbanization.
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http://dx.doi.org/10.3897/zookeys.770.22554DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6041352PMC
July 2018

The more-individuals hypothesis revisited: the role of community abundance in species richness regulation and the productivity-diversity relationship.

Ecol Lett 2018 06 16;21(6):920-937. Epub 2018 Apr 16.

School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.

Species richness increases with energy availability, yet there is little consensus as to the exact processes driving this species-energy relationship. The most straightforward explanation is the more-individuals hypothesis (MIH). It states that higher energy availability promotes a higher total number of individuals in a community, which consequently increases species richness by allowing for a greater number of species with viable populations. Empirical support for the MIH is mixed, partially due to the lack of proper formalisation of the MIH and consequent confusion as to its exact predictions. Here, we review the evidence of the MIH and evaluate the reliability of various predictions that have been tested. There is only limited evidence that spatial variation in species richness is driven by variation in the total number of individuals. There are also problems with measures of energy availability, with scale-dependence, and with the direction of causality, as the total number of individuals may sometimes itself be driven by the number of species. However, even in such a case the total number of individuals may be involved in diversity regulation. We propose a formal theory that encompasses these processes, clarifying how the different factors affecting diversity dynamics can be disentangled.
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http://dx.doi.org/10.1111/ele.12941DOI Listing
June 2018

Equilibrium dynamics of European pre-industrial populations: the evidence of carrying capacity in human agricultural societies.

Proc Biol Sci 2018 01;285(1871)

Center for Theoretical Study, Charles University and Academy of Sciences of the CR, Jilská 1, Praha 1, 110 00, Czech Republic.

Human populations tend to grow steadily, because of the ability of people to make innovations, and thus overcome and extend the limits imposed by natural resources. It is therefore questionable whether traditional concepts of population ecology, including environmental carrying capacity, can be applied to human societies. The existence of carrying capacity cannot be simply inferred from population time-series, but it can be indicated by the tendency of populations to return to a previous state after a disturbance. So far only indirect evidence at a coarse-grained scale has indicated the historical existence of human carrying capacity. We analysed unique historical population data on 88 settlements before and after the Thirty Years War (1618-1648), one the longest and most destructive conflicts in European history, which reduced the population of Central Europe by 30-50%. The recovery rate of individual settlements after the war was positively correlated with the extent of the disturbance, so that the population size of the settlements after a period of regeneration was similar to the pre-war situation, indicating an equilibrium population size (i.e. carrying capacity). The carrying capacity of individual settlements was positively determined mostly by the fertility of the soil and the area of the cadastre, and negatively by the number of other settlements in the surroundings. Pre-industrial human population sizes were thus probably controlled by negative density dependence mediated by soil fertility, which could not increase due to limited agricultural technologies.
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http://dx.doi.org/10.1098/rspb.2017.2500DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5805945PMC
January 2018

Golden jackal () in the Czech Republic: the first record of a live animal and its long-term persistence in the colonized habitat.

Zookeys 2016 16(641):151-163. Epub 2016 Dec 16.

Institute of Botany, Department of Invasion Ecology, The Czech Academy of Sciences, CZ-25243 Průhonice, Czech Republic; Department of Ecology, Faculty of Science, Charles University, Viničná 7, CZ-12844 Prague 2, Czech Republic.

A golden jackal () individual was recorded ~40 km east of Prague in the Czech Republic. It is the first record of a living golden jackal in the country; up to now several individuals have been recorded but all of them were either shot dead or killed by a vehicle. The observed animal was documented by camera traps set up for research of carnivore diversity in different habitats in the study area. It was first photographed on 19 June 2015, and in total there were 57 records made by 12 traps until 24 March 2016 when the animal was still present in the area. Forty-nine of the 57 records were made in a shrubby grassland over an area of ~100 ha, 39% of sightings were during the day and 61% in the night. There were two distinct peaks in the circadian activity of the animal, from 4 to 10 a.m., and from 6 p.m. to midnight. We also review the verified records of the golden jackal in the Czech Republic, some of which were only published in local hunting magazines. However, the observation reported in this paper represents the first evidence of a long-term occurrence in Europe of the same golden jackal individual, that persisted for at least nine months and over winter, northwest of Hungarian-Austrian border where the population has been known to reproduce.
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http://dx.doi.org/10.3897/zookeys.641.10946DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5240352PMC
December 2016

On the decline of biodiversity due to area loss.

Nat Commun 2015 Nov 17;6:8837. Epub 2015 Nov 17.

Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street, New Haven, Connecticut 06520-8106, USA.

Predictions of how different facets of biodiversity decline with habitat loss are broadly needed, yet challenging. Here we provide theory and a global empirical evaluation to address this challenge. We show that extinction estimates based on endemics-area and backward species-area relationships are complementary, and the crucial difference comprises the geometry of area loss. Across three taxa on four continents, the relative loss of species, and of phylogenetic and functional diversity, is highest when habitable area disappears inward from the edge of a region, lower when it disappears from the centre outwards, and lowest when area is lost at random. In inward destruction, species loss is almost proportional to area loss, although the decline in phylogenetic and functional diversity is less severe. These trends are explained by the geometry of species ranges and the shape of phylogenetic and functional trees, which may allow baseline predictions of biodiversity decline for underexplored taxa.
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http://dx.doi.org/10.1038/ncomms9837DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4660053PMC
November 2015

Niche and metabolic principles explain patterns of diversity and distribution: theory and a case study with soil bacterial communities.

Proc Biol Sci 2015 Jun;282(1809):20142630

Department of Biology, University of New Mexico, Albuquerque, NM, USA.

The causes of biodiversity patterns are controversial and elusive due to complex environmental variation, covarying changes in communities, and lack of baseline and null theories to differentiate straightforward causes from more complex mechanisms. To address these limitations, we developed general diversity theory integrating metabolic principles with niche-based community assembly. We evaluated this theory by investigating patterns in the diversity and distribution of soil bacteria taxa across four orders of magnitude variation in spatial scale on an Antarctic mountainside in low complexity, highly oligotrophic soils. Our theory predicts that lower temperatures should reduce taxon niche widths along environmental gradients due to decreasing growth rates, and the changing niche widths should lead to contrasting α- and β-diversity patterns. In accord with the predictions, α-diversity, niche widths and occupancies decreased while β-diversity increased with increasing elevation and decreasing temperature. The theory also successfully predicts a hump-shaped relationship between α-diversity and pH and a negative relationship between α-diversity and salinity. Thus, a few simple principles explained systematic microbial diversity variation along multiple gradients. Such general theory can be used to disentangle baseline effects from more complex effects of temperature and other variables on biodiversity patterns in a variety of ecosystems and organisms.
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http://dx.doi.org/10.1098/rspb.2014.2630DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4590432PMC
June 2015

Differential effects of temperature change and human impact on European Late Quaternary mammalian extinctions.

Glob Chang Biol 2015 Apr 26;21(4):1475-81. Epub 2014 Nov 26.

Department of Ecology, Faculty of Science, Charles University, Vinicná 7, 128 44 Praha 2, Prague, Czech Republic; Departamento de Ecologia, Instituto de Ciências Biológicas, Universidade Federal de Goiás, CxP 131, Goiania, GO, 74001-970, Brasil.

Species that inhabited Europe during the Late Quaternary were impacted by temperature changes and early humans, resulting in the disappearance of half of the European large mammals. However, quantifying the relative importance that each factor had in the extinction risk of species has been challenging, mostly due to the spatio-temporal biases of fossil records, which complicate the calibration of realistic and accurate ecological niche modeling. Here, we overcome this problem by using ecotypes, and not real species, to run our models. We created 40 ecotypes with different temperature requirements (mean temperature from -20 °C to 25 °C and temperature range from 10 °C to 40 °C) and used them to quantify the effect of climate change and human impact. Our results show that cold-adapted ecotypes would have been highly affected by past temperature changes in Europe, whereas temperate and warm-adapted ecotypes would have been positively affected by temperature change. Human impact affected all ecotypes negatively, and temperate ecotypes suffered the greatest impacts. Based on these results, the extinction of cold-adapted species like Mammuthus primigenius may be related to temperature change, while the extinction of temperate species, like Crocuta crocuta, may be related to human impact. Our results suggest that temperature change and human impact affected different ecotypes in distinct ways, and that the interaction of both impacts may have shaped species extinctions in Europe.
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http://dx.doi.org/10.1111/gcb.12763DOI Listing
April 2015

Comment on "High-resolution global maps of 21st-century forest cover change".

Science 2014 May;344(6187):981

Department of Ecology, Faculty of Science, Charles University in Prague, Vinicna 7, CZ-128 44 Praha 2, Czech Republic. Center for Theoretical Study, Charles University in Prague and Academy of Sciences of the Czech Republic, Jilska 1, CZ-110 00 Praha 1, Czech Republic.

Hansen et al. (Reports, 15 November 2013, p. 850) published a high-resolution global forest map with detailed information on local forest loss and gain. We show that their product does not distinguish tropical forests from plantations and even herbaceous crops, which leads to a substantial underestimate of forest loss and compromises its value for local policy decisions.
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http://dx.doi.org/10.1126/science.1248753DOI Listing
May 2014

Ecological causes of decelerating diversification in carnivoran mammals.

Evolution 2013 Aug 3;67(8):2423-33. Epub 2013 May 3.

Department of Ecology and Evolution, Stony Brook University, Stony Brook, New York 11794-5245, USA.

Clade diversification is a central topic in macroevolutionary studies. Recently, it has been shown that diversification rates appear to decelerate over time in many clades. What causes this deceleration remains unclear, but it has been proposed that competition for limited resources between sympatric, ecologically similar species slows diversification. Employing carnivoran mammals as a model system, we test this hypothesis using a comprehensive time-calibrated phylogeny. We also explore several conceptually related explanations including limited geographic area and limited rates of niche evolution. We find that diversification slowdowns are strong in carnivorans. Surprisingly, these slowdowns are independent of geographic range overlap between related species and are also decoupled from rates of niche evolution, suggesting that slowdowns are unrelated to competition and niche filling. When controlling for the effects of clade diversity, diversification slowdowns appear independent of geographic area. There is a significant effect of clade diversity on diversification slowdowns, but simulations show that this relationship may arise as a statistical artifact (i.e., greater clade diversity increases the ability of the gamma statistic to refute constant diversification). Overall, our results emphasize the need to test hypotheses about the causes of diversification slowdowns with ecological data, rather than assuming ecological processes from phylogenies alone.
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http://dx.doi.org/10.1111/evo.12126DOI Listing
August 2013

Universal species-area and endemics-area relationships at continental scales.

Nature 2012 Aug;488(7409):78-81

Center for Theoretical Study, Charles University, Praha, Czech Republic.

Despite the broad conceptual and applied relevance of how the number of species or endemics changes with area (the species-area and endemics-area relationships (SAR and EAR)), our understanding of universality and pervasiveness of these patterns across taxa and regions has remained limited. The SAR has traditionally been approximated by a power law, but recent theories predict a triphasic SAR in logarithmic space, characterized by steeper increases in species richness at both small and large spatial scales. Here we uncover such universally upward accelerating SARs for amphibians, birds and mammals across the world’s major landmasses. Although apparently taxon-specific and continent-specific, all curves collapse into one universal function after the area is rescaled by using the mean range sizes of taxa within continents. In addition, all EARs approximately follow a power law with a slope close to 1, indicating that for most spatial scales there is roughly proportional species extinction with area loss. These patterns can be predicted by a simulation model based on the random placement of contiguous ranges within a domain. The universality of SARs and EARs after rescaling implies that both total and endemic species richness within an area, and also their rate of change with area, can be estimated by using only the knowledge of mean geographic range size in the region and mean species richness at one spatial scale.
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http://dx.doi.org/10.1038/nature11226DOI Listing
August 2012

Between geometry and biology: the problem of universality of the species-area relationship.

Am Nat 2011 Nov 6;178(5):602-11. Epub 2011 Oct 6.

Center for Theoretical Study, Charles University and the Academy of Sciences of the Czech Republic.

The species-area relationship (SAR) is considered to be one of a few generalities in ecology, yet a universal model of its shape and slope has remained elusive. Recently, Harte et al. argued that the slope of the SAR for a given area is driven by a single parameter, the ratio between total number of individuals and number of species (i.e., the mean population size across species at a given scale). We provide a geometric interpretation of this dependence. At the same time, however, we show that this dependence cannot be universal across taxa: if it holds for a taxon composed from two subsets of species and also for one of its subsets, it cannot simultaneously hold for the other subset. Using three data sets, we show that the slope of the SAR considerably varies around the prediction. We estimate the limits of this variation by using geometric considerations, providing a theory based on species spatial turnover at different scales. We argue that the SAR cannot be strictly universal, but its slope at each particular scale varies within the constraints given by species' spatial turnover at finer spatial scales, and this variation is biologically informative.
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http://dx.doi.org/10.1086/662176DOI Listing
November 2011

Range size heritability in Carnivora is driven by geographic constraints.

Am Nat 2011 Jun;177(6):767-79

Department of Zoology, University of South Bohemia, Branisovska, Ceske Budejovice, Czech Republic.

Range size heritability refers to an intriguing pattern where closely related species occupy geographic ranges of similar extent. Its existence may indicate selection on traits emergent only at the species level, with interesting consequences for evolutionary processes. We explore whether range size heritability may be attributable to the fact that range size is largely driven by the size of geographic domains (i.e., continents, biomes, areas given by species' climatic tolerance) that tend to be similar in phylogenetically related species. Using a well-resolved phylogeny of Carnivora, we show that range sizes are indeed constrained by geographic domains and that the phylogenetic signal in range sizes diminishes if the domain sizes are accounted for. Moreover, more detailed delimitation of species' geographic domain leads to a weaker signal in range size heritability, indicating the importance of definition of the null model against which the pattern is tested. Our findings do not reject the hypothesis of range size heritability but rather unravel its underlying mechanisms. Additional analyses imply that evolutionary conservatism in niche breadth delimits the species' geographic domain, which in turn shapes the species' range size. Range size heritability patterns thus emerge as a consequence of this interplay between evolutionary and geographic constraints.
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http://dx.doi.org/10.1086/659952DOI Listing
June 2011

Taxonomic variation in size-density relationships challenges the notion of energy equivalence.

Biol Lett 2011 Aug 30;7(4):615-8. Epub 2011 Mar 30.

NERC Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.

The relationship between body mass and abundance is a major focus for research in macroecology. The form of this relationship has been suggested to reflect the partitioning of energy among species. We revisit classical datasets to show that size-density relationships vary systematically among taxonomic groups, with most variation occurring at the order level. We use this knowledge to make a novel test of the 'energy equivalence rule', at the taxonomic scale appropriate for the data. We find no obvious relationship between order-specific exponents for abundance and metabolic rate, although most orders show substantially shallower (less negative) scaling than predicted by energy equivalence. This finding implies greater energy flux among larger-bodied animals, with the largest species using two orders of magnitude more energy than the smallest. Our results reject the traditional interpretation of energy equivalence as a predictive rule. However, some variation in size-density exponents is consistent with a model of geometric constraints on foraging.
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http://dx.doi.org/10.1098/rsbl.2011.0128DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3130248PMC
August 2011

Predictions of Taylor's power law, density dependence and pink noise from a neutrally modeled time series.

J Theor Biol 2010 Jul 20;265(1):78-86. Epub 2010 Apr 20.

Department of Ecology, Faculty of Science, Charles University, Vinicna 7, 12844 Praha 2, Czech Republic.

There has recently been increasing interest in neutral models of biodiversity and their ability to reproduce the patterns observed in nature, such as species abundance distributions. Here we investigate the ability of a neutral model to predict phenomena observed in single-population time series, a study complementary to most existing work that concentrates on snapshots in time of the whole community. We consider tests for density dependence, the dominant frequencies of population fluctuation (spectral density) and a relationship between the mean and variance of a fluctuating population (Taylor's power law). We simulated an archipelago model of a set of interconnected local communities with variable mortality rate, migration rate, speciation rate, size of local community and number of local communities. Our spectral analysis showed 'pink noise': a departure from a standard random walk dynamics in favor of the higher frequency fluctuations which is partly consistent with empirical data. We detected density dependence in local community time series but not in metacommunity time series. The slope of the Taylor's power law in the model was similar to the slopes observed in natural populations, but the fit to the power law was worse. Our observations of pink noise and density dependence can be attributed to the presence of an upper limit to community sizes and to the effect of migration which distorts temporal autocorrelation in local time series. We conclude that some of the phenomena observed in natural time series can emerge from neutral processes, as a result of random zero-sum birth, death and migration. This suggests the neutral model would be a parsimonious null model for future studies of time series data.
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http://dx.doi.org/10.1016/j.jtbi.2010.04.014DOI Listing
July 2010

Rapoport's rule, species tolerances, and the latitudinal diversity gradient: geometric considerations.

Ecology 2009 Dec;90(12):3575-86

Center for Theoretical Study, Charles University and Academy of Sciences of the Czech Republic, Jilská 1, 110 00, Praha 1, Czech Republic.

The most pervasive species-richness pattern, the latitudinal gradient of diversity, has been related to Rapoport's rule, i.e., decreasing latitudinal extent of species' ranges toward the equator. According to this theory, species can have narrower tolerances in more stable climates, leading to smaller ranges and allowing coexistence of more species. We show, using a simple geometric model, that the postulated decrease of species' potential range sizes toward the tropics would itself lead to a latitudinal gradient opposite to that observed. In contrast, an increase in extent of potential ranges toward the tropics would lead to the observed diversity gradient. Moreover, in the presence of geographic barriers constraining actual species' ranges, Rapoport's rule emerges if the latitudinal trend in extents of potential ranges (as defined by climatic tolerance) is opposite to that postulated or if variability in potential range extents decreases toward the poles. A strong implicit latitudinal diversity gradient (i.e., higher concentration of midpoints of species' potential ranges in the tropics), however, produces both observed macroecological patterns without the contribution of any latitudinal trends in species climatic tolerances or in potential range sizes. Our model underscores the necessity of discriminating theoretical processes and principles from the patterns we observe, and it is well supported by data on global distribution of species' range sizes.
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http://dx.doi.org/10.1890/08-1129.1DOI Listing
December 2009

Taking species abundance distributions beyond individuals.

Ecol Lett 2009 Jun;12(6):488-501

Center for Ecology and Evolutionary Biology, University of Oregon, Eugene, OR, USA.

The species abundance distribution (SAD) is one of the few universal patterns in ecology. Research on this fundamental distribution has primarily focused on the study of numerical counts, irrespective of the traits of individuals. Here we show that considering a set of Generalized Species Abundance Distributions (GSADs) encompassing several abundance measures, such as numerical abundance, biomass and resource use, can provide novel insights into the structure of ecological communities and the forces that organize them. We use a taxonomically diverse combination of macroecological data sets to investigate the similarities and differences between GSADs. We then use probability theory to explore, under parsimonious assumptions, theoretical linkages among them. Our study suggests that examining different GSADs simultaneously in natural systems may help with assessing determinants of community structure. Broadening SADs to encompass multiple abundance measures opens novel perspectives in biodiversity research and warrants future empirical and theoretical developments.
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http://dx.doi.org/10.1111/j.1461-0248.2009.01318.xDOI Listing
June 2009

Biodiversity scales from plots to biomes with a universal species-area curve.

Ecol Lett 2009 Aug 26;12(8):789-97. Epub 2009 May 26.

Energy and Resources Group, University of California at Berkeley, 310 Barrows Hall, Berkeley, CA 94720, USA.

Classic theory predicts species richness scales as the quarter-power of area, yet species-area relationships (SAR) vary widely depending on habitat, taxa, and scale range. Because power-law SAR are used to predict species loss under habitat loss, and to scale species richness from plots to biomes, insight into the wide variety of observed SAR and the conditions under which power-law behavior should be observed is needed. Here we derive from the maximum entropy principle, a new procedure for upscaling species richness data from small census plots to larger areas, and test empirically, using multiple data sets, the prediction that up to an overall scale displacement, nested SAR lie along a universal curve, with average abundance per species at each scale determining the local slope of the curve. Power-law behaviour only arises in the limit of increasing average abundance, and in that limit, the slope approaches zero, not (1/4). An extrapolation of tree species richness in the Western Ghats to biome scale (60,000 km(2)) using only census data at plot scale ((1/4) ha) is presented to illustrate the potential for applications of our theory.
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http://dx.doi.org/10.1111/j.1461-0248.2009.01328.xDOI Listing
August 2009

Rarity, commonness, and the contribution of individual species to species richness patterns.

Am Nat 2009 Jul;174(1):82-93

Center for Theoretical Study, Jilská 1, 110 00, Prague 1, Czech Republic.

Common species have a greater effect on observed geographical patterns of species richness than do rare ones. Here we present a theory of the relationship between individual species occurrence patterns and patterns in species richness, which allows purely geometrical and statistical causes to be distinguished from biological ones. Relationships between species occupancy and the correlation of species occurrence with overall species richness are driven by the frequency distribution of species richness among sites. Moreover, generally positive relationships are promoted by the fact that species occupancy distributions are mostly right skewed. However, biological processes can lead to deviations from the predicted pattern by changing the nestedness of a species' spatial distribution with regard to the distributions of other species in an assemblage. We have applied our theory to data for European birds at several spatial scales and have identified the species with significantly stronger or weaker correspondence with the overall richness pattern than that predicted by the null model. In sum, whereas the general macroecological pattern of a stronger influence of common species than of rare species on species richness is predicted by mathematical considerations, the theory can reveal biologically important deviations at the level of individual species.
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http://dx.doi.org/10.1086/599305DOI Listing
July 2009

Species abundance distribution results from a spatial analogy of central limit theorem.

Proc Natl Acad Sci U S A 2009 Apr 3;106(16):6691-5. Epub 2009 Apr 3.

Center for Theoretical Study, Charles University and Academy of Sciences of the Czech Republic, Jilská 1, 110 00 Praha 1, Czech Republic.

The frequency distribution of species abundances [the species abundance distribution (SAD)] is considered to be a fundamental characteristic of community structure. It is almost invariably strongly right-skewed, with most species being rare. There has been much debate as to its exact properties and the processes from which it results. Here, we contend that an SAD for a study plot must be viewed as spliced from the SADs of many smaller nonoverlapping subplots covering that plot. We show that this splicing, if applied repeatedly to produce subplots of progressively larger size, leads to the observed shape of the SAD for the whole plot regardless of that of the SADs of those subplots. The widely reported shape of an SAD is thus likely to be driven by a spatial parallel of the central limit theorem, a statistically convergent process through which the SAD arises from small to large scales. Exact properties of the SAD are driven by species spatial turnover and the spatial autocorrelation of abundances, and can be predicted using this information. The theory therefore provides a direct link between SADs and the spatial correlation structure of species distributions, and thus between several fundamental descriptors of community structure. Moreover, the statistical process described may lie behind similar frequency distributions observed in many other scientific fields.
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http://dx.doi.org/10.1073/pnas.0810096106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2672478PMC
April 2009

The quest for a null model for macroecological patterns: geometry of species distributions at multiple spatial scales.

Ecol Lett 2008 Aug;11(8):771-84

Center for Theoretical Study, Charles University, Jilská 1, 11000 Praha 1, Czech Republic.

There have been several attempts to build a unified framework for macroecological patterns. However, these have mostly been based either on questionable assumptions or have had to be parameterized to obtain realistic predictions. Here, we propose a new model explicitly considering patterns of aggregated species distributions on multiple spatial scales, the property which lies behind all spatial macroecological patterns, using the idea we term 'generalized fractals'. Species' spatial distributions were modelled by a random hierarchical process in which the original 'habitat' patches were randomly replaced by sets of smaller patches nested within them, and the statistical properties of modelled species assemblages were compared with macroecological patterns in observed bird data. Without parameterization based on observed patterns, this simple model predicts realistic patterns of species abundance, distribution and diversity, including fractal-like spatial distributions, the frequency distribution of species occupancies/abundances and the species-area relationship. Although observed macroecological patterns may differ in some quantitative properties, our concept of random hierarchical aggregation can be considered as an appropriate null model of fundamental macroecological patterns which can potentially be modified to accommodate ecologically important variables.
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http://dx.doi.org/10.1111/j.1461-0248.2008.01206.xDOI Listing
August 2008

Spatial scale, abundance and the species-energy relationship in British birds.

J Anim Ecol 2008 Mar 13;77(2):395-405. Epub 2007 Nov 13.

Biodiversity & Macroecology Group, Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.

1. The spatial scale of analysis may influence the nature, strength and underlying drivers of macroecological patterns, one of the most frequently discussed of which is the relationship between species richness and environmental energy availability. 2. It has been suggested that species-energy relationships are hump-shaped at fine spatial grains and consistently positive at larger regional grains. The exact nature of this scale dependency is, however, the subject of much debate as relatively few studies have investigated species-energy relationships for the same assemblage across a range of spatial grains. Here, we contrast species-energy relationships for the British breeding avifauna at spatial grains of 1 km x 1 km, 2 km x 2 km and 10 km x 10 km plots, while maintaining a constant spatial extent. 3. Analyses were principally conducted using data on observed species richness. While survey work may fail to detect some species, observed species richness and that estimated using nonparametric techniques were strongly positively correlated with each other, and thus exhibit very similar spatial patterns. Moreover, the forms of species-energy relationships using observed and estimated species richness were statistically indistinguishable from each other. 4. Positive decelerating species-energy relationships arise at all three spatial grains. There is little evidence that the explanatory power of these relationships varies with spatial scale. However, ratios of regional (large-scale) to local (small-scale) species richness decrease with increasing energy availability, indicating that local richness responds to energy with a steeper gradient than does regional richness. Local assemblages thus sample a greater proportion of regional richness at higher energy levels, suggesting that spatial turnover of species richness is lower in high-energy regions. Similarly, a crude measure of temporal turnover, the ratio of cumulative species richness over a 4-year period to species richness in a single year, is lower in high-energy regions. These negative relationships between turnover and energy appear to be causal as both total and mean occupancy per species increases with energy. 5. While total density in 1 km x 1 km plots correlates positively with energy availability, such relationships are very weak for mean density per species. This suggests that the observed association between total abundance and species richness may not be mediated by population extinction rates, as predicted by the more individuals hypothesis. 6. The sampling mechanism suggests that species-energy relationships arise as high-energy areas support a greater number of individuals, and that random allocation of these individuals to local areas from a regional assemblage will generate species-energy relationships. While randomized local species-energy relationships are linear and positive, predicted richness is consistently greater than that observed. The mismatch between the observed and randomized species-energy relationships probably arises as a consequence of the aggregated nature of species distributions. The sampling mechanism, together with species spatial aggregation driven by limited habitat availability, may thus explain the species-energy relationship observed at this spatial scale.
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http://dx.doi.org/10.1111/j.1365-2656.2007.01332.xDOI Listing
March 2008

Topography, energy and the global distribution of bird species richness.

Proc Biol Sci 2007 May;274(1614):1189-97

Biodiversity and Macroecology Group, Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.

A major goal of ecology is to determine the causes of the latitudinal gradient in global distribution of species richness. Current evidence points to either energy availability or habitat heterogeneity as the most likely environmental drivers in terrestrial systems, but their relative importance is controversial in the absence of analyses of global (rather than continental or regional) extent. Here we use data on the global distribution of extant continental and continental island bird species to test the explanatory power of energy availability and habitat heterogeneity while simultaneously addressing issues of spatial resolution, spatial autocorrelation, geometric constraints upon species' range dynamics, and the impact of human populations and historical glacial ice-cover. At the finest resolution (1 degree), topographical variability and temperature are identified as the most important global predictors of avian species richness in multi-predictor models. Topographical variability is most important in single-predictor models, followed by productive energy. Adjusting for null expectations based on geometric constraints on species richness improves overall model fit but has negligible impact on tests of environmental predictors. Conclusions concerning the relative importance of environmental predictors of species richness cannot be extrapolated from one biogeographic realm to others or the globe. Rather a global perspective confirms the primary importance of mountain ranges in high-energy areas.
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http://dx.doi.org/10.1098/rspb.2006.0061DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2189561PMC
May 2007

Energy, range dynamics and global species richness patterns: reconciling mid-domain effects and environmental determinants of avian diversity.

Ecol Lett 2006 Dec;9(12):1308-20

Spatial patterns of species richness follow climatic and environmental variation, but could reflect random dynamics of species ranges (the mid-domain effect, MDE). Using data on the global distribution of birds, we compared predictions based on energy availability (actual evapotranspiration, AET, the best single correlate of avian richness) with those of range dynamics models. MDE operating within the global terrestrial area provides a poor prediction of richness variation, but if it operates separately within traditional biogeographic realms, it explains more global variation in richness than AET. The best predictions, however, are given by a model of global range dynamics modulated by AET, such that the probability of a range spreading into an area is proportional to its AET. This model also accurately predicts the latitudinal variation in species richness and variation of species richness both within and between realms, thus representing a compelling mechanism for the major trends in global biodiversity.
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http://dx.doi.org/10.1111/j.1461-0248.2006.00984.xDOI Listing
December 2006

The species-area-energy relationship.

Ecol Lett 2005 May;8(5):487-92

Center for Theoretical Study, Charles University, Jilská 1, 110 00-CZ Praha 1, Czech Republic Department of Ecology, Faculty of Sciences, Viničná 7, 128 44-CZ Praha 2, Czech Republic Biodiversity and Macroecology Group, Department of Animal & Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.

Area and available energy are major determinants of species richness. Although scale dependency of the relationship between energy availability and species richness (the species-energy relationship) has been documented, the exact relationship between the species-area and the species-energy relationship has not been studied explicitly. Here we show, using two extensive data sets on avian distributions in different biogeographic regions, that there is a negative interaction between energy availability and area in their effect on species richness. The slope of the species-area relationship is lower in areas with higher levels of available energy, and the slope of the species-energy relationship is lower for larger areas. This three-dimensional species-area-energy relationship can be understood in terms of probabilistic processes affecting the proportions of sites occupied by individual species. According to this theory, high environmental energy elevates species' occupancies, which depress the slope of the species-area curve.
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http://dx.doi.org/10.1111/j.1461-0248.2005.00740.xDOI Listing
May 2005