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“Food Web Complexity and Species Diversity” (Paine 1966) is the most-cited empirical article published in the American Naturalist. In short, Paine removed predatory sea stars (Pisaster ochraceus) from the rocky intertidal and watched the key prey species, mussels (Mytilus californianus), crowd out seven subordinate primary space-holding species. However, because these mussels are a foundational species, they provide three-dimensional habitat for over 300 associated species inhabiting the mussel beds; thus, removing sea stars significantly increases community-wide diversity. In any case, most ecologists cite Paine (1966) to support a statement that predators increase diversity by interfering with competition. Although detractors remained skeptical of top-down effects and keystone concepts, the paradigm that predation increases diversity spread. By 1991, “Food Web Complexity and Species Diversity” was considered a classic ecological paper, and after 50 years it continues to influence ecological theory and conservation biology. [ABSTRACT FROM AUTHOR]

Understanding the effects of biodiversity on community persistence and productivity is key to managing both natural and production systems. Because rare species face greater danger of extinction, species evenness, a measure of how similar abundances are across species in a community, is seen as a key component of biodiversity. However, previous studies have failed to find a consistent association of species evenness with species survival and biomass production. Here we provide a theoretical framework for the relationship among these three elements. We demonstrate that the lack of consistent outcomes is not an idiosyncratic artifact of different studies but can be unified under one common framework. Applying a niche theory approach, we confirm that under demographic stochasticity evenness is a general indicator of the risk of future species extinctions in a community, in accordance with the majority of empirical studies. In contrast, evenness cannot be used as a direct indicator of the level of biomass production in a community. When a single species dominates, as expressed by the constraints imposed by the population dynamics, biomass production depends on the niche position of the dominating species and can increase or decrease with evenness. We demonstrate that high species evenness and an intermediate level of biomass production is the configuration that maximizes the average species survival probability in response to demographic stochasticity. [ABSTRACT FROM AUTHOR]

Theory suggests that the structure of evolutionary history represented in a species community may affect its functioning, but phylogenetic diversity metrics do not allow for the identification of major differences in this structure. Here we propose a new metric, ELDERness (for Evolutionary Legacy of DivERsity) to estimate evolutionary branching patterns within communities by fitting a polynomial function to lineage-through-time (LTT) plots. We illustrate how real and simulated community branching patterns can be more correctly described by ELDERness and can successfully predict ecosystem functioning. In particular, the evolutionary history of branching patterns can be encapsulated by the parameters of third-order polynomial functions and further measured through only two parameters, the “ELDERness surfaces.” These parameters captured variation in productivity of a grassland community better than existing phylogenetic diversity or diversification metrics and independent of species richness or presence of nitrogen fixers. Specifically, communities with small ELDERness surfaces (constant accumulation of lineages through time in LTT plots) were more productive, consistent with increased productivity resulting from complementary lineages combined with niche filling within lineages. Overall, while existing phylogenetic diversity metrics remain useful in many contexts, we suggest that our ELDERness approach better enables testing hypotheses that relate complex patterns of macroevolutionary history represented in local communities to ecosystem functioning. [ABSTRACT FROM AUTHOR]

For two competing species, intraspecific competition must exceed interspecific competition for coexistence. To generalize this well-known criterion to multiple competing species, one must take into account both the distribution of interaction strengths and community structure. Here we derive a multispecies generalization of the two-species rule in the context of symmetric Lotka- Volterra competition and obtain explicit stability conditions for random competitive communities. We then explore the influence of community structure on coexistence. Results show that both the most and least stabilized cases have striking global structures, with a nested pattern emerging in both cases. The distribution of intraspecific coefficients leading to the most and least stabilized communities also follows a predictable pattern that can be justified analytically. In addition, we show that the size of the parameter space allowing for feasible communities always increases with the strength of intraspecific effects in a characteristic way that is independent of the interspecific interaction structure. We conclude by discussing possible extensions of our results to nonsymmetric competition. [ABSTRACT FROM AUTHOR]

The finding that adaptive evolution can often be substantial enough to alter ecological dynamics challenges traditional views of community ecology that ignore evolution. Here, we propose that evolution might commonly alter both local and regional processes of community assembly. We show how adaptation can substantially affect community assembly and that these effects depend on regional (metacommunity) factors, including environmental heterogeneity and its spatial structure. In particular, early colonists can often arrive from a nearby community, adapt to local conditions, and subsequently alter the establishment or abundance of late-arriving species, often producing an evolutionary priority effect. We also discuss how interaction type and relative rates of colonization, evolution, and community interactions determine divergent community outcomes. We describe new conceptual approaches that provide insights into these dynamics and statistical methods that can better evaluate their importance. Overall, we demonstrate that accounting for adaptation during community assembly opens up novel ways for making progress on fundamental questions in community ecology. [ABSTRACT FROM AUTHOR]

The ecological principle of competitive exclusion states that species competing for identical resources cannot coexist, but this principle is paradoxical because ecologically similar competitors are regularly observed. Coexistence is possible under some conditions if a fluctuating environment changes the competitive dominance of species. This change in competitive dominance implies the existence of trade-offs underlying species' competitive abilities in different environments. Theory shows that fluctuating distance between resource patches can facilitate coexistence in ephemeral patch competitors, given a functional trade-off between species dispersal ability and fecundity. We find evidence supporting this trade-off in a guild of five ecologically similar nonpollinating fig wasps and subsequently predict local among-patch species densities. We also introduce a novel colonization index to estimate relative dispersal ability among ephemeral patch competitors. We suggest that a dispersal ability-fecundity trade-off and spatiotemporally fluctuating resource availability commonly co-occur to drive population dynamics and facilitate coexistence in ephemeral patch communities. [ABSTRACT FROM AUTHOR]

Dominance of free-floating plants poses a threat to biodiversity in many freshwater ecosystems. Here we propose a theoretical framework to understand this dominance, by modeling the competition for light and nutrients in a layered community of floating and submerged plants. The model shows that at high supply of light and nutrients, floating plants always dominate due to their primacy for light, even when submerged plants have lower minimal resource requirements. The model also shows that floating-plant dominance cannot be an alternative stable state in light-limited environments but only in nutrient-limited environments, depending on the plants' resource consumption traits. Compared to unlayered communities, the asymmetry in competition for light—coincident with symmetry in competition for nutrients—leads to fundamentally different results: competition outcomes can no longer be predicted from species traits such as minimal resource requirements (R* rule) and resource consumption. Also, the same two species can, depending on the environment, coexist or be alternative stable states. When applied to two common plant species in temperate regions, both the model and field data suggest that floating-plant dominance is unlikely to be an alternative stable state. [ABSTRACT FROM AUTHOR]

Many studies have aimed to identify common predictors of successful introductions of alien species, but the search has had limited success, particularly for animals. Past research focused primarily on mean trait values, even though genetic and phenotypic variation has been shown to play a role in establishment success in plants and some animals (mostly invertebrates). Using a global database describing 511 introduction events representing 97 mammalian species, we show that intraspecific variation in morphological traits is associated with establishment success, even when controlling for the positive effect of propagule pressure. In particular, greater establishment success is associated with more variation in adult body size but, surprisingly, less variation in neonate body size, potentially reflecting distinct trade-offs and constraints that influence population dynamics differently. We find no mean trait descriptors associated with establishment success, although species occupying wider native distribution ranges (which likely have larger niches) are more successful. Our results emphasize the importance of explicitly considering intraspecific variation to predict establishment success in animal species and generally to understand population dynamics. This understanding might improve management of alien species and increase the success of intentional releases, for example, for biocontrol or reintroductions. [ABSTRACT FROM AUTHOR]

Demographic equivalence is the central assumption of the neutral theory of species diversity and has attracted much criticism, since species clearly differ from each other in many traits. Two simple answers-that is, dispersal limitation and demographic tradeoffs- have been suggested to resolve this problem. Both processes are considered to be capable of making interspecific differences in fitness smaller on their own, thus potentially reconciling neutrality with reality. However, when the two mechanisms operate simultaneously, as theymust do in natural communities, we are surprised to find that they interfere with each other in such a way that dispersal limitation favors more fecund species. Fitness equivalence is no longer guaranteed by a perfect trade-off, and contrary to popular belief, dispersal limitation is found to impede rather than facilitate the stochastic coexistence of species. Still, more species can coexist than allowed through demographic equivalence, providing a potentially alternative explanationfor biodiversity maintenance in nature. [ABSTRACT FROM AUTHOR]

Variation is essential to ecological and evolutionary dynamics, but genetic variation of quantitative traits may be concentrated in a limited number of dimensions, constraining ecoevolutionary dynamics. We describe high-dimension variation in natural accessions of the model alga, Chlamydomonas reinhardtii, and test the hypothesis that extensive fitness variation across 30 environments is constrained to a small number of axes., We used high-throughput phenotyping to investigate morphological, fitness, and genotype × environment (G × E) variation in 18 natural C. reinhardtii accessions in 30 environments., The organismal phenotypes of cell cycle, cell size, and phototactic behavior exhibited substantial genetic variation between lines, and we found up to 74-fold fitness variation across accessions and environments. Approximately 47% of the extensive G × E variation is accounted for by the first two principal components (PCs) of the G-matrix corresponding to covariation in metals response, nitrogen availability, or salt and nutrient response., The natural variation of C. reinhardtii accessions supports the hypothesis that, despite abundant genetic variation across single environments, the species' adaptive response should be constrained along few major axes of selection. These results highlight the utility of natural accessions for integrating ecoevolutionary and genetic research. [ABSTRACT FROM AUTHOR]

Ecological communities are structured by processes operating at multiple spatial scales, which results in an often daunting complexity. Here we present a simple graphical theory to study the interaction of two fundamental community processes: resource competition at the local scale and dispersal at the regional scale. We consider a metacommunity model with two habitat patches in which consumer species compete for a spatially distributed resource. We introduce a graphical construction of the equilibrium metacommunity composition, analogous to traditional competition theory for two resources. As in the nonspatial case, the zero net growth isoclines (ZNGIs) play a central role in the analysis. We show that a consumer species' ZNGI depends on its dispersal characteristics, and this dependence leads to a unification of various dispersal-based coexistence mechanisms. We illustrate this unification using four specific mechanisms: species-specific dispersal rates, spatially asymmetric dispersal, resource-dependent dispersal, and competition between habitat specialists and generalists. [ABSTRACT FROM AUTHOR]

Community assembly is a combination of ecological, evolutionary, and stochastic processes. Separating out the abiotic and biotic processes (such as limiting similarity or environmental filtering) from stochastic processes is central to developing a cogent approach for understanding patterns in ecological community structure and organization. Using butterfly communities in a fragmented landscape, we tested the hypothesis that local environmental filtering drives character convergences in traits of species belonging to different clades. We found that, while many traits were determined both by phylogeny and environment, trait convergence within the phylogeny was extensive and eroded the phylogenetic structure associated with habitat use. Traits associated with habitat use are shown to be only moderately phylogenetically conserved in chalk grassland butterfly assemblages, and further analysis revealed that traits associated with environmental filtering may be highly labile rather than phylogenetically conserved. In general, a significant phylogenetic signal is therefore neither sufficient to demonstrate a lack of trait convergence, nor to determine whether communities are likely to be phylogenetically structured. We conclude that explicit trait-based approaches should be used in preference to the more indirect approach based on phylogenetic conservatism for understanding metacommunity assembly processes. [ABSTRACT FROM AUTHOR]