The neutral theory for community structure and biodiversity is dependent on the assumption that species are equivalent to each other in all important ecological respects. We explore what this concept of equivalence means in ecological communities, how such species may arise evolutionarily, and how the possibility of ecological equivalents relates to previous ideas about niche differentiation. We also show that the co-occurrence of ecologically similar or equivalent species is not incompatible with niche theory as has been supposed, because niche relations can sometimes favor coexistence of similar species. We argue that both evolutionary and ecological processes operate to promote the introduction and to sustain the persistence of ecologically similar and in many cases nearly equivalent species embedded in highly structured food webs. Future work should focus on synthesizing niche and neutral perspectives rather than dichotomously debating whether neutral or niche models provide better explanations for community structure and biodiversity.

/pdf/coexistence-of-the-niche-and-neutral-perspectives-in-24vs08qxg5.pdf

Coexistence of the niche and neutral perspectives in community ecology.

Ecological character displacement, mostly seen as increased differences of size in sympatry between closely-related or similar species, is a focal hypothesis assuming that species too similar to one another could not coexist without diverging, owing to interspecific competition. Thus, ecological character displacement and community-wide character displacement (overdispersion in size of potential competitors within ecological guilds) were at the heart of the debate regarding the role of competition in structuring ecological communities. The debate has focused on the evidence presented in earlier studies and generated a new generation of rigorous, critical studies of communities. Character displacement research in the past two decades provides sound statistical support for the hypothesis in a wide variety of taxa, albeit with a phylogenetically skewed representation. A growing number of studies are strongly based in functional morphology, and some also demonstrate actual morphologically related resource partitioning. Phylogenetic models and experimental work have added to the scope and depth of earlier research, as have theoretical studies. However, many challenging ecological and evolutionary issues, regarding both selective forces (at the inter- and intraspecific level) and resultant patterns, remain to be addressed. Ecological character displacement and community-wide character displacement are here to stay as the focus of much exciting research.

Ecological and community‐wide character displacement: the next generation

Summary

1
We review theoretical and empirical studies to identify instances where evolutionary processes significantly affect the dynamics of populations, communities and ecosystems.

2
Early theoretical work on eco-evolutionary dynamics was concerned with the effect of (co)evolution on the stability of two-species predator–prey systems and the occurrence of character displacement in simple competitive systems. Today's theoretical ecologists are extending this work to study the eco-evolutionary dynamics of multispecies communities and the functioning and evolutionary emergence of ecosystems.

3
In terms of methodology, eco-evolutionary modelling has diversified from simple, locus-based population genetic models to encompass models of clonal selection, quantitative trait dynamics and adaptive dynamics.

4
The few empirical studies on community dynamics that explicitly considered evolutionary processes support the view that evolutionary and ecological dynamics often occur on similar time-scales, and that they co-determine the dynamical behaviour of ecological communities.

http://max2.ese.u-psud.fr/epc/conservation/PDFs/HIPE/Fussmann2007.pdf

Eco‐evolutionary dynamics of communities and ecosystems

Aim: More powerful tests of biodiversity theories need to move beyond species richness and explicitly focus on mechanisms generating diversity via trait composition The rise of trait-based ecology has led to an increased focus on the distribution and dynamics of traits across broad geographic and climatic gradients and how these distributions influence ecosystem function However, a general theory of trait-based ecology, that can apply across different scales (eg species that differ in size) and gradients (eg temperature), has yet to be formulated While research focused on metabolic and allometric scaling theory provides the basis for such a theory, it does not explicitly account for differences in traits within and across taxa, such as variation in the optimal temperature for growth Here we synthesize trait-based and metabolic scaling approaches into a framework that we term ‘Trait Driver Theory’ or TDT It shows that the shape and dynamics of trait and size distributions can be linked to fundamental drivers of community assembly and how the community will respond to future drivers To assess predictions and assumptions of TDT, we review several theoretical studies and recent empirical studies spanning local and biogeographic gradients Further, we analyze how the shift in trait distributions influences ecosystem processes across an elevational gradient and a 140-year-long ecological experiment We show that TDT provides a baseline for (i) recasting the predictions of ecological theories based on species richness in terms of the shape of trait distributions and (ii) integrating how specific traits, including body size, and functional diversity then ‘scale up’ to influence ecosystem functioning and the dynamics of species assemblages across climate gradients Further, TDT offers a novel framework to integrate trait, metabolic/allometric, and species-richness-based approaches to better predict functional biogeography and how assemblages of species have and may respond to climate change

Scaling from Traits to Ecosystems: Developing a General Trait Driver Theory via Integrating Trait-Based and Metabolic Scaling Theories

Environmental variability and adaptive foraging behavior have been shown to favor coexistence of specialists and generalists on an ecological timescale. This leaves unaddressed the question of whether such coexistence can also be expected on an evolutionary timescale. In this article, we study the attainability, through gradual evolution, of specialist‐generalist coexistence, as well as the evolutionary stability of such communities when allowing for immigration. Our analysis shows that the potential for specialist‐generalist coexistence is much more restricted than originally thought and strongly depends on the trade‐off structure assumed. We establish that ecological coexistence is less likely for species facing a trade‐off between per capita reproduction in different habitats than when the trade‐off acts on carrying capacities alone. We also demonstrate that coexistence is evolutionarily stable whenever it is ecologically stable but that in most cases, such coexistence cannot be reached throu...

/pdf/evolution-restricts-the-coexistence-of-specialists-and-4q5ydw7y4w.pdf

Evolution restricts the coexistence of specialists and generalists: the role of trade-off structure.

This article investigates some simple models of the evolutionary interaction between two prey species that share a common resource and a common predator. Each prey species is characterized by a trait that determines both the rate of resource capture and vulnerability to a predator. In a simple model of a three‐species food chain, such traits usually increase in response to an imposed reduction in resource density. When the per capita growth rates of each of two prey species depend linearly on resource density, such traits will change in opposite directions when the two prey come into sympatry. In addition, the ratio of the effect of the predator on prey fitness to the effect of the resource on prey fitness will diverge from the corresponding ratio in a second prey species when those species coexist in sympatry. These simple predictions need not hold under several alternative assumptions, which may be more common in biological systems. Parallel changes in sympatry may occur if the relationship be...

https://www.jstor.org/stable/10.1086/342822

The Evolution of Traits Affecting Resource Acquisition and Predator Vulnerability: Character Displacement under Real and Apparent Competition

Here, we use some simple models to investigate the impact of between-prey competition on the nature of the indirect evolutionary interaction between prey species via shared predators. Sympatry with a second prey species is likely to alter the population size of the shared predator population(s) and thereby affect the adaptive evolution of anti-predator (vulnerability) traits in the first prey species. Such predation-driven character shift has been investigated previously in models that either assumed no resource-based competition between prey species, or complete overlap in resource use by prey. This study examines the intermediate situation in which prey species compete, but are able to co-exist in the absence of the predator. This scenario is capable of producing either of the two most common responses observed in the limiting cases: parallel change in anti-predator characteristics or divergent change in those characteristics. Parallel change characterizes situations with relatively low competition, and those with high competition when the asymmetry in competition coefficients is less extreme than the asymmetry in the ratio of values of the two prey to the predator. Divergent change occurs with high competition or with moderate competition given sufficient asymmetry in competition coefficients. The factors determining the magnitude of character shifts are explored. Potential examples of such evolutionary responses to sympatry with additional prey species are discussed.

/pdf/the-effect-of-competition-between-prey-species-on-the-1c6u1p0taq.pdf

The effect of competition between prey species on the evolution of their vulnerabilities to a shared predator

How would ecological restoration affect multiple ecosystem service supplies and tradeoffs? A study of mine tailings restoration in China

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The Evolution of Traits Affecting Resource Acquisition and Predator Vulnerability: Character Displacement under Real and Apparent Competition

The effect of competition between prey species on the evolution of their vulnerabilities to a shared predator

How would ecological restoration affect multiple ecosystem service supplies and tradeoffs? A study of mine tailings restoration in China