Submit an abstract for our eco-evo symposium at Evolution 2018, Montpellier, France

S59. Towards a unified biology of populations: Integrating ecology, evolution and demography

Organizers: Ron Bassar, Timothée Bonnet, Erik Postma, Matthew Wolak

Individual variation in fitness is the outcome of a complex and dynamic interplay of genes, the environment and chance, and provides the raw material for natural selection. The concept of fitness is hence central to evolutionary biology in general, and to understanding the individual- and population-level consequences of environmental change in particular. Although fitness appears in the fundamental equations of both evolutionary genetics and population dynamics, attempts to predict changes in individual fitness and project these onto population growth rates are often unsuccessful. Indeed, such attempts to integrate evolution and demography face several major theoretical and empirical challenges. First, we lack a quantitative and comprehensive understanding of the role of both adaptive and non-adaptive evolution, phenotypic plasticity, and age/stage structure in shaping trait distributions in space and time. Furthermore, existing methods are poorly equipped to deal with the complexities inherent to most natural populations, including environmental change and degradation, frequency- and density-dependence, and the ‘hardness’ of selection. This symposium will assemble researchers that take innovative theoretical and empirical approaches to address the above challenges to bring us closer to the ultimate aim of a unification of evolutionary and population dynamics.

Invited speaker: Isabel Smallegange “The role of eco-evolutionary feedbacks in population dynamics: from alternative phenotype expression to demography and back”

Our new paper on species coexistence is out in Ecology

A longstanding problem in ecology is whether structured life cycles impede or facilitate coexistence between species. Theory based on populations with only two discrete stages in the life-cycle indicates that for two species to coexist, at least one must shift its niche between stages and each species must be a better competitor in one of the niches. However, in many cases, niche shifts are associated with changes in an underlying continuous trait like body size and we have few predictions concerning conditions for coexistence for such a widespread form of ontogenetic development. We develop a framework for analyzing species coexistence based on Integral Projection Models (IPMs) that incorporates continuous ontogenetic changes in both the resource niche and competitive ability. We parameterize the model using experimental data from Trinidadian guppies and show how niche shifts and competitive symmetries impact species coexistence. Overall, our results show that the effects of competition on fitness depend upon trait-mediated niche-separation, trait-mediated competitive asymmetry in the part of the niche that is shared across body sizes, and the sensitivity of fitness to body size. Interactions among these processes generate multiple routes to coexistence. We discuss how our modelling framework expands results from two-stage models to mutli-stage or continuous stage models and allows for deriving predictions that can be tested in populations displaying continuous changes in niche use and competitive ability.

The paper can be found here.

New paper on guppy phenotype effects in nature.

Congratulations to Troy Simon, past graduate student on the guppy project, on his new paper on guppy phenotype effects in Trinidadian streams.

While previous studies have shown that evolutionary divergence alters ecological processes in small-scale experiments, a major challenge is to assess whether such evolutionary effects are important in natural ecosystems at larger spatial scales. At the landscape scale, across eight streams in the Caroni drainage, we found that the presence of locally adapted populations of guppies (Poecilia reticulata) is associated with reduced algal biomass and increased invertebrate biomass, while the opposite trends were true in streams with experimentally introduced populations of non-locally adapted guppies. Exclusion experiments conducted in two separate reaches of a single stream showed that guppies with locally adapted phenotypes significantly reduced algae with no effect on invertebrates, while non-adapted guppies had no effect on algae but significantly reduced invertebrates. These divergent effects of phenotype on stream ecosystems are comparable in strength to the effects of abiotic factors (e.g. light) known to be important drivers of ecosystem condition. They also corroborate the results of previous experiments conducted in artificial streams. Our results demonstrate that local adaptation can produce phenotypes with significantly different effects in natural ecosystems at a landscape scale, within a tropical watershed, despite high variability in abiotic factors: five of the seven physical and chemical parameters measured across the eight study streams varied by more than one order of magnitude.  Our findings suggest that ecosystem structure is, in part, an evolutionary product and not simply an ecological pattern.

Find the full paper here.