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Servan, C. A.

Publications and source records attributed to Servan, C. A..

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Effects of phylogeny on coexistence in model communities

A species traits influence the way in which it interacts with the environment. Thus, we expect traits to play a role in determining whether a given set of species coexists. Traits are, in turn, the outcome of an eco-evolutionary process summarized by a phylogenetic tree. Therefore, the phylogenetic tree associated with a set of species should encode information about the assembly properties of the community. Many studies have high-lighted the potentially complex ways in which phylogenetic information is translated into species ecological properties. However, much less emphasis has been placed on developing expectations for community properties under a particular hypothesis. In this work, we couple a simple model of trait evolution on a phylogenetic tree with local community dynamics governed by Lotka-Volterra equations. This allows us to derive properties of the community of coexisting species as a function of the number of traits, tree topology and the size of the species pool. Our results highlight how phylogenies and traits, in concert, affect the coexistence of a set of species. In this way, our work provides new baseline expectations for the ways in which phylogenetic information is reflected in the structure of and coexistence within local communities.

ecology

Tractable models of ecological assembly

Ecological assembly, the way natural communities form under ecological time-scales, is a fundamental and yet poorly understood process. Recent theoretical and empirical approaches to assembly consider systems in which a group of species is introduced in a new environment, and dynamics prune the system down to a sub-community of coexisting species. This "top-down" assembly approach contrasts with the well-studied "bottom-up", or sequential, assembly, in which species from a pool enter the system one at a time, giving rise to priority effects and complex dynamics. Here we determine under which conditions the two approaches are equivalent, i.e., lead asymptotically to the same exact set of coexisting species. To achieve this result, we represent the assembly process as a network in which nodes are sub-communities and edges stand for invasions shifting the composition of the ecological community from a stable configuration to another. This abstraction makes it easy to determine which states the community can occupy, as well as highlight the potential for priority effects or cyclic species composition. We discuss how the equivalence between bottom-up and top-down assembly can advance our understanding of this challenging process from an empirical and theoretical point of view, informing the study of ecological restoration and the design and control of ecological communities.

ecology