Monday, August 4, 2008 - 2:50 PM

COS 6-5: Is food-web stability greater than the sum of its parts?

Daniel B. Stouffer and Jordi Bascompte. Estación Biológica de Doñana


Food webs aim to provide a thorough representation of the trophic interactions found in an ecosystem. From both an empirical and theoretical perspective, however, much of our understanding of food-web stability and dynamics stems from investigations of smaller sub-webs---"community modules"---which are often easier to experiment with in the field or laboratory or more analytically tractable in theory.

The dynamic stability of community modules has been investigated previously with particularly compelling results regarding the role of weak interactions. These bottom-up studies provide a theoretical foundation for the stability of individual modules, but leave open the question of which modules empirical food webs are actually composed of. To address this question, scientists have investigated food-web "motifs", the structural counter-part to community modules. These top-down studies provide an indication of whether and how specific sub-webs appear within empirical food webs, but are unable to address if there is a dynamic justification for why a sub-web appears with greater or less frequency.

In this presentation, we will integrate the bottom-up and top-down approaches to demonstrate the relationship between the local stability of a module and whether or not that sub-web appears more or less frequently in an entire food web. We will also demonstrate the magnitude of the relationship between local stability of a module and the stability of the entire food web in which it is embedded.

The identification of each modules' contribution to community stability will provide crucial information regarding the forces acting upon the ecosystem. We will answer an important question regarding the mechanisms responsible for maintaining stability in the presence of external perturbations. Namely, is a community stable because it is composed of stable sub-elements? Or is a community stable because of more complex cooperative and synergistic interactions between both stable and unstable sub-elements? Is food-web stability greater than the sum of its parts?