Dr Daniel Stouffer, Integrative Ecology Group, Estación Biológica de Doñana, Spain

Abstract: Food webs provide a thorough representation of the trophic interactions found in an ecosystem. Understanding food web stability is a long-term objective of ecology because of its relevance in predicting the persistence of biodiversity. Much of our understanding of food-web stability and persistence stems from investigations of smaller sub-webs, called trophic modules, which are easier to experiment with in the field and laboratory or more analytically tractable in theory. These studies provide a foundation for the stability of individual modules and a means to try to scale-up and infer how entire food webs behave as a whole. Recent top-down approaches have investigated how empirical food-web structure is built up from constituent modules.

We integrate such bottom-up and top-down approaches in order to better understand the relationship between the modules which make up a network and that network's long-term persistence. We find that there is not a direct relationship between the persistence of modules in isolation and their effect on persistence of a complete food web. We do find, however, that there is strong correlation between whether the presence of individual modules increase or decrease entire food-web persistence and whether those same modules appear more or less frequently in empirical food webs. As a consequence of our study, food-web stability and persistence can be regarded as an excellent example of the whole being greater than the sum of its parts.