Everything is a Network, but the Network is Not Everything: Dynamics of Stage-Structured Food Webs
Abstract: Ecological communities are traditionally viewed as networks of negative and positive interactions between species, while the species themselves are seen as collections of identical individuals. Using this conceptualization, however, it has been difficult to explain the importance of biodiversity. In fact, analysis of the topology of ecological interaction networks has shown that “diversity begets instability”: more complex and more diverse communities tend to be dynamically unstable and hence not persist. Complex communities are predicted to be stable only when species growth rates are mostly limited by intraspecific self-regulation (within-node limitation) rather than by interactions with resources, competitors, and predators.
In this talk I show how adding a second axis of complexity to the study of ecological interaction networks yields contrasting predictions about the relation between community diversity and stability. This second axis recognizes that conspecific individuals are different from one another, first and foremost, because they are in different stages of development. Using food web models that account for juvenile and adult individuals of species, I show that commonly observed differences between juveniles and adults in foraging capacity and predation risk result in larger, more complex communities than predicted by models without stage structure. Based on their species interaction networks these complex and diverse communities would be expected to be unstable, but these destabilizing effects of species interactions are overruled by stabilizing changes in juvenile–adult stage structure. Differences between juvenile and adult individuals hence offer a natural resolution to the diversity–stability enigma of ecological communities.