On Some Causes and Consequences of Patterns in Food Web Structure

Food webs, the graphical depictions of feeding interactions between species, have long fascinated ecologist. They now occupy a key role in ecological science due to the unique perspective on the staggering complexity of natural systems that they provide. There have been several attempts at developing theories to explain the structural properties of these ecological networks, which have met with relatively good success. However, we are as yet lacking a mechanistic understanding of the processes that structure food webs. Recently, in an attempt to address this, the focus of food web studies has shifted to the role of the individual consumer and whether we can scale from our understanding of foraging behaviour to predict the structural and dynamical properties of food webs. As a result of this there has arisen a need for individual based models and empirical datasets to provide us with a firm foundation to scale across levels of ecological organisation. In this thesis I demonstrate, using a mathematical model, how the foraging behavior at the level of individuals can provide us with novel and useful insights into the causes and consequences of patterns in food webs structure. I also present results analyzing a novel individual based data set to survey and enrich these links across levels of organization. My findings strongly suggest that understanding the variation of size structure among ecological networks requires knowledge about the causes of variation in individual foraging behaviour. Other work included in this thesis demonstrates both how modelling foraging behaviour of individuals and its effects on food web topology alters our expectations about the likely consequences of extinctions in food webs. And finally how insights gained from modelling individual based foraging can enable us to build theoretical tools to compensate for the sampling effects that have dogged food web data sets. The results of this thesis contribute in a significant to the growing synthesis of ideas linking individuals to ecosystems.