Ecological structural instability at multiple spatial scales.

PhD Theses.IINTRODUCTION. The biosphere is a network: a network of biogeochemical fluxes, sporadically clustered in organic structures. Increasingly ecosystems are explored, probed and categorized on the basis of the properties of the mathematical networks that can be constructed to represent them. A ‘metacommunity’ is a macroecological network-of-networks, represented at the regional scale by a spatial network of ecological communities, between which species disperse. At the local scale, ecological networks describe the complex web of interactions amongst those species. The central aim of this thesis is to explore the processes responsible for spatio-temporal biodiversity pattern formation in metacommunities: how do local population dynamical processes propagate up the organizational scales to define the regionalscale structure of a macroecological assemblage? In particular, we aim to discover how ecological structural instability, an important property of ecological networks, may impact diversity patterns in spatially explicit systems. We begin, therefore, with a brief introduction to the theory of structural instability and how it has been applied in the study of ecological communities. We summarize how structural instability impacts the robustness of ecological networks to perturbations in external conditions, how the loss of robustness entails an important ecological constraint on community structure, and how that constraint may lead to the community-scale, systematic selection of specific network architectures. Systematic selection of this type can be seen in an over-representation of the selected-for configurations; thus we 8 close with a summary of those patterns in macroecology that are seemingly general in nature, and in which the onset structural instability may play an important, mechanistic role