The assembly and disassembly of ecological networks

Abstract

Global change has created a severe biodiversity crisis. Species are driven extinct at an increasing rate, and this has the potential to cause further coextinction cascades. The rate and shape of these coextinction cascades depend very much on the structure of the networks of interactions across species. Understanding network structure and how it relates to network disassembly, therefore, is a priority for system-level conservation biology. This process of network collapse may indeed be related to the process of network build-up, although very little is known about both processes and even less about their relationship. Here we review recent work that provides some preliminary answers to these questions. First, we focus on network assembly by emphasizing temporal processes at the species level, as well as the structural building blocks of complex ecological networks. Second, we focus on network disassembly as a consequence of species extinctions or habitat loss. We conclude by emphasizing some general rules of thumb that can help in building a comprehensive framework to understand the responses of ecological networks to global change.

Figure 1

The different approaches to food web research. Traditionally, ecologists have either studied the dynamics of simple trophic modules (left) or the statistical properties of entire food webs (right). In the last few years, ecologists have tried to bridge between these two research agendas by exploring how well represented are these trophic modules in entire food webs (black arrow). Some of these modules are over-represented; they are called networks motifs and can be regarded as the basic building blocks of complex food webs. The next step in understanding network assembly is to focus on the mesoscale by exploring how trophic modules relate to each other and what components of food web stability can be explained by the stability of the basic blocks versus the stability of their combination (grey arrows).