Biodiversity Loss and Ecological Network Structure

The world is currently experiencing exceptionally high rates of species extinctions, largely as as result of human activity (Lawton and May 1996). Currently, most conservation research on habitat destruction focuses on the species as the unit of study, looking at either the impact of habitat destruction on individual species, or collections of species from particular habitats. There is, however, increasing recognition that species and species lists are not the only, nor perhaps the best, units for study by conservation biologists. This is because species are linked to other species in a variety of critical ways, for example as predators or prey, or as pollinators or seed dispersers. Consequently, the extinction of one species can lead to secondary extinctions in complex ecological networks (Dunne et al. 2002a; Memmott et al. 2004; Solé and Montoya 2001). The presence of links between species can also lead to community closure after the loss of a species, with the result that this species cannot then be reintroduced (Lundberg et al. 2000). Moreover, in the case of restoration biology, restoration will not be sus-