Destruction and diversity: Effects of habitat loss on ecological communities

In many parts of the world habitat is being destroyed at an alarming rate. Many major ecosystems have lost more than half of their original area, and some much more than this [Millennium Ecosystem Assessment, Ecosystems and Human Well-Being: Synthesis (2005); World Wildlife Fund, Insight into Europe's Forest Protection (2001)]. At the same time biodiversity is fast declining [Butchart et al., Science 328:1164-1168, 2010]. Habitat loss is a major threat to biodiversity [Brooks et al., Conserv. Biol. 16:909-923, 2002; Baillie et al., 2004 IUCN Red List of Threatened Species: A Global Assessment (2004)], but the effects of the destruction are sometimes difficult to predict [Debinski and Holt, Conserv. Biol. 14:342-355, 2000; Prugh et al., Proc. Natl. Acad. Sci. USA 105:20770-20775, 2008; Hanski, AMBIO 40:248-255, 2011], and the effect of habitat loss and fragmentation on predator-prey interactions in particular is unclear [Ryall and Fahrig, Ecology 87:1086-1093, 2006]. One reason for the lack of clarity may be that the species-occupancy patterns that underlie diversity patterns in fragmented landscapes have often been overlooked [Prugh et al., Proc. Natl. Acad. Sci. USA 105:20770-20775, 2008; Ovaskainen and Hanski, Ecol. Lett. 6:903-909, 2003]. The patch-occupancy metapopulation paradigm, despite its simplicity, has proved successful in developing some understanding of how habitat destruction affects the local flora and fauna. We shall review and derive some results arising from this approach for single species, for competitive and mutualistic communities, for predator-prey systems and food chains, and finally for a simple food web, a predator interacting with two competing prey. We show that although the outcome of habitat destruction in terms of species extinctions may be straightforward for the simplest models and communities, it may be subtly parameter-dependent and counter-intuitive with even a small increase in complexity. Progress towards a theory for more complex food webs [Leibold et al., Ecol. Lett. 7:601-613, 2004; Leibold and Miller, From metapopulations to metacommunities (2004); Pillai et al., Theor. Ecol. 3:223-237, 2010] will be difficult until we have a thorough understanding of these basic building blocks.