Biodiversity and Ecosystem Functioning
During the last decade interest has shifted from explaining species diversity to understanding the functional consequences of biodiversity. Biodiversity is a broader concept than species diversity because it includes all aspects of the diversity of life—including molecules, genes, behaviors, functions, species, interactions, and ecosystems. Accordingly, it can be approached from multiple perspectives. Although the classical approach in taxonomy, ecology, and conservation biology has been based on species and species numbers, other approaches focus on the diversity of functional traits (Diaz and Cabido 2001; Naeem and Wright 2003) or phylogenies (Faith 1992). So far, however, most studies have concerned species diversity. As we saw in the previous chapter, community ecology has much to say on species diversity. But its focus has traditionally been on the processes that generate and maintain species diversity and has been largely theoretical or fundamental.
When ecologists and environmental scientists started to become interested in the relationship between biodiversity and ecosystem functioning, it was with a more practical viewpoint. Biodiversity is increasingly threatened by human activities and its environmental impacts, in particular, changes in land use, biological invasions, overexploitation of biological resources, pollution, and, more recently, climate change. Conservation efforts had mainly concerned individual species—most often, large, charismatic vertebrates because of their aesthetic value or for ethical reasons. But what about the multitude of other species that surround us? And what about the broader consequences of biodiversity loss? Living organisms drive energy flows and biogeochemical cycles in ecosystems from local to global scales: could the loss of their diversity affect the functioning of ecosystems and the “services” they deliver indirectly to humans?
When these important questions were first asked in the early 1990s (Schulze and Mooney 1993), neither community ecology nor ecosystem ecology was able to provide clear answers. There was much theoretical, experimental, and observational evidence for the importance of vertical diversity, in particular, for the critical roles played by top predators and