During the last decade, much attention has centered on the question of whether altered species diversity (primarily species richness) affects the functioning of ecosystems (Loreau et al. 2002) and the goods and services they provide to society (Daily et al. 2000). Because one of the
consequences of species loss may be the alteration or loss of certain ecosystem processes, understanding how changes in biodiversity affect the flow of energy and the cycling of nutrients and carbon remains a primary focus of ecological research (Kinzig et al. 2002, Loreau et al. 2002, Naeem and Wright 2003). Theory (Tilman 1999,Yachi and Loreau 1999, Loreau 2000) predicts that ecosystem functioning is likely to be less affected by the loss of species in species-rich communities than in equivalent species-poor communities, but empirical data in support of this prediction were initially lacking. Although a wealth of knowledge exists both on the patterns of biodiversity changes and on ecosystem processes, firm conclusions from observational and experimental studies about the relationship between the two have often been hampered by confounding factors, by difficulties in experimental design, and by problems in the unequivocal interpretation of data (Mikola et al. 2002).