Functional diversity and productivity peak at intermediate levels of dispersal in evolving meta-communities

The relationship between species richness and ecosystems properties such as productivity (Loreau et al 2001, Hooper et al 2005) is central to our understanding of biodiversity. It is generally thought that ecological mechanisms driving species coexistence are responsible for the shape of this relationship (Cardinale et al. 2000, Mouquet et al 2002). Here we show, using the bacteria Pseudomonas fluorescens SBW25 that evolution in experimental metacommunities with intermediate levels of dispersal leads to maximal functional diversity and productivity. As predicted by models of niche differentiation, higher complementarity in resource use strategies allows greater coverage of the heterogeneous environment leading to higher productivity (Loreau 1998, Tilman et al 1997). Our results demonstrate for the first time that a positive relationship between functional diversity and productivity can emerge through evolution of complementary types. Functional diversity determines ecosystem properties while dispersal and environmental heterogeneity determine the emergence and maintenance of this diversity within the metacommunity.