Ecosystem-level consequences of invasions by native species as a way to investigate relationships between evenness and ecosystem function

Abstract

Biodiversity is currently undermined worldwide principally as a result of human activities. The irreversibility of species extinction has encouraged the research community to investigate the potential effect of declining species or functional group diversity and/or composition on ecosystem function since the beginning of the 1990s. However, while changes in relative abundance among species (i.e., evenness) are more frequent than extinction of species and are able to cause important changes in ecosystem function, most studies have curiously not examined thoroughly the potential role of that diversity component. The few small-scale experimental manipulations that have so far examined the relationship between evenness and ecosystem function have produced ambiguous results, sometimes indicating an effect on selected functions, and sometimes not. Because one reason for the inconsistency of the previous results may be scale-dependency issues, we propose here an alternative approach, investigation of this relationship directly at the system-level through the opportunity offered by field studies of ecosystem-level consequences of invasions by native species. Indeed, the specificities of changes in ecosystem structure induced by native invaders compared to exotic ones could constitute a useful tool to improve our understanding of the relationship between evenness and ecosystem function as well as to evaluate the importance of the spatial arrangement of species in the stability of ecosystems.