Document: KAT-3-35-39

Species richness does not always enhance productivity: Priority effects and competition for space in wetland plant communities.

ENGELHARDT, K.A.M.*, M.E.RITCHIE and J.A.KADLEC

Utah State University ¹

Abstract:
Species diversity should enhance productivity whenever species use resources in complementary ways, i.e., each species can use resources that others cannot so that total resource use by all species is greater than that of any individual species. We hypothesize that some species interactions, such as competition for space, prohibit complementarity from being expressed. If this is true, species richness may not always enhance productivity. We studied functional traits of four submersed aquatic macrophyte species to understand how these species differ in their effects on ecosystem functioning. All species significantly varied in their effects on resources (nitrogen, phosphorus, light) such that complementarity should exist among the four species. We also studied space occupation and priority effects in competition for resources and found that species significantly differed in percent space occupied and each species dominated in competition when initially most abundant. An experiment that manipulated species richness of the four submersed macrophyte species showed that species richness could not explain differences of productivity among treatments. However, when accounting for the effects of good space colonizers on productivity, species richness had a significant positive effect on productivity. We therefore propose a new hypothesis explaining the relationship between species richness and productivity. This hypothesis suggests that species richness may not always enhance ecosystem function, especially in systems where complementarity of resource use is prevented by species that are good space colonizers and that can pre-empt space.

Keywords: richness, wetland, ecosystem functioning, priority effects, competition, complementarity

This abstract is being presented at: 11:30 AM in session:
Oral Session #19: Grassland Restoration.