PARENT SESSION
Oral Session #40: Biodiversity and Ecosystem Function: Do species and species richness matter?. Presiding: R. Dirzo.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Madison Ballroom D.
Mechanisms maintaining ecosystem function after species loss: Numerical and per capita compensation by stream insects.
Srivastava, Diane1, Ruesink, Jennifer2, 1 2
ABSTRACT- The effects of species loss on ecosystem function will depend on the response of the remaining species. In principle, ecosystem function could be maintained after species loss in two ways: the remaining species could increase their processing rates (per capita compensation) or they could increase in abundance (numerical compensation). We were able to distinguish between these two types of compensation by manipulating stream insect communities in flow-through enclosures and measuring the effects on an ecosystem function, processing of leaf litter. We also compared the effects of removing each of two dominant species separately, the stonefly Pteronarcys californica and the caddisfly Lepidostoma unicolor. To test for per capita compensation, we compared leaf processing rates in full-diversity communities with those in similar communities missing one dominant species, i.e. reduced in both species number and abundance. Per capita compensation occurred after Pteronarcys loss but not Lepidostoma loss. To test the effectiveness of numerical compensation, we experimentally increased abundances in these depleted-diversity communities so that the expected metabolic capacity of the assemblage returned to original levels. These increases in abundance were always effective in maintaining rates of leaf breakdown after Pteronarcys loss, but not always after Lepidostoma loss. In the latter case, it mattered which of the remaining species increased in abundance. In summary, the effect of species loss in our study depended on which species was lost, which species responded to this loss, and how they responded. These results indicate that a variety of different mechanisms may underlie patterns between biodiversity loss and ecosystem function.
KEY WORDS: biodiversity, ecosystem function, leaf processing, stream insects