Evol Ecol Res 1: 73-95 (1999)     Full PDF if your library subscribes.

Biodiversity and nutrient enrichment in pond plankton communities

Mathew A. Leibold

Department of Ecology and Evolution, University of Chicago, 1101 E. 57th Street, Chicago, IL 60637, USA

e-mail: mleibold@midway.uchicago.edu


There are at least four mathematically developed models that predict unimodal diversity–productivity relations in local communities. I attempt to distinguish among these theories using data from surveys of planktonic organisms in 31 fishless ponds in southern Michigan by relating plant and herbivore diversity and composition to pond nutrient levels. The density of plants (phytoplankton) was positively correlated with nutrient levels and the density of herbivores (zooplankton) was positively correlated with the density of plants. Species richness of plants and of herbivores were declining or unimodal functions of nutrient levels. The composition of each trophic level changed significantly with eutrophication as indicated by significant correlations between nutrient levels and site scores (obtained by reciprocal averaging ordination on occurrences). A concomitant lack of correlation between site scores and species richness for both trophic levels further shows that the patterns of species distributions form gradients of species replacements rather than nested subsets. Taxonomic ordination scores also showed that the algae found at low nutrient levels consisted disproportionately of small, unprotected forms (thought to be fast-growing but grazer-susceptible), whereas the algae found at high nutrient levels were larger and often sheathed or gelatinous (thought to be slow-growing but more resistant to grazers). The results of this analysis of changes in the patterns of distribution of planktonic organisms are consistent with a hypothesis of productivity-dependent ‘keystone-predation’ causing the unimodal relation between diversity and productivity.

Keywords: biodiversity, phytoplankton, predation, productivity, zooplankton.

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