Abstract

Lake phytoplankton richness data were analyzed to reveal the effects of area and scale on the richness-elevation relationship. Lakes provide a unique opportunity to accomplish this because of their well-defined boundaries, which clearly define local communities and their habitat area. Local phytoplankton richness (alpha diversity) was found to decrease with increasing elevation, even when the effect of lake area was accounted for. This decrease coincided with a decrease in lake productivity with increasing elevation. Additionally, pairwise dissimilarity calculations suggested that isolation by distance was less important in structuring local phytoplankton richness than isolation by either elevation or environmental distance. In contrast, phytoplankton richness calculated for elevation bands (gamma diversity) showed a hump-shaped dependence on elevation, with a mid-elevation maximum, consistent with the predictions of a mid-domain null model. Moreover, mean pairwise dissimilarity within elevation bands shows compositional dissimilarity to be highest at high elevations and low environmental distances, emphasizing the isolated character of high-elevation lakes. We suggest that the form of the phytoplankton richness-elevation relationship is scale-dependent, and that geometric constraints, differences in the possibility of horizontal and vertical dispersal, environmental heterogeneity and an underlying monotonic trend in productivity, are likely to be responsible for the patterns in alpha and gamma diversity observed along elevation gradients

Published in

Oikos
2006, volume: 115, number: 3, pages: 433-442
Publisher: BLACKWELL PUBLISHING

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