Biogeographical Patterns of Species Richness and Abundance Distribution in Stream Diatoms Are Driven by Climate and Water Chemistry
Contraintes environnementales et spatiales sur la richesse et l'abondance des diatomées
Résumé
This is the first inter-continental comparative assessment of diatom richness and species abundance distribution (SAD) along spatial, climatic, and water chemistry gradients using stream data from the US and Finland. We tested a number of hypotheses about the causes of variability in richness and by extension, the SAD, including the metabolic theory, the species-energy, the more individuals, the climatic variability, and the climatic tolerance hypotheses. We found no support for any of these concepts, given that the relationships of richness with explanatory variables were non-existent, weak or unexpected. Diatom richness and the SAD responded more strongly to climatic variability, climatic extremes, and water chemistry, especially nutrient levels, than to mean temperature. A consequence of the weak energy dependence was a non-linear latitudinal gradient of richness in both countries, and a non-linear latitudinal gradient of the SAD in the US. The SAD was not entirely driven by richness but displayed distinct responses to spatial, climatic, and water chemistry factors, indicating that the environment had complementary effects on richness and the SAD. This emphasizes the utility of the SAD for ecological research.
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