Contribution of spatial position and local environmental factors to stream insect species richness assessed across multiple spatial scales.
Astorga, Anna*,1, 2, Heino, Jani1, Muotka, Timo1, 2, 1 Finnish Environment Institute, Helsinki, Finland2 University of Oulu, Oulu, Finland
ABSTRACT- Species richness in ecological communities results from the interplay of various local abiotic and biotic factors, as well as regional factors, such as broad-scale climatic factors and dispersal limitation. The relative importance of each of these factors may change with the spatial extent considered, and understanding the determinants of local species richness should thus include scaling effects. We examined the relative importance of spatial location and local environmental variables for the species richness of three groups of stream insects (mayflies, stoneflies and caddisflies) at three different geographical extents (bioregional, ecoregional and drainage system level). Stream insects were sampled at 220 stream riffle sites across Finland. Several riparian and in-stream environmental variables and spatial coordinates were recorded for each site. Our statistical approach was to partition the variation of species richness among pure environmental component, spatially structured environmental component and pure spatial component at three different geographical extents using partial linear regression. Our results showed that local environmental variables and associated spatial gradients were important determinants of mayfly and stonefly species richness, with no clear differences between the three different geographical extents analyzed. Species richness of caddisflies was strongly spatially structured, especially at the larger geographical extents. We tentatively hypothesize that the observed differences amongst these three insect orders may be caused by differences in their dispersal abilities.
Key words: stream insects, species richness, variance decomposition, spatial analyses
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