Taxonomical and functional diversity of rotifers in two distinct basins of Lake Tovel, what do they tell us about community assembly?

Community composition depends on environmental parameters and species interactions. We analysed the rotifer community structure from a taxonomical and a functional perspective for five consecutive years (2002-2006) in the two distinct, but connected basins of Lake Tovel. The shallow basin (basin B; depth 4 m) is characterized by a larger temperature gradient and lower water residence time compared to the deeper basin (basin A; depth 39 m). Monthly zooplankton samples were taken at discrete depths in both basins and mean abundance for zooplankton was calculated over the whole water column. We used morphological characteristics as functional traits and applied non-metric multidimensional scaling (NMDS) to investigate community structure in both basins. Species richness and abundance was generally lower in basin B than in A. In NMDS based on species abundance, a clear separation between basin A and B was found while when based on functional traits this separation was less clear. In B, many littoral species were found, while in basin A most species were pelagic. Our data indicated that the two basins are different from a taxonomical perspective, but are quite similar from a functional perspective. Our study highlights that by focusing on functional traits, a more complete picture of community composition can be obtained.