Elements of metacommunity structure and community-environment relationships in stream organisms

Most metacommunity studies aim to explain variation in community structure using environmental and spatial variables. An alternative is to examine patterns emerging at the level of an entire metacommunity, whereby six models of metacommunity structure (i.e. random, chequerboards, nestedness, evenly spaced, Gleasonian gradients and Clementsian gradients) can be examined. We aimed to test the fit of six competing models of metacommunity structure to extensive survey data on diatoms, bacteria, bryophytes and invertebrates from three drainage basins in Finland, along a latitudinal gradient from 66 degrees N to 70 degrees N. Species were mainly distributed independently of one another (following the Gleasonian model) in the southernmost drainage basin (66 degrees N), whereas there were discrete community types, with sets of species responding similarly along environmental gradients (following the Clementsian model), in the northernmost drainage basin (70 degrees N). The patterns found were not directly related to an expected relationships between environmental heterogeneity and metacommunity structures, but rather to the geographical location of the drainage basin. There is evidently among-region variation in the best-fit models of metacommunity structure of stream organisms. These metacommunity patterns may show some similarities among biologically disparate organismal groups sampled at the set of the same sites, although the underlying environmental drivers of those patterns may vary between the groups.