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

SUMMARY 1. Most metacommunity studies aim to explain variation in community structure using environmen-tal and spatial variables. An alternative is to examine patterns emerging at the level of an entiremetacommunity, whereby six models of metacommunity structure (i.e. random, chequerboards, nest-edness, evenly spaced, Gleasonian gradients and Clementsian gradients) can be examined.2. We aimed to test the fit of six competing models of metacommunity structure to extensive surveydata on diatoms, bacteria, bryophytes and invertebrates from three drainage basins in Finland, alonga latitudinal gradient from 66°Nto70°N.3. Species were mainly distributed independently of one another (following the Gleasonian model) inthe southernmost drainage basin (66°N), whereas there were discrete community types, with sets ofspecies responding similarly along environmental gradients (following the Clementsian model), inthe northernmost drainage basin (70°N). The patterns found were not directly related to an expectedrelationships between environmental heterogeneity and metacommunity structures, but rather to thegeographical location of the drainage basin.4. There is evidently among-region variation in the best-fit models of metacommunity structure ofstream organisms. These metacommunity patterns may show some similarities among biologicallydisparate organismal groups sampled at the set of the same sites, although the underlying environ-mental drivers of those patterns may vary between the groups.Keywords: bacteria, biological communities, bryophytes, diatoms, fresh waters, invertebrates