Abstract
Both environmental heterogeneity and mode of dispersal may affect species co-occurrence in metacommunities. Aquatic invertebrates were sampled in 20–30 streams in each of three drainage basins, differing considerably in environmental heterogeneity. Each drainage basin was further divided into two equally sized sets of sites, again differing profoundly in environmental heterogeneity. Benthic invertebrate data were divided into three groups of taxa based on overland dispersal modes: passive dispersers with aquatic adults, passive dispersers with terrestrial winged adults, and active dispersers with terrestrial winged adults. The co-occurrence of taxa in each dispersal mode group, drainage basin, and heterogeneity site subset was measured using the C-score and its standardized effect size. The probability of finding high levels of species segregation tended to increase with environmental heterogeneity across the drainage basins. These patterns were, however, contingent on both dispersal mode and drainage basin. It thus appears that environmental heterogeneity and dispersal mode interact in affecting co-occurrence in metacommunities, with passive dispersers with aquatic adults showing random patterns irrespective of environmental heterogeneity, and active dispersers with terrestrial winged adults showing increasing segregation with increasing environmental heterogeneity.
Highlights
Understanding patterns and underlying mechanisms of species co-occurrence is a core area of community ecology
The aim of the present study is to extend on the previous findings of the co-occurrence of species, and to examine the effects of changing environmental heterogeneity and dispersal mode on the co-occurrence of species
In the Iijoki drainage basin, the mean Euclidean distance to group centroid was clearly higher for the high heterogeneity subset than the low heterogeneity subset (F = 13.284, P = 0.003), and the same self-evident pattern was found for the Koutajoki drainage basin (F = 45.055, P = 0.001) and the Tenojoki drainage basin (F = 10.057, P = 0.007)
Summary
Understanding patterns and underlying mechanisms of species co-occurrence is a core area of community ecology. Biotic (e.g., interspecific competition), abiotic (e.g., environmental heterogeneity), and historical (e.g., differential colonization) factors are considered important for the co-occurrence of species among sites (Diamond 1975; Gilpin and Diamond 1982; Belyea and Lancaster 1999; Gotelli and McCabe 2002). Considering interspecific competition, Diamond (1975) coined a number of “assembly rules”, revolving around the idea that competing species should not occur together This idea has subsequently been tested in various organisms groups, environmental contexts and geographical regions, and a meta-analysis of a large number of data sets revealed that species tend to coexist less than expected by chance (Gotelli and McCabe 2002). Any two species differing in environmental responses are expected to be, at least partially, segregated across a set of sites if there is variation in environmental conditions
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