Stream insect occupancy-frequency patterns and metapopulation structure
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An understanding of the distribution patterns of organisms and the underlying factors is a fundamental goal of ecology. One commonly applied approach to visualize these is the analysis of occupancy-frequency patterns. We used data sets describing stream insect distributions from different regions of North America to analyze occupancy-frequency patterns and assess the effects of spatial scale, sampling intensity, and taxonomic resolution on these patterns. Distributions were dominated by satellite taxa (those occurring in ≤10% of sites), whereas the occurrence of core taxa (occurring in ≥90% of sites) determined the overall modality of occupancy-frequency patterns. The proportions of satellite taxa increased with spatial scale and showed positive relationships with sampling intensity (r 2=0.74–0.96). Furthermore, analyses of data sets from New York (USA) showed that generic-level assessments underestimated the satellite class and occasionally shifted occupancy-frequency distributions from unimodal to bimodal. Our results indicate that, regardless of species- or generic-level taxonomy, stream insect communities are characterized by satellite species and that the proportion of satellite species increases with spatial scale and sampling intensity. Thus, niche-based models of occupancy-frequency patterns better characterize stream insect communities than metapopulation models such as the core-satellite species hypothesis.
KeywordsAquatic insect Core-satellite Distribution Sampling intensity Spatial scale
Support for this research was provided by the National Science Foundation LTER Network Office. Tokeshi’s tests were performed using spreadsheets kindly provided by B. Bossuyt. Stream invertebrate sampling in Maryland was supported by an EPA STAR grant ®-82801201). The New York data set was collected as part of a Safe Drinking Water project funded by New York State Department of Environmental Conservation and the United States Environmental Protection Agency. The comments of Suzanne Stapleton and two anonymous reviewers greatly improved the quality of the manuscript.
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