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The spatial extent and the dispersal strategy of species shape the occupancy frequency distribution of stream insect assemblages
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  • Ildikó Szivák,
  • Zoltán Csabai,
  • Dénes Schmera,
  • Arnold Móra
Ildikó Szivák
Balaton Limnological Research Institute
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Zoltán Csabai
University of Pécs
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Dénes Schmera
Balaton Limnological Research Institute
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Arnold Móra
University of Pecs Faculty of Sciences

Corresponding Author:[email protected]

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Abstract

Several theoretical models have been proposed as the underlying mechanisms behind occupancy frequency distribution (OFD) patterns. For instance, the metapopulation dynamic model predicts bimodal OFD pattern indicating the dominance of dispersal processes in structuring the assemblages, while the niche-based model predicts unimodal right-skewed OFD pattern, and thus assemblages are driven mostly by niche processes. However, it is well known that the observed OFD pattern reflects the interplay of several other factors (e.g., habitat heterogeneity, species specificity, sampling protocol parameters). It follows that the individual contribution of each factor to the OFD pattern is rather complicated to explore. Our main objective was to examine the role of the spatial extent of the sampling and the dispersal strategies of species in shaping OFD pattern. For this, we collected samples of stream insect assemblages inhabiting near-natural streams in the Pannon Ecoregion. We formed groups of species representing contrasting dispersal strategies (referred to as dispersal groups). Applying a computer program algorithm, we produced samples from different levels of a stream habitat hierarchy (reach, subbasin, basin, and regional) representing different spatial sample extents. We found that with increasing spatial extent, the OFD pattern changed from bimodal to unimodal for two dispersal groups. Insect groups with contrasting dispersal strategies differed in OFD patterns at reach, subbasin and basin levels. Dispersal groups also differed considering the change in OFD patterns with increasing spatial extent. Our results reflected the underlying changes in the niche and dispersal processes that structure assemblages with increasing spatial extent. We also concluded that the stream insect dispersal strategy influenced the relative role of dispersal and niche processes with increasing spatial extent. Based on our results, we could define spatial extents and dispersal strategies within which different metacommunity models (dispersal and niche processes) could be applied.