Untangling the relationships among regional occupancy, species traits, and niche characteristics in stream invertebrates

Authors

  • Jani Heino,

    Corresponding author
    1. Finnish Environment Institute, Natural Environment Centre, Oulu, Finland
    2. Department of Biology, University of Oulu, Oulu, Finland
    • Correspondence

      Jani Heino, Finnish Environment Institute, Natural Environment Centre, P.O. Box 413, FI-90014 Oulu, Finland. Tel: +358 400 148 653; Fax: +358 8 816 2872; E-mail: jani.heino@environment.fi

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  • Mira Grönroos

    1. Finnish Environment Institute, Natural Environment Centre, Oulu, Finland
    2. Department of Biology, University of Oulu, Oulu, Finland
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Abstract

The regional occupancy and local abundance of species are affected by various species traits, but their relative effects are poorly understood. We studied the relationships between species traits and occupancy (i.e., proportion of sites occupied) or abundance (i.e., mean local abundance at occupied sites) of stream invertebrates using small-grained data (i.e., local stream sites) across a large spatial extent (i.e., three drainage basins). We found a significant, yet rather weak, linear relationship between occupancy and abundance. However, occupancy was strongly related to niche position (NP), but it showed a weaker relationship with niche breadth (NB). Abundance was at best weakly related to these explanatory niche-based variables. Biological traits, including feeding modes, habit traits, dispersal modes and body size classes, were generally less important in accounting for variation in occupancy and abundance. Our findings showed that the regional occupancy of stream invertebrate species is mostly related to niche characteristics, in particular, NP. However, the effects of NB on occupancy were affected by the measure itself. We conclude that niche characteristics determine the regional occupancy of species at relatively large spatial extents, suggesting that species distributions are determined by environmental variation among sites.

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