Browsing by Subject "environmental heterogeneity"

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  • Kivinen, Sonja; Nummi, Petri; Kumpula, Timo (IOP Science, 2020)
    Environmental Research Letters 15 9 (2020)
    Beavers (Castor sp.) are ecosystem engineers that cause significant changes to their physical environment and alter the availability of resources to other species. We studied flood dynamics created by American beaver (C. canadensis K.) in a southern boreal landscape in Finland in 1970–2018. We present for the first time, to our knowledge, a temporally continuous long-term study of beaver-induced flood disturbances starting from the appearance of beaver in the area. During the 49 years, the emergence of new sites flooded by beaver and repeated floods (61% of the sites) formed a dynamic mosaic characterized by clustered patterns of beaver sites. As beaver dispersal proceeded, connectivity of beaver sites increased significantly. The mean flood duration was approximately three years, which highlights the importance of datasets with high-temporal resolution in detecting beaver-induced disturbances. An individual site was often part of the active flood mosaic over several decades, although the duration and the number of repeated floods at different sites varied considerably. Variation of flood-inundated and post-flood phases at individual sites resulted in a cumulative number of unique patches that contribute to environmental heterogeneity in space and time. A disturbance mosaic consisting of patches differing by successional age and flood history is likely to support species richness and abundance of different taxa and facilitate whole species communities. Beavers are thus a suitable means to be used in restoration of riparian habitat due to their strong and dynamic influence on abiotic environment and its biotic consequences.
  • He, Siwen; Soininen, Janne; Chen, Kai; Wang, Beixin (2020)
    Metacommunity theory provides a useful framework to describe the underlying factors (e.g., environmental and dispersal-related factors) influencing community structure. The strength of these factors may vary depending on the properties of the region studied (e.g., environmental heterogeneity and spatial location) and considered biological groups. Here, we examined environmental and dispersal-related controls of stream macroinvertebrates and diatoms in three regions in China using the distance-decay relationship analysis. We performed analyses for the whole stream network and separately for two stream network locations (headwater and downstream sites) to test the network position hypothesis (NPH), which states that the strength of environmental and dispersal-related controls varies between headwater and downstream communities. Community dissimilarities were significantly related to environmental distances, but not geographical distances. These results suggest that communities are structured strongly by environmental filtering, but weakly by dispersal-related factors such as dispersal limitation. More importantly, we found that, at the whole network scale, environmental control was the highest in the regions with highest environmental heterogeneity. Results further showed that the influence of environmental control was strong in both headwaters and downstream sites, whereas spatial control was generally weak in all sites. This suggests a lack of consistent support for the NPH in our studied stream networks. Moreover, we found that local-scale variables relative to basin-scale variables better explained community dissimilarities for diatoms than for macroinvertebrates. This indicates that diatoms and macroinvertebrates responded to environment at different scales. Collectively, these results suggest that the importance of drivers behind the metacommunity assembly varied among regions with different level of environmental heterogeneity and between organism groups, potentially indicating context dependency among stream systems and taxa.