Flow-related disturbance creates a gradient of metacommunity types within stream networks
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Metacommunities are sets of local communities linked by dispersal. Their characteristics are defined by both large-scale spatial processes such as dispersal, and local environmental processes, although which factors are likely to predominate in a given situation is poorly understood.
We investigated whether flow regime at the network-scale helped explain the relative importance of spatial and local-environmental processes in structuring stream metacommunities.
Spatial sampling of stream macroinvertebrates was carried out in stream networks in New Zealand. Local environmental variables were also measured throughout the stream networks, while hydrographs were modelled and calibrated with field measurements.
Significant associations with both spatial and local-environmental predictor variables were found, consistent with several metacommunity types. In particular, two measures of flow regime were associated with different metacommunity types. Thus, stream networks characterised by a period of stability just before sampling, and networks sampled after a long period of instability, had more significant spatial structuring of metacommunities than those of intermediate flow stability. The importance of spatial processes in structuring the network metacommunities also increased with time since the last community-resetting flow. Our results therefore suggested that metacommunity type depended on the flow regime. Dispersal traits and network topology also helped explain some of the variation among the metacommunities.
Overall, our findings conform to theoretical predictions related to dispersal limitation and topology, and indicate that metacommunity models need to be dynamic to capture processes in both space and time.
KeywordsDispersal Disturbance Local environment Macroinvertebrates Metacommunity Neutral Regional Stream networks Spatial scale
We thank members of the Freshwater Ecology Research Group at the University of Canterbury for assistance with field and laboratory work. Otago data sets were provided by Colin Townsend. The manuscript was improved greatly by comments on drafts from Jon O’Brien, Colin Townsend, Russell Death, Jake Overton and two anonymous reviewers. The project was funded by the Brian Mason Scientific and Technical Trust. REC was supported by a Tertiary Education Commission Top Achiever Doctoral Scholarship.
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