Ecological communities are structured by a combination of local processes like habitat filtering and species interactions, and regional forces driven by the dispersal of organisms between localities on a landscape. Previous studies suggest that the position of local communities within a dispersal network can greatly influence the relative influence of these two sets of processes on community assembly. However, the majority of previous investigations have used models or inferences based on observational data to investigate these hypotheses, while experiments directly addressing this question have been rare. We experimentally investigated the relative influence of local and regional processes in structuring benthic invertebrate communities using artificial streams. We manipulated three factors—source pool for the macroinvertebrate community (headwater vs. mainstem) as a surrogate of network location, habitat complexity (high vs. low) in the flume, and dispersal (high vs. low)—and followed changes in macroinvertebrate community structure for 8 weeks. Previous research suggests that because headwater ( Both of our predictions were strongly supported by the results of the experiment. For flumes with These results support the hypothesis that dispersal driven processes are a more important structuring force in well‐connected areas of networks by experimentally demonstrating the responsiveness of previously isolated communities to experimentally induced dispersal. They also demonstrate that this responsiveness is not due to an inherent difference in habitat affinity since source communities from both
Wetlands are critical components of freshwater biodiversity and provide ecosystem services, but human activities have resulted in large‐scale loss of these habitats across the globe. To offset this loss, mitigation wetlands are frequently constructed, but their ability to replicate the functions of natural wetlands remains uncertain. Further, monitoring of mitigation wetlands is limited and often focuses exclusively on vegetation and physical characteristics. Wetland fauna are assumed to be present if suitable habitat restoration is achieved, but this assumption is rarely tested. We used the macroinvertebrate community as a proxy for wetland function to compare recently created mitigation wetlands, natural wetlands impacted but not destroyed by road construction activity, and unimpacted reference wetlands along a highway corridor in the Greater Yellowstone Ecosystem. Unlike most other studies of invertebrate communities in created wetlands which have occurred in warm climates, our study area has a cold temperate climate with short growing seasons. We estimated macroinvertebrate taxonomic richness and used linear models to test for effects of wetland design features (wetland age, isolation, depth, vegetation, size, and Taxonomic richness of macroinvertebrates was lower in created wetlands than impacted or reference wetlands, whereas richness was similar in impacted and reference wetlands. Wetland age was positively correlated with taxonomic richness. The amount of aquatic vegetation in wetlands had the greatest influence on taxonomic richness, so that recently created wetlands with little vegetation had the simplest invertebrate communities. Community composition of invertebrates in created wetlands also differed from community composition in reference and impacted wetlands. Most notably, created wetlands lacked some passive dispersers that were common in other wetland types, although we found no relationship between taxonomic richness and wetland isolation. Overall, constructed wetlands had diminished and altered macroinvertebrate communities relative to reference and impacted wetlands, suggesting that periods in excess of 5 years may be required for wetland mitigation projects in cold temperate climates to attain full functionality.
- NSF-PAR ID:
- 10459630
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Freshwater Biology
- Volume:
- 64
- Issue:
- 5
- ISSN:
- 0046-5070
- Page Range / eLocation ID:
- p. 942-953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract HW ) streams are isolated within river networks,HW s are less influenced by regional processes relative to more well‐connected mainstems (MS s). We therefore predicted (i) that flumes colonised from aHW source community would respond more strongly to our dispersal treatment than those colonised byMS communities becauseMS were already largely structured through dispersal‐driven processes, and (ii) that bothHW andMS communities would respond to manipulations of local habitat, indicating that responses to the dispersal treatment were a direct result of dispersal driven dynamics rather than specific affinity for conditions in the flumes.HW source pools, the high dispersal treatment had significantly higher diversity than low dispersal flumes. However, this difference only occurred in flumes withHW source pools and did not occur in flumes withMS sources. There was also strong evidence of community composition inHW flumes shifting significantly towards the macroinvertebrate composition in our experimental dispersal treatment. The major effect of experimental dispersal was to introduce new species in fairly low abundances as would be expected from dispersal via drift over a relatively short time. BothMS andHW colonised flumes showed highly significant signals of habitat filtering, though the influence of specific habitat differed between the source types.HW s andMS s responded to manipulation of habitat variables. This experiment only simulated one type of dispersal process in streams—drifting—and did not include simulated dispersal from other sources, nor did it include population dynamics given the relatively short duration of the experiment. Nevertheless, the sensitivity of previously isolated communities to one type of simulated dispersal is a powerful indication of the mechanisms that structure these systems. -
Abstract Wetlands are especially vulnerable to invasive plants because seasonal movements of sediments, water, nutrients, and debris from adjacent terrestrial habitats create ecological conditions suitable for invasion.
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