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.
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
- NSF-PAR ID:
- 10041491
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Freshwater Biology
- Volume:
- 63
- Issue:
- 1
- ISSN:
- 0046-5070
- Page Range / eLocation ID:
- p. 48-61
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract pH ) on invertebrate richness. We also used non‐metric multidimensional scaling to visualise differences in community composition among wetland types and used indicator species analysis to determine which taxa were causing observed differences. -
more » « less
Abstract Understanding how nutrient limitation affects algal biomass and production is a long‐standing interest in aquatic ecology. Nutrients can influence these whole‐community characteristics through several mechanisms, including shifting community composition. Therefore, incorporating the joint responses of biomass, taxonomic composition, and production of algal communities, and relationships among them, is important for understanding effects of nutrient enrichment.
In shallow subarctic Lake Mývatn, Iceland, benthic algae compose a majority of whole‐lake primary production, support high secondary production, and influence nutrient cycling. Given the importance of these ecosystem processes, the factors that limit benthic algae have a large effect on the function and dynamics of the Mývatn system.
In a 33‐day nutrient enrichment experiment conducted in Lake Mývatn, we measured the joint responses of benthic algal biomass, primary production, and composition to nitrogen (N) and phosphorus (P) supplementation. We enriched N and P using nutrient‐diffusing agar overlain by sediment, with three levels of N and P that were crossed in a factorial design.
We found little evidence of community‐wide nutrient limitation, as chlorophyll‐
a concentrations showed a negligible response to nutrients. Gross primary production (GPP ) was unaffected by P and inhibited by N enrichment after 10 days, although the inhibitory effect of N diminished by day 33.In contrast to biomass and primary production, community composition was strongly affected by N and marginally affected by P, with some algal groups increasing and others decreasing with enrichment. The taxa with the most negative and positive responses to N enrichment were Fragilariaceae and
Scenedesmus , respectively.The abundances of particular algal groups, based on standardised cell counts, were related to
GPP measured at the end of the experiment.Oocystis was negatively associated withGPP but was unaffected by N or P, while Fragilariaceae andScenedesmus were positively associated withGPP but had opposite responses to N. As a result, nutrient‐induced compositional shifts did not alterGPP .Overall, our results show that nutrient enrichment can have large effects on algal community composition while having little effect on total biomass and primary production. Our study suggests that nutrient‐driven compositional shifts may not alter the overall ecological function of algal communities if (1) taxa have contrasting responses to nutrient enrichment but have similar effects on ecological processes, and/or (2) taxa that have strong influences on ecological function are not strongly affected by nutrients.
-
more » « less
Abstract Whether niche processes, like environmental filtering, or neutral processes, like dispersal limitation, are the primary forces driving community assembly is a central question in ecology. Here, we use a natural experimental system of isolated tree “islands” to test whether environment or geography primarily structures fungal community composition at fine spatial scales. This system consists of isolated pairs of two distantly related, congeneric pine trees established at varying distances from each other and the forest edge, allowing us to disentangle the effects of geographic distance vs. host and edaphic environment on associated fungal communities. We identified fungal community composition with Illumina sequencing of
ITS amplicons, measured all relevant environmental parameters for each tree—including tree age, size and soil chemistry—and calculated geographic distances from each tree to all others and to the nearest forest edge. We applied generalized dissimilarity modelling to test whether total and ectomycorrhizal fungal (EMF ) communities were primarily structured by geographic or environmental filtering. Our results provide strong evidence that as in many other organisms, niche and neutral processes both contribute significantly to turnover in community composition in fungi, but environmental filtering plays the dominant role in structuring both free‐living and symbiotic fungal communities at fine spatial scales. In our study system, we foundpH and organic matter primarily drive environmental filtering in total soil fungal communities and thatpH and cation exchange capacity—and, surprisingly, not host species—were the largest factors affectingEMF community composition. These findings support an emerging paradigm thatpH may play a central role in the assembly of all soil‐mediated systems. -
Weighting effective number of species measures by abundance weakens detection of diversity responsesmore » « less
Abstract The effective number of species (
ENS ) has been proposed as a robust measure of species diversity that overcomes several limitations in terms of both diversity indices and species richness (SR). However, it is not yet clear ifENS improves interpretation and comparison of biodiversity monitoring data, and ultimately resource management decisions.We used simulations of five stream macroinvertebrate assemblages and spatially extensive field data of stream fishes and mussels to show (a) how different
ENS formulations respond to stress and (b) how diversity–environment relationships change with values ofq , which weightENS measures by species abundances.Values of
ENS derived from whole simulated assemblages with all species weighted equally (true SR) steadily decreased as stress increased, andENS ‐stress relationships became weaker and more different among assemblages with increased weighting.The amount of variation in
ENS across the fish and mussel assemblages that was associated with environmental gradients decreased with increasingq .Synthesis and applications . Species diversity is valued by many human societies, which often have policies designed to protect and restore it. Natural resources managers and policy makers may use species richness and diversity indices to describe the status of ecological communities. However, these traditional diversity measures are known subject to limitations that hinder their interpretation and comparability. The effective number of species (ENS ) was proposed to overcome the limitations. Unfortunately, our analyses show thatENS does not improve interpretability of how species diversity responds to either stress or natural environmental gradients. Moreover, incorporating the relative abundance of individuals in different species (evenness) into diversity measures as implemented inENS can actually weaken detection of diversity responses. Natural resources managers and policy makers therefore need to be cautious when interpreting diversity measures, includingENS , whose values are jointly influenced by richness and evenness. We suggest that both researchers and practitioners measure and report three aspects of diversity (species richness, evenness, and composition) separately when assessing and monitoring the diversity of ecological communities. -
more » « less
Abstract Non‐native species are now common in community assemblages, but the influence of multiple introductions on ecosystem functioning remains poorly understood. In highly invaded systems, one promising approach is to use functional traits to scale measured individuals’ effects on ecosystem function up to the community level. This approach assumes that functional traits provide a common currency among species to relate individuals to ecosystem functioning.
The goals of this study were to (i) test whether the relationship between body size and ecosystem functioning (per capita nutrient recycling) was best described by general or species‐specific scaling models; (ii) relate community structure (total biomass, average body size, non‐native dominance) to aggregated, community‐level nutrient recycling rates and ratios; and (iii) determine whether conclusions regarding the relationships between community structure and aggregate ecosystem functioning differed between species‐specific and general scaling approaches.
By combining experimental incubations and field surveys, we compare consumer‐mediated nutrient recycling of fish communities along a non‐native dominance gradient in the Verde River watershed of central Arizona,
USA . Data from ˜340 field‐sampled freshwater fish demonstrated support for general allometric relationships predicted by the metabolic theory of ecology (NH 4‐N scaling coefficient = 0.72 [0.64–0.80];PO 4‐P = 0.67 [0.47–0.86]). However, the best‐fit models for N and P included species‐specific random effects for both allometric slopes and intercepts.According to species‐specific models, stream fish communities recycled 1–12 mmol
NH 4‐N/hr (median = 2.8 mmol/hr) and 0.02–0.74 mmolPO 4‐P/hr (median = 0.07 mmol/hr) at N:P ratios between 13.3 and 83.5 (median = 28.8). General models generated similar estimates forNH 4‐N recycling but less accurate estimates forPO 4‐P. Stochastic simulations that incorporated error around allometric parameter estimates led to qualitatively similar but larger differences between general and species‐specific results.Community structure influenced aggregate nutrient recycling, but specific conclusions depended on the scaling approach. Total biomass explained much of the among‐community variation in aggregate
NH 4‐N andPO 4‐P for both model types, whereas non‐native dominance alone best predicted variation in aggregate N:P. Surprisingly, species‐specific and general models both reached significant yet quantitatively opposing conclusions regarding the relationship between N:P supply and non‐native dominance.Study results indicate that shifting fish community structure can substantially alter ecosystem functioning in this river system. However, some inferred relationships between community structure and aggregate nutrient recycling varied depending on whether general or species‐specific scaling approaches were taken. Although trait‐based approaches to link environmental change, community structure and ecosystem function hold much promise, it will be important to consider when species‐specific versus general models are necessary to scale from individuals to ecosystems.
