1. A fundamental goal of community ecology is to understand the drivers of community assembly and diversity. Local factors acting on community assembly are typically related to environmental conditions while regional factors are typically related to dispersal. Previous research has not consistently demonstrated | 1679

1. Trichoptera is an ecologically and taxonomically diverse order, and caddisfly species are under increasing pressure from anthropogenic threats to larval habitats, rivers, and streams.2. This study evaluated long-term changes in caddisfly communities of the Ogeechee River, a subtropical blackwater river in the south-eastern U.S. Coastal Plain, to understand how changes manifest as a result of ongoing human impacts. Two datasets separated by more than 30 years were used, each representing a 2-year monthly quantitative sampling effort (1981-1983; 2015-2017).3. Community structure of the Ogeechee River caddisflies significantly changed, though not in ways that were predicted. The average sensitivity values of the caddisfly community declined, contrary to the expectation that increasing human impacts on a river ecosystem would promote the survival of more pollution-tolerant taxa. 4. Generic richness increased in the 2010s from the 1980s, perhaps as a result of relaxed competition following declines of large, dominant taxa. The increases in various taxa have resulted in similar overall abundance metrics between time periods, although other studies of Ogeechee River invertebrates indicate that the biomass of the new taxa is far lower than that produced by the assemblages of the 1980s. Functional richness, evenness, and dispersion were higher in the 2010s, but divergence was not.5. This suggests that more nuanced monitoring efforts, focused on the threats to ecological function and the role of caddisflies (and other sensitive freshwater organisms), will be required to evaluate the changes in community structure and determine which taxa are most adversely affected.

Genetic sequencing (with mtCOI) was used to associate larvae with two new Vietnamese caddisfly (Trichoptera) species from Bach Mã National Park, Hydromanicus calyx n. sp. (Hydropsychidae) and Drepanocentron dentatum n. sp. (Xiphocentronidae). Adult Drepanocentron dentatum n. sp. is distinguishable by the toothy dorsal margin of the male inferior appendages; the most similar species, D. vercaius, has teeth on the ventral, but not the dorsal margins of the inferior appendages. The larva of D. dentatum is fully described herein, the first larva to be described in the genus Drepanocentron; it can be separated from the other two known xiphocentronid larvae (Xiphocentron messapus and Cnodocentron yavapai) by the smooth, thin mesal margin of each mandible. Adult Hydromanicus calyx n. sp. is distinguishable by the cupped apices of the male harpagones; this character is absent in morphologically similar species (H. nieuwenhuisi, H. abiud, and H. serubabel). The larva of H. calyx is morphologically most similar to that of H. inferior, but can be distinguished by the presence of faint muscle scars interrupting the lateral margins of the stridulatory areas on the venter of the head.

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Around the world, researchers are reporting declines in insect fauna. Although uncommonly evaluated in high‐profile studies of insect declines, the community context of population trends can facilitate interpretation of the causes and consequences of such losses. Here, we aimed to explore the shifts in a well‐studied invertebrate community of a blackwater river and identify potential catalysts of such change. We compared the density, biomass and community structure of freshwater invertebrate assemblages separated by more than 30 years in the Ogeechee River, in the southeastern U.S.A., and found biomass declines. We also evaluated long‐term trends in river discharge, water temperature and precipitation. Overall, the biomass in the 2010s was approximately 60% of the total in the 1980s. Community analyses indicated that this decline was associated with reduced densities of large‐bodied, filter‐feeding insects, particularly Hydropsychidae caddisflies (Trichoptera). Conversely, predators and small‐bodied primary consumers increased in density, although their contributions to overall biomass were minimal and their increased density was not sufficient to compensate for biomass declines. Seasonal shifts in both invertebrate populations and environmental parameters were evident, especially when focusing on discharge and dissolved organic carbon. Through a combination of direct analysis and the use of established research on the metabolic dynamics of the study site, we determined that the overall decline of freshwater invertebrate biomass may have been driven by climate‐related changes in flood dynamics: seasonal flooding that facilitates delivery of floodplain carbon to filter‐feeding consumers had decreased over several decades. Water temperature also had increased and was likely to have had effects on the invertebrate assemblages. Whole‐community evaluations such as this one, in contrast to single‐taxon and abundance‐based studies, provide critical information to elucidate the dynamics of freshwater impairment and insect loss in the Anthropocene.

Aim Metacommunities are assembled through a combination of local and regional processes, with the relative importance of the drivers of assembly depending on ecological context. Global change can alter community assembly at both local and regional levels, potentially shifting communities into disequilibrium with their local environmental conditions. We evaluated the spatial variation in environmental filtering and habitat matching of 1078 riverine macroinvertebrate communities distributed across nine ecoregions. Location Conterminous United States. Taxon Freshwater macroinvertebrates. Methods Patterns in environmental filtering, habitat matching and functional trait diversity were compared among ecoregions. Boosted regression trees were used to identify (1) functional trait predictors of environmental filtering and habitat matching and (2) environmental, landscape and network variables that predict functional trait abundances. Results Environmental filtering but not habitat matching varied strongly by ecoregion. Functional trait diversity varied by ecoregion, but not as strongly as the signatures of environmental filtering. Functional trait predictors of environmental filtering and habitat matching were not consistent, with trait predictors instead varying by individual traits, trait categories and ecoregions. Notwithstanding inconsistent trait predictors, environmental filtering was primarily influenced by habitat preference traits, whereas habitat matching was primarily influenced by both habitat preference and dispersal traits. Predictors of functional traits also varied by trait category and ecoregion, with habitat preference and dispersal traits primarily influenced by network variables. Main conclusions Our study demonstrates the contingent patterns and drivers of environmental filtering and habitat matching on a macroecological scale. We provide the foundation on which trait–environment relationships can be further quantified and causal explanations established in the context of community disequilibrium and applied to conservation and management of freshwater systems.

AimMetacommunities are assembled through a combination of local and regional processes, with the relative importance of the drivers of assembly depending on ecological context. Global change can alter community assembly at both local and regional levels, potentially shifting communities into disequilibrium with their local environmental conditions. In this study, we evaluated the spatial variation in environmental filtering and habitat matching of 1078 riverine macroinvertebrate communities distributed across nine ecoregions within the conterminous United States.LocationConterminous United States.TaxonFreshwater macroinvertebrates.MethodsWe first quantified spatial patterns in environmental filtering, habitat matching, and functional trait diversity. We then used boosted regression trees to identify (1) functional trait predictors of environmental filtering and habitat match and (2) environmental, landscape, and network variables that predict functional trait abundances.ResultsOur results demonstrated that environmental filtering but not habitat matching varied strongly by ecoregion. We also found that functional trait diversity varied by ecoregion, but not as strongly as the signatures of environmental filtering. We did not identify consistent functional trait predictors for both environmental filtering and habitat matching, with trait predictors instead varying by individual traits, trait categories, and ecoregions. Notwithstanding inconsistent trait predictors, environmental filtering was primarily influenced by habitat preference traits while habitat matching was primarily influenced by both habitat preference and dispersal traits. Predictors of functional traits also varied by trait category and ecoregion, with habitat preference and dispersal traits primarily influenced by network variables.Main conclusionsOur study demonstrates the contingent patterns and drivers of environmental filtering and habitat matching on a macroecological scale. We aim for this work to provide the foundation on which trait-environment relationships can be further quantified and causal explanations established in the context of community disequilibrium and applied to conservation and management of freshwater systems.

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