Aim Meta-community structure is a function of both local (site-specific) and regional (landscape-level) ecological factors, and the relative importance of each may be mediated by the dispersal ability of organisms. Here, we used aquatic invertebrate communities to investigate the relationship between local and regional factors in explaining distance decay relationships (DDRs) in fragmented dendritic stream networks.Location Dryland streams distributed within a 400-km 2 section of the San Pedro River basin, south-eastern Arizona, USA.Methods We combined fine-scale local information (flow and habitat characteristics) with regional-scale information to explain DDR patterns in community composition of aquatic invertebrate species with a wide range of dispersal abilities. We used a novel application of a landscape resistance modelling approach (originally developed for landscape genetic studies) that simultaneously assessed the importance of local and regional ecological factors as well as dispersal ability of organisms.Results We found evidence that both local and regional factors influenced aquatic invertebrate DDRs in dryland stream networks, and the importance of each factor depended on the dispersal capacities of the organisms. Local and weak dispersers were more affected by site-specific factors, intermediate dispersers by landscape-level factors, and strong dispersers showed no discernable pattern. This resulted in a strongly hump-shaped relationship between dispersal ability and landscape-level factors, where only moderate dispersers showed evidence of DDRs. Unlike most other studies of dendritic networks, our results suggest that overland pathways, using perennial refugia as stepping-stones, might be the main dispersal route in fragmented stream networks.Main conclusions We suggest that using a combination of landscape and local distance measures can help to unravel meta-community patterns in dendritic systems. Our findings have important conservation implications, such as the need to manage river systems for organisms that span a wide variety of dispersal abilities and local ecological requirements. Our results also highlight the need to preserve perennial refugia in fragmented networks, as they may ensure the viability of aquatic meta-communities by facilitating dispersal.

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Summary 1. Variation among individuals within size or age classes can have profound effects on community dynamics and food‐web structure. We investigated the potential influence of habitat disturbance on intrapopulation niche variation. 2. Amphibians occupy a range of lentic habitats from short‐hydroperiod intermittent ponds to long‐hydroperiod permanent ponds. We quantified ontogenetic diet variation and individual specialisation in wood frog tadpoles (Lithobates sylvaticus) and blue‐spotted salamander larvae (Ambystoma laterale) to investigate the influence of hydroperiod on population niche width across a natural hydroperiod gradient using stable isotope and gut content analyses. In one of the few tests using larval forms, we tested the niche variation hypothesis, which predicts that populations with larger niche widths also have increased individual variation. 3. Our results support the niche variation hypothesis, indicating that more generalised populations exhibit higher within‐individual diet variation. We report gradual changes in the relative importance of diet items, decreased dietary overlap and increased trophic position in L. sylvaticus throughout development. A. laterale became more enriched in δ13C and increased in δ15N throughout its larval period. We did not find a relationship between hydroperiod and niche parameters, indicating that niches are conserved across heterogeneous habitats. In contrast to most documented cases, we estimated low levels of individual specialisation in amphibian larvae. 4. Amphibians are an important link between aquatic and terrestrial ecosystems, whereby diet shifts can influence food‐web structure by altering energy flow pathways and the trophic position of higher consumers, ultimately changing food‐chain length.

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Hydrology is the main environmental filter in aquatic ecosystems and may result in shared tolerances and functional traits among species in disparate ecosystems. We analyzed the associations between taxonomic and functional facets of diversity within aquatic ecosystems (ponds vs. streams) across a hydroperiod gradient (1–365 d) to untangle the hydrologic drivers of aquatic invertebrate diversity. We used invertebrate assemblage data from seven arid‐land streams in southeastern Arizona, United States collected over 2 yr and nine temperate woodland ponds in Ontario, Canada collected over 2 yr. Our results showed that although invertebrate assemblages from streams and ponds differ taxonomically, hydroperiod had similar influence on invertebrate trait structure regardless of biogeographic and habitat differences. Streams and ponds independently showed strong positive relationships between functional richness and taxonomic richness; however, the relationship showed a shallower slope in ponds, indicating higher functional redundancy. Intermittent ponds and streams tended to have lower functional and taxonomic richness than their perennial counterparts, but harbored greater beta diversity. Our results suggest that even though ponds and streams are fundamentally different habitats with distinct faunas and unique ecological processes, hydrology produces convergent patterns in both trait composition and diversity patterns.

Tadpoles are diverse and abundant consumers, and knowledge of their feeding ecology and trophic status is essential in understanding their functional roles within aquatic habitats. Here we revisit Altig, Whiles, and Taylor (2007)'s paper, which highlighted the knowledge gaps in tadpole feeding ecology and the application of modern techniques, such as stable isotope and fatty acid analyses to better quantify dominant food resources, food assimilation, and the trophic status of tadpoles. We reviewed the ecological studies that have been published since 2007 that used stable isotopes and fatty acid analyses, also metagenomics and ecological stoichiometry analyses. We describe the ecological roles of tadpoles in freshwater ecosystems and identify knowledge gaps regarding tadpole feeding ecology across biogeographic regions. Worldwide declines in amphibian abundance and diversity create an urgent need to document their feeding ecology and trophic status. As consumers, tadpoles play important functional roles in nutrient cycling, energy flow, and bioturbation. They also exhibit context‐dependent trophic plasticity in response to abiotic and biotic gradients, which complicates understanding of their trophic roles. Most studies of tadpole trophic ecology have been conducted primarily on species from the families Ranidae, Bufonidae, and Hylidae from Neotropic and Nearctic regions, while species in tropical regions such as Africa and Asia lack ecological information for tadpoles. There continues to be a need for studies of tadpole diets and/or trophic ecology in Africa and Southeast Asia regions where species endemism is threated by the growth of anthropogenic activities. The majority of studies have focused on trophic ecology of tadpoles from the perspective of single species or at relatively small spatial and temporal scales. Studies that address questions from an ecosystem perspective were scarce, but are critical for conservation and management. Future research should aim to address the role of tadpoles as consumers across broader spatiotemporal scales.

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Migration is a widespread phenomenon among animals and has a profound influence on the evolution of species traits. Diadromous fishes provide an extreme example of migration, moving between marine and freshwaters, often travelling thousands of kilometres for feeding and reproduction. Diadromy has been linked to changes in feeding ecology, body size and various life-history attributes. However, most studies have focused on intraspecific variation and associated mechanisms. In this study, we use phylogenetic comparative methods to analyse body size and trophic position across Clupeiformes (anchovies, herring, shad and allies), a large clade of fishes that includes both diadromous and non-diadromous species. We found that diadromous species are larger than non-diadromous species, but there is no difference in trophic position, and that these patterns are not attributable to common ancestry. Diadromous species show a decoupling of body size and trophic position, whereas non-diadromous clupeiforms have a positive relationship between body size and trophic position. Using a model-fitting approach, we detected a signal of strong selection driving diadromous fishes to different adaptive peaks from non-diadromous fishes for body size, but a single adaptive peak for trophic position. We suggest that diadromous fishes have evolved larger body size than obligate marine and freshwater species as an adaptation to maximize energy expenditure during long-distance migration.