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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