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Abiotic and biotic processes shape species distributions and ecological communities across spatial scales Amundrud, Sarah Louise

Abstract

Species distributions and the composition of ecological communities result from the interplay of three constraints: physical barriers to dispersal, species-specific environmental requirements, and species interactions. However, how spatial scale and environmental context affect the relative importance of these constraints is still poorly understood. I combined manipulative experiments, observational surveys along environmental gradients, and species distribution models to explore the relative importance of abiotic and biotic constraints on aquatic invertebrate communities inside bromeliads across a range of spatial scales. At the geographic scale (Central and South America), the distribution of a bromeliad-specialist damselfly was strongly limited by dispersal barriers and climate, but not by biotic interactions from other bromeliad-dwelling odonates. At the regional scale (along two elevational gradients in Costa Rica), the relative importance of abiotic and biotic constraints on species distributions and community assemblages depended on environmental context: while thermal tolerances (i.e., abiotic effects) explained invertebrate distributions under moist conditions, biotic interactions from crane fly larvae, which became predatory under drought, explained their distributions under dry conditions. At the local scale (the bromeliad), biotic interactions from crane fly larvae were disproportionally important in mediating the effects of drought and warming on community structure and ecosystem functions. This hierarchical set of studies demonstrates the scale-dependence of the interplay of abiotic and biotic processes in affecting species distributions and community assemblages. While species interactions were the main drivers of community change at the local scale of the habitat, biotic effects were not important at the large geographic scale. Notably, the relative importance of abiotic and biotic processes at the landscape scale depended on environmental context, an important insight given that environmental conditions are already shifting as a result of climate change.

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