Scaling temperature-dependent dispersal rates to metacommunity dynamics: An experimental test

Changes in community structure under shifting thermal regimes depend on how both local population dynamics and regional dispersal respond to temperature. Processes underlying dispersal, such as movement speed and density dependence, are constrained by temperature-dependent metabolic rates; however, the temperature dependence of population dispersal rate, and effect of this relationship on local and regional diversity patterns, have received little attention in the metabolic scaling literature. Here, we propose and experimentally test a framework that relates temperature effects on individual dispersal probability, to thermal performance curves (TPCs) for population dispersal rates, to colonization dynamics in metacommunities. Using multi-patch well plate microcosms, we measured thermal performance curves for dispersal rate in several naturally co-occurring ciliate species, and contrasted species-specific dispersal TPCs at different intra- and inter-specific densities and time scales. Dispersal rate TPCs in monoculture differed at low versus high population densities, potentially suggesting distinct temperature effects on the density-independent (individual movement probability and speed) and density-dependent (quorum-sensing and resource competition) components of dispersal. Species-specific dispersal rate TPCs in polyculture metacommunities explained differences in colonization dynamics across temperature treatments. Dispersal rate TPCs differed from intrinsic growth rate TPCs, such that better dispersers had higher-than-expected per capita population growth at the regional (whole-metacommunity) scale compared to predictions from standard growth TPCs measured in single-patch monoculture. Together, these results suggest that ignoring temperature-dependent dispersal can yield an incomplete understanding of biodiversity change in spatially structured systems exposed to warming.