Macroecology of food webs: integration of large-scale dispersal and local interactions

Background/Question/Methods

In recent decades, two rapidly advancing areas of research have addressed (1) how macroecological processes influence biogeographic patterns in biodiversity and (2) how interaction processes in food webs influence biodiversity stability in local communities. The different spatial scales - biogeographic and local - and the limited knowledge of mesoscale processes between these scales have made systematic integration difficult. Here we introduce concepts of how processes across these spatial scales can be integrated to understand and predict biodiversity patterns. We propose a novel approach to systematically integrate processes at all scales, from the local to the biogeographic. This integration is promoted by consistently using biomass fluxes as the unit for these processes. At the local scale, food webs are established through biomass flows between consumer and resource populations. At the mesoscale, local communities are connected through dispersal, which generates biomass flows between populations of the same species across different habitat patches. At the biogeographic scale, species dispersal patterns are caused by migration that shifts biomasses across continents. This similarity of process units facilitates model integration of processes across spatial scales.

Results/Conclusions

We present conceptual models that integrate processes across these spatial scales while accounting for large differences in their rates, ranging from instantaneous (local interactions) to slow (migration across biomes). Quantitative modeling examples are provided for integrating local and mesoscale processes to predict biodiversity patterns in meta-food webs. These results illustrate the interdependence of mesoscale dispersal processes and local interactions in creating biodiversity patterns. Local interactions determine species density, which affects emigration rates and thus the strength of dispersal links between habitat patches. Mesoscale dispersal processes alter local community composition through rescue and drainage effects. Together, they shape local alpha diversity and beta diversity between habitat patches. Finally, we outline concepts of how to include constraints by biogeographic migration and range-shift processes into these synthetic modeling approach.