Under ongoing global change, natural ecosystems experience a multitude of external stressors that often occur in combination. For example, land-use change affects the isolation and size of remaining habitats as well as their nutrient status. However, we are still lacking integrative ecological theory on how different drivers of global change interact. We studied the combined effects of habitat isolation and nutrient enrichment on the stability of a tri-trophic food-chain. We expanded bioenergetic models to spatially explicit systems of two habitat patches using empirically-derived allometric relationships of animal migration. We found that increasing habitat isolation causes top-predator starvation by weaker per-unit biomass energy influxes. While top predators can easily integrate across isolated habitat patches, the lower biomass densities of their resources that suffer from migrational loss in fragmented landscapes eventually cascades up the food chains. Moreover, we found strong interactions between stressors: the starvation effects of isolation were counteracted by nutrient enrichment that increased energy fluxes along the food chains. In consquence, habitat-isolation has stabilizing effects in eutrophic systems but undermines species diversity in oligotrophic systems. Overall, our mechanistic analyses on how external stressors interactively affect ecosystem energy fluxes provide deeper insights into the future global change of ecological communities.
Patch isolation and enrichment effects on the persistence of a three-species food chain