Signatures of human-induced instability in food web architecture

Habitat fragmentation and nutrient enrichment represent two of the more pressing perturbations visited upon ecosystem through human activities.  Given that the quantification of food web responses to such perturbations across spatially expansive scales and over ecologically relevant time periods still remains elusive, ecologists must begin to look for architectural clues to general stability properties of food webs.  Here, we use theoretical analysis to generate specific predictions about the structure and behaviour of food webs in the presence of habitat alteration.  First, we examine the influence of food web compression (analogous to habitat fragmentation) on food web stability and architecture.  While the theoretical analysis predicts more spatially compressed food web to be less stable, it also predicts that such unstable system should have steeper biomass pyramids.  Further, our theoretical analysis points to the importance of habitat heterogeneity in conferring stability to compartmentalized food webs, predicting that the dominance of trophic energy transfer by single pathways will result in instability.   To test these predictions, we examine the biomass pyramids and temporal dynamics of freshwater and soil ecosystems along gradients of both ecosystem size and trophic status.