The effect of forest canopy and flood disturbance on New Zealand stream food web structure and robustness

Abstract The effects of disturbance on communities have been a focus of both theoretical and empirical inquiries for many years. Food web stability is hypothesized to be affected by disturbance and the nature of the energy pathways (i.e. allochthonous or autochthonous) of a community. In this study, we investigated whether food webs at paired sites, one in forest and the other in grassland, in ten New Zealand streams along a disturbance gradient differ in their topological structure and robustness. Food web robustness (an indicator of web resistance) assesses the ease with which secondary extinctions permeate the food web following an initial random extinction (disturbance). We found that neither the nature of the energy source nor physical disturbance affected structural metrics or web robustness. As stream systems, particularly in New Zealand, are exposed to regular, unpredictable and dramatic physical disturbance from flooding, it may simply be that the floods result in generalist species dominating and increasing robustness irrespective of the energy source.