Structural properties of mutualistic networks withstand habitat degradation while species functional roles might change.

摘要

Species diversity and interactions vary on a landscape scale and are sensitive to landscape alterations, such as landscape fragmentation and habitat degradation. At the same time, the species position within food webs or mutualistic networks (e.g. generalist or specialist, network hub or peripheral vertex) may affect their ability to persist after perturbations. This study was conducted in a heavily managed boreal forest landscape in southeastern Norway, using study plots situated in forest stands with contrasting disturbance history: old growth forest (least disturbed), young forest (intermediate) and clear cuts (most disturbed). By studying 12 pollination networks with contrasting disturbance history we found that important network descriptors were conserved after perturbation. Link-diversity was higher, both overall and per site, in the more disturbed communities while link-turnover was highest in the least disturbed community. We conclude that despite an increase in diversity in the more degraded habitat, the higher link-turnover in the least degraded, old growth forest, community indicates a homogenization of the plant-pollinator networks as a result of habitat degradation. Finally, we found that the degree (number of interacting partners) and network functional role for particular species changed along the disturbance gradient, though not in any systematic way. We conclude that structural properties of the pollination network are conserved after perturbations, but that particular species' network functional roles may change.