Structure and dynamics of a highly-invaded plant-pollinator network

Networks of mutualistic interactions such as those between plants and pollinators are characterized by weak, asymmetric interactions organized in a nested pattern, in which the community is anchored by a core of interactions among generalist species. This characteristic structure contributes to community stability and diversity but may be disrupted by invasion of the network by non-native species. I used a network approach to characterize the community of interactions in an old field in New Jersey in which a high proportion of the plant species were non-native. I described the entire plant-pollinator community at Hutcheson Memorial Forest (HMF) and asked whether this network displayed the characteristic structural properties of mutualistic networks. Next, I examined how the non-native subset of the plant community compared to the native subset in terms of their interactions with pollinators. Finally, I considered the temporal dynamics of the network for this community by addressing inter-annual and intra-annual changes in network structure and examining how the role of non-native plants changed through time. Despite the high proportion of non-native plants species in the community, network properties were consistent with those described for other mutualistic networks. Non-native plants were visited less than native plants, but interactions with pollinators were organized similarly for both groups of plants. Network structure was consistent between years but varied widely on a monthly scale. Variation in the role of non-native plants emerged when the network was examined intra-annually. Non-native plants were subordinate to natives in terms of their importance to the pollinator community during most of the flowering season, except during a lull in native floral abundance, when non-native plants became more important. Overall, non-native plants as a set displayed a similar range of generalization as the native plant community, suggesting that non-native plants are exploiting the same strategies for participation in the plant-pollinator community as native plants. The structure of mutualistic networks appears to promote assimilation on non-native species while remaining robust to changes which threaten the stability of the community.