COS 231-6 - The role of intra-guild indirect interactions in assembling plant-pollinator networks

Abstract: Global change is driving novel assemblages of ecological communities through species invasions, extinctions, and range shifts. Among those perturbed communities are plant-pollinator networks, which support terrestrial biodiversity and pollination services to crops. Understanding and predicting the emergent structure and dynamics of novel plant-pollinator networks is critical to anticipating how global change will affect the ecosystem services these networks provide. Dynamic network analyses can advance such understanding by elucidating the effects of species’ direct and indirect interactions on network assembly. Indirect interactions within a guild (pollinators or plants) occur when multiple species share the benefits of a mutualistic partner and therefore can have competitive or facilitative effects on one another. Here, we investigate the role of intra-guild indirect interactions on assembling plant-pollinator networks by developing: 1) an assembly model that includes population dynamics and adaptive foraging, and 2) a motif analysis tracking the effects of colonizing species throughout assembly. We observed the highest rate of colonizer establishment in motifs where competitive pollinators, or attractive plants, share mutualistic resources with less competitive, or attractive, species in their guild. The most competitive pollinators are generalists because they are the most abundant and have the greatest capacity for adaptive foraging. The most attractive plants are specialists because they provide the most exclusive floral rewards. Further, these colonizers maintain dominance of their mutualistic resources which inhibits future colonizers from establishing within their niche. Adaptive foraging, however, reduces the otherwise strong effect of indirect competition to maintain the coexistence of species within a guild possessing variable niche breadths. This produces nested networks, a feature commonly observed in mutualistic networks. Our finding support theory that mutualisms mediate species coexistence and that mechanisms of coexistence between indirectly connected species determine the structure and stability of novel species assemblages.