Conservation of pollinator services is essential to creating sustainable agricultural practices. Planting native species on field edges may support and enhance populations of crop pollinators by increasing the availability of pollen and nectar resources outside the crop bloom period. In the fall of 2007, a replicated assemblage of twenty-five native plant species was established on the perimeter of an agricultural landscape to investigate the merits of different plant species. In the summers of 2008 and 2009, visiting insect pollinators were sampled from flowering plants throughout each season on a biweekly basis. Sampled bees (Hymenoptera; Apoidea) were identified to species-level, allowing for the construction of a bipartite interaction network between plant and pollinator species. In our analysis, we focused on network properties that reflect phenological patterns, especially node longevity. Node longevity represents the number of sampling periods one species interacted with another throughout the season. The node longevity of a plant species represents its strength as a pollinator host while that of a pollinator represents the magnitude of pollination services it provides. We then compared this phenological pattern of interactions with floral abundance to determine the role of plant resource availability in our network.
Results/Conclusions
Species in our network broadly conformed to four main categories. Generalist species with high node longevity included Bombus impatiens among the pollinators and Eupatorium perfoliatum among the plant species. Specialist species with high node longevity included Halictus ligatus among the pollinators and Tradescantia ohiensis among the plants. Generalist species with high node longevity were much more common among pollinator species than plant species. Generalists and specialists with low node longevity were also present in our network. Additionally, average floral abundance over the season did not predict the node longevity or degree of generalization of plant species, which indicates that pollinators are not visiting plants at random, but are making decisions based on species identity while foraging. Generalist species with high node longevity may provide the greatest contribution to the species they interact with because they support the greatest number of species over the greatest length of time. This underscores the importance of evaluating species-specific interactions over time when selecting plants which support pollinator services, and when focusing on key pollinator species.
