Bees, as active gatherers of pollen from plants, provide an important ecosystem service. Recent studies have considered this mutualistic relationship at the community level, focusing on the frequency and number of interactions between bees and the plants they visit, as well as on patterns in these networks with respect to the contributing members (e.g. specialists or generalists, invasive or native). Many of these studies have addressed the consequences of removing members with varying levels of connectedness. The general conclusion is that those members participating in the greatest number of interactions (quantitatively or qualitatively) will most severely change the dynamics of an ecosystem if removed. Few studies, however, have considered networks in a temporal context. How do interactions change over the course of a flowering season or across years? Determining the dynamics of networks over time is of some merit. Are the same species acting as network hubs each year or continually within a year? More specifically, do conclusions about the importance of generalists to ecosystem stability change with the incorporation of a temporal variable? Using data from a four year study of a bee community in Grand Staircase-Escalante National Monument, in xeric Southern Utah, we assessed the dynamics of network properties both within a season and between consecutive years. Bees were collected on all blooming plants in one-hectare plots for 45-minutes twice a day; an interaction was any visit of a bee to a plant. Sites of collection were located in diverse habitats and visited bi-weekly for the duration of the flowering season. Sites often included non-native, bee-attractive plants, providing an opportunity to observe not only how networks change as flowers and bees come and go, but how communities incorporate these invasives.
Results/Conclusions
We found that invasive plants, specifically Tamarix sp., provided an inter-annually consistently visited resource during months when little else was in bloom (late June through mid August). We observed core plant species that were consistently well-visited across years, providing a resource to both a rich bee fauna and numerous individuals. Within a year, some plant species were considerably more long-lived than any interacting bee species. Bee diversity was variable from year to year, and different species participated in the greatest number of interactions during the same two week interval between years. We conclude by considering the implications of invasives to bee-plant community structure, and the importance of considering networks with a long-term perspective.
