Bumble bees (Bombus spp.) are among the most important wild pollinators worldwide, and therefore understanding factors regulating their populations is of great interest. In recent years, dozens of studies have evaluated correlations between landscape patterns of resource availability and/or land cover types with bumble bee abundance. This analysis is appropriate if landscapes and populations are at equilibrium, but these static patterns may be misleading if environmental conditions are changing, or if populations are still equilibrating to new environmental conditions (i.e., transient dynamics). In this talk, I present a brief overview of models we have used to predict transient dynamics of bumble bee populations in space and time. I also present a more detailed analysis of an experimental study, in which we watched bumble bee colonies grow through time in response to temporal variation in resource availability. I ask specifically whether changes in colony growth rate are consistent with expected transient dynamics due to changes in size structure of individual bees within colonies.
Results/Conclusions
Transient dynamics in population models: In spatially heterogeneous environments, bumble bee populations may show transient dynamics due to time delays between habitat destruction or creation and equilibration of population densities with new landscape conditions. These transient dynamics mean that the long-term effects of habitat alteration may not be apparent until 3-5 years after management is put in place. Within a growing season, the size of the initial cohort of workers had lasting effects on colony size. Transient dynamics in experimental populations: The order in which colonies experienced environmental conditions affected long-term colony growth rate and, ultimately, queen production. Colonies that experienced resource supplementation followed by ambient conditions grew faster in ambient conditions, than colonies that experienced ambient conditions followed by resource supplementation. These results are consistent with transient dynamics caused by production of larger, longer-lived workers during the resource pulse, who continued to bring more resources to the colony after the pulse ended.