Print PageSuccessful plant invasions are often facilitated or reinforced by the recruitment of pollinators away from native flowering plants. However, the repercussions of collecting novel floral rewards for native pollinator populations have rarely been explored. Linaria vulgaris is a Eurasian forb that has aggressively invaded the western United States. With dense, showy inflorescences and abundant nectar and pollen, L. vulgaris is often preferentially visited by bumble bees relative to native flowering plants. To assess whether this invasive plant is affecting native bumble bee populations, we compared the bumble bee colony density and genetic diversity of bees foraging at sites with and without L. vulgaris. We sampled bumble bees at six paired sites in and around the Rocky Mountain Biological Lab, three sites invaded by L. vulgaris and three sites that were free of L. vulgaris. We focused on two common western bumble bee species that forage on L. vulgaris, Bombus bifarius and B. appositus, and collected a middle leg from each netted worker for molecular analysis. We genotyped 9-10 microsatellite loci in 491 workers, scored alleles with Genemapper and used the freeware package COLONY to evaluate kinship and colony density at each site.
Results/Conclusions
Preliminary analyses indicate a trend for sites with L. vulgaris to attract foraging workers from a greater number of colonies than sites containing only native plants. However, the estimated effective population sizes of bumble bees visiting invaded sites were significantly higher than those caught foraging on native plant sites. These results are irrespective of bumble bee species, although short-tongued B. bifarius did have higher colony densities, on average, than the long-tongued B. appositus. Ongoing work will determine if gene diversity (HE) differs between bumble bee populations foraging in invaded vs. native sites and whether increased effective population sizes translate into long-term fitness benefits for bumble bee populations. Our study suggests that pollinators can benefit from the presence of an invasive plant and invasive plants may therefore play an important role in sustaining, and perhaps even increasing, pollinator abundance and genetic diversity. With recent work linking reduced genetic diversity to declines in bumble bees, invasive plants may provide a critical safeguard for native pollinator populations.
