When attention deficit pays: Bumble bee foraging breadth expands to compensate for declining flower resources under climate change
Results/Conclusions: In response to a 2°C increase in mean minimum summer temperature, flower densities of historically preferred bumble bee host plants have declined by 22% over 35 years in the alpine meadows of Pennsylvania Mountain, CO (USA). In congruence with OFT, bumble bees (Bombus balteatus) foraging freely on Pennsylvania Mountain are more likely to switch to less-preferred, shallow flowers when flower densities are low. Additionally, alpine bumble bee foragers at Niwot Ridge Long Term Ecological Research station and Mount Evans Wilderness Area have become more generalized over 40 years, foraging from a greater diversity of plant species with shorter, more variable flower tube depths. Results from a foraging model that describes the energetic tradeoffs between specialist and generalist strategies suggest that these patterns may not be unique to alpine bumble bees. As resources decline and search times increase, the advantage of being a generalist forager increases. For example, the decline in flower densities on Pennsylvania Mountain has decreased the advantage of specializing by up to 14% in lower alpine zones. Both theoretical and empirical data indicate that pollinators will expand their foraging niches when resource density declines in response to climate change generating functional mismatches and reducing pollination quality for host plants.