Comparing historic and contemporary plant-pollinator interaction networks to investigate the effects of climate change and invasive species

Background/Question/Methods

Like many critical ecosystem services, pollination is being disrupted by anthropogenic activities. Climate change and invasive species may alter the abundance, distribution, and phenology of plants and pollinators and disrupt their historic interactions. However, the degree to which these interactions are flexible at the community level over time (i.e., whether pollinators can shift their behavior to feed on new host plants when preferred species become extinct or no longer overlap in phenology) is not known. We currently lack a comprehensive understanding of how climate change and species invasions are affecting pollination in communities, in part because we typically do not have historical information about plant-pollinator interactions prior to such disruptions. In the late 1800’s, the eminent entomologist Charles Robertson meticulously detailed all of the interactions between plants and pollinators in Carlinville, IL. We re-collected these data to compare historic interaction networks with those that persist today. Two of the objectives of this research were to determine (1) how climate warming has altered the phenology of native and alien plants and pollinators and thus disrupted their interactions and (2) whether alien plants and pollinators have become integrated into the interaction network, usurping links compared to Robertson’s time, and the degree to which the network can recover lost interactions when alien plants were removed.

Results/Conclusions

Preliminary results from early-season species indicate that the phenologies of both plants and pollinators are earlier than they occurred historically, with pollinator activity advancing to a greater degree than plants and resulting in interaction mismatches. However, generalist pollinator species provide novel links, which may help buffer interaction networks from large structural changes over time. Alien plants and pollinators appear to become more integrated into the interaction network with increasing time since colonization, and generalist pollinators reestablish old links in the absence of alien flowers. This work tests important predictions about the flexibility of species interactions and suggests that plant-pollinator interaction networks may be robust to some of the effects of climate change and species invasions, highlighting the importance of generalist species as key interactors and the susceptibility to loss of specialists.