Adaptive foraging stabilizes pollination networks via apparent altruism

Background/Question/Methods

Researchers are increasingly interested in the factors that help stabilize networks in general and, more specifically, mutualistic networks such as those among plants and animals, among humans, and also among corporations. Scientists are also increasingly recognizing that network dynamics often depends on different types of interactions. However, the models that are used to disentangle the factors that stabilize one of the most studied and iconic mutualistic networks, those of plants and their pollinators (or frugivores), generally lack a fundamental type of interaction: the feeding relationships involving the trophic resources provided by the plants to their animal pollinators. Another essential element of such systems receiving increasing attention is the widely observed preference of consumers for more available resources called adaptive foraging.  To better understand mutualistic networks both generally and more specifically, we explore adaptive foraging in models involving both feeding and pollination interactions.  We focus here on the joint effect of adaptive foraging and network structure in terms of connectance, species richness, and nestedness on the stability of pollination networks. To inform the generality and applicability of our model, we compared results of the model with distributions of pollinators’ preference within those in 41 empirically observed pollination networks.

Results/Conclusions

Our analyses suggest "apparent altruism” as an important mechanism by which adaptive foraging and the structure of real pollination networks interact to stabilize pollination systems. The foraging is altruistic because generalist pollinators exhibiting adaptive foraging stabilize the networks while decreasing their own abundance and increasing the persistence of specialists that consume the same resources as the generalists.  Rather than being classic altruism, it is apparent altruism because the generalists' behavior prefers plants that provide the most trophic resources rather than seeking to help out other species. This apparent altruism produces an even allocation of food resources among pollinator species and of reproductive vectors among plant species and increases overall persistence of species. The abundance of generalist pollinators is reduced because increased pollinator diversity in the system decreases the total availability of floral resources. The modeled distribution of preferences among pollinators are generally consistent with preferences seen in the 41 empirical networks in that generalist pollinators prefer specialist plants in 73% of these networks and the distribution of preferences predicted by the model precisely matches the distributions in 32% of these networks.  Our analyses suggest that other classically selfish interactions may be effectively altruistic in complex networks.