Plant competition under simultaneous adaptation by herbivores and pollinators

Abstract

Two plants can influence one another indirectly by affecting population dynamics of shared exploiters and/or shared mutualists, giving rise to apparent competition or apparent mutualism, respectively. Indirect interactions between plants also occur when the preferences of exploiters and mutualists adapt to changes in relative plant densities. Here we study simultaneous effects of adaptive herbivore and pollinator preferences on the dynamics of two competing plant populations. As a result of feedbacks between plant dynamics and adaptive animal preferences, plants coexist at alternative stable states. This outcome is favored at low abundances of herbivores and pollinators when consumers tend to specialize on a single plant. As herbivore and pollinator abundances increase, generalism becomes more common. This promotes plant coexistence by balancing antagonistic and mutualistic effects between plants. Plant community dynamics become also more predictable due to reduction in the number of alternative stable states. This shows that the global decline in insect populations can lead to structural changes in plant communities that are difficult to predict.