Plant evolution and environmental variation create a geographic mosaic of predator-prey interactions and natural selection

Abstract

A major goal of ecology and evolutionary biology is to understand patterns of species interactions, their resulting natural selection and how these change across space and time. Studies show that variation in predator-prey interactions causes variation in natural selection on prey phenotypes. Other studies have shown that plant genetic variation can influence predator attack rates on prey. However, no study to our knowledge has linked these two phenomena to see if plant evolution can influence predator attack rates on prey, how predators cause natural selection on prey and how these patterns differ geographically. We studied a plant-gall-predator system in the wild across three tree sites spanning an elevation/climate gradient, across which trees have evolved in response to climate variation and other factors. We also worked in a common garden, in which trees were drawn from the same three wild sites. In the wild, attack by birds on galls was ~ 4x higher at the mid-elevation site compared to the low and high elevation sites. Further, birds selectively foraged on small galls, resulting in bird-mediated natural selection at the mid elevation, but not at the low and high elevation sites. In the common garden with respect to predator-prey interactions, we found similar patterns to the wild, providing evidence that evolved variation in the tree influenced attack rates by predators. In terms of natural selection, we found mixed evidence for the hypothesis that plant evolution would shape patterns of predator-caused natural selection on galls. Our findings broaden our understanding of geographic mosaics of community interactions and their resultant patterns of natural selection.