Life-history trade-offs are a paradigm in evolutionary ecology. For plants, it is assumed that defending against herbivores comes at a cost to growth, resulting in negative correlations between growth and defense. While growth-defense trade-offs are commonly documented across plant species, there is less support for trade-offs within species. Several mechanisms can account for the mixed empirical support within-species but teasing them apart requires explicit comparisons of growth and defense relationships within and among populations, an approach seldom employed. Here we evaluate growth-defense correlations within- and among-populations of a native perennial plant that originate from divergent resource environments.
Results/Conclusions
Herbivore abundance and pressure increased across the resource gradient, indicating selection for higher levels of defense may be favored in higher resource environments. We found strategic trade-offs in growth and defense between high- and low-resource populations that matched patterns commonly documented across species. These trade-offs were not universal in that we found different patterns within-populations. Growth and defense were negatively correlated within a population originating from a low-resource environment but neutral or positively correlated within a population originating from a high-resource environment. These results show how resource availability can mediate growth-defense correlations within-species across different levels of biological organization and highlight the context-dependency of plant-herbivores interactions. We discuss the implications of these results for understanding intraspecific variation in plant defense.