COS 18-3 - Plant diversity determines differences in plant-herbivory interactions in native and exotic plants

Abstract: Biological invasions are one of the main drivers of global change. Understanding the ecological mechanisms that enable exotic species to succeed in novel environments is a central goal in ecology. It has been hypothesized that exotic plants escape their co-evolved herbivores and should benefit from lower herbivory in new environments (Enemy Release Hypothesis). Alternatively, exotic plants could be recognized by native herbivores based on their similarities to native plants. The characteristics of the plant community play a key role in determining which exotic species succeed. For instance, observational studies have found that habitats of low plant diversity are more vulnerable to plant invasions than habitats of high plant diversity, the latter being more resistant to invasions because of competitive exclusion by natives making use of all available resources. In low diversity environments thus, exotic plants with different characteristics to the native community should benefit from the presence of empty niches and unexploited resources. Contrarily, in high-diversity environments, only exotic plants with similar characteristics to some of the natives can coexist or outcompete the native species. These differences might determine how exotic plants interact with native herbivores.

In a global assessment of herbivory patterns in 790 populations of 503 plant species across 11 biomes, we explore whether exotic and native plant populations exhibit different herbivory patterns under different levels of plant diversity. We expect that in low-diversity environments, natives should present high mean levels of herbivory and low variability among individuals, while exotic plants should escape the attack of native herbivores and present low mean levels of herbivory and low variability among individuals. Contrarily, in high-diversity environments, because of associational resistance, natives and exotics should exhibit low mean levels of herbivory and high variability in herbivory among individuals.

We found differences in the distribution of herbivory for exotic and native plants with different levels of plant diversity. For native species, variability in herbivory increases from low to high levels of alpha-diversity, while exotic species present high variability in herbivory distributions at high and low levels of plant diversity. We show that exotic species do not necessarily benefit from enemy release in novel environments. The interaction between exotic plants and native herbivores depends on the characteristics of the exotic species and of the recipient environment.