Generalization alters the probability of plant community invasion

Abstract

The effects of native plant species diversity on community susceptibility to invasion are currently unclear. While species rich communities are often thought to be more robust to invasion as a consequence of high redundancy in mutualistic interactions, a positive association between native and exotic species richness is often observed. In animal-pollinated plants, higher plant species richness may dilute pollinator visitation to individuals, especially in the face of a limited pollinator pool. On the other hand, the presence of showy exotic plants at low densities has been shown to facilitate the pollination of natives by attracting generalist pollinators to the community. Here we model the invasion of a resident plant community with the goal of examining whether allocation to floral display in an invasive plant affects the outcome of competition for pollination with a native species on a disturbed landscape, and whether the diversity of pollinator-sharing species in a community influences its resistance to invasion. We find evidence for an optimal resource trade-off between floral and seed allocation in exotic plants, as invaders with low floral allocation do not attract enough visits for full seed set, while high investment in floral attraction results in the limitation of seed set. Increased pollinator sharing in the resident community increases the probability of invasion, presumably because the invader is usurping pollinator visits from natives that share a common pollinator pool.