Earlier phenology of a nonnative plant increases impacts on native competitors

Abstract

Adaptation to climate is expected to increase the performance of invasive species and their community-level impacts. However, while the fitness gains from adaptation should, in general, promote invader competitive ability, empirical demonstrations of this prediction are scarce. Furthermore, climate adaptation, in the form of altered timing of life cycle transitions, should affect the phenological overlap between nonnative and native competitors, with potentially large, but poorly tested, impacts on native species persistence. We evaluated these predictions by growing native California grassland plants in competition with nonnativeLactuca serriola, a species that flowers earlier in parts of its nonnative range that are drier than its putative European source region. In common garden experiments in southern California withL. serriolapopulations differing in phenology, plants originating from arid climates bolted up to 48 d earlier than plants from more mesic climates, and selection favored early flowering, supporting an adaptive basis for the phenology cline. The per capita competitive effects ofL. serriolafrom early flowering populations on five early flowering native species were greater than the effects ofL. serriolafrom later flowering populations. Consequently, the ability of the native species to increase when rare in competition withL. serriola, as inferred from field-parameterized competition models, declined with earlierL. serriolaphenology. Indeed, changes toL. serriolaphenology affected whether or not one native species was predicted to persist in competition withL. serriola. Our results suggest that evolution in response to new climatic conditions can have important consequences for species interactions, and enhance the impacts of biological invasions on natural communities.