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 nonnative Lactuca 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 with L. serriola populations 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 of L. serriola from early flowering populations on five early flowering native species were greater than the effects of L. serriola from later flowering populations. Consequently, the ability of the native species to increase when rare in competition with L. serriola, as inferred from field-parameterized competition models, declined with earlier L. serriola phenology. Indeed, changes to L. serriola phenology affected whether or not one native species was predicted to persist in competition with L. 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. biological invasions | coexistence | competition | ecoevolutionary dynamics | phenology Author contributions: J.M.A. and J.M.L. designed research; J.M.A. performed research; J.M.A. analyzed data; and J.M.A. and J.M.L. wrote the paper.The authors declare no conflict of interest.

The role of seasonal timing and phenological shifts for species coexistence

“…Urban & De Meester ; De Meester et al )). Yet, there is a rich body of empirical work demonstrating that differences in arrival time (phenology) within a season can alter outcome of interactions within a generation even in the absence of any numerical effects (Geange & Stier ; Hernandez & Chalcraft ; Kardol et al ; Rasmussen et al ; Rudolf ; Alexander & Levine ). In these studies, priority effects are typically mediated by changes in traits (e.g., via behaviour or size) that directly or indirectly (e.g., via ‘niche modification’ (Fukami et al )) determine per‐capita effects.…”

“…Unfortunately, we currently have few empirical estimates for any of these relationships (e.g. Farzan & Yang ; Rudolf ; Alexander & Levine ). Even studies on priority effects typically use before/after type treatments or arrival order instead of an arrival time gradient (Alford & Wilbur ; Hernandez & Chalcraft ; Stier et al ; Tucker & Fukami ; Cleland et al ; Rudolf & McCrory ), and thus cannot be used to infer importance of interannual variance or make predictions about how changes in mean arrival time affect species.…”

“…Since early arriver advantage is by far the best documented pattern in natural system (Fukami 2015), I largely focus on this scenario for model analyses and numerical simulations. This type of arrival advantage (or priority effect) is well-documented in plant, animal and microbial communities in variety of terrestrial, freshwater and marine systems (Connell & Slatyer 1977;Geange & Stier 2009;Dickie et al 2012;Hernandez & Chalcraft 2012;Kardol et al 2013;Rasmussen et al 2014;Devevey et al 2015;Stuble & Souza 2016;Rudolf 2018;Alexander and Levine, 2019). While a variety of direct and indirect mechanisms can create this effect (Fukami 2015), it commonly arises in seasonal communities due to size-mediated priority effects (sensu Rasmussen et al 2014), which are generated when interactions occur among growing individuals and per-capita interaction strength scales positively with size.…”

“…However, how quickly the competitive effect increases or declines with difference in relative arrival time (i.e., the slope of is likely to differ across species since species can vary in their sensitivities to shifts in relative arrival time (e.g. Stuble & Souza ; Rudolf ; Alexander & Levine ). Note that the same negative correlation and general pattern hold true in systems with late arrival advantage for both species; in this scenario results are simply a mirror images (switched signs) for both species.…”

“…Furthermore, phenologies vary naturally across years and sites leading to interannual variation in relative timing of species interactions (Høye & Forchhammer 2008;Thackeray et al 2016;Rudolf 2018) and this variation is likely to increase with climate change (Pearse et al 2017). Recent studies indicate that even small changes in the timing of species interactions can result in substantial changes in the outcome of species interactions (Stier et al 2013;Godoy & Levine 2014;Rasmussen et al 2014;Cleland et al 2015;Young et al 2015;Murillo-Rinc on et al 2017;Rudolf 2018;Alexander and Levine, 2019). This implies that per-capita interaction strengths are typically not constant, but instead naturally change over time with shifts in the relative phenologies of interacting species within and across years (e.g., Fig.…”