Abstract
The question of whether species’ origins influence invasion outcomes has been a point of substantial debate in invasion ecology. Theoretically, colonization outcomes can be predicted based on how species’ traits interact with community filters, a process presumably blind to species’ origins. Yet, exotic plant introductions commonly result in monospecific plant densities not commonly seen in native assemblages, suggesting that exotic species may respond to community filters differently than natives. Here, we tested whether exotic and native species differed in their responses to a local community filter by examining how ant seed predation affected recruitment of eighteen native and exotic plant species in central Argentina. Ant seed predation proved to be an important local filter that strongly suppressed plant recruitment, but ants suppressed exotic recruitment far more than natives (89% of exotic species vs. 22% of natives). Seed size predicted ant impacts on recruitment independent of origins, with ant preference for smaller seeds resulting in smaller seeded plant species being heavily suppressed. The disproportionate effects of provenance arose because exotics had generally smaller seeds than natives. Exotics also exhibited greater emergence and earlier peak emergence than natives in the absence of ants. However, when ants had access to seeds, these potential advantages of exotics were negated due to the filtering bias against exotics. The differences in traits we observed between exotics and natives suggest that higher-order introduction filters or regional processes preselected for certain exotic traits that then interacted with the local seed predation filter. Our results suggest that the interactions between local filters and species traits can predict invasion outcomes, but understanding the role of provenance will require quantifying filtering processes at multiple hierarchical scales and evaluating interactions between filters.
Highlights
Efforts to understand biological invasions have increased exponentially in recent decades, yet advances in understanding and predicting invasion outcomes remain elusive [1]
In the Caldenal of central Argentina, we found that ant seed predation was a powerful local filter to plant recruitment
This sizedependent seed selection resulted in far greater impacts on exotic plant recruitment - an outcome driven by the fact that seeds of exotics were smaller than those of natives in our system
Summary
Efforts to understand biological invasions have increased exponentially in recent decades, yet advances in understanding and predicting invasion outcomes remain elusive [1]. Debate continues as to whether the processes affecting exotic species invasions differ at all from those affecting native colonization [2,3]. The question of whether provenance plays an important role in invasion could be tested by manipulating filters and quantifying native and exotic species responses. If local filters are examined, such an approach could elucidate the role of community context in invasion outcomes. The extensive efforts made to predict invader success by evaluating invader traits independent of community context have met with limited success [5,6]. Accumulating studies suggest that invasion outcomes are best understood in the context of community-specific processes [7,8,9]
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