Loralee Larios, Dean E. Pearson and John L. Maron

Community ecologists seek to understand the relative strength of local processes in determining the identity and number of species that establish in any given location. Increasingly, plant ecologists have focused on plant traits and how these may determine which species can live together and which species may be outcompeted locally. However, despite many studies illustrating that post-dispersal seed predators can contribute substantially to seed loss, contemporary assessments of how this influences the composition of local plant communities are lacking. Here we review the unique features of post-dispersal seed predation and describe how seed predator effects can be integrated into emerging theories of how competing species coexist, what species are likely to co-occur and the likelihood that communities will become invaded by exotic species.

The specific ways in which post-dispersal seed predation influences plant communities are shaped by predator foraging because seed predators often select seeds with specific seed traits (e.g., seed size, coat hardness, nutritional content). Despite these preferences, seed predators may simply forage on the most abundant species in the seed pool. These various foraging strategies can strongly influence the subsequent diversity and abundance of species within a community.

Plants that produce a few large seeds are often thought to be good competitors whereas species that produce many small seeds are thought to be good colonizers.  More recently it has been proposed that large seeded species may be more stress tolerant (as opposed to being superior competitors). Both of these ideas attempt to explain how species that differ in the number and size of seeds produced can coexist. However both of these theories overlook the effects of seed predators that can select for seeds of a particular size, thereby potentially influencing influence plant coexistence. We note the ways in which seed predation may interact with these classic seed-size trade offs, particularly when species are seed limited.

Increasingly, ecologists are using plant trait distributions to infer the importance of different processes that might influence plant community composition.  Much of this work has focused on traits associated with resource acquisition, as a way to distinguish between the filtering effects of the environment and the impacts of resource competition among species.  However, these approaches have also overlooked the effects of post-dispersal seed predators. We highlight the different ways in which foraging strategies may shift the trait composition of species available to colonize local communities. Finally we highlight that seed predators may have varied effects on plant invasions. Selective foraging may result in seed predators helping to resist invasions, or may conversely result in the reinforcement of an invader if seed predators preferentially forage for native species.

More broadly, we argue that seed predation by generalist consumers should be better incorporated into plant community theory. We note areas for potential research to fill important knowledge gaps that will advance our understanding of the role that generalist consumers play in regulating plant coexistence and community assembly.

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Photograph provided by authors.