PhD Candidate in Ecology and Evolutionary Biology, Cornell University
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Does pollinator sharing affect the distribution of floral traits in communities?

Does pollinator sharing affect the distribution of floral traits in communities?


Closely related species are often predicted to compete for the same resources, yet many communities contain closely related species.

Two processes that can promote the coexistence of closely related species are ecological sorting and character displacement. Ecological sorting occurs when strong competition during community assembly excludes inferior competitors from a community, while character displacement occurs when species experience selection in sympatry to evolve trait differences that reduce competition.

While both of these processes were first articulated as being driven by resource competition, shared interactions with predators, mutualists, or facilitators can also generate ecological sorting and character displacement.

Because pollinators are often shared among co-occurring plants and can be essential for reproduction, the indirect interactions among co-occurring plants that share pollinators can lead to ecological sorting and character displacement.

 
Clarkia unguiculata blooming in the greenhouse common garden at Cornell University.

Clarkia unguiculata blooming in the greenhouse common garden at Cornell University.

 
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This figure represents the expected distribution of traits if pollinator sharing generates ecological sorting or character displacement.

Ecological sorting will occur when two plants rely on the same pollinator, but one plant is significantly more attractive to that pollinator (A). Because the less attractive species will not receive sufficient pollination, it will be eliminated from the community; the resulting community will contain species that utilize different pollinators and have different floral traits.

Character displacement will occur when sharing pollinators does not lead to competitive exclusion but instead generates selection for phenotypic change. If pollinator sharing has negative consequences for plant fitness, species phenotypes will diverge to promote specialization on existing pollinators (B). Alternatively, if pollinator sharing has positive consequences for plant fitness, species phenotypes may diverge to attract a new pollinator to the community (C) or converge to attract the same pollinator (D).

We wanted to know: Do plants from different communities show differences in their floral traits when grown in a common environment?

To determine if community context impacts selection on floral traits, we grew Clarkia from seed from different communities that contain 1, 2, or all 4 species. Pollination-related traits were measured to determine if there are trait differences between co-occurring species that may compete strongly for pollinators (ecological sorting) or between sympatric and allopatric populations of a species (character displacement).

This work is in prep for submission, so check back soon for the results of this study.