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Abstract:
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Pollinator-mediated selection is one of the most
important factors driving adaptation in flowering plants.
However, as ecological conditions change through habitat
loss and fragmentation, the interactions among species may
evolve in new and unexpected directions. Human-induced
environmental variation is likely to affect selection
regimes, but as yet no empirical examples have been
reported. In the study reported here, we examined the
influence of human-induced habitat transformation on the
composition of pollinator assemblages and, hence, pollinator-
mediated selection on the flower phenotype of Viola
portalesia (Violaceae). Our results indicate that pollinator
assemblages differed substantially in terms of species
composition and visitation rate between nearby native and
transformed habitats. Similarly, the insect species that
contributed most to visitation rates differed between plant
populations. While the magnitude and sign of pollinatormediated
selection on flower length and width did not
differ between sites, selection for flower number lost significance
in the transformed habitat, and a significant pattern
of disruptive selection for flower shape, undetected in
the native habitat, was present in the transformed one.
Overall, the results of this study suggest that humaninduced
habitat change may not only modify the species
composition of pollinator assemblages, relaxing the selection
process on some flower characters, but they may also
create new opportunities for fitness-trait covariation not
present in pristine conditions. |