Shading by invasive shrub reduces seed production and pollinator services in a native herb |
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Authors: | Amy M McKinney and Karen Goodell |
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Institution: | (1) Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, 318 W 12th Ave, Columbus, OH 43210, USA;(2) Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, 1179 University Dr, Newark, OH 43055, USA |
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Abstract: | Plant invasions disrupt native plant reproduction directly via competition for light and other resources and indirectly via
competition for pollination. Furthermore, shading by an invasive plant may reduce pollinator visitation and therefore reproduction
in native plants. Our study quantifies and identifies mechanisms of these direct and indirect effects of an invasive shrub
on pollination and reproductive success of a native herb. We measured pollinator visitation rate, pollen deposition, and female
reproductive success in potted arrays of native Geranium maculatum in deciduous forest plots invaded by the non-native shrub Lonicera maackii and in two removal treatments: removal of aboveground L. maackii biomass and removal of flowers. We compared fruit and seed production between open-pollinated and pollen-supplemented plants
to test for pollen and light limitation of reproduction. Plots with L. maackii had significantly lower light, pollinator visitation rate, and conspecific pollen deposition to G. maculatum than biomass removal plots. Lonicera
maackii flower removal did not increase pollinator visitation or pollen deposition compared to unmanipulated invaded plots, refuting
the hypothesis of competition for pollinators. Thus, pollinator-mediated impacts of invasive plants are not limited to periods
of co-flowering or pollinator sharing between potential competitors. Geranium maculatum plants produced significantly fewer seeds in plots containing L. maackii than in plant removal plots. Seed set was similar between pollen-supplemented and open-pollinated plants, but pollen-supplemented
plants exhibited higher seed set in plant removal plots compared to invaded plots. Therefore, we conclude that the mechanism
of impact of L. maackii on G. maculatum reproduction was increased understory shade. |
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