Abstract
Florivores are present in many pollination systems and can have direct and indirect effects on both plants and pollinators. Although the impact of florivores are commonly examined in facultative pollination mutualisms, their effects on obligate mutualism remain relatively unstudied. Here, we used experimental manipulations and surveys of naturally occurring plants to assess the effect of florivory on the obligate pollination mutualism between yuccas and yucca moths. Yucca filamentosa (Agavaceae) is pollinated by the moth Tegeticula cassandra (Lepidoptera: Prodoxidae), and the mutualism also attracts two florivores: a generalist, the leaf-footed bug Leptoglossus phyllopus (Hemiptera: Coreidae), and a specialist, the beetle Hymenorus densus (Coleoptera: Tenebrionidae). Experimental manipulations of leaf-footed bug densities on side branches of Y. filamentosa inflorescences demonstrated that feeding causes floral abscission but does not reduce pollen or seed production in the remaining flowers. Similar to the leaf-footed bugs, experimental manipulations of beetle densities within individual flowers demonstrated that beetle feeding also causes floral abscission, but, in addition, the beetles also cause a significant reduction in pollen availability. Path analyses of phenotypic selection based on surveys of naturally occurring plants revealed temporal variation in the plant traits important to plant fitness and the effects of the florivores on fitness. Leaf-footed bugs negatively impacted fitness when fewer plants were flowering and leaf-footed bug density was high, whereas beetles had a positive effect on fitness when there were many plants flowering and their densities were low. This positive effect was likely due to adult beetles consuming yucca moth eggs while having a negligible effect on floral abscission. Together, the actions of both florivores either augmented the relationship of plant traits and fitness or slightly weakened the relationship. Overall, the results suggest that, although florivores are always present during flowering, the impact of florivores on phenotypic selection in yuccas is strongly mitigated by changes in their densities on plants from year to year. In contrast, both florivores consistently influenced pollinator larval mortality through floral abscission, and H. densus beetles additionally via the consumption of pollinator eggs.
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Acknowledgments
We thank K. Glennon and A. Moe for helpful comments on the manuscript. T. Starmer provided much appreciated advice on statistics, and M. Deyrup identified the beetle. We are indebted to B. Cunningham for designing and making the insect cages, A. Johncox for assisting with surveys, and M. Sklaney for help with the field work and pollen staining. The Archbold Biological Station provided access to field sites and intellectual support for this study. Funding was provided by the National Science Foundation grant DEB 0743101 to K. Segraves and D. Althoff. The experiments comply with the current laws of the United States of America in which the experiments were performed.
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Communicated by Christina Caruso.
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Althoff, D.M., Xiao, W., Sumoski, S. et al. Florivore impacts on plant reproductive success and pollinator mortality in an obligate pollination mutualism. Oecologia 173, 1345–1354 (2013). https://doi.org/10.1007/s00442-013-2694-8
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DOI: https://doi.org/10.1007/s00442-013-2694-8