Costs of two non-mutualistic species in a yucca/yucca moth mutualism |
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Authors: | Judith L Bronstein Yaron Ziv |
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Institution: | (1) Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA, US |
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Abstract: | Mutualisms often involve significant costs for participants. Costs are inflicted by mutualists themselves, as well as by associated,
non-mutualistic species. These costs are rarely quantified, however, particularly the ones extrinsic to the pairwise interaction.
We compare costs inflicted by an obligate mutualist pollinator and two common exploiters of an Arizona yucca over a 2-year
period. The magnitude of seed damage from seed and fruit-feeding beetle larvae (Carpophilus longus, Nitidulidae) was similar to damage from the seed-eating larvae of Yucca schottii's pollinator moth Tegeticula yuccasella (Prodoxidae), averaging about 15 seeds destroyed per fruit in each case. The two seed predators usually fed within the same
fruits, although rarely side by side. In contrast, the presence of fruit-galling moth larvae (Prodoxusy-inversus, Prodoxidae) appeared to benefit the yucca: individual Tegeticula destroyed only half as many seeds in galled fruits as they did in ungalled fruits. We discuss three general implications
of these results. Firstly, the costs of non-mutualists to the two mutualistic partners are not necessarily parallel. Secondly,
measurable costs of non-mutualists do not necessarily translate into an impact on the success of the mutualism itself, because
they may be incurred after mutualistic activities take place. Finally, the costs of mutualists to each other can differ substantially
depending on the presence or absence of non-mutualistic species.
Received:17 July 1996 / Accepted:10 June 1997 |
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Keywords: | Yucca Tegeticula Yucca moth Mutualism Seed predation |
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