Seed predation and climate impacts on reproductive variation in temperate forests of the southeastern USA
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Climatic effects on tree recruitment will be determined by the interactive effects of fecundity and seed predation. Evaluating how insect and vertebrate seed predators mediate tree reproductive responses to climate depends on long-term studies of seed production, development, and predation. In this study, our objectives were to (1) assess the effects of interannual climate variation on seed abortion rates, (2) assess the impact of seed density on predation rates, and (3) examine the degree to which density-dependent seed predation would amplify or dampen interannual variation in fecundity associated with seed abortion. We used a 19-year study of seed abortion and pre-dispersal predation rates by insects and vertebrates (birds and rodents) for five temperate tree species across forest plots from the North Carolina Piedmont to the Southern Appalachian Mountains in the southeastern USA. We found that rates of seed abortion and predation increased reproductive variation for oaks (Quercus species). Probability of seed abortion was greatest during years with cool, dry springs. Responses of seed predation on Quercus species to current year’s seed density varied by species, but exhibited positive density-dependence to previous year’s seed density consistent with numerical responses of seed predators. Seed abortion and predation rates for two drupe species responded little to variation in climate or seed density, respectively. Given that predation increased interannual variation in seed availability and the negative density-dependence to previous year’s seed density, our results indicate that consistent numerical responses of oak seed predators may amplify interannual variation due to climate-mediated processes like seed abortion.
KeywordsMasting Reproductive ecology Seed abortion Seed predation Trees
We would like to thank Norman Christensen, Fred Hain, Matthew Kwit, Megan Mobley, Ram Oren, Carl Salk, Anne Stein, Denis Valle, Kai Zhu, Ines Ibanez, and three anonymous reviewers for comments on the manuscript. The research was supported by NSF Grants BSR-9444146, DEB 9453498, DEB-9632854, DEB-9981392, IDEA-0308498, DEB 0425465, SEII 0430693 and DDDAS 0540347, as well as the USDA Forest Service Pacific Northwest Research Station. The experiments comply with the current laws of the United States of America in which the experiments were performed.
Author contribution statement
DMB and JSC conceived of and designed the study. JSC provided the long-term seed archives and DMB performed measurements. DMB designed and implemented the statistical modeling. DMB and JSC wrote the manuscript.
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