Authors: Caralyn B Zehnder Kirk W Stodola Robert J Cooper Mark D Hunter
Publish Date: 2010/08/14
Volume: 164, Issue: 4, Pages: 1017-1027
Abstract
Predation pressure and resource availability often interact in structuring herbivore communities with their relative influence varying in space and time The operation of multiple ecological pressures and guildspecific herbivore responses may combine to override simple predictions of how the roles of plant quality and predation pressure vary in space For 2 years at the Coweeta LTER in the Southern Appalachian Mountains we conducted a bird exclosure experiment on red oak Quercus rubra saplings to investigate the effects of bird predation on red oak arthropod communities We established bird exclosures at six sites along an elevational gradient and estimated variation in foliar nitrogen and bird predation pressure along this gradient Foliar nitrogen concentrations increased with elevation while our index of bird predation pressure was variable across sites Greater arthropod densities were detected inside exclosures however this result was mainly driven by the response of phloem feeders which were much more prevalent inside exclosures than on control trees There was little evidence for an effect of bird predation on the other arthropod guilds Consequently there was no evidence of a trophic cascade either in terms of leaf damage or tree growth Finally we found more variation in arthropod density among trees within sites than variation in arthropod density among sites indicating the importance of microsite variation in structuring arthropod communitiesWe thank K Leavelle A Mahoney L Willenbring M Parrish C Okraska P Scarr B Maley M White S Mitchell B Ball C Hall K Wickings W Duncan C Frost M Fleming D Egetter B Joyce and M Parris for field help We thank Tom Maddox and the Analytical Lab at UGA for foliar nitrogen analysis The manuscript was greatly improved by comments from S Frank L Tao H Gan R Vannette E Wason S Kabat N Haan and three anonymous reviewers The research was supported by NSF grant DEB 0342750 to MDH and RJC This research was partially supported by NSF award DEB0823293 from the Long Term Ecological Research Program to the Coweeta LTER Program at the University of Georgia
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