PARENT SESSION
Oral Session # 41: Herbivory III: Forests and Soils.
Presiding: R Jones
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.

Feeny revisited: Condensed tannins and leaf-chewing insect communities of Quercus.

Forkner, Rebecca¹, Marquis, Robert¹, Lill, John², ¹ Department of Biology, St. Louis, MO² Department of Biological Sciences, Washington, D.C.

ABSTRACT- Community level oak-tannin-insect patterns have been largely unexplored since the ground-breaking work by Paul Feeny. For herbivores of black and white oak (Quercus velutina and Q. alba, respectively) in the Missouri Ozarks, we tested the hypothesis that abundance and richness of leaf-chewing herbivores would be negatively correlated with foliar condensed tannin concentration (CTC). In 2001, we quantified foliar CTC and nitrogen in the understory and canopy of these two species and simultaneously sampled their herbivores at three times: in May as leaves were expanding, and in June and August when leaves were fully expanded. Of the more than 30 common species encountered, only two species, Acronicta increta (Noctuidae) and Attelabus sp. (Curculionidae), both oak specialists, were negatively correlated with CTC in the canopy of Q. alba. One additional species, Chionodes pereyra (Gelechiidae), also an oak specialist, was marginally negatively correlated with CTC in the understory of Q. velutina. In the understory, species richness of spring-feeding herbivores was negatively correlated with CTC for Q. velutina. In the canopy, both total insect density and richness of August species on Q. alba were negatively correlated with CTC. Species determined to be understory "specialists" (i.e., tannin avoiders, as CTC was lowest in the understory) were not negatively correlated with CTC when feeding in the canopy on foliage with high CTC. Overall, our results indicate that 1) specialists were more likely than generalists to show negative correlations; 2) both early and late season fauna were impacted by tannins; 3) species were more likely to show responses to CTC when feeding on Q. alba and when feeding in the canopy, and 4) CTC contributed to differences in community structure between forest strata and between oak species. Our results support Feeny's original view that tannins play an important role in structuring the herbivore fauna of Quercus.

Key words: condensed tannins, Quercus, insect communities, leaf-chewing herbivores