Elevated atmospheric CO 2 alters the arthropod community in a forest understory

Jason Hamilton, Ithaca College
Arthur R. Zangerl, University of Illinois Urbana-Champaign
May R. Berenbaum, University of Illinois Urbana-Champaign
Jed P. Sparks, Cornell University
Lauren Elich, Ithaca College
Alissa Eisenstein, University of Illinois Urbana-Champaign
Evan H. DeLucia, University of Illinois Urbana-Champaign

Abstract

The objective of this study was to determine the extent to which overall population sizes and community composition of arthropods in a naturally occurring forest understory are altered by elevated CO . The Free Air Concentration Enrichment (FACE) method was used to fumigate large, replicated plots in the Piedmont region of North Carolina, USA to achieve the CO concentration predicted for 2050 (~580μll ). In addition, the extent to which unrestricted herbivorous arthropods were spatially delimited in their resource acquisition was determined. Stable isotope data for spiders (δ C and δ N) were collected in ambient and elevated CO plots and analyzed to determine whether their prey species moved among plots. Elevated CO had no effect on total arthropod numbers but had a large effect on the composition of the arthropod community. Insects collected in our samples were identified to a level that allowed for an assignment of trophic classification (generally to family). For the groups of insects sensitive to atmospheric gas composition, there was an increase in the numbers of individuals collected in primarily predaceous orders (Araneae and Hymenoptera; from 60% to more than 150%) under elevated CO and a decrease in the numbers in primarily herbivorous orders (Lepidoptera and Coleoptera; from -30 to -45%). Isotopic data gave no indication that the treatment plots represented a " boundary" to the movement of insects or that there were distinct and independent insect populations inside and outside the treatment plots. A simple two-ended mixing model estimates 55% of the carbon and nitrogen in spider biomass originated external to the elevated CO plots. In addition to changes in insect performance, decreases in herbivorous arthropods and increases in predaceous arthropods may also be factors involved in reduced herbivory under elevated CO in this forest. © 2012 Elsevier Masson SAS. 2 2 2 2 2 2 2 -1 13 15