PARENT SESSION
Oral Session # 32: Herbivory II: Grasslands.
Presiding: K Suttle
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.
Vole-driven dominance in experimental restorations.
Howe, Henry1, Lane, Diana2, 1 University of Illinois-Chicago, Chicago, IL2 Stratus Consulting, Boulder, CO
ABSTRACT- We used 18 replicated plantings of 16 tallgrass prairie species in wet-mesic soils in western Wisconsin to test for the effects of vole (Microtus pennsylvanicus) herbivory over 48 months on perennials that had reached reproductive age after 26 months of protection. Once voles were admitted, an otherwise common legume (Desmodium canadense) and grass (Elymus virginicus) were all but eliminated (combined cover 27% where voles were excluded, 4% where voles were admitted). Vole herbivory accelerated an existing succession to domination by an unpalatable mint (Pycnanthemum virginianum) and black-eyed Susan (Rudbeckia subtomentosa) (combined cover 33% where voles were excluded, 63% where voles were admitted). Cover of other common species (Echinacea purpurea, Heliopsis helianthoides, Lobelia silphitica, Silphium integrifolium) changed over four years without being influenced directly or indirectly by vole access. Repeated measures ANOVA revealed that net decreases (D. canadense, E. virginicus) or increases (P. virginianum, R. subtomentosa, Solidago graminifolia) in cover as a function of vole herbivory masked a variety of first order, second order, and third order effects that imply transient vole-driven dynamics during divergent successional processes. Access of vegetation protected from for 26 months to voles resulted in a >50% drop in proportional diversity during the ensuing 4 years, reflecting vole-driven simplification of these communities. Unlike previous experiments in this genre, in which voles gained access to designated plots at planting, vole-driven changes in species composition were not accompanied by drastic changes in aggregate characteristics (species richness, standing crop, cover) that might confound effects of selective herbivory by voles.
Key words: Microtus pennsylvanicus, herbivory, succession , tallgrass