PARENT SESSION
Symposium #13: Trophic cascades in complex and simple terrestrial systems.

Organized by: MD Moran and WE Snyder
Tuesday, August 6. 1:00 PM to 4:30 PM. Crystal Ballroom, TCC.

Trophic cascades in natural and human-maintained grasslands.

Moran, Matthew^*,1, ¹ Hendrix College, Conway, AR

ABSTRACT- The strength of top-down processes in terrestrial systems has been a topic of great debate in ecology. Recent reviews of the trophic cascades in terrestrial systems indicate that top-down effects are prevalent, although weaker than in aquatic systems. Although there are typically few published studies for any particular terrestrial habitat, grassland systems have received a substantial amount of attention from ecologists studying top-down processes. By focusing on the variation within one habitat type, it might be possible to determine the factors that influence the strength of trophic cascades within the chosen habitat, and subsequently increase our understanding of generalized patterns of terrestrial cascades. I performed a meta-analysis of the response of plants to carnivore removal in grassland communities using published literature from a variety of authors and unpublished data from my own research. Grasslands can be broadly classified into two types: those that are naturally occurring and those that are maintained by intensive human manipulation (i.e. old-fields). The meta-analysis indicated that trophic cascades exist in grasslands overall, but were much stronger in old-fields. The response in natural grasslands, although negative, was not significantly different from zero. Old-fields generally have higher productivity than natural grasslands, since the natural systems tend to exist in arid environments. A regression analysis showed that plants respond more strongly to carnivore removal as the productivity of the system increases. This supports the hypothesis that top-down control becomes more prevalent as productivity increases, and may explain the differences in the strength of top-down control between old-fields and natural grasslands.

KEY WORDS: trophic cascade, grasslands, old-fields, meta-analysis