PARENT SESSION
Contributed Oral Session 24: Disturbance Ecology: Management; Response to Fire
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 516 D, Level 5, Palais des congrès de Montréal

Effects of habitat complexity on ant-parasitoid interactions: Another look at how disturbance regimes can change community dynamics.

Wilkinson, Elliot¹, Feener, Donald¹, ¹ University of Utah, Salt Lake City, UT

ABSTRACT- The influence that a disturbance event such as fire or grazing has on natural communities is often studied through its direct effects on species abundance and diversity. We address a little studied but important mechanism through which disturbance events can affect natural communities: grazing and fire simplify the structural complexity of habitats in which organisms interact. Indirect effects of habitat complexity on the outcome of species interactions may in turn alter community composition. We implemented a factorial design to investigate the importance of habitat complexity to interactions between three host ants of the Pheidole genus and their specialist ant-decapitating parasitoids (Diptera: Phoridae). Decreasing habitat complexity (leaf litter) had a significant (P<0.05) or nearly significant (P<0.06) negative effect on the number of soldiers of all three host species harvesting resources in the presence of parasitoids. Decreasing habitat complexity also significantly decreased the number of workers harvesting resources in 2 out of 3 host species. In at least one species this was due to increased harassment of the worker caste by parasitoids. Strong positive correlations between numbers of either soldiers or workers harvesting resources and resource return rate suggest that alterations to habitat complexity can have profound effects on colony fitness by changing foraging behavior. Disturbance events that alter habitat complexity have the potential to affect the relative importance of parasitism and competition in determining community structure. Although ant community structure is typically controlled by competition, fire and grazing are expected to increase the relative importance of parasite control over community structure.

Key words: disturbance, community structure, ant, habitat complexity