THE ROLE OF CADDISFLY CASES IN DETERRING PREDATORS ALONG A HYDROPERIOD GRADIENT IN SUBALPINE WETLANDS

Wissinger,S.A.(1,2), Whissel,J.(1), Eldermire,C.(1), & Brown W.S. (2). (1) Biology Dept., Allegheny College, Meadville, PA, USA; (2) Rocky Mountain Biological Laboratory, Crested Butte, CO, USA.

Along the hydroperiod gradient from permanent to autumnal to vernal subalpine wetlands in central Colorado, caddisflies are preyed on by salamander larvae (Ambystoma), beetle larvae (Dytiscus), and other caddisflies, respectively. We conducted lab and field experiments in which we manipulated cases to determine whether their antipredatory efficacy correlated with patterns of caddisfly distribution. Cases of all species were effective against salamanders, but caddisfly behaviors and not case construction explained differences in species' vulnerability to salamanders. Cases of Agrypnia and Limnephilus spp. that coexist with Dytiscus were effective at reducing beetle predation, but those of Asynarchus were not. Asynarchus larvae develop rapidly and most pupate in stone-covered cases before Dytiscus larvae become abundant. In mesocosms, pupae in cases with stones had significantly higher survival than those without stones. Finally, removal of cases in all limnephilid species resulted in increased rates of cannibalism and intraguild predation (IGP). Even the partial removal of cases (especially the posterior) had this effect. Our results suggest that 1) the antipredator function of cases is species- and predator-specific, and 2) cases play an important role in reducing cannibalism and IGP both in species that do and do not engage in these foraging behaviors when cases are intact.