PARENT SESSION
Contributed Oral Session 81: Invertebrate Ecology: Communities; Populations; Disturbance
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal
Scirtid beetles, resource levels, and insect assemblages: Investigating processing chains and community structure in treeholes.
Burkhart, John*,1, Smith, Leslie1, Villalpando, Shawn 2, Kegan, Ben1, Paradise, Chris1, 1 Davidson College, Davidson, NC2 Appalachian State University, Boone, NC
ABSTRACT- The structure of insect communities in treeholes is limited in large part by resources. The primary resource of temperate forest treeholes is the annual input of leaf litter. Leaf litter in treeholes exists along a continuum of decay and particulate size, and different insects specialize on the resource in a particular state of decay. Scirtid beetles (Helodes pulchella) may take part in a processing chain interaction, by shredding leaf litter and freeing it for consumption by browsing and filter-feeding dipteran larvae. By altering resource condition, scirtids could influence community structure. We are examining the effects of scirtid beetles and resource levels in simulated treeholes. The experiment employs a two-factor fully crossed design (3 resource levels and 3 scirtid densities) with 4 replicates per treatment combination. We have monitored abundance of common insects, species richness, pupal mass of randomly selected emerging mosquitoes (primarily Ochlerotatus triseriatus), and scirtid survival since April 2004. Species richness was unaffected by scirtid densities, but was higher and peaked earlier in high resource treatments than in low and intermediate resource treatments. In late spring, when mosquito densities were highest, there appeared to be slightly higher densities in intermediate scirtid density treatments. We also found that at low (1 g/L) and intermediate (5 g/L) resource levels mean male pupal mass was greatest at intermediate scirtid densities (25/L). Mean female pupal mass was greatest at intermediate scirtid densities, regardless of resource level. Higher densities of mosquitoes should lead to lower mass of adults, so the fact that treatments with intermediate scirtid densities contained higher densities of larger mosquitoes than other scirtid densities suggests facilitation. We also found that midge (Culicoides guttipennis) densities were highest at low scirtid and high resource levels, suggesting resource competition. Scirtid mortality was high at low resources and high scirtid densities (100/L). Their decay may provide a resource to the community, however there was no observable effect on insect densities or pupal mass of mosquitoes. It is not known whether these patterns will repeat annually, so experiments will run through the coming field season.
Key words: treehole, mosquito, facilitation, resource