Factors affecting the abundance of scirtid beetles in container habitats

The processing of whole leaves into smaller particles by leaf-shredding mac roinvertebrates may be important to macroinvertebrates that feed on fine pa rticles. Such interactions, termed processing chains, have also been propos ed for larvae of leaf-scraping scirtid beetles (family Scirtidae) and filte r-feeding mosquitoes (eg., Aedes triseriatus Say) found in container commun ities. We examined how container type (i.e., natural vs artificial), contai ner size, and amount of leaf litter influenced the abundance of scirtids. W e nondestructively sampled 12 tree holes and 8 discarded automobile tires m onthly, for 11. mo, counting all living scirtids and A. triseriatus. We als o measured maximum container volume and the initial amount of accumulated l eaf litter and sediment for each container. Multivariate analysis of varian ce (MANOVA) with profile analysis showed that, in comparison to tires, tree holes supported significantly greater densities of scirtids both monthly i n the late fall and cumulatively for the entire year. A 2nd MANOVA showed t hat mean container sizes and amount of leaf litter were npt significantly d ifferent between tree holes and tires. Path analysis suggested no direct ef fect of litter amount on scirtid abundances, but container volume strongly influenced both litter amount and scirtid abundances. Thus, scirtid abundan ce and the amount of leaf litter were positively correlated because both we re determined by container size.