Constraints on caddisfly distributions along permanence gradients & ramifications for ecosystem function

Within many groups of aquatic insects, the distribution of species is correlated with if, when, and for how long habitats dry. In the first part of the talk I will describe distributional patterns of cased caddisflies (Limnephilidae and Phyrganeidae) in high-elevation ponds and wetlands, and the underlying mechanisms that constrain each species along the permanence gradient. The limnephilids are mainly detritivores, and in the second part of the talk, I will describe how their abundance affects 1) detritus processing rates, 2) the re-entry of detrital energy and nutrients into consumer food webs, and 3) the degree to which excreted nutrients in turn affect algal growth. At our study sites, permanent ponds typically have only one common limnephilid species, and there are no other macro-detritivorous taxa. Thus, it appears that there is little or no functional redundancy with respect to detritus processing and that fluctuations in the abundance of just one species can have a major impact on ecosystem function.