PARENT SESSION
Poster Session # 21: Biogeography, Biodiversity, Populations, and Genetics.

Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Does microorganism productivity influence macroinvertebrate richness in aquatic detritus-based communities?

Yee, Donald^*,1, Juliano, Steven ¹, ¹ Illinois State University, Normal, Illinois, U.S.A.

ABSTRACT- The food web of water-filled tree holes is an ideal system to test alternative hypotheses for relationships between productivity and species richness. Tree hole communities are dependent on exogenous inputs of detritus, which support a microorganism assemblage, which in turn supports numerous macroinvertebrate species. We conducted an 11 month field study in artificial tree holes to determine if: a) different initial inputs of detritus (senescent leaves, dead invertebrates) affect microorganism productivity and abundance; 2) the rate of subsequent input affects microorganism productivity and abundance; and 3) microorganism productivity or abundance influence richness or abundance of macroinvertebrates. We established 6 replicates of 4 initial input treatments (0.25x, 0.5x, 1x, 4x observed field detritus inputs) that were open to colonization for one month. Following that period, 2 containers of each initial input treatment were assigned one of 3 subsequent input treatments: None (no additional detritus); Once (all detritus at the beginning); and Weekly (equal detritus additions over 6 weeks). Both Once and Weekly subsequent inputs ultimately yielded a doubling of the initial detritus amount. Every 3 weeks we measured microorganism productivity as respiration rate (L of O₂ hr^-1) of fluid and leaf samples, microorganism abundance, and abundance and richness of macroinvertebrate species in each container. During the initial phase, the two highest detritus treatments produced significantly higher diversity and abundance. There were non-significant trends of decreased leaf-associated productivity and increased fluid-associated productivity as total detritus increased. Richness was significantly higher in containers receiving detritus all at once compared to other addition rates. Abundance was affected by both initial and subsequent input treatments. In all sampling periods, there were significant positive relationships between richness and abundance. This is one of the first studies of the effects of microorganism productivity on richness and abundance of macroinvertebrate species over an extended period.

Key words: tree hole, productivity, bacteria, insect larvae