Doctor of Philosophy (PhD)
Volume is a proxy for biomass in hard bodied arthropods (P < 0.0001). I constructed biomass-volume equations for Neotropical (P < 0.0001), temperate (P < 0.0001) and 12 Neotropical genera of scarabs, of which 11 were highly significant. The effect of short term (< 1 year) alcohol storage on volume was negligable. I found scarab volume on geologically old soils in the Amazon was one-third that of the geologically young Amazon (P < 0.0001). Species richness (P = 0.0002), Chao 1 (P = 0.0003), Fisher’s (P = 0.008) and Margalef indices (P = 0.0003) were greater on young soils. Menhinick (P = 0.54), Simpson (P = 0.54) and rarefied species richness (P = 0.24), which correct for sample size differences, indicated no difference in diversity. Young Amazonian soils likely support a higher volume and abundance of scarabs than old soils, but diversity across Amazonia may be similar. I compared beta-diversity of scarab communities across Amazonia. Species rank-abundance curves did not differ among sites whereas volume-abundance distributions and volume-rank abundance curves indicated a larger range of scarab sizes in Brazil than Ecuador. At local levels (<62 km), communities were similar whereas at large distances (>1750 km), they were different. Differences between Brazil and Ecuador may be explained by varied soil age and productivity. I examined the effects of tropical forest fragmentation on scarabs, comparing my results with three other studies from the same site. Among 1, 10, and 100-ha fragments and continuous forest, I found two important trends; beetle biomass and species richness increased with fragment area per sampling effort. Comparing all four studies, diversity increased with fragment size, and by my rarefaction analyses, two studies demonstrated beetle volume increased with fragment size. Average beetle size increased with fragment area, suggesting a shift in dung beetle guild structure and functionality. Tropical-temperate comparsions demonstrated a lower scarab species richness and larger average body size in temperate forests compared with tropical forests. Volume and abundance per trap-day did not segregate along these divisions. The observed latitudinal gradient may be explained by spatial heterogeneity hypotheses and the body size gradient resembles Bergmann’s rule.
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Radtke, Meghan Gabrielle, "Tropical Pyramids: Dung Beetle Richness, Abundance, and Biomass" (2006). LSU Doctoral Dissertations. 364.
G. Bruce Williamson