BODY-SIZE AND ENERGY USE IN TERMITES (ISOPTERA) - THE RESPONSES OF SOIL FEEDERS AND WOOD FEEDERS DIFFER IN A TROPICAL FOREST ASSEMBLAGE

Studies of log body size/log energy use in local animal assemblages re veal a range of distributional patterns from those with a negative upp er bound slope (NUBS), showing energy use to be dominated by smaller b odied species, to those with a positive upper bound slope (PUBS), indi cating that larger bodied species dominate energy use. We investigated the log body size/log energy use relationships for a local termite as semblage at the Mbalmayo Forest Reserve in Cameroon, and compared the patterns for wood and soil feeding groups. We measured the biomass den sities of 75 species of termites across three forest sites. Termite sp ecies metabolic rates were derived either directly (25 species), or by regression estimates (50 species), from Warburg manometry measurement s of termite xO(2) at 28 degrees C. The combined data From the three s ites revealed a marked difference in log body size:log energy use dist ributions between wood and soil feeding groups. While wood feeders sho wed a polygonal distribution, with a negative upper bound slope (NUBS) , soil feeders showed a (statistically very significant) positive dist ribution. The data for soil feeders are also exceptional, in compariso n with the vast majority of other animal assemblage data, in showing s ignificantly greater 'total' energy use for larger, compared with smal ler, body size categories. Furthermore, the modal body size category f or number of individual termites does not coincide with that for numbe r of termite species. We interpret these results in the context of the likely constraints imposed by the food substrates of termites and the economies of scale. Specifically, soil feeders utilise a low energy, universally abundant substrate compared with wood Feeders which feed o n a patchily distributed, higher energy resource. Digestive efficiency is likely to be at a premium in soil feeders, driving selection towar ds larger body size (and hence larger gut volume and transit time), co mpared with wood feeders.