Efeitos ambientais sobre as abundâncias e biomassas de três espécies de cupins construtores (Insecta: Isoptera) em uma floresta de terra firme na Amazônia Central

Abstract

Ecological theory suggests that biological responses to environmental variation are frequently subject to interactions among limiting factors, but its methodological implications for the study of species distributions are controversial. This work uses patterns of spatial variation in abundance of a palm (Arecaceae) and a soil mite species (Acari) to motivate a simulation that shows how deterministic processes can generate apparently random patterns, hampering ecological analysis. Quantile regression is suggested as a method that takes this phenomenon into account, being then applied to the study of abundance limitation in three species of nest-building termite, noplotermes banksi (Emerson), Neocapritermes braziliensis (Snyder) and Labiotermes labralis (Holmgren), along gradients of soil clay content, food (soil organic matter content for the humivorous A. banksi and L. labralis, and volume of fallen dead wood for the xylophagous N. braziliensis), and median colony size (a proxy for space saturation by colonial territories). It was also considered how different definitions of abundance (nests or individuals) affect the observed patterns. A. banksi had 43.35 nests/ha, 1,573,393 individuals/ha, and 1.97 kg/ha; N. braziliensis had 14.32 nests/ha, 1,310,986 individuals/ha and 4.04 kg/ha (using biomass data from a slightly smaller species, N. talpoides); and L. labralis had 3.35 nests/ha, 815,898.7 individuals/ha, and 3.95 kg/ha. Abundances of nests and individuals were highly redundant in A. banksi and N. braziliensis, as well as their responses to the gradients. L. labralis patterns were more variable, depending on the definition of abundance. Responses of the three species to the gradients of soil texture and food were predominantly bimodal, suggesting an indirect effect mediated by soil moisture in the first case, and exclusion from the mesic portions of the gradient by species with higher competitive ability in the latter. The three species showed unimodal responses to median colony size, refletinc intraspecific competition for space. Besides, nest and individual abundances decreased as a function of body size. These results caution against simplistic descriptions of species responses and suggest a decoupling between the population dynamics at the levels of nests and individuals with increasing body size in termites.