Linking functional trade-offs, population limitation and size structure: Termites under soil heterogeneity

Organismal fitness is fuelled by resources. However, resource acquisition often involves conflicting functional demands that may ultimately shape broader ecological patterns. For instance, termites play major roles in ecosystem functioning through their foraging and building activities. Yet, while experiments suggest improved foraging in sand, nest construction depends on clay. Hence, these functions may trade off, with species optima reflecting interspecific variation in building requirements. We investigated whether a foraging–building trade-off could affect termite populations by using three species differing in building requirements, namely Neocapritermes braziliensis, Anoplotermes banksi and Labiotermes labralis. We characterized their populations in relation to soil texture and food amount across a tropical rain forest landscape, and then compared the observed patterns. Colony density was unrelated to food amount in the three species. However, A. banksi was denser at balanced mixtures of sand and clay, consistent with a compromise between foraging and building demands. Further, the species building more mineralized nests (L. labralis) was more abundant on clayish soils, whereas the species relying less on soil for nest construction (N. braziliensis) was more abundant on sandy soils. Changes in colony density correlated with changes in size structure: in N. braziliensis and A. banksi, colony mass variability increased with density due to a sharp decrease in minimum colony mass, consistent with higher productivity and/or size-asymmetric competition. This study suggests a novel functional trade-off that may help drive population density and size structure both within and across termite species.