Meeting Abstract
The complex mound architectures of certain species of social termite have long been associated with passive, internal climate control function, while existing theories pointed to different specific mechanisms and driving forces, such as wind and metabolic activity. Recent, direct measurements of their internal temperature and flow patterns suggest that the mounds of Odontotermes obesus of South Asia harness instead diurnal oscillations in ambient temperature for driving circulation between subterranean nest and the mound above, a crucial step in their colonial respiratory function. Subsequent study of Macrotermes michaelseni, in Southern Africa, reveals the same general mechanism: circulating flow driven by transient thermal gradients; despite significant differences in environmental conditions and mound morphology. In contrast with the more shaded Asian mounds, however, thermal gradients in the African mounds appear to be directly influenced by the motion of the sun in the sky, adding a solar-powered component in the flow pattern. CO_2 measurements additionally show that African mounds are better mixed throughout day and night, suggesting that their respiratory function is limited by diffusive exchange across the mound wall rather than internal circulation, unlike that of the Asian mounds. The fundamental dependence on transient forcing for passive ventilation, displayed by both mounds, have natural implications for human engineering.
