The role of mound functions and local environment in the diversity of termite mound structures

Mound structures that soil termites build have diverse morphologies. Previous observational studies documented that mounds are built to provide regulated environments for the termites that live within them and their structures are formed in ways to support this purpose under the influence of the mounds' immediate environment. The objective of this study is to provide a methodology and a predictive computational model to investigate the reason behind the different but systematic shapes of termite mounds, considering all the relevant forces imposed on them and their thermoregulatory and gas-exchange functions. The gas-exchange function accounts for the capacity of the mound to diffuse metabolic gases generated in the mound's underground nest, while the thermoregulatory function satisfies the connection between the underground nest and deep ground temperatures. The proposed predictive model is based on the principles of heat transfer and thermodynamics and allows optimized mechanically stable structures to freely emerge. The results indicate that, while the model is free to generate any mechanically stable structure, under the relevant environmental and metabolic conditions, it produces structures with forms and geometrical characteristics similar to those of natural mounds. Investigation of the connection between the local environment and the mound shapes indicated that the Sun and wind play an important role in the mound structural form. Mounds exposed to stronger solar irradiance exhibit cone-shaped structures that are pointed towards the Sun, while shaded mounds are observed to be vertical domes. The local wind is observed to affect the external shape of the mound by preventing them to grow tall while controlling the features of the internal structure. By investigating the similarities between structures in different regions (i.e., India, Namibia, and Brazil), it is revealed that, unlike mounds with a strong need for gas-exchange, mounds with a significant demand for thermoregulation exhibit deeper nests, thicker external walls, and well-defined cone- (as opposed to the dome-) shaped structures. Overall, the form of termite mounds is strongly correlated to both regulatory functions and local environments, and the resulting mound shape arises as a combination of these factors.