Gaseous templates in ant nests

We apply a diffusion model to the atmosphere of ant nests. With particular reference to carbon dioxide (CO2), we explore analytically and numerically the spatial and temporal patterns of brood- or worker-produced gases in nes ts. The maximum concentration within a typical one-chamber ant nest with ap proximately 200 ants can reach 12.5 times atmospheric concentration, reachi ng 95% of equilibrium concentrations within 15 min. Maximum concentration i ncreases with increasing number of ants in the nest (or production rate of the gas), distance between the centre of the nest ants and the nest entranc e, entrance length, wall thickness, and with decreasing entrance width, wal l permeability and diffusion coefficient. The nest can be divided into thre e qualitatively distinct regions according to the shape of the gradient: a plateau of high concentration in the back half of the nest; an intermediate region of increasingly steep gradient towards the entrance; and a steep li near gradient in the entrance tunnel. These regions are robust to changes i n gas concentrations, but vary with changes in nest architecture. The patte rn of diffusing gases contains information about position and orientation r elative to gas sources and sinks, and about colony state, including colony size, activity state and aspects of nest architecture. We discuss how this diffusion pattern may act as a "dynamic template", providing local cues whi ch trigger behavioural acts appropriate to colony needs, which in turn may feed back to changes in the gas template. In particular, wall building occu rs along lines of similar concentration for a variety of nest geometries; t here is surprising convergence between the period of cycles of synchronousl y active ants and the time taken for CO2 levels to equilibrate; and the qua litatively distinct regions of the "dynamic template" correspond to regions occupied by different groups of ants. (C) 2000 Academic Press.