A two-dimensional individual-based model of territorial behaviour: possible population consequences of kinship in red grouse

A two-dimensional simulation model of territory establishment and maintenance by individual male red grouse investigated whether differences in aggressive behaviour between kin and non-kin might cause population cycles or other demographic instability. Two behavioural phenotypes were envisaged. intolerant cocks were equally aggressive to all neighbours, while kin-tolerant cocks were less aggressive to their close kin. The model's dynamics showed that: (i) pure populations of intolerants reached low but quite stable densities; whereas (ii) pure populations of kin-tolerant cocks attained higher densities with larger fluctuations; while (iii) populations of kin-tolerant cocks able to disperse showed even wider fluctuations. Mixed populations of intolerants and kin-tolerants co-existed at intermediate frequencies, with marked fluctuations. Thus kin-tolerant behaviour destabilised the model, giving it the potential to bifurcate to a cycle, but cycles were not observed. Two variants of the model altered grouse behaviour in response to changes in density, by changing either their kin tolerance or their number of dispersal attempts. Sensitivity tests showed these variants often produced density cycles, with periods around 6-15 years. We concluded that: differential aggressive behaviour between kin and non-kin during territorial disputes can destabilise a two-dimensional model population that has a life history similar to red grouse; dispersal may have a big effect on the stability of such model populations; some realistic variant models produced density cycles with periods and amplitudes comparable to those observed in some studies of wild red grouse. (C) 1997 Elsevier Science B.V.