Population density and adult sex ratio of the tortoise Testudo hermanni inGreece: evidence for intrinsic population regulation

The idea that the size of animal populations may be regulated by factors in trinsic to them, such as behaviour, has a long history in ecology. Although this idea is now rejected as a general mechanism, it may apply in some spe cies where females are damaged during courtship attempts, such as the Medit erranean tortoise Testudo hermanni. The sex ratios (adult males : adult fem ales) of most dense Greek populations were more extreme lover 1.5:1) than c ould be accounted for by the earlier age at maturity of males, and some ran ged to over 6:1. The sex ratio was correlated with the population density o f adult males and the frequency of courtship attempts on females, and negat ively correlated with the longevity of females. A high population density o f males limits the density of adult females. This intrinsic regulation of p opulation size is a consequence, rather than a goal, of a particular type o f courtship behaviour (persistent thrusts by the male using a tail with a s harp terminal spur) in T. hermanni. Existing population densities at many G reek sites are probably unnaturally high, owing to the reduction of natural predators.