Variation of adult body size of the tortoise Testudo hermanni in Greece: proximate and ultimate causes

Seventeen populations of T. hermanni in Greece differed substantially in me an adult body size? over a range of about one and a half times in length an d three times in mass. Females were the larger sex in all populations: the degree of sexual size dimorphism did not vary with mean body size. The prox imate cause of the variation of body size among populations was differences in the duration of growth, rather than egg or hatchling size or the growth rates of juveniles. The age at maturity (alpha) increased with body size i n the 17 populations. while the Bertalanffy growth constant (li) decreased with body size. The quantities alpha M and M/k (where M is the instantaneou s mortality rate) were invariant with body size, suggesting that difference s between populations were adaptive rather than the result of short-term di sturbance. Body size was greater in cooler areas. and increased with both l atitude and altitude. This pattern is opposite to that found in most ectoth erms (the reverse Bergmann's rule), and to that which occurs between tortoi se species. Several hypotheses about the possible ultimate causes of variat ion of body size were rejected, including adaptation to long-term habitat d isturbance (land use), character displacement, social factors, energetics, thermoregulation, r-K selection, the length of the season available for inc ubation, or differences in juvenile mortality. The most likely ultimate cau se of size variation between sites is differences in adult mortality, the c orrelation with environmental temperature being through the frequency of fi res.