engleski

The mystery of the missing toes: extreme levels of natural mutilation in island lizard populations.

Ecological interactions that involve aggressive confrontations between animals are importantin shaping the evolution of morphology, behaviour and life history. However, as such confronta- tions are rarely witnessed, direct quantification of the intensity of these processes in natural pop-ulations is notoriously difficult. While the utilization of the frequency of non-lethal injuries isfraught with difficulties, it may pro vide information concerning different types of interaction, such as predation, intraspecific aggression and interspecific interference compet ition.2. In this paper, we report on an exceptionally large difference in toe loss incidence between twopopulations of Podarcis sicula lizards living on small, neighbouring islands in the Adriatic Sea.We caught 900 lizards and recorded the number and location of missing toes. Subsequently, weinvestigated five non-mutually exclusive hypotheses concerning differen ces in bite force capacity, bone strength, predation intensity, average age and intraspecific aggression that may provideproximate explanations for the observed differences in injury frequencies.3. Bite force differences differed considerably between the populations, but bone strength wasfound to be stronger in the populations with a higher frequency of natural scars. Predation pres-sure clearly differed between the populations, but we found higher injury rates under predationrelaxation.4. Our results indicate that density and consequently an increased intraspecific competition is themost likely explanation for the observed high frequencies of injuries. We suggest that the inten-sity of toe amputation between lizard populations may be a useable indirect indication for theintensity of intraspecific competition.5. This study shows how a combination of morphological, physiological, behaviou ral and eco-logical measurements can be used to test assumptions implicit to alternative explanations of anobserved phenomenon. Such tests can reveal how likely each of these explanations is, even if theprocesses leading to the phenomenon are difficult to observe directly.

intraspecific competition ; injury frequency ; density ; sex ratio ; Podarcis sicula ; social behaviour ; aggression

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