Although rapid adaptive changes in morphology on ecological time scales are now well documented in natural populations, the effects of such changes on whole-organism performance capacity and the consequences on ecological dynamics at the population level are often unclear. Here we show how lizards have rapidly evolved differences in head morphology, bite strength, and digestive tract structure after experimental introduction into a novel environment. Despite the short time scale (≈36 years) since this introduction, these changes in morphology and performance parallel those typically documented among species and even families of lizards in both the type and extent of their specialization. Moreover, these changes have occurred side-by-side with dramatic changes in population density and social structure, providing a compelling example of how the invasion of a novel habitat can evolutionarily drive multiple aspects of the phenotype.

Within populations, individual animals may vary considerably in morphology and ecology. The degree to which variation in morphology is related to eco

We studied the impact of restrictions by the thermal environments on body temperatures (Tbs) and microhabitat use of the lacertid lizards Podarcis melisellensis and Podarcis muralis in a Mediterranean area (Croatia) during autumn. The thermal conditions at available microhabitats were assessed with copper models that measured the operative temperatures (Te) at different sites. We estimated the thermal suitability of microhabitats by quantifying the extent of similarity between the Tes and the range of selected temperatures (i.e., the Tbs that lizards maintain in zero-cost conditions in a laboratory thermogradient; Tsel). Both species maintained, throughout most of day, Tbs that were on average 2–4 C below both Tsel and the Tbs recorded in the field during summer. Nevertheless, the Tbs measured during autumn were in the upper range of available Tes and were much closer to the Tsel than were the Tes. In addition, lizards were most often observed in the warmest microhabitats and were often seen bask...

Summary: 1. Ecological interactions that involve aggressive confrontations between animals are important in shaping the evolution of morphology, behaviour and life history. However, as such confrontations are rarely witnessed, direct quantification of the intensity of these processes in natural populations is notoriously difficult. While the utilization of the frequency of non‐lethal injuries is fraught with difficulties, it may provide information concerning different types of interaction, such as predation, intraspecific aggression and interspecific interference competition. 2. In this paper, we report on an exceptionally large difference in toe loss incidence between two populations 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, we investigated five non‐mutually exclusive hypotheses concerning differences in bite force capacity, bone strength, predation intensity, average age and intraspecific aggression that may provide proximate explanations for the observed differences in injury frequencies. 3. Bite force differences differed considerably between the populations, but bone strength was found to be stronger in the populations with a higher frequency of natural scars. Predation pressure clearly differed between the populations, but we found higher injury rates under predation relaxation. 4. Our results indicate that density and consequently an increased intraspecific competition is the most likely explanation for the observed high frequencies of injuries. We suggest that the intensity of toe amputation between lizard populations may be a useable indirect indication for the intensity of intraspecific competition. 5. This study shows how a combination of morphological, physiological, behavioural and ecological measurements can be used to test assumptions implicit to alternative explanations of an observed phenomenon. Such tests can reveal how likely each of these explanations is, even if the processes leading to the phenomenon are difficult to observe directly.