Effects of fragmentation on island populations of the Aegean wall lizard Podarcis erhardii

Background information

Fragmentation of continuous natural habitats into small isolated patches by human activities, is one of the most important mechanisms leading to the endangerment and the extinction of wildlife populations. Recent research demonstrates that following fragmentation, isolated wildlife populations are simultaneously subjected to multiple threats. The survival of such populations can vary dramatically dependent on both historic contingencies and present environmental conditions. Unfortunately, population biologists don’t have a good understanding how such factors (including habitat fragment size, isolation from other fragments, and the overall genetic health of the population) interact with each other to determine the fate of the population. It is also not clear why some populations are able to persist over long periods of time, while others die out quickly. 

In this project we utilize a natural habitat fragmentation process that occurred in the Mediterranean Sea. Following the end of the last ice age, rising sea levels have fragmented what used to be hilltops in a continuous coastal landscape into today’s Aegean Sea islands. As a result of this process, lizard populations that lived on these hilltops are now isolated on so-called landbridge islands. Because it is known when exactly each island became isolated, and because the study lizards are incapable of crossing even narrow water straits, this study system constitutes an outstanding model for evaluating the effects of long-term fragmentation on the survival of isolated wildlife populations.

Together with our collaborators (Nicola Anthony, [Univ. of New Orleans], P.Pafilis [Univ. of Athens], Dennis Hasselquist [Univ. of Lund]), we aim to compare the characteristics of small island populations of the Aegean Wall lizard (Podarcis erhardii) of known age and size, with those of larger, unfragmented populations. Scientists have postulated that one of the main mechanisms that mediate the effects of habitat fragmentation on population survival is the genetic condition of a population. Loss of genetic diversity can for example impact the ability to mount effective immune defenses and ultimately result in increased rates of parasitism. At the moment however, there exists surprisingly little empirical information on the value of genetic diversity for the survival of small populations. 

To understand these issues we are evaluating in this study: 

1. the genetic diversity, 

2. the ability to mount effective responses to standardized immune challenges, and

3. the rates of parasitism by ectoparasites and blood parasites

in several small populations of P. erhardii occurring on small land-bridge islands in the Aegean Sea. This study will shed light on how habitat fragmentation impacts small populations and will ultimately help guide future conservation efforts.