Grazing by goats on islands affects the populations of an endemic Mediterranean lizard

Abstract

AbstractGrazing of goats on Mediterranean islets is a common practice. Its consequences on plant communities are well documented, although not on vertebrates. We aim to shed light on the effect of livestock farming on lizards by investigating five populations of the insular lizard, Podarcis gaigeae, differing in the duration and intensity of grazing. Data on grazing regime, invertebrate abundance, tick prevalence, infestation levels, gull nests and lizard densities were collected during a period of 6 consecutive years. Grazing had a negative impact on insect populations, thus decreasing food availability for lizards. Tick prevalence and infestation levels were higher in places of continuous grazing. Goat activity disturbed gulls, which avoid nesting, so depriving the islets of marine subsidies. As a consequence of all these factors, lizard densities were higher in ungrazed and lower in grazed biotopes. Grazing effects were more severe on islets communities than on the main island populations. Our data imply that management action should be taken to conserve the highly diverse islet populations.