Grazing by goats on islands affects the populations of an endemic Mediterranean lizard P. Pafilis 1 , I. Anastasiou 1 , K. Sagonas 2 & E. D. Valakos 2 1 Department of Zoology and Marine Biology, School of Biology, University of Athens, Athens, Greece 2 Department of Animal and Human Physiology, School of Biology, University of Athens, Athens, Greece Keywords anthropogenic activities; insularity; population density; species interaction. Correspondence Panayiotis Pafilis, Department of Zoology and Marine Biology, School of Biology, University of Athens, Panepistimiopolis, Ilissia 157-84, Athens, Greece. Tel: ++30 210 7274 544; Fax: ++302107274604 Email: ppafil@biol.uoa.gr Editor: Mark-Oliver Rödel Received 25 November 2012; revised 19 February 2013; accepted 19 February 2013 doi:10.1111/jzo.12032 Abstract Grazing 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 preva- lence, infestation levels, gull nests and lizard densities were collected during a period of 6 consecutive years. Grazing had a negative impact on insect popula- tions, 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. Introduction Habitat deterioration, due to anthropogenic activities, is one of the most important factors in the extinction of animal species (Primack, 1998). Even activities with low environmen- tal cost can alter habitat and cause significant negative effects (Amo, López & Martín, 2006). Grazing is a major factor, which has led to large-scale ecosystem devastation after the ‘industrialization’ of livestock farming during the last 150 years (Fleischner, 2002). The impact of livestock grazing on vegetation is well docu- mented (Fleischner, 1994). Vegetation structure complexity is of pivotal importance for the welfare of animal communities, and lizards are no exception (D’Cruze & Kumar, 2011). Grazing-induced changes in vegetation cause numerous prob- lems to lizards by altering microhabitats and razing refuges (Pettigrew & Bull, 2011), causing shifts in the thermal quality of habitats (Vitt et al., 1998) and decreasing terrestrial arthro- pod communities (Woodcock et al., 2005). The final outcome is expressed as lower lizard population densities (Bock, Smith & Bock, 1990). Further to this, grazing has another, indirect, effect on lizards. Livestock carry many ectoparasites, notably mites and ticks (Liebisch, 1997). Many species of hard ticks (Ixodidae) parasitize reptiles, especially lizards (Casher et al., 2002). Although infestation by ticks is probably not a direct cause of mortality (Schall, Prendeville & Hanley, 2000), ticks have been reported to affect lizards in many ways such as they may induce secondary infections and diseases by transmitting blood parasites (Bull & Burzacott, 1993), remove blood and induce anaemia (Chilton & Bull, 1993), reduce reproductive performance (Vaclav, Prokop & Fekia, 2007) and cause behavioural changes (Main & Bull, 2000). Such changes may have deleterious effects on the survival of insular populations, which are more susceptible to extinction than their mainland peers (Foufopoulos, Marm & Ives, 2011). An interesting case of grazing is the use of islets as pastures for free-roaming goats, which is common throughout the Mediterranean Sea (Bergmeier & Dimopoulos, 2003). Stock- breeders release goats, providing no food or water. Goats feed on the islets’ vegetation, isolated in these natural folds until shepherds collect them. Grazing causes perturbation to the fragile islet ecosystems. Vegetation decreases and con- sequently invertebrate communities, the main lizard prey, are most probably affected as well (e.g. Rambo & Faeth, 1999). Although food availability is restricted in the islands, and especially in Mediterranean islets (Castilla, Vanhooydonck & Catenazzi, 2008), an additional nutrient input supports some islet communities: marine subsidies. Sea birds are respon- sible for the energy inflow from sea to terrestrial ecosystems through guano, fish scraps and their decomposing carcasses (Anderson & Polis, 1999). This ‘manna from heaven’ fuels local plant, arthropod and eventually, lizard communities (Barrett et al., 2005). Journal of Zoology Journal of Zoology. Print ISSN 0952-8369 Journal of Zoology 290 (2013) 255–264 © 2013 The Zoological Society of London 255