Abundance, diet and prey selection of arboreal lizards in a grazed tropical woodland ERIC J. NORDBERG,* PAUL MURRAY, ROSS ALFORD AND LIN SCHWARZKOPF College of Science and Engineering, James Cook University, Townsville, Queensland 4810, Australia (Email: ericjnordberg@gmail.com) Abstract The diet of predators is a critical determinant of their ecological effects. Small vertebrate predators of invertebrates are often characterized as diet generalists based on diet descriptions, but few studies examine prey availability to determine whether prey choice occurs. We studied the prey availability in relation to the diet of two common and abundant, but understudied small vertebrates: Gehyra dubia, an arboreal nocturnal gecko, and Cryptoblepharus australis, an arboreal diurnal skink. We sampled lizards in two major woodland habitat types, Reid River box (Eucalyptus brownii) and Silver-leaf ironbark (Eucalyptus melanophloia) and among four cattle grazing regimes (ranging from moderate – heavy stocking). Cryptoblepharus australis were more abundant in the Silver-leaf ironbark habitat, but there was no effect of grazing regime on their abundance. In contrast, G. dubia did not differ significantly in abundance in relation to habitat type, but were more abundant in paddocks with heavier stocking rates. We quantified invertebrate prey available to lizards in these habitats using defined-area searches and light trapping. Invertebrate community composition did not differ significantly between the habitat types or among the four grazing regimes. Although G. dubia and C. australis both occu- pied the same microhabitats, they were temporally segregated based on their activity times. While both species are apparently habitat generalists, we found that G. dubia and C. australis are selective in their diets. Only half of the invertebrate groups available in the environment occurred in the diets of either lizard species. Both spe- cies positively selected Coleoptera (beetles), Araneae (spiders), and Scorpiones (scorpions), and they exhibited high dietary niche overlap (O = 0.97). We suggest the increased availability of the top three preferred prey groups (beetles, spiders, and scorpions) may contribute to the high abundances of G. dubia in heavily grazed areas. Key words: Arthropods, Australia, electivity, feeding ecology, reptiles. INTRODUCTION Knowing the diet, foraging mode, and prey choice of predators are fundamental to understanding their effects on the ecology, behaviour, and distributions of prey among ecosystems (Johnson 1980; Dayton 2003). For example, generalist predators may stabi- lize ecosystem dynamics, whereas specialists may drive prey cycles or cause extinction of their prey (e.g. Turchin 2003). However, the nature of preda- tion by many small vertebrate predators is often poorly known (Manicom 2010), even though the bio- mass of such species may be high, and their ecologi- cal effects are likely large. Lizards are excellent model organisms with which to quantify the nature of predation by small verte- brates, as they are important predators of a wide vari- ety of invertebrates. Insectivorous lizards make interesting model organisms to study prey selection because in many environments, invertebrate abun- dance and richness are high, providing an opportunity for selective foraging (Stamps & Tanaka 1981; Manicom & Schwarzkopf 2011). Although many studies describe diet (Bustard 1968; Floyd & Jenssen 1983; Sales & Freire 2015), few estimate prey availability as well (Dubas & Bull 1991; Griffiths & Christian 1995; Manicom & Schwarzkopf 2011; Lisboa et al. 2012). To estimate prey selectivity, a description of the diet must be compared with some measure of prey availability (Diaz & Carrascal 1991). The majority of studies of the diet and feeding strategies of Australian lizards describe terrestrial or leaf litter species (e.g. Pianka 1969; Crome 1981; Brown 1986, 1988; James 1991; Abensperg-Traun & Steven 1997; Manicom & Schwarzkopf 2011). Although the diversity of Australian arboreal lizards is high, few studies have examined diet with the exception of some varanid lizards (Pianka 1971, 1982, 1994; Shine 1986; Weavers 1989; Thompson et al. 1999) and frill-neck lizards (Chlamydosaurus kingii, Shine & Lambeck 1989; Griffiths & Christian 1995). Australia’s native house gecko (Gehyra dubia), belonging to a group of geckos called ‘dtellas’, and the inland snake-eyed skink (Cryptoblepharus australis) are wide-spread lizard species that occur in eastern *Corresponding author. Accepted for publication November 2017. © 2017 Ecological Society of Australia doi:10.1111/aec.12570 Austral Ecology (2017) , –