Differences in Diet among Frogs and Lizards Coexisting in Subtropical Forests of Australia

Abstract

-This study investigates predator size and prey type as potential proximal causes of differences among diets of three lizard species (family Scincidae) and three frog species (subfamily Limnodynastinae) that coexist in wet subtropical forest in eastern Australia. Frogs eat smaller prey than lizards having the same gape size and there were significant differences in the types of arthropods eaten by frogs and lizards. Differences among species within frogs and lizards were small and not statistically significant Frogs ate more amphipods, mites, and ants than the lizards, and lizards ate more termites, millipedes, isopods, and orthopterans than the frogs. Other categories were eaten in similar quantities by both frogs and lizards. The degree of specialization in types and sizes of prey often changes with the body size of a predator. Change of diet with ontogeny has been related to changes in prey size in lizards (Schoener and Gorman, 1968; Rose, 1976; Dominguez and Salvador, 1990; Magnusson and Silva, 1993). Frogs change both prey type and prey size as they grow (Pengilley, 1971; Labanick, 1976; Christian, 1982; Donnelly, 1991; Simon and Toft, 1991; Wiggins, 1992). The latter authors suggested that the change in prey types is a result of the shift in prey size, because different types of arthropods have different mean sizes. However, diet composition differs among species in some assemblages of frogs (Lima and Magnusson, 1998) and lizards (Magnusson and Silva, 1993), and the shift in prey types with growth is more than a passive effect of selection for larger prey in seven species of leaf-litter frogs of Central Amaz6nia (Lima and Moreira, 1993; Lima, 1998). Caldwell and Vitt (1999) showed consistent differences between species of lizards and species of frogs in one Amazonian locality, but there are no other published studies of differences in diet between syntopic lizards and frogs. In this study, we make use of extensive collections of subtropical lizards and frogs in the Australian Museum to investigate the effects of predator size and species identity on diet composition within and between three species of lizards (family Scincidae) and three species of frogs (subfamily Limnodynastinae) that coexist in subtropical rainforest in eastern Australia. MATERIALS AND METHODS The frogs and lizards were collected during a New South Wales National Parks and Wildlife 40 This content downloaded from 157.55.39.239 on Thu, 15 Sep 2016 05:29:31 UTC All use subject to http://about.jstor.org/terms DIFFERENCES IN DIET AMONG FROGS AND LIZARDS Service (NSW NPWS) project coordinated by Harry Hines between 1988 and 1992 and deposited in the Australian Museum in Sydney. The collections were made in Nightcap National Park, Dome Mountain Area, Eastern Border Ranges National Park, Mount Warning National Park, Spirabo State Forest, Forestland State Forest, and adjacent areas in areas of humid subtropical forest in northern New South Wales. In most areas, pitfall traps with formalin were used by members of the NSW NPWS survey team to sample invertebrates, and the capture of vertebrates was accidental. Frogs and lizards (35% of individuals) deposited in the museum that had been collected in the same region but lacking exact geographic coordinates were used to increase sample sizes. We used only specimens that were available in the collection of the Australian museum and did not collect or kill any of the animals ourselves. Only three species of scincid lizards, Calyptotis scutirostrum (N = 39), Eulamprus murrayi (N = 23), and Saproscincus challengeri (N = 30) and three species of frogs of the family Myobatrachidae (Limnodynastinae), Assa darlingtoni (N = 36), Lechriodus fletcheri (N = 26), and Philoria loveridgei (N = 18) were sufficiently common and had enough items in the stomach to justify analysis. The animals were fixed in formalin and maintained in