Frog Ecology in Modified Australian Landscapes: a Review
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CSIRO PUBLISHING www.publish.csiro.au/journals/wr Wildlife Research, 2003, 30, 193–205 Frog ecology in modified Australian landscapes: a review Donna Hazell Centre for Resource and Environmental Studies, The Australian National University, Canberra, ACT 0200, Australia. Email: [email protected] Abstract. Frog decline in Australia has often occurred where habitat is relatively intact. Habitat alteration and loss do, however, threaten many species. Widespread degradation of aquatic and terrestrial systems has occurred since European settlement, with only 6.4% of Australia’s landmass reserved for conservation. But what do we know about how frogs use modified Australian landscapes? Do wildlife managers have the information required to ensure that frog habitat is considered in the management and revegetation of these areas? This review examines published Australian research on frogs to determine knowledge on processes of habitat loss and degradation. Literature that informs landscape restoration and revegetation is also examined to determine whether the habitat needs of frogs are considered. While many threats associated with frog habitat loss and change have been identified there is little quantitative information on frog–habitat relationships in modified landscapes, habitat fragmentation or knowledge of the connectivity required between terrestrial and aquatic frog habitat. Without this information frogs have largely been ignored in efforts to revegetate and manage for the conservation of Australian biota outside reserves. Ecological frog research in modified landscapes is required to avoid land-management decisions and conservation strategies based on inappropriate assumptions of how biota respond to landscape change. WR02075 FrD.og Ha ecol zelogy l in modified Australian l andscapes Introduction to this situation, further research is needed in systematic Frogs exhibit the highest level of endemism amongst major population monitoring and investigation of potential agents animal groups in Australia (State of the Environment of decline, such as disease, pollutants, climate change, UV-B Advisory Council 1996) with 208 species listed in the radiation and altitudinal influences as well as synergistic Action Plan for Australian Frogs (Tyler 1997). Thirty-one effects (Goldingay et al. 1999; Hines et al. 1999; Osborne et Australian frog species are listed as extinct, endangered or al. 1999). Potential impacts of climate change (Osborne et vulnerable by the new Commonwealth Environment al. 1999; Broomhall et al. 2000) and pathogens (Trenerry et Protection and Biodiversity Conservation Act (1999). al. 1994; Laurance et al. 1996; Berger et al. 1998, 1999) have Recent recommendations to the IUCN increase this number received particular attention (but see Laurance 1996; Hero to 40 (J.-M. Hero, personal communication). Since 1985 and Gillespie 1997). eleven frog species have declined or disappeared in Habitat alteration and loss have not been major foci for northern Queensland from relatively undisturbed habitat in research on frog decline as major losses have often occurred World Heritage Areas, secure National Parks and State where habitat is relatively intact. These processes have, Forests. These include several species of Taudactylus, however, been emphasised as important considerations for Rheobatrachus, Mixophyes and Litoria (McDonald and frog conservation. Rawlinson (1981) noted that past research Alford 1999). While there are several hypotheses on Australian frogs had focussed on taxonomy, evolution and postulating the reasons for these declines, causal factors ecology and that little attention has been paid to the effects have yet to be confirmed (Hero 1996; McDonald and of human impacts, in spite of their ecological significance. Alford 1999). He stressed the need for researchers and wildlife authorities Unexplained frog declines have received considerable to direct their attention to the impact of humans on the attention (e.g. Czechura 1991; Tyler 1991a, 1991b, 1991c; Australian frog fauna. This situation has not altered greatly. Couper 1993; Ingram and McDonald 1993; Trenerry et al. Tyler (1997) recognised that while European land uses have 1994; Hero 1996; White 1996). Such attention is essential, as greatly altered the Australian landscape, the effects of these these species may become extinct if the threatening activities on frog conservation and habitat availability has processes at work are not identified and halted. In response remained largely unknown. © CSIRO 2003 10.1071/WR02075 1035-3712/03/030193 194 Wildlife Research D. Hazell Since 1788 forest cover across Australia has been reduced There are also species currently without status that are by an estimated 38% (National Forest Inventory Australia considered threatened by habitat loss and fragmentation. 1998). Australia’s streams and their associated wetlands and Populations of Notaden melanoscaphus in coastal areas near billabongs have suffered widespread degradation through Townsville are disappearing as a result of urbanisation land clearing and engineered modifications, harvesting for (McDonald and Alford 1999), although this species also water and the introduction of pollutants and exotic taxa (see occurs in many areas where habitat loss is not occurring. Lake and Marchant 1990; Barmuta et al. 1992; State of the Litoria cirtropa, L. phyllochroa, L. nudidigitus and Environment Advisory Council 1996). In Victoria L. barringtonensis are considered susceptible to habitat approximately 27% of all streams are considered to be in fragmentation and change (Gillespie and Hines 1999), as are ‘poor to very poor’ condition (Mitchell 1990). Assa darlingtoni (Lemckert 1999) and Philoria sphagnicola Land reserved for conservation covers only 6.4% of (Knowles and Mahony 1997). With increasing salinity Australia’s total land area (Australian Bureau of Statistics problems in areas that have been extensively cleared, Roberts 2001). Several ecosystems are poorly represented within et al. (1999) warned that Western Australian frog species these areas, including arid and semi-arid environments, face an uncertain future. native grassland and wetlands (Department of the Species that lack protection through threatened status Environment, Sport and Territories 1996b). Ehmann and may still be exposed to habitat loss and modification and Cogger (1985) noted that a small percentage of Australia was thus warrant attention. Mahony (1996) listed several species reserved for nature conservation and stressed the need for the that have shown no evidence of decline but argued that it conservation of herpetofauna (reptiles and frogs) outside should not be assumed they are common or secure. Changes reserves. But what is known about how frogs use modified in frog numbers may go unnoticed unless they are of a Australian landscapes? What is known about the impacts of considerable magnitude (Tyler 1991a). In the absence of habitat loss and changes on population dynamics, habitat monitoring, gradual species decline may be overlooked. connectivity and processes of dispersal and immigration? Do Mahony (1996) advocated regular monitoring of common wildlife managers have the information required to ensure species. The presence of common species may be recorded that frog habitat is considered in the management and during surveys for threatened species and warrants revegetation of modified Australian landscapes? publication for future comparison (e.g. Gillespie and Hollis The aim of this paper is to review published Australian 1996; Lemckert and Morse 1999). research on frogs and determine current knowledge The impacts of habitat loss and change on widespread regarding processes and associated impacts of habitat loss, species may go unnoticed because of their extensive degradation and landscape change. Australian research distribution. Declines at a local level caused through literature that supports and informs landscape restoration deterministic processes, such as habitat destruction or and revegetation is also examined to determine the extent to pollution, may contribute to a gradual breakdown in the which the characteristics and habitat needs of frogs have connectivity of extant populations. In the case of the been considered. Frog conservation outside reserves is also relatively abundant species Bufo bufo in the United discussed. This review draws primarily from published Kingdom, it has been demonstrated that habitat sources and is not a comprehensive account of the grey fragmentation resulting from urban development is (unpublished) literature. International literature is discussed associated with lower levels of genetic diversity and fitness where relevant. (Hitchings and Beebee 1998). In addition, there is a positive correlation between genetic diversity and developmental stability of tadpoles (i.e. growth abnormalities), as well as Habitat loss, modification and frog decline tadpole survival. The study concluded that the long-term The magnitude of landscape change across Australia is viability of urban populations appeared to be in doubt. reflected by the considerable number of frog species for Evidence suggested that population isolation occurred which habitat loss and/or change is recognised as a approximately 60 years prior to the study (Hitchings and threatening process. Of 41 species recently recommended Beebee 1998). This is a substantial time lag between habitat for IUCN listing as near threatened, vulnerable, endangered isolation and the resulting population effects. or critically