Austral amphibians – Gondwanan relicts in peril

Abstract

Over 30% of Australasian amphibians are currently threatened with extinction. While habitat loss, introduced species and disease have been identified as major threats, the impacts of climate change are understudied. Threatened frogs fall into distinct biogeographical and ecological groupings that can be linked to specific threats (e.g. mountain- top endemics and climate change; stream-dwelling wet forest frogs and disease; and small island endemics and feral pests). The impacts of gradual climate change over millions of years has isolated specific species into climatic refugia (resulting in restricted geographic ranges), which combined with the ecological traits of these species (e.g. small clutch-size) dramatically increases extinction risk. Australasian frogs demonstrate intrinsic links between biogeographic history, species ecology and conservation status. The solutions to most threats are clear at a broad level, stop land clearing, reduce CO emissions and control feral animals; however, declines linked to the disease chytridiomycosis are not easily resolved. Chytridiomycosis is not a universal threat and understanding the causes of variation in impact is critically important. While the threats of land clearing, disease and introduced species are regional and/or species specific, the impacts of climate change must be examined carefully as all species are likely to affected. Here we cover these issues for Australasian frogs, presenting regional examples that highlight threats and avenues for future research and management. Phylogenetic and biogeographic history Over 30% of amphibian species are threatened with extinction globally making them the most threatened of the vertebrate groups (Wake and Vredenburg 2008). There are multiple threats to Austral frogs: e.g. disease – critically chytrid fungus for species with more aquatic lifestyles; small clutch size and limited range associated with higher decline or extinction risk; introduced species (Gambusia and trout in Australia, Gillespie and Hero, 1999; Murray et al., 2011; Rattus in New Zealand, Thurley and Bell, 1994; and mongoose in the Pacific Islands, Pernetta and Watling, 1979) and less specific threats,identified in both Austral and global analyses of amphibian declines: e.g. climate change (Hero et al., 2006, 2008; Hof et al., 2011) and habitat loss and fragmentation (Hero et al., 2008). These factors pose serious threats in many other regions of the world (Stuart, 2008) and their impacts vary among species and genera, depending on their current distribution and habitat use (Table 21.1).