Drought-driven change in wildlife distribution and numbers: a case study of koalas in south west Queensland

Abstract

Context. Global climate change will lead to increased climate variability, including more frequent drought and heatwaves, in many areas of the world. This will affect the distribution and numbers of wildlife populations. In south-west Queensland, anecdotal reports indicated that a low density but significant koala population had been impacted by drought from [2001][2002][2003][2004][2005][2006][2007][2008][2009], in accord with the predicted effects of climate change.Aims. The study aimed to compare koala distribution and numbers in south-west Queensland in 2009 with pre-drought estimates from 1995-1997.Methods. Community surveys and faecal pellet surveys were used to assess koala distribution. Population densities were estimated using the Faecal Standing Crop Method. From these densities, koala abundance in 10 habitat units was interpolated across the study region. Bootstrapping was used to estimate standard error. Climate data and land clearing were examined as possible explanations for changes in koala distribution and numbers between the two time periods.Key results. Although there was only a minor change in distribution, there was an 80% decline in koala numbers across the study region, from a mean population of 59 000 in 1995 to 11 600 in 2009. Most summers between 2002 and 2007 were hotter and drier than average. Vegetation clearance was greatest in the eastern third of the study region, with the majority of clearing being in mixed eucalypt/acacia ecosystems and vegetation on elevated residuals.Conclusions. Changes in the area of occupancy and numbers of koalas allowed us to conclude that drought significantly reduced koala populations and that they contracted to critical riparian habitats. Land clearing in the eastern part of the region may reduce the ability of koalas to move between habitats.Implications. The increase in hotter and drier conditions expected with climate change will adversely affect koala populations in south-west Queensland and may be similar in other wildlife species in arid and semiarid regions. The effect of climate change on trailing edge populations may interact with habitat loss and fragmentation to increase extinction risks. Monitoring wildlife population dynamics at the margins of their geographic ranges will help to manage the impacts of climate change.

Extinction in Eden: identifying the role of climate change in the decline of the koala in south-eastern NSW

“…Thus, there is an increasingly urgent need to minimise those threats that can be managed locally, such as logging of koala habitat, road traffic, fire and dogs across the region, so as to maximise the chances for the existing populations to survive and to enable individuals to recolonise currently unoccupied or rehabilitated habitat. Drought and heatwaves have been identified as having adverse impacts on koala populations in other regions (Gordon et al 1988;Ellis et al 2010;Seabrook et al 2011;Lunney et al 2012a). Drought was found to be a significant factor, contributing to an 80% reduction of koala numbers in western Queensland, especially on the semiarid western margin of the koala range where the remaining koalas were limited to riparian habitats (Seabrook et al 2011;Smith et al 2013).…”

“…Drought and heatwaves have been identified as having adverse impacts on koala populations in other regions (Gordon et al 1988;Ellis et al 2010;Seabrook et al 2011;Lunney et al 2012a). Drought was found to be a significant factor, contributing to an 80% reduction of koala numbers in western Queensland, especially on the semiarid western margin of the koala range where the remaining koalas were limited to riparian habitats (Seabrook et al 2011;Smith et al 2013). Ellis et al (2010), working in central Queensland, found that lack of leaf moisture had an impact on koala survival during periods of high temperature.…”

“…The koala (Phascolarctos cinereus) has been affected by landuse change (Phillips 1990;Melzer et al 2000;McAlpine et al 2006;Rhodes et al 2011) and by climate change (Seabrook et al 2011;Lunney et al 2012a). In the present study, we examined both simultaneously.…”

“…Several factors that reflect human population increase also threaten koala recovery, such as dog predation and vehicular collisions. The impact of climate change on koala populations is increasingly being recognised, particularly through increased drought and heatwaves (Seabrook et al 2011;Lunney et al 2012a), decreased leaf moisture (Ellis et al 2010) and decreased leaf nutrition (Lawler et al 1997;Gleadow et al 1998;Barton et al 2010;Moore et al 2010).…”

Faecal particle size and tooth wear of the koala (Phascolarctos cinereus)

“…Non-invasive methods of evaluating koala distribution, such as mapping faecal pellet distributions, are important tools for conserving such cryptic species because they produce an unequivocal record of presence with minimal effort Ellis et al 2013). The analysis of faecal pellet distributions has been particularly useful for studying koala population trends (Seabrook et al 2011) because they can have large home ranges of up to 100 ha (Ellis et al 2002) and are often difficult to observe during surveys of their habitat (Dique et al 2003;Phillips and Callaghan 2011;Woosnam-Merchez et al 2012). In addition to information about which trees koalas use and eat, recent work suggests that fresh pellets may be analysed to produce information on endocrine profiles (Davies et al 2013;Narayan et al 2013) and genetic information for free-ranging koalas (Wedrowicz et al 2013).…”