Evaluating threats and identifying recovery priorities for a species in decline
In April 2012 the koala was listed as vulnerable in Queensland, New South Wales and the Australian Capital Territory under national environmental law (the EPBC Act). The koala is currently widely distributed across eastern Australia, but the listing acknowledges that the species is declining rapidly across much of its range and protection is critical. Having invoked Commonwealth protection, a major challenge now is to develop strategies for recovering declining populations so as to ensure the koala’s persistence into the future.
The koala’s wide distribution is a double-edged sword. On one hand, having populations spread widely helps to reduce the chance that the species goes extinct because it means we don’t have all our eggs in one basket.
On the other hand, it also means that, because it is spread across many different land-uses, climatic zones and vegetation types, it is exposed to different threats in different places. This makes it incredibly difficult to plan for koala recovery because we don’t have a ‘one-size-fits-all’ recovery strategy that we can apply everywhere. Rather, successful koala recovery is likely to require very different recovery strategies in different places. Identifying what these strategies might look like and where to apply them across the koala’s range will be a fundamental component of developing a national recovery strategy for the koala.
An objective way to identify what the best mix of recovery actions might be, as well as where and when to implement them, is to frame this question as a decision problem, which is exactly what researchers from the NERP Environmental decisions Hub have been doing for New South Wales.
The first steps that we have been undertaking to be able to identify sensible recovery strategies is to map koala distributions and threats and to develop tools that allow us to predict outcomes for koalas under alternative recovery actions.
Mapping distributions and threats.
The key threatening processes for koalas in New South Wales include loss of habitat, changing climate and climate extremes, roads, urban development, and disease. However, we lack basic spatial information about the distribution of these threats in relation to the distribution of koalas.
We addressed this by using data obtained from the general public on their sightings of koalas over time (something often referred to as citizen science, see the next article ‘Citizen science survey data’). This public-based data provided information on the past and present distribution of koalas across New South Wales since 1987 and this allowed us to spatially map the effect of each threatening process (apart from disease) on koalas (Santika et al, 2014). Importantly, we were able to quantify the effect of these multiple threats on the persistence of koalas and their distributions and identify where different threats were highest and lowest across New South Wales. A similar finer-scale analysis was also conducted in Eden in the south
east of the state (Lunney et al., 2014).
The most striking pattern that this work revealed was that koala extinction risk was estimated to be substantially higher in the west of the state than in the east (see figure 1). This was primarily associated with differences in the levels of eucalyptus forest cover, but maximum summer temperature was also an important determinant of extinction risk.
The effect of urban development on extinction risk was also found to be important, but was ameliorated by forest cover. Consequently, the major threats to koalas in New South Wales appear to be loss of forest cover and changes in maximum summer temperatures together, but these effects vary across the state. However, the presence of roads were also shown to negatively impact on koalas.
In Eden, the koala population has exhibited a significant contraction over the past 35 years. Our finer scale analysis in Eden revealed climate, fire, and human population growth as key factors driving the observed decline in this region. This is consistent with the statewide analysis, but with some idiosyncratic threats around factors such as fire being important in this region.
Predicting outcomes for koalas
An important application of our model’s treatment of distributions and threats across NSW is in predicting the likely trajectory of koala distributions based on alternative future scenarios, including alternative recovery strategies. Based on a continuation of recent land-cover change patterns into the future and an A1FI future emission climate scenario our model suggests a continued contraction of the distribution of koalas in NSW. This suggest that carefully planned strategies to recover koala populations in NSW will be required if this decline is to be reversed.
More info: Jonathan Rhodes firstname.lastname@example.org
Lunney D, E Stalenberg, T Santika & JR Rhodes. (2014). Extinction in Eden: identifying the role of climate change in the decline of the koala in south-east NSW. (2014) Wildlife Research. http://www.publish.csiro.au/view/journals/dsp_journals_pip_abstract_scholar1.cfm?nid=144&pip=WR13054
Santika T, CA McAlpine, D Lunney, KA Wilson & JR Rhodes (2014). Modelling species distributional shifts across broad spatial extents by linking dynamic occupancy models with public-based surveys. Diversity and Distributions. DOI: 10.1111/ddi.12189