Management of multiple threats achieves meaningful koala conservation outcomes

Abstract

Management actions designed to mitigate development or anthropogenic impacts on species of conservation concern are often implemented without quantifying the benefit to the species. It is often unclear what combinations and intensities of management actions are required to achieve meaningful conservation outcomes. We investigate whether disease and predator control can reverse population declines of koalas (Phascolarctos cinereus). Based on longitudinal monitoring of the epidemiological and demographic status of over 500 animals over 4 years, coupled with an intensive disease and predator management programme, we use survival analyses to estimate annual age‐specific survival rates and population growth, and simulations to quantify the benefit of these actions. Predation and disease accounted for 63% and 29% of mortality, respectively, across all years, with wild dog (dingoes or dingo‐hybrids: Canis dingo, C. dingo × Canis familiaris), carpet pythons (Morelia spilota) and domestic dogs (C. familiaris) accounting for 82%, 14% and 4% of confirmed predation mortalities, respectively. In the first 2 years, before disease and dog control had major impact, the population was declining rapidly with annual growth rates of 0.66 and 0.90. In the third and fourth years, after interventions had been fully implemented, the population growth rate had increased to 1.08 and 1.20. The intrinsic survival rate of joeys was 71.2% (excluding deaths resulting from the death of the mother). Adult survival rates varied as a function of sex, age and year. Even in a declining koala population, management actions can achieve meaningful conservation outcomes (population growth rates greater than one). However, benefits may be short‐lived in the absence of longer term strategies to manage threats. This work also identifies wild dogs as a major threat to koalas, highlighting the need to better understand how wild dog impacts vary in space and time. Policy implications. Offsetting policy that addresses habitat loss alone may achieve little or no meaningful benefit to declining koalas populations. Management must address suites of threats affecting these populations and ensure that the cumulative effects of these actions achieve positive population growth rates.

Inbreeding and disease avoidance in a free‐ranging koala population

“…Absence of active inbreeding avoidance behaviour has also been documented in other species, although in highly outbred or well‐connected populations, such an absence may not have a great impact on individual fitness (e.g., reindeer Rangifer tarandus [Holand et al., 2007], great reed warblers Acrocephalus arundinaceus [Hansson et al., 2006]). In species already under pressure from multiple anthropogenic impacts, though, this is a concerning trend (Beyer et al., 2018). For artificially small koala populations, particularly those isolated and condensed by anthropogenic habitat fragmentation, the inability to actively avoid inbreeding may critically impact their survival.…”

Predation by carpet pythons (Morelia spilota) is an important cause of mortality in a free‐living koala (Phascolarctos cinereus) population in South East Queensland

“…Carpet python predation, with or without ingestion, has not previously been documented as an important cause of natural mortality in koala populations, because few free‐living koala populations have been monitored and studied intensively enough for the causes of mortality to be accurately quantified at the population level. Both population viability analyses and development of conservation management plans benefit from robust cause‐of‐death data collected during longitudinal monitoring studies. These can ensure that conservation management measures are targeted to the most important threats.…”

“…Predation is rarely recorded as a cause of death in hospital records, other than with respect to traumatic injuries caused by domestic dogs. A comprehensive and mechanistic understanding of causes of mortality and their relative frequency is important for informing management strategies that result in meaningful outcomes for koala populations …”

Climate‐driven shifts in the distribution of koala‐browse species from the Last Interglacial to the near future

“…Adams-Hosking et al (2012) also predicted the contraction of koala habitats based on a single modelling framework (MaxEnt), concluding that the koala and its dietary species are likely to experience range contractions as climate change progresses, sometimes to regions outside the current distribution. This is of particular concern because the vulnerable conservation status of the species in most of its remaining range arises mainly from deforestation, disease, road kill and dog attacks (Beyer et al 2018). While there could be some scope for retaining koalas in formerly unoccupied habitats, especially in South Australia (Sequeira et al 2014), and possibly re-introducing them to long-unoccupied habitats in south-western Western Australia, or even new ones elsewhere, the outlook is not encouraging.…”