Long-term impacts of DFTD on wild Tasmanian devils
A collaboration between multiple institutions has played a vital role in increasing our knowledge of trends in wild Tasmanian devil populations. Mathias Tobler from San Diego Zoo Global collaborated with the Save the Devil Program (STDP) to analyse trends in spotlight counts and devil densities across the State.
Spotlight count data for devils have been systematically collected by DPIPWE’s Wildlife Management Branch since 1985, and were analysed in conjunction with trap-release data collected annually by the STDP from nine sites. Trap-release data has been collected with assistance from the University of Tasmania and funded by Toledo Zoo since 2015.
The results of the collaboration have been published in a research paper titled “Density trends and demographic signals uncover the long term impact of transmissible cancer in Tasmanian devils”. The paper shows that the overall numbers of devils in the wild have declined by around 80% as a result of the emergence of DFTD, and there is evidence of ongoing small decline.
Despite this, devils have persisted to-date in the wild. Investigation of the underlying causes for trends in devil densities showed that devils in diseased areas are now breeding younger and having more pouch young, and this earlier breeding means that they are contracting DFTD younger, often as one-year olds.
The data indicates that like many threatened species which exist in small isolated populations, the reduced densities, change in age structure, and breeding patterns wrought by DFTD means devil populations are impacted more by other threats. These threats include roadkill, bushfire, loss of genetic diversity, and changes in food availability caused by drought.
Moreover the shift towards low densities of predominantly young devils in areas where DFTD is present means the influence of devils on the ecosystem through predation, scavenging, and life in general, has likely changed dramatically. DFTD has spread across over 80% of Tasmania, so these ecosystem changes are widespread.
Efforts to manage DFTD are ongoing, but remain in a research and development phase. This means that recovery efforts focus on maintaining the small populations that have persisted with DFTD. The STDP are addressing this by reducing the incidence of devil roadkill in known blackspot areas, and augmenting devil numbers, age structure, and genetic diversity by translocating Tasmanian devils into the wild.
Understanding the long-term impact of DFTD and the population status and trends of wild devils is fundamental to guiding the extent and form of future recovery actions. The combination of techniques used by the STDP to monitor devils, which include spotlight counts, trap-release, and camera surveys, have been shown to be a robust approach as evidenced by acceptance of the results in an internationally peer-reviewed journal.
The increased understanding arising from this research and monitoring is not limited to devils: the publication of the research in the Journal of Applied Ecology means that insights are shared with conservation managers of threatened species around the world.
You can read the paper here http://onlinelibrary.wiley.com/doi/10.1111/1365-2664.13088/full
Image caption: Save the Tasmanian Devil Program’s wildlife biologist and lead author Dr Billie Lazenby