Tag Archives: epidemiology

Light At The End Of The Tunnel For The Tasmanian Devil

Image Credit: Mattias Appel, CC BY-ND 2.0

Image Credit: Mattias Appel, CC BY-ND 2.0, Image Cropped

Quantifying 25 years of disease‐caused declines in Tasmanian devil populations: host density drives spatial pathogen spread (2021) Cunningham et al., Ecology Letters, https://doi.org/10.1111/ele.13703

The Crux

While the Tasmanian Tiger has made news this last month for all the wrong reasons, there’s still another famous species of Tasmanian mammal which deserves just as much attention (probably more given that we can still save this one from extinction). The Tasmanian devil has seen its populations declined considerably over the last three decades, largely due to the emergence of a transmissible facial tumour, the devil facial tumour disease (DFTD).

The way the devils interact mean that even at low densities, the disease can still be transmitted through a population. The aggressive nature of Tasmanian devil mating (which occurs even when there are few devils around) is a big transmission vector. This unfortunately means that extinction due to DFTD was recently thought to be a likely endpoint.

Today’s authors wanted to test to how strongly the devil density influenced the spread of DFTD, and whether the drop in population that the disease causes means that we’re likely to see the disease’s effects wear off at some point, and Tasmanian devil populations stabilise.

What They Did

Long-term data is an absolute must for a study like this. Luckily, the Tasmanian government has run ‘spotlight surveys’ along 172 road transects for the last 25 years. These involve driving slowly along a 10 kilometre stretch of road and recording mammal presence using a handheld spotlight. This was combined with further surveys designed to obtain density at smaller scales to come up with a predictive estimate of devil density in Tasmania from 1985 to 2035.

The team also used occurrence data for DFTD to figure out how quickly it initially spread through Tasmania, and modelled the spread into a new region against the density of the devils in that region.

Did You Know: Devil Reintroduction

The Tasmanian devils are an Australian icon, and a lot of money has been put into figuring out how to save their species. Suggestions have been made to reintroduce DFTD-free population back onto mainland Australia, where their presence may even help reduce the effect of cats and foxes. However it is also possible that the introduction of a new predator could instead put added pressure on mainland species already threatened by invasive predators. Studies into this are ongoing, and you can check out more on them at the articles linked below.

Read More: Releasing the Devil

What They Found

Tasmanian devil density may have played a large role in the initial spread of the disease, explaining why it spread so quickly through certain parts of Tasmania. This isn’t hugely surprising, though the precision with which the authors modelled its spread will be absolutely crucial for effective conservation.

What is really interesting is that the Tasmanian devil population back before the disease struck were probably much lower than initially thought. If this sounds depressing, the other big takeaway is that based on the predictions here, the decline in devil numbers should ease off soon, meaning the disease is unlikely to result in the extinction of Tasmania’s most iconic endemic species.

The study predicts that Tasmanian devil extinction is unlikely, but that doesn’t mean we can relax just yet (Image Credit: Mathias AppelCC0 1.0)

Problems

Normally authors will mention interesting future research which could build on the research they’ve carried out. Standard practice. Here, my ‘problem’ is that the authors mention some research so incredibly tantalising I’m angry at them for bringing it up. What will be important in the future is looking at devil genotypes. The genetic makeup of some devils will make them more resistant to the disease, and identifying and moving these individuals to areas where the disease is rampant could help fight DFTD. Having said that, it could also help produce more aggressive strains of the disease. GIVE ME ANSWERS.

So What?

This is a good news story, which often feel quite scant in the world of ecology. But it doesn’t mean the devil is out of the woods yet. Actually the woods themselves are a massive problem, seeing as Australia’s rates of deforestation are among the worst in the world. We need to constantly monitor the population to figure out where local extinctions are likely.

This study is also a fantastic example of how important long-term monitoring is for ecologists. Studies like the one used here are hard to fund (more on that here), but their value to ecologists in allowing us to figure out what drives population fluctuations is enormous.

Sam Perrin is a freshwater ecologist currently completing his PhD at the Norwegian University of Science and Technology who has spent way too much time looking at photos of Tasmanian mammals over the last 2 weeks. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.

From Deforestation to the Pandemic: How Destroying Ecosystems Increases Novel Infectious Diseases

This is a guest post by Professor Emma Despland

Zoonotic diseases, or diseases that jump from animals to people, are not a new phenomenon.  Many well-known human diseases first originated in animal populations. In some cases, animals are the main sources of human infection and human-to-human transmission is rare or null (e.g. rabies); other diseases persist in animal populations and occasionally jump to humans, seeding a human outbreak (e.g. plague), and yet others jumped from animals to people long ago and have been circulating in human populations ever since (e.g. measles).  However, novel zoonotics have been appearing with disturbingly increasing frequency.  

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In Silico Science: Ecology Without the Nature

When dealing with complicated ecological concepts, theoretical models – though they may seem abstract – often help create bridges to fill in our understanding, writes Thomas Haaland (Image Credit: Aga Khan, CC BY-SA 4.0, Image Cropped)

It should not come as a surprise any more that most ecologists don’t spend all that much (work) time outside. Numerous posts on this blog about data management and ecological modelling draw a picture of a modern biologist spending most of their time in front of a computer rather than out in the field. However, the work is still intimately related to the natural world. Gathering the data is simply the first step on the way to scientific understanding, and between organizing data, analyzing data, interpreting results and writing them up, the computer hours just vastly outweigh the outdoor hours. But there is another, more mysterious breed of researchers that has even less to do with nature: theoretical biologists.

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