Somewhere in Madagascar’s most pristine rainforests, right at this very moment*, a feral cat is killing an adorable, chubby rat with fur the color of rust.
It’s old news. Cats are dicks. In Madagascar, in particular, they can prey on all sorts of wildlife, ranging from the evolutionarily unique tenrec to scaly ground-rollers. Our study found that they’re the most influential non-native predator in the forest, affecting where species are and how easy it is to get pictures of them on our cameras.
And they aren’t the only new predator in Madagascar’s forests. There are also free-ranging dogs and small Indian civets present that cause havoc.
But why does this matter, you ask? Surely this is just a fluke. Dogs and cats can’t do too much harm to native animals just because they happen to be introduced somewhere…
30 species of non-native predator are accused of causing up to 58% of all bird, mammal, and reptile extinctions. And which of these predators have some of the biggest impacts? Cats and dogs. Of which there are plenty of in Madagascar’s rainforests. And which areas were most affected? Islands filled with endemic (read: can’t be found anywhere else) wildlife. Just like Madagascar.
So we knew that we potentially had a worst-case scenario. An island filled with one-of-a-kind species had gone to the dogs (and cats and civets). But no one had looked into the situation. So we took up the job to figure out a) if dogs, cats, and civets were affecting native species and b) which of the three affected the most species.
WHAT DID WE FIND?
We mentioned before that feral cats had a huge impact, influencing the presence or detection of six native species. But, A CHALLENGER APPEARS!
The small Indian civet, originally from southeast Asia, also influenced six native species. Together they both affected seven native species. Which was kind of surprising, since these two are both smaller than dogs. But we believe this is because, although feral cats and civets are smaller than dogs, dogs tend to only come into the forest during the day with their humans. The cats and civets are there 24/7.
We also found that how much non-native predators and native prey overlapped in space depended on the habitat quality.
Here we see that as you get into better red forest rat habitat (more rainforest), the rats avoid dogs less often. We’re not sure why this might be — but it does mean that the pressure dogs exert on red forest rats might increase in small rainforest patches, leading to their increased avoidance.
That’s not all! Being able to detect an animal if its there is really important; that’s how we get our data. But just the presence of non-native predators makes it harder to detect native wildlife.
There were also interesting interactions between the presence of two non-native predators. In the above graph, as you get more cats at the camera location, you detect red-breasted couas less often (the lines trend down). But how quickly you lose the ability to detect red-breasted couas depends on whether civets are also present. If civets aren’t there (purple), you very quickly stop seeing red-breasted couas. But if civets are present (pink), there needs to be more cats at the site for you to stop seeing couas.
WHAT DOES THIS MEAN?
This means that there’s a lot going on in Madagascar’s rainforests that we need to look into. We see that habitat quality affects how much native species avoid the non-native predators, and we see that just having a cat or dog at a camera location makes it harder for us to get pictures of native wildlife. Most interestingly (to me), we see that whether there is more than one non-native predator affects how quickly we stop seeing species. This suggests to me that there are interactions happening among the dog, cat, and civet that we weren’t able to analyze.
Either way, keep your fucking cats and dogs inside. Thanks!
[here’s a link to our study: pdf]
In ‘Makira Lessons’, a series in the making, I’ll sum up the main findings of our published Madagascar research — and any bonus unpublishable tidbits — in a way that is accessible to everyone. If you have any questions, feel free to hit me up on twitter: @am_anatiala.
*Truth has been stretched for dramatic effect; I don’t know if a feral cat is killing a native rat in Madagascar right at this very moment as you are reading this.