By Bill Bateman. Living on an island can have an effect on your behaviour. You might have noticed this yourself if you associate islands with holidays and relaxation. On an evolutionary scale something analogous happens.
Darwin said: “At the Galapagos Islands, I pushed a hawk off a tree with the muzzle of my gun, and the little birds drank water out of a vessel in my hand”. He also noted the tameness of the Falkland Islands wolf, or warrah (Dusicyon australis). This relaxed attitude is called ‘island tameness’ and is the result of most islands having a reduced number and diversity of predators. Avoiding predation has to be one of the most fundamental selective pressures, and in most parts of the world we expect animals to be wary. Not so on islands. Darwin was aware of this: “[the marine iguana] is adapted to swim and dive perfectly… No doubt it must be exposed to danger from sharks, and consequently, though quite tame on the land, I could not drive them into the water, and when I threw them in, they always swam directly back to the shore.”
In Western Australia, we have a prime example of this island tameness – the Rottnest island quokka (Setonix brachyurus). The Rotto quokka, having spent 6,000 years on a predator-free island, has been effectively doing the evolutionary equivalent of sitting by the pool sipping on a daiquiri. Rotto quokkas are therefore extremely island tame, although they aren’t completely free of the vestiges of anti-predator behaviour. Blumstein et al. (2001) found that they foraged more and showed less vigilance behaviour as their group size increased, which seems a typical ‘group size effect’ recorded for many species. Quokkas in groups of ten or more showed no vigilance at all! This may be due reduced anti-predator behaviour or increased foraging competition.
Eventually humans always come along and spoil the party – the Falkland Islands wolf mentioned earlier is now extinct. Darwin said that they were so tame that: “The Gauchos … have frequently killed them … by holding out a piece of meat in one hand, and in the other a knife ready to stick them”. He went on to prophesy grimly “within a very few years after these islands shall have become regularly settled, in all probability this fox will be classed with the dodo, as an animal which has perished from the face of the earth.” He was right.
We have a new paper out looking at the phenomenon of island tameness in Rotto quokkas – ‘Are tourism and conservation compatible for ‘island tame’ species?’ in the journal Animal Conservation (http://onlinelibrary.wiley.com/doi/10.1111/acv.12301/full). Rottnest Island is a popular tourist destination, but the quokkas on the island face different degrees of disturbance from humans, both temporally (in and out of tourist season) and spatially (more tourists in some parts of the island than others).
Quokkas have been said to be comfortable or unperturbed around humans (Mclean et al., 2000; Blumstein et al., 2001) but it appears that it is not quite that simple: even quokkas in their island paradise respond negatively to humans who push their luck.
Teele Worrell studied these animals for her honours, and found that even the laid-back Rotto quokka is more wary of humans in areas where they meet fewer humans. These animals are also more likely to move away from humans in larger, noisier groups. Touching was also a no-no as far as the quokkas were concerned. Teele also found that quokkas spent more time in group behaviour and locomotion, but less in vigilance and feeding in high tourism sites than in low tourism sites.
If you go to Rottnest, say hello to the quokkas, but, just as you would for any animal, don’t crowd them or make too much noise. They’ll appreciate it, and maybe they’ll let you take a selfie with them http://news.nationalgeographic.com/news/2015/03/150306-quokkas-selfies-animals-science-photography-australia/
Blumstein, D.T., Daniel, J.C. & McLean, I.G. (2001). Group size effects in quokkas. Aust. J. Zool. 49, 641.
Mclean, I.G., Schmitt, N.T., Jarman, P.J., Duncan, C. & Wynne, C.D.L. (2000). Learning for life: training marsupials to recognise introduced predators. Behaviour 137, 1361