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Cats control lizard populations but the reptiles adapt well

By Dave Armstrong - 18 Jun 2014 7:59:0 GMT
Cats control lizard populations but the reptiles adapt well

This is another species of the Podarcis genus, all of whom inhabit the Mediterranean area ; Wall lizard image; Credit: © Shutterstock

The feral cat is a wild or semi-wild domestic cat that is held responsible for more extinctions than any other species. We love cat species, and cats with bells who don't go out at night. The accountability of our feline rodent operatives can now be exposed by a study of their effect on reptile species on Greek islands. Li Binbin and his colleagues from the University of Michigan, Eastern Michigan Universty, Duke University and the University of Athens present their results in The Proceedings of the Royal Society B paper called - Effects of feral cats on the evolution of anti-predator behaviours in island reptiles: insights from an ancient introduction.

The ancient introduction, of course, was of cats, Felis sylvestris catus, associated with farmers as an invasive species to island ecosystems that are always vulnerable to disruption. They have been implicated in 8.2% of all extinctions of prey and 13.9% of all bird, mammal and reptilian declines. Native predators could have been present on some of the Cyclades, but the theory here is that anti-predator defences would be developed by the reptiles, at some energetic cost.

9,500 years ago, the islands of Thera and Kea had their first cats, during the Bronze Age. These Cycladean islands are situated directly north of Crete and east of the Peloponnese. They form part of the Mediterranean biodiversity hotspot that includes 461 amphibian and reptile endemics. Among these the Aegean wall lizard, Podarcis erhardii, live on the dry stone walls that typify Greek island landscapes.

Cat numbers reached 16.3 per square km, especially near human habitations with zero cats found on isolated, low cat density sites. Lizards doubled in numbers at the low cat density sites. The results showed numbers at 10.33, dropping to 4.85 per 100m of wall in the high cat density sites. Although lizards are only a small part of these cats' diet, cats are known to affect prey populations significantly even when they are few in number.

Tail shedding is the well-known anti-predator response of many lizards such as these. The loss is worth it to the animas, because the wriggling tail distracts most predators from the individual's escape route. Islet lizards have few cat predators and so shed their tails less often when a "fake" cat is run near them by experimenters. Evolution could be shown by the plasticity of this response, but behavioural adaptation is obviously in play too. But islet lizards, some without cat predation for 6000 years, still managed to respond better with various anti-predation responses after 3 exposures to the cat decoy.

Again, where few cats were present, the reptiles shed their tails less and showed less anti-predator behaviour. The wall lizard has an ancestral plasticity that allows a change in behaviour. This keeps them up to date with the current predator situation. It was only on tiny islets that an independent evolution apparently happened. These isolated populations would often roam further from their refuges and 60% failed to bother with a refuge for at least one of the "presentations" of a fake cat. 70% actually approached the fake and then ran away. So curiosity didn't only kill cats - it kills lizards too. These intrepid types investigated buckets, fishing equipment and backpacks, perhaps associated with their very high population levels. Scarce food items could be in that backpack!

Mando Island split from large Naxos only 5 years ago and yet the tail-loss trick is already less readily used by this species. The benefit of retaining a sizeable chunk of your body, instead of losing it by caudal autotomy could affect individuals in a populous island. Conservationists now need to consider if lacertid lizards like these could be trained to avoid predation, whether by cats, rats or the native stone martens. Mammals and birds such as New Zealand robins have already been "taught" such anti-predator behaviours. This is a significant inroads into our knowledge of how invasive species can be countered. How prey species adapt is key, both in the short and the long term. The history of dingoes and wallabies in Australia, Madagascan species' adaptations and even small island changes such as in these reptiles contribute to a science that will ease our terrible rate of extinctions.