Leapin' Lizards: Ancient Defenses Help Island Reptiles Adapt to New Threats

June 17, 2014

Tim Lucas, 919-613-8084, tdlucas@duke.edu

Note: Li Binbin can be reach for additional comment at (734) 546-7537 (U.S.), +86 (1) 381-025-1904 (China) or binbin.li@duke.edu. For an advance copy of the embargoed study, contact the Royal Society press office at +44 (0) 207 451 2250 or press@royalsociety.org.

DURHAM, N.C. -- Predation by introduced cats is known to have a devastating effect on endangered bird, mammal and reptile species on islands around the world. But insights from a new Duke University-led study may help reverse these declines and guide re-introduction of endangered species.

Feral cats are found on nearly 179,000 islands and have been implicated in 8.2 percent of extinctions and 13.9 percent of all declines of endangered island populations of bird, mammal and reptile species worldwide.

A study appearing June 18 in the peer-reviewed British journal Proceedings of the Royal Society B examines the long-term impacts of feral cat populations on Aegean wall lizards on the Greek island of Naxos and four surrounding uninhabited islets. Cats were introduced to the region’s islands by humans thousands of years ago and large feral populations are found on many of the islands.

“At sites with high feral-cat densities, such as around villages on Naxos, we found that wall lizard populations were reduced by half,” said lead author Li Binbin, a PhD student at Duke’s Nicholas School of the Environment. “Field and laboratory trials also showed that the long-term presence of the feral cats at these sites had a significant impact on the speed and ease with which the lizards initiated anti-predator escape behaviors.”

Lizards from sites with high cat densities fled from a wheeled cat decoy much sooner than lizards from sites with low cat densities or no cats. They also were able to shed their tails --  a last-ditch escape behavior of many lizard species -- with greater ease.

The differences were most pronounced during initial trials, when lizards from sites with low cat densities allowed the decoy to get nearly twice as close before they fled, and more than 70 percent of lizards from islets with no cats actually approached it before fleeing. By the third round of decoy trials, flight initiation distances had increased for lizards from all three groups, with lizards from islets with no cats more than doubling the distance at which they began to flee.

“This suggests that wall lizards retain ancestral plasticity in their anti-predator behavior that allows them to change their behavior relatively quickly in response to changing predation levels,” Li said. “Even lizards from islets with no cat populations were able to regain their fear behaviors, despite having lived without the risk of feral cat predation for thousands of years.”

From a conservation perspective, such behavioral plasticity could allow Aegean wall lizards and other island lizard species, including those that are endangered, to be trained to recognize and avoid exotic predators. Further studies are needed to see if similar ancestral plasticity occurs in other species, including endangered mammals and birds.  

“Island species inhabit relatively small geographic ranges so they are disproportionately threatened by decline or extinction, and predation by exotic species is often the driving force,” Li said. “Being able to train them to respond more strongly to predation would bolster their odds of survival.”

Interestingly, while Li’s research showed that wall lizards could be trained to regain some ancestral defense responses, it also revealed the speed with which they could lose defenses when predation risks dropped. Lizards from the near-shore islet of Mando, which was separated from Naxos and its feral cats by a storm in 2006, exhibited similar flight initiation distances as lizards from the main island but had diminished ability to shed their tails as an escape behavior. 

“Shedding a tail is a costly anti-predator response for lizards, because intact tails indicate social status and play important roles in locomotion, courtship, fat storage and defense,” Li explained. “This contrast between anti-predator responses matches predictions from evolutionary theory, which says that in the face of relaxed predation, ‘expensive’ behaviors such as tail-shedding will be lost much sooner than ‘cheap’ behaviors such as longer flight initiation distances.”  

“Although our findings show that cheap anti-predator behaviors can be regained or intensified quickly, it’s still unknown if they can be regained soon enough to defend vulnerable island ecosystems against introductions by new invasive species of predators," Li said. "In other words, on islands where populations of feral cats have not yet been established, keep your cats indoors.”  

Li coauthored the new study with scientists from the University of Michigan (U-M), the University of Athens and Eastern Michigan University. Funding was provided by U-M’s School of Natural Resources and Environment and Rackham Graduate School. Li’s faculty advisor at Duke is Stuart L. Pimm, Doris Duke Professor of Conservation Ecology.


CITATION: “Effects of feral cats on the evolution of anti-predator behaviours in island reptiles: insights from an ancient introduction,” Li Binbin, Anat Belasen, Panayiotis Pafilis, Peter Bednekoff, Johannes Foufopoulos. Proceedings of the Royal Society B, June 18, 2014. DOI: http://dx.doi.org/10.1098/rspb.2014.0339.


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