City lizards 'talk' less, run faster
Study finds how the peninsula rock agama has adapted to urbanisation
- Published 23.04.17
New Delhi, April 22: As a six-year-old child, Maria Thaker chased garden lizards to hold them in her hands, a game she recalls as fun and challenging. That fascination has endured over the years and now drawn her into discovering how India's cities are changing lizard behaviour.
Thaker, now an ecologist at the Indian Institute of Science (IISc), Bangalore, and her students have found that city lizards appear less afraid of humans, can escape potential predators faster, and yet are slower when "talking" to each other than rural lizards.
Their findings provide fresh insights into how urbanisation and persistent human presence may be changing the behaviour and traits of lizards which occupy a critical position in the food chain, eating myriad insects and being eaten by eagles, hawks and kites.
"We're seeing how some lizards are changing to coexist with humans in urban environments," said Thaker, an assistant professor at the IISc Centre for Ecological Sciences. "Usually, when humans alter environments, wildlife disappears, but these lizards seem to cope, and adapt."
But their research, focused on the colour-changing, chameleon-like lizard called the peninsula rock agama, has also suggested that urbanisation may be altering the lizards' capacity for communicating between themselves - whether for courtship or to display aggression.
The long, slender rock agama communicates with its own through changes in the colour of its back and sides. A male courting a female will feature a bright red back and black sides, while a male wishing to show aggression to another male will display a bright yellow back and orange sides.
Thaker and her students Anuradha Batabyal and Shashank Balakrishna set up laboratory experiments placing city and rural agamas in situations of courtship and aggression and observed the urban male lizards were slower to change colour and displayed duller, paler colours compared to rural lizards.
The scientists speculate that the changes in communication may be the result of habitat fragmentation in urban areas.
In cities, lizards are likely to find themselves clustered with many of their own species in fragmented habitats. The resulting higher population density of lizards within restricted spaces in urban areas, compared to larger rural spaces, might be habituating males to repeated close-range interactions, thus lowering their sensitivity to communication, the researchers have suggested.
Their findings have been accepted for publication in the research journals Animal Behaviour and Behavioral Ecology and Sociobiology.
Thaker, who was born and grew up in Singapore, recalls running after lizards in her neighbourhood and public parks, an interest that, she says, convinced her parents and friends she'd steer herself towards a career in wildlife science even before she did.
India's diversity of lizards, she says, was among factors that prompted her to take up an academic position in Bangalore. "New lizard species are being described every other year and their ecology and behaviour remain completely unstudied," she said.
The field observations during which the researchers walked towards lizards in open urban spaces and measured how quickly they ran away suggest urban lizards have become habituated to people and do not view them as predators - even after a few encounters. Urban lizards allow humans to get much closer to them than rural lizards.
"Such studies tell us how adaptive and flexible some species can be," Thaker said. "We think the charismatic rock agamas here will coexist with humans for many generations - with a little help to maintain some of the rocky habitats and insects that they need."
Conservation biologists view such studies as part of broader efforts to understand how species react to stress, whether from forest loss or urban growth or climate change.
"Such behavioural studies are very important, but there has been a lack of such studies in India," said Sathyabhama Das Biju, professor and amphibian biologist at the University of Delhi who was not associated with the IISc research.
Most studies on how human-driven changes might impact animals have focused on population declines resulting from changes in habitat. "But it is also important to understand how species change at a behavioural level," Biju said. "Such knowledge can help guide conservation policies."