How the lizards evolved
A new research has confirmed that competition, and not predation, is the primary selective force in island lizards.
London: A new research has confirmed that competition, and not predation, is the primary selective force in island lizards.
In one of its kind ecological field experiment, entire islands in the Bahamas were wrapped with netting, snakes introduced to two other islands and the fitness of hundreds of lizards was measured using treadmills.
The research has resolved a long-standing question about the evolution of lizards.
As part of their research, Ryan Calsbeek and Robert Cox of Dartmouth College in Hanover, New Hampshire, excluded predators from two small, uninhabited islands in the Bahamas by wrapping the islands – about 1000 square metres each – with netting to keep out predatory birds. Meanwhile, they enhanced predation on two other islands by introducing lizard-eating snakes.
Also, they seeded one of each pair of islands with high densities of Anolis sagrei lizards, and the other with lower densities of the animals.
Before release, they marked and measured each one and tested its stamina by running it to exhaustion on a treadmill.
"Your Lance Armstrong lizards can run about 7 minutes. Your overweight field-biologist lizard runs for about 2 minutes. We spent several hours a day just running the animals, and we did that day in and day out for several weeks," New Scientist quoted Calsbeek, as saying.
After a period of four months, the experts returned to the island and recaptured every remaining lizard.
Larger, longer-legged and higher-stamina lizards had survived better than smaller, wimpier ones on higher-density islands where competition was more intense, they found.
However, these traits did not affect the chance of survival in the face of predation. This supports the idea that competition, and not predation, is the primary selective force in these island lizards, says Calsbeek.
David Reznick, an evolutionary biologist at the University of California, Riverside, said: "To me, that``s surprising. I would have thought that predation would matter."
The study has been published in the Journal Nature. (ANI)