Island lizards are evolving – in one year’s time.

Scientific American steps into the fast lane, unexpectedly, on the island of Redonda. People wiped out the local (invasive) populations of rats and goats, and instead of taking centuries for the local lizards to evolve in response to the changes, it took them less than a year:

A year ago when I arrived here by helicopter with researchers Colin Donihue and Anthony Herrel, this small Caribbean island was a moonscape.

Over the course of several months last year officials led the removal of about 50 goats, most flown to Antigua, where they are valued for their supposed ability to survive drought. Conservationists and rock climbers dispensed rat poison in bait stations across the island to clear out the rodents, too.

Today the landscape is covered in green grasses, tree saplings and flowering plants—all able, for the first time in decades, to flourish. The quick recovery was a surprise for us during our return trip in March 2018, but has apparently been an even greater delight for the lizards—they are flourishing. And their bodies seem to be changing in short order.

Of course, the number of lizards has risen sharply now that more plants support more insects for them to eat—and fewer rats are eating them. Last year during several surveys around the island, Herrel counted an average of 67 so-called tree lizards, a species of anole named Anolis nubilis. A year later, almost to the day, the number had jumped to 169.

The number of ground lizards, Pholidoscelis atratus — shiny, jet-black and with incredibly long tails — had likewise risen from 92 to 136.

On three different occasions during our March visit we saw a ground lizard chase down and catch an anole, running off with its prize to devour it elsewhere, like a dog that had grabbed a juicy hunk of meat. We had never seen such behavior before. “There’s a new resource, and they’re just going for it,” Herrel says. “There’s a lot of really high-quality food that wasn’t really available before,” Donihue adds. Now that the rats are gone, the ground lizards may be reclaiming their rightful place at the top of the food web.

It also appears the ground lizards have had shifts in some body measurements—specifically in the length of their forelimbs, which appear to be slightly longer, on average, than they were a year ago. Herrel says there are several possible explanations for such a shift. Longer front legs could help the lizards maneuver better through the returning undergrowth—helpful if they’re chasing down or fleeing from their fellow lizards. So lizards with longer forelimbs might have survived better over the past year. Or lizards hatched in the last year just have more resources, enabling them to grow longer forelimbs. The eradication of rats means the average limb length could be shifting simply because the predatory selective pressure related to rats has been removed, says biologist Yoel Stuart of The University of Texas at Austin who studies rapid evolution in lizards but was not involved in this project.

As trees mature they will shade out grasses and shrubs that have sprung up, and further stabilize the island’s soil and slow its erosion into the sea. And as the anoles return to those trees, Herrel says, he expects to see bigger toe pads and longer forelimbs for holding on to branches, for example.