Stories from the lab
Lizard Island: watching evolution happen in Miami
Since 2015, twice a year, we have caught every lizard on one small island in Miami, to measure how natural selection acts on a whole community of species in real time.
Lizard Island is small, about 6,000 square meters of trees and lawn inside Fairchild Tropical Botanic Garden in Miami, a little smaller than a soccer pitch. At any given time it holds between 800 and 1,000 anole lizards. Since the fall of 2015 we have tried to catch every one of them, every spring (May and June) and every fall (October and November), with a forced break during COVID.
Each lizard is measured and marked with tiny fluorescent tags, 3 mm long, placed in both hind legs, then released. When we come back six months later, the lizards we catch again have survived; the ones that are gone, mostly, have not. Survival is a simple but robust measure of fitness, and tracking it for every individual lets us see which body shapes are favored, season by season, in each species.
Why an island in a botanic garden?
Long-term studies of natural selection in the wild are rare, and studies that follow a whole community of species are rarer still: 163 of 168 published studies of selection in the wild have focused on a single species. The most famous exception is Peter and Rosemary Grant's 40-year study of Darwin's finches on Daphne Major in the Galápagos, and Lizard Island is our attempt at a lizard equivalent.
The island's community was originally four species, each specialized for a different part of the habitat: the Cuban brown anole near the ground, the Hispaniolan bark anole on tree trunks, and two canopy species, the native green anole and the Cuban knight anole. Because they share one small island, the same season's weather, food and predators act on all of them at once.
Species that change and stay the same
Many species look much the same for millions of years. The textbook explanation is stabilizing selection, which favors the average form and weeds out the extremes, yet field studies almost never detect it. Biologists call this the “paradox of stasis.” One of our first major results from Lizard Island, published in PNAS in 2023 and based on 1,692 lizards, offers a way out. Selection on brown anoles swung from stabilizing in the winter of 2015 to directional in the winter of 2016 and back to stabilizing in 2017, with quiet periods of little or no selection in between. Added up over many seasons, these shifting pressures keep each species near its own peak on a shared “fitness landscape,” with valleys between the peaks that keep the species distinct. The species stay put not because selection is constant, but because it keeps changing.
A newcomer arrives
In late 2017 a fifth species turned up: the Puerto Rican crested anole, an ecological near-twin of the brown anole. We had two years of data from before its arrival, which made what came next a rare natural experiment. Within four years brown anoles fell from 75% of adult anoles on the island to 18%, and adult males from 168 to 54, while crested anoles rose to 66%. Selection on brown anoles shifted to favor relatively longer hind limbs, matching the difference we see between brown anoles that live with and without crested anoles across Miami. The result, published in Nature Communications in 2024, is direct evidence of natural selection driving character displacement in the wild.
Every branch on the island
Anoles are built for the perches they use, so we measure the habitat as carefully as the lizards. Annual terrestrial LiDAR scans now map the island's structure so completely that we know the position and size of every branch, and we are building machine-learning tools to measure lizard X-rays and toepad scans automatically. In 2025 the study was recognized with a Maxwell/Hanrahan Award in Field Biology, and the next phase, asking how behavior shapes natural selection, is funded by a Packard Fellowship in Science and Engineering.
In the news
- The Washington Post What the secret lives of lizards tell us about evolution
- Scientific American 'Living Fossil' Lizards Are Constantly Evolving: You Just Can't See It
- Quanta Magazine Evolution: Fast or Slow? Lizards Help Resolve a Paradox.
- Atlas Obscura Cracking Open Evolution's Black Box on 'Lizard Island'
- South Florida Sun Sentinel The Lizard Wars of South Florida Help Reveal How Evolution Works
- South Florida Sun Sentinel How South Florida Lizards Are Reshaping Darwin's Theory of Evolution
- The Conversation Amid a tropical paradise known as 'Lizard Island,' researchers are cracking open evolution's black box
- Phys.org Scientists witness evolution in action when two lizard species meet for the first time
Read the research
- Fluctuating selection maintains distinct species phenotypes in an ecological community in the wild. Proceedings of the National Academy of Sciences (2023)
- Observing character displacement from process to pattern in a novel vertebrate community. Nature Communications (2024)
- Long-term studies provide unique insights into evolution. Nature (2025)
- What the secret lives of lizards tell us about evolution. The Washington Post (2025)
- Amid a tropical paradise known as 'Lizard Island,' researchers are cracking open evolution's black box. The Conversation (2025)
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