A recent study has shown that an evolutionary change in the length of lizards’ legs can have a significant impact on vegetation growth and spider populations on small islands in the Bahamas. This is one of the first times, the researchers say, that such dramatic evolution-to-environment effects have been observed.
The study, published in the journal Science, involved manipulating the leg length of brown anole lizards (Anolis sagrei) by introducing a predator, the curly-tailed lizard (Leiocephalus carinatus), which prefers to eat long-legged anoles. The researchers found that after six years, the anoles on islands with predators had evolved shorter legs than those on islands without predators.
But the leg length change also had unexpected consequences for the island ecosystems. The short-legged anoles were less efficient at jumping and running, which made them spend more time on the ground and less time on trees. This reduced their consumption of tree-dwelling insects, such as caterpillars, which in turn increased the leaf damage on trees. The increased leaf damage also reduced the amount of leaf litter on the ground, which affected the soil moisture and nutrient levels.
Moreover, the short-legged anoles were more vulnerable to ground-dwelling spiders, which increased their predation pressure and reduced their population size. The reduced anole population also meant less competition for spiders, which allowed them to grow larger and more abundant. The researchers estimated that spider biomass increased by 30% on islands with short-legged anoles compared to islands with long-legged anoles.
The study demonstrates that evolutionary changes in one species can cascade through the food web and alter the structure and function of entire ecosystems. The researchers suggest that such evolution-to-environment effects may be more common than previously thought, especially in isolated habitats with few species and strong interactions.
