The Other Side of the Story: How Evolution Affects the Environment

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A new study by researchers at the University of Rhode Island shows some of the best evidence yet for a feedback loop phenomenon in which species evolution drives ecological change. Credit: Kolbe Labs/University of Rhode Island

The story of the peppered moths is a textbook evolutionary tale. As coal smoke darkened the bark of trees near English cities during the Industrial Revolution, the white-bodied peppered moths became obvious targets for predators and their numbers declined rapidly. Meanwhile, black-bodied moths, which had been rare, thrived and became dominant in their newly darkened environment.

Peppered moths have become a classic example of how environmental change drives the evolution of species. But in recent years, scientists have begun to think about the reverse process. Could there be a feedback loop where species evolution drives ecological change? Now, a new study by researchers at the University of Rhode Island shows some of the best evidence for this phenomenon.

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In a research published in Proceedings of the National Academy of Sciences, researchers show that an evolutionary change in lizard leg length can have a significant impact on vegetation growth and spider populations on small islands in the Bahamas. This is one of the first times, say the researchers, that such dramatic effects on environmental evolution have been documented in a natural setting.

“The idea here is that, in addition to the environment shaping the traits of organisms through evolution, those trait changes should fuel and drive changes in predator-prey relationships and other ecological interactions between species,” Jason said. Kolbe, professor of biological sciences. sciences at the University of Rhode Island and one of the study’s senior authors. “And we really need to understand how these dynamics work so that we can make predictions about how populations will persist and what kind of ecological changes might result.”

For the past 20 years, Kolbe and his colleagues have observed the evolutionary dynamics of anole lizard populations on a chain of tiny islands in the Bahamas. The chain is made up of about 40 islands ranging from a few dozen to a few hundred meters in an area small enough for researchers to keep an eye out for the lizards that live there. And the islands are far enough apart that lizards can’t easily hop from island to island, so distinct populations can be isolated from one another.

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Previous research has shown that brown anoles adapt quickly to the characteristics of the surrounding vegetation. In habitats where the diameter of brush and tree branches is smaller, natural selection favors lizards with shorter legs, which allow individuals to move more quickly when evading predators or looking for a snack. Conversely, slender lizards tend to fare better where trees and plant limbs are thicker. Researchers have shown that this limb length trait can rapidly evolve into brown anolesin within a few generations.

For this new study, Kolbe and his team wanted to see how this evolved limb length trait might affect the ecosystems of tiny islands in the Bahamas. The idea was to separate short- and long-legged lizards on their islands, then look for differences in how lizard populations affect the ecology of their islands.

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Male brown anole lizard. Credit: Oriol Lapiedra

Armed with specialized gearpole fighting lizards with tiny strings made of dental floss at the end, the team captured hundreds of brown anoles. They then measured the length of each lizard’s legs, keeping those whose limbs were particularly long or particularly short, and returning the rest to the wild. Once they had distinct populations of short and long lizards, they released each population onto islands that previously had no lizards living on them.

Since the experimental islands were mostly covered by vegetation of smaller diameters, the researchers expected that the short-legged lizards would be better adapted to that environment, i.e. more maneuverable and more capable of catching prey in trees and scrub. . The question the researchers wanted to answer was whether the ecological effects of those highly effective hunters could be detected.

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After eight months, the researchers resurveyed the islands to look for ecological differences between the islands populated by the short- and long-legged groups. The differences, it turned out, were substantial. On islands with shorter-legged lizards, populations of web spiders, a key prey item for brown anoles, were reduced by 41 percent compared to islands with lanky lizards. There were significant differences in plant growth as well. Because the short-legged lizards were better at preying on herbivorous insects, the plants flourished. On islands with short-legged lizards, buttonwood trees had twice as much shoot growth as trees on islands with long-legged lizards, the researchers found.

The findings, Kolbe says, help bring the interaction between ecology and evolution full circle.

“These findings help us close that feedback loop,” Kolbe said. “We knew from previous research that ecological factors shape limb length, and now we show the reciprocal relationship of that evolutionary change on the environment.”

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Understanding the full extent of the interactions between evolution and ecology will be helpful in predicting environmental outcomes, say the researchers, particularly as human activities accelerate the pace of both evolutionary and ecological change around the world.

More information:
Kolbe, Jason J. et al, Experimental simulation of the evolution-ecology connection: Divergent predator landforms alter natural food webs, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2221691120

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About the magazine:
Proceedings of the National Academy of Sciences

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