Evolution makes the world less ragged

How does evolution impact ecological patterns? It helps smooth out the rough edges, says UConn Ecology and Evolutionary Biology Professor Mark Urban. Urban led an international team of researchers through a review of the history of ecological and evolutionary research to establish a framework to better understand evolution's impact on ecosystem patterns. The research is published as a perspective in the Proceeding of the National Academy of Sciences.

Urban says the project started years ago in the course of his field research when he encountered a trend that he had trouble explaining.

"Ever since I was a grad student I've been thinking about how evolution across landscapes happens, and then how it affects the ecology of those systems. At some point I was struggling to describe a pattern that I was seeing in the amphibian system I work in," he says.

Urban explains that historically, ecologists and evolutionary biologists have worked fairly isolated from one another. The reason is due to assumptions that evolution happens over time periods and distances that have little immediate impact on ecological systems. Ecologists and evolutionary biologists go to their own academic meetings and conferences and publish in their own journals, says Urban, and as a result, members of the fields rarely collaborate. However, Urban suspected the explanation for the puzzling pattern he was seeing relied on a merging of the disciplines.

Urban partnered with colleagues from across the globe, calling on experts from evolutionary biology and ecology, to tackle the question. The project involved an extensive review of the literature, a process that Urban says at times felt unending, yet quite fun. The process was also exciting because early on, the researchers began to notice patterns supporting their hypothesis that local adaptation alters spatial patterns.

Sean Giery, co-author and a former UConn post-doctoral researcher who's now an Eberly Research Fellow at Pennsylvania State University says, "Finding new evidence in old scientific papers was always rewarding. And collectively, these efforts show that the effects of evolution on how much communities and ecosystems vary across landscapes simply can't be overlooked."

The impetus for the undertaking, Urban says, came from a familiar figure: the salamander.

Salamander populations adapt to predators via different strategies -- from changes in body shape and size to the types and quantities of foods that they eat, which suggests a connection between evolution and ecology.

"In particular, I got excited by the evolution of foraging traits, because that could have a clear ecological impact," Urban says.

For example, Urban found that salamanders evolve to forage more in a pond with limited resources, and as a result they amplify the original ecological pattern of low resources by eating more of the already limited resources. In other cases, local adaptation of other traits dampens existing spatial patterns. Urban next turned to the existing literature to find out how general these patterns were, not just in salamanders, but in everything from bacteria to birds.

Based on a review of 500 studies, the authors found evolutionary adaptations at the local level can amplify, dampen, or even create new ecological patterns across landscapes. They identified 14 different mechanisms that affect the direction of evolution's impact, but overall the researchers found that evolution tended to dampen or smooth out variations.

"Evolution clearly plays an important role at these large scales, especially by reducing the effects of abiotic factors and biotic interactions that can limit the abundance and distribution of species. By dampening the impacts of these effects, evolution tends to reduce ecological heterogeneity across space," says Giery.

Adds Urban: "Our exhaustive review indicated that evolution usually dampens ecological spatial patterns, characterizing 85% of studies. Consequently, we do not observe the true spatial heterogeneity of nature because evolution has smoothed it out and hidden its rough edges. Evolution makes the world less ragged, which to me is a pretty cool take-home message."

An example of the smoothing can be seen again with salamanders, says Urban: "The salamanders that ate more also tended to dampen out the effect of the predator on the overall diversity of species across ponds. The prey salamander was eating different species than the predator, so in the end evolution actually maintains similar diversities of species across ponds even though, ecologically, the predator strongly decreases diversity."

Urban says these spatial patterns can be seen everywhere: "The interesting thing to me is that anyone can walk through nature and see these spatial patterns -- maybe different vegetation types. We see all of this spatial variation and we think of it as just being ecological or physical, just part of the environment and that's it. But that environmental spatial variation may be affected by the evolution of the organisms in the environment and that is what we are finding in experiments around world."

Giery says, "I'm pleased to have been a part of this project. And I'm excited to see how our efforts will influence the way people think about the role of evolution in ecological dynamics in space. This seems like one of those rare instances where a relatively simple idea is still transformative. Working on developing this idea has changed how I see and think about natural systems. I imagine our perspective will have the same impact on others."

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