Evidence that Evolution Impacts Ecology
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| A male and female guppy in a natural stream in Trinidad, site of the recent study. Courtesy of Paul Bentzen |
Biologists have long known that ecology, the interaction between organisms and their environment, plays a significant role in forming new species and in modifying living ones. The traditional view is that ecology shapes evolution. The environment defines a template for the process of evolution: natural selection shapes organisms to fit that template. Some studies suggest, however, that evolutionary processes reciprocate by influencing ecology.
Now, biologists present evidence that ecology and evolution are indeed reciprocally interacting processes, a fundamental shift in scientists’ understanding of the relationship between evolution and ecology. The results appear in the online early edition of the journal Proceedings of the National Academy of Sciences (PNAS).
“By documenting that rapid, adaptive evolution within single species can cause substantial changes in ecosystem structure and function, this study makes a significant contribution to merging ecological and evolutionary theory,” said Alan Tessier, program director in the National Science Foundation (NSF)’s Division of Environmental Biology, which funded the research.
NSF supported the research as part of a five-year, multi-investigator grant funded by the Frontiers in Integrative Biological Research (FIBR) initiative.
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| An artificial stream in which biologists studied the relationship between ecology and evolution. Courtesy of Ron Bassar |
“Our results represent a first significant step in showing that evolution cannot be ignored when studying ecological interactions,” said David Reznick, an evolutionary biologist at the University of California at Riverside (UCR), who led the study.
In earlier work, Reznick demonstrated that guppies, the study organism, can evolve very rapidly. In this new study, he and collaborators quantify the ecological consequences of such rapid adaptation. The scientists compared guppies — small freshwater fish that have been the subject of long-term studies — adapted to two different stream communities in Trinidad. One stream community had a diverse group of fish species, some of which were predators on guppies. The other stream community included guppies and one or a few non-predatory species.
In the experiments, the researchers collected guppies from the two different communities and quantified their impact on a stream ecosystem by placing them in replicate, artificial streams built alongside a natural stream. The researchers chose the locations of the artificial streams so they could divert water from a spring that flowed into the nearby natural stream. The diverted spring water first flowed through the artificial research streams, then emptied back into the natural stream.
Next, the biologists seeded the artificial streams with organisms, such as insect larvae, from the natural stream. The artificial streams had similar ecosystems at the start of the experiment.
They found that guppies from the two types of fish communities had substantially different impacts — after only four weeks — on the structure and function of their ecosystems.
“Guppies from the more diverse fish communities ate more insect larvae, while the low-predation guppies — guppies from the simple fish communities — ate more algae,” said scientist Ronald Bassar of UCR, the first author of the PNAS paper.
“These differences in diet resulted in the artificial streams with guppies from diverse communities having more algae and fewer invertebrates than streams stocked with guppies from the simple communities.”
There also were corresponding differences in how and at what rate nutrients, like nitrogen and phosphorus, were recycled. The streams with high-predation guppies — guppies from the more diverse fish communities — had less plant production and oxygen consumption, a slower breakdown of leaves that had fallen into the water, and a slower accumulation of the resulting detritus.
The researchers’ findings mirrored their observations in guppies across natural streams in Trinidad.
“By doing our experiments in artificial streams, we are able to pin down guppies as a likely cause of what we see in natural streams,” Bassar said.
“The experiments show that local adaptation causes the evolution of differences in diet, which, in turn, causes differences in ecosystem structure. Our next step is to characterize how this changed ecosystem, in turn, shapes how the guppies adapt to it.”
Bassar and Reznick were joined in the study by several biologists, including Michael Marshal and Cathy Pringle from the University of Georgia; Eugenia Zandonà of Drexel University; Douglas Fraser from Siena College; Joseph Travis from Florida State University; Alexander Flecker from Cornell University; and Steven Thomas from the University of Nebraska. The team also included Sonya Auer and Andrés López-Sepulcre of UCR.
