Biologists have known for long 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 and the
process of evolution by natural selection shapes organisms to fit that
Some specialized theory, a few laboratory experiments and studies of
natural populations suggest, however, that evolutionary processes
reciprocate by influencing ecology in turn.
Now a team of biologists presents evidence that ecology and evolution
are indeed reciprocally interacting processes, presenting a fundamental
shift in our understanding of the relationship between evolution and
"Ecology for the most part ignores evolution because organisms are
treated as constants," said David Reznick, an evolutionary biologist at
the University of California, Riverside, who led the study. "This does
not mean that ecologists don’t believe in evolution. It means the
general assumption is that ecological interactions happen on such a
short time scale in comparison to evolution that evolution can be
ignored — similar to the way physicists can often safely ignore
relativity in the majority of their experiments.
"Our results represent a first significant step in showing that
evolution cannot be ignored when studying ecological interactions. In
earlier work, we had shown that guppies, our study organism, can evolve
very rapidly. In this new study we quantify the ecological consequences
of such rapid adaptation."
Study results appear this week in the online early edition of the Proceedings
of the National Academy of Sciences.
Reznick’s team compared guppies — small freshwater fish that have
been the subject of long-term studies — that had adapted to two
different types of stream communities in Trinidad. One stream community
had a diverse group of fish species, some of which were serious
predators on guppies. The other type of community included guppies and
just one or a few non-predatory species.
Previously, Reznick and colleagues had established that predators
cause a substantial increase in guppy mortality rates, resulting in
guppies that are younger at maturity, produce more babies, and display
different behavior, escape abilities and body shapes.
In the new experiments, the researchers collected guppies from the
two different types of communities, and quantified their impact on the
stream ecosystem by placing them in replicate, artificial streams built
alongside a natural stream. The researchers chose this location for the
artificial streams so that they could divert water from a spring that
normally flowed into the stream in such a way that it first flowed
through the artificial streams, emptying later into the natural stream.
Next, they seeded the artificial streams with organisms such as
insect larvae from the natural stream so that all 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 Ronald Bassar, a graduate student
in Reznick’s lab and the first author of the research paper. "These
differences in diet resulted in the artificial streams with guppies from
the diverse communities having substantially more algae and fewer
invertebrates than streams stocked with guppies from the simple
"There were corresponding differences in how and at what rate
nutrients, like nitrogen or 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
detritus, the breakdown product of leaves."
The researchers found, too, that their findings from their
experiments in the artificial streams mirrored their observations in
guppies across natural stream communities in Trinidad.
"By doing our experiments in the artificial streams we are able to
pin down guppies as a likely cause of what we see in the 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."
The National Science Foundation supported this research as part of a
five year, multi-investigator grant funded by the Frontiers in
Integrative Biological Research initiative.
Source : University
of California – Riverside