A study of populations of tiny water fleas is helping ecologists to
understand population dynamics, which may lead to predictions about the
ecological consequences of environmental change.
The study is published in October 29 in the journal Nature. The water
flea, called Daphnia, plays a key role in the food web of many lakes.
Co-author Roger Nisbet, an ecologist based at the University of
California, Santa Barbara, explained that a few animal populations,
notably some insects, show huge "boom and bust" cycles. The populations
alternate between periods of explosive growth when food is plentiful,
followed by crashes when food is replaced too slowly to support the
resulting large population.
This behavior is well understood by ecologists, and has been
described by many simple mathematical models. However, most animal
populations don’t behave in this extreme way. "A key question is why,"
To answer the question, Nisbet and his two Canadian co-authors took a
three-pronged approach that required synthesizing evidence from field
observations, experiments, and mathematical models. The theoretical
foundation for this latest study was a mathematical theory developed
several years ago by Nisbet and collaborators.
The new insight came by using this theory to help interpret the
results of experiments by first author Edward McCauley, an ecologist at
the University of Calgary.
McCauley was able to study the performance of individual water fleas
within lab populations. Some of these were executing boom and bust
cycles; others were not. This second group of populations exhibited
what the investigators called "small amplitude" cycles.
A key prediction of the theory, worked out through some innovative
mathematical work by Bill Nelson, co-author from Queens University in
Ontario, was that in the small amplitude cycles, individual animals
would take much longer to develop to reproductive maturity. This was
confirmed by the new experiments.
"More broadly, the work illustrates that ecologists at UCSB and
elsewhere are getting a deeper understanding of how the physiological
response of organisms to a changing environment –– food availability, in
these experiments –– is eventually expressed as population change,"
The researchers hope that the processes involved are general, and
that the improved understanding of population dynamics will improve
their ability to predict the ecological consequences of environmental