Geoscience Reference
In-Depth Information
What Is a Hypothesis?
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Hypotheses must be universal in their application, but the meaning of
univer-
sal
in ecology is far from clear. Not all hypotheses are equal. Some are more
universal than others, and we accept this as one criterion of importance. A
hypothesis of population regulation that applies only to rodents in snowy envi-
ronments may be useful because there are many populations of many species
that live in such environments. But we should all agree that a better hypothe-
sis would explain population regulation in all small rodents in all environ-
ments. And a hypothesis that applies to all mammals would be even better.
Hypotheses predict what we will observe in a particular ecological setting,
but to move from the general hypothesis to a particular prediction we must
add background assumptions and initial conditions. Hypotheses that make
many predictions are better than hypotheses that make fewer predictions.
Popper (1963) emphasized the importance of the falsifiability of a hypothesis,
and asked us to evaluate our ecological hypotheses by asking “What does this
hypothesis forbid?” Ecologists largely ignore this advice. Try to find in your
favorite literature a list of predictions for any hypothesis and a list of the obser-
vations it forbids.
Recommendation 1: Articulate a clear hypothesis and its predictions.
If we test a hypothesis by comparing our observations with a set of predictions,
what do we conclude when it fails the test? There is no topic on which ecolo-
gists disagree more. Failure to observe what was predicted may have four causes:
the hypothesis is wrong, one or more of the background assumptions or initial
conditions were not satisfied, we did not measure things correctly, or the
hypothesis is correct but only for a limited range of conditions. All of these rea-
sons have been invoked in past ecological arguments, and one good example is
the testing of the predictions of the theory of island biogeography (MacArthur
and Wilson 1967; Williamson 1989; Shrader-Frechette and McCoy 1993).
A practical illustration of this problem is found in the history of wolf con-
trol as a management tool in northern North America. The hypothesis is usu-
ally stated that wolf control will permit populations of moose and caribou to
increase (Gasaway et al. 1992). The background assumptions are seldom
clearly stated: that wolves are reduced to well below 50 percent of their origi-
nal numbers, that the area of wolf control is large relative to wolf dispersal dis-
tances, that a sufficient time period (3-5 years) is allowed, and that the
