Biology Reference
In-Depth Information
CHAPTER 2
Testing
Hypotheses
in Behavioural
Ecology
Photo © Susana Carvalho
A rigorous scientific approach to the function of behaviour involves four stages:
observations, hypotheses, predictions and tests. The first two, observation and
hypotheses, often go hand in hand. It may take some time getting to know a particular
species before it is possible to ask good questions about its behaviour and ecology. Niko
Tinbergen's work on gulls was the result of many years' painstaking observations of
their behaviour in the wild. Having observed some aspect of behaviour that we do not
understand, how should we proceed?
Let us assume, for example, that we want to discover why our animal lives in a group
as opposed to on its own. We may get a strong hint about the function of this simply
from observation. For example, if the animal only lived in a group in the breeding season
we might suspect that it gained some advantage in terms of increased reproductive
success, whereas if it only lived in a group in winter we may suspect some advantage
concerned with improved adult survival through feeding efficiency or avoiding
predation. We can test our ideas in three main ways:
(1)
Comparison between individuals within a species
. Individuals in groups may have
greater success at feeding or avoiding predators than solitary individuals.
Furthermore, success may vary with group size. The problem, however, is that there
may be confounding variables: solitary individuals may be poorer competitors and
this, rather than their solitary existence per se, may explain their lower success, or
individuals in groups may live in better quality habitats, and so on.
(2)
Experiments
. It is often better, therefore, to perform an experiment. With an
experiment we can vary one factor at a time; for example, we could change group
size and see how this influenced success under a particular set of conditions. Niko
Tinbergen pioneered the method of elegant field experimentation to answer
Three methods of
hypothesis testing
