Biology Reference
In-Depth Information
Observation
Causal explanations
Functional explanations
Table 1.1
Summary of
causal and
functional
explanations for
two aspects of
reproductive
behaviour in lions
(Bertram, 1975;
Packer and Pusey,
1983a, 1983b).
1 Females are
synchronous in
oestrus
Chemical cues?
Take-overs by males
Better cub survival
Young males survive better
and have greater
reproductive success when
they leave pride if in a group
2 Young die when
new males take
over pride
Abortion
Females come into oestrus
more quickly
Male removes older cubs
which would compete with
his young
Take-over males kill or
evict young
The differences between the causal and functional explanations of these two aspects
of reproductive behaviour in the lions are summarized in Table 1.1. The key point is that
causal explanations are concerned with mechanisms, while functional explanations
are concerned with why these particular mechanisms (rather than others) have been
favoured by natural selection.
Causal and
functional
explanations of
lion behaviour
Natural selection
The aim of behavioural ecology is to try and understand how an animal's behaviour is
adapted to the environment in which it lives. When we discuss adaptations we are
referring to changes brought about during evolution by the process of natural selection.
For Charles Darwin, adaptation was an obvious fact. It was obvious to him that eyes were
well designed for vision, legs for running, wings for flying and so on. What he attempted
to explain was how adaptation could have arisen without a creator or, put another way,
how you could get the appearance of design without a designer. His theory of natural
selection, published in the
Origin of Species
(Darwin, 1859), can be summarized as
follows:
(1)
Individuals within a species differ in their morphology, physiology and behaviour
(
variation
).
(2)
Some of this variation is
heritable
; on average offspring tend to resemble their parents
more than other individuals in the population.
(3)
Organisms have a huge capacity for increase in numbers; they produce far more
offspring than give rise to breeding individuals. This capacity is not realized because
the number of individuals within a population tends to remain more or less constant
over time. Therefore, there must be
competition
between individuals for scarce
resources, such as food, mates and places to live.
(4)
As a result of this competition, some variants will leave more offspring than others.
These will be those that are best at competing for the scarce resources. Their offspring
Heritable
variation with
competition for
survival and
reproduction
