Chapter 53: Behaviour and Behavioural Ecology
53.1. What Questions Do Biologists Ask About Behaviour?
• Ethology: the study of animal behaviour from an evolutionary perspective
• For many animals, much of their behaviour is like the web-spinning behaviour
of spiders –unlearned and highly stereotypic.
• Stereotypic behaviour is often species-specific – most individual of a given
species perform the behaviour in the same way.
53.2 How Do Genes and Environment Interact to Shape Behaviour?
• Genes do not encode behaviours, rather affect behaviour by setting motion a
series of gene-environment interactions that underlie the development of
proximate mechanisms that enable certain behavioural responses.
Experiments can distinguish between genetic and environmental
influences on behaviour
• Deprivation experiment: rear young animal so it is deprived of all experiences
relevant to the behaviour understudy. If it still exhibits the behaviour, we may
assume that the behaviour can develop without opportunities to learn it.
• Genetic experiment: investigators alter the genomes of organisms by
interbreeding closely related species, by comparing individuals that differ in
only one or a few genes or by knocking out or inserting specific genes to
determine how these manipulations affect their behaviour.
Genetic control of behaviour is adaptive under many conditions
• Individuals might fail to acquire the appropriate behaviour, or acquire the
appropriate behaviour, or acquire inappropriate behaviour, if genes did not
exert strong influences on the development of the behaviour.
• Inherited behaviour is also adaptive when mistakes are costly or dangerous.
• Inheritance of behaviour patterns used to avoid predators or capture
dangerous prey is obviously adaptive; allow no room for mistakes.
• Releaser—an object, event, or condition required to elicit behaviour.
Imprinting takes place at a specific point in development
• Some types of learning take place only at a specific time in animal’s
development critical period.
• Imprinting –animal learns a set of stimuli during a limited critical period
(e.g. behaviour learned by imprinting is the recognition of offspring by their
parents and of parents by their offspring).
• Individual recognition must often be learned quickly; opportunity to do so
may arise only once.
• Imprinting requires only a brief exposure, but its effects are strong and can
last a long time.
• The critical period for imprinting may be determined by a brief development
of hormonal state.
Hormones influence behaviour at genetically determined times
• In multicellular organisms, all behaviour depends on the nervous system for
initiation, coordination, and execution.
• Hormones of the endocrine system determine when a particular behaviour is
performed, as well as when certain behaviours can be learned.
53.3 How Do Behavioural Responses to the Environment Influence Fitness? Choosing where to live influences survival and reproductive success
• Environment in which an organism lives is called its habitats.
• Cues most organisms use to select suitable habitats have a common feature:
they are good predictors of conditions suitable for future survival and
• Visual information can also provide useful cues about the quality of a habitat.
Many animals use the presence of already settled individuals as an indication
that the habitat may be good.
• Some highly social animals actually “vote” on the quality of habitats.
Defending a territory has benefits and costs
• When high-quality habitats are in limited supply, animals may compete for
access to them.
• An animal may improve its fitness by establishing exclusive use of its chosen
• Most common way is by establishing a territory from which in excludes
conspecifics (same species) and sometimes those of other species as well by
advertising that it owns the area or by chasing others away; but this takes a
lot of energy which could have been used for beneficial purposes.
• Cost-benefit approach assumes that an animal has only a limited amount
of time and energy to devote to its activities. Animals cannot long perform
behaviours whose total costs are greater than the sum of their benefits.
• The benefits of behaviour are the improvements in survival and reproductive
success. The total cost of any behaviour typically has three components:
o Energetic cost: difference between the energy the animal would have
expended had it rested and the energy expended in performing the
o Risk cost: increased chance of being injured or killed as a result of
performing the behaviour, compared w/resting.
o Opportunity cost: sum of the benefits the animal forfeits by not being
able to perform other behaviours during the same time interval.
Animals choose what foods to eat
• When an animal forages how much time should it spend searching an area
before moving, to another site? Which foods should it eat or ignore?
• Foraging theory helps us understand the survival value of feeding choices.
The primary benefits are the nutritional value. The costs of foraging are
similar to those for territorial defense: energy expended, time lost for other
activities that could enhance fitness, and the risk of increased exposure to
• If most valuable food type is abundant enough an animal gains the most
energy per unit of time spent foraging by taking only the most valuable type
and ignoring all others. As the abundance of the most valuable type
decreases, an animal adds less valuable types to its diet to maintain its
optimum energy yield.
• Some animals incur large energetic costs and the risks of traveling great
distances to obtain essential minerals.
• Animals may ingest some foods for reasons other than the energy or
nutrients they provide.
An animal’s choice of associates influences its fitness • Important decision made by individuals of all sexually reproducing species is
the choice of mating partners. May be based on the inherent qualities of a
potential mate, on the resources it controls, or on combinations of the two.
• Males of most species initiate courtship, seldom reject receptive females and
often fight for opportunities to mate with females; females seldom fight over
males and often reject courting males. Why?
• Sperm are small and cheap to produce, on male produces enough to father a
very large number of offspring and can improve their reproductive success by
mating with many females.
• Eggs are typically much larger and expensive to produce. A female cannot
increase her reproductive output very much by increasing the number of
male mates. The reproductive success of a female may depend on the quality
of genes she receives from her mate, the resources he controls, or the
amount of assistance he provides in the care for offspring.
• Females may cause the evolution of traits that reliably signal male quality
• A male may use courtship behaviour to signal his good capacities as a mate.
• Females can improve their reproductive success if they can correctly assess
the genetic quality and health of potential mates, the quantity of parental
care they may provide, and the quality of the resources they control.
• By paying particular attention to those signals that males cannot fake,
females have favoured the evolution of “reliable signals.”
Responses to the environment must be timed appropriately
• CIRCADIAN RHYTHMS CONTROL THE DAILY CYCLE OF BEHAVIOUR:
o The persistence of daily cycles in the absence of environmental time
cues suggests that animals have an endogenous clock (seldom exactly
24 hours) circadian rhythms.
o When two rhythms completely match, they are in phase, and if a
rhythm is shifted, it is phase-advanced or phase-delayed.
o Since the period of circadian rhythm is not exactly 24 hours, it must be
phase-advanced or phase-delayed to remain in phase with the daily
cycle of the environment; rhythm has to be entrained to the cycle of
light and dark in the animal’s environment.
o Animal kept in constant conditions will not be entrained to the cycle of