BIOL 4P58 Lecture Notes - Endocrine System, Natural Selection, Circadian Clock
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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?
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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:
oEnergetic cost: difference between the energy the animal would have
expended had it rested and the energy expended in performing the
oRisk cost: increased chance of being injured or killed as a result of
performing the behaviour, compared w/resting.
oOpportunity 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
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