ANSWERS TO REVIEW QUESTIONS – CHAPTER 30
1.
Define the four suggested answers to the question ‘Why do male bowerbirds construct and
decorate bowers?’ as either ultimate or proximate explanations. Explain your reasoning.
(p. 717)
Causation—this is a proximate explanation, because it explains a particular behaviour at a particular
time.
Development—this is a proximate explanation, because it explains a particular behaviour at a particular
time.
Adaptive value—this is an ultimate explanation, because it is concerned with the evolution and
function of the bower-building behaviour.
Evolutionary history—this is an ultimate explanation, because it is concerned with the evolution and
function of the bower-building behaviour.
2.
What evidence is required to demonstrate that a particular behaviour has a genetic basis?
(pp. 717–718)
The text takes the view that all behaviour has a genetic basis and is therefore subject to natural
selection. Some students will be very uncomfortable with this, arguing that it implies a form of genetic
determinism. However, if one accepts the view that the capacity to learn is itself inherited, then it can
be seen that the concept of behaviour having a genetic basis still allows for great variation in animal
behaviour. The text identifies three broad techniques for identifying genetic components in behaviour:
the use of genetic markers, selection experiments and comparisons between geographically separated
populations of the same species. Of these, selection experiments have the greatest potential when a
particular characteristic is chosen for investigation.
3.
How can behaviour that is learned be distinguished from that which has developed? (pp.
718–721)
Learned behaviour is a change in behaviour as a result of experience, whereas behaviour that has
developed is expressed as a result of age, not experience. It can be difficult to decide whether a
particular behaviour is learned or has developed. When complex behaviour is displayed without
any opportunity to learn from others, then the behaviour is clearly developmental.
4.
What kinds of ‘decisions’ are made by foraging animals? Illustrate your answer with
examples. (pp. 721–724)
Foraging behaviour is complex and often requires animals to make decisions. One example is a webspinning spider. It must decide where to locate its web and how long to remain there if it does not catch
prey. If a potential prey strikes the web, the spider must decide whether to attack at once or seek more
information, possibly by plucking the web. If it does move to the prey, it can choose to attack it by
biting it or wrapping it in silk, or to reject the prey as unsuitable by cutting it from the web. If the prey
is attacked, it may need to be subdued by one or multiple bites. Finally, the spider may elect to feed
immediately or to wrap the prey for a later meal. Each decision involves the spider in energy
expenditure, so it must balance the expenditure of energy against the likely energy returns to be
provided by the prey. For example, a small prey may not be worth the energy involved in biting and
storing it, so it may be most economical to cut it from the web and wait for a larger meal.
5.
What are the advantages of foraging in a group? Are all individuals in the group similarly
advantaged? (pp. 724–725)
Foraging in a group confers several advantages in reducing the risk of predation. If an attacking
predator makes only one kill, then risk to one individual is reduced if there are more animals in the
area. When a predator attacks it may be confused if all the animals in a group scatter and run, or the
prey may join forces and mob the predator. Animals in groups may also have a better chance of
detecting a predator, or animals may take turns at feeding and watching for predators. However, not all
animals in a group receive the same advantages. Young, old or unhealthy animals may be forced to the
extremities of herds when danger threatens, so they are more likely to be attacked.
6.
Explain why animal contests are usually resolved before serious injury occurs. (pp. 725–726)
Contests between animals vary in intensity because of the strength or skill of the rivals, the value of the
resource in dispute to each contestant, and which animal currently controls access to the resource. The
winner will gain benefits in terms of access to the resource, but may also incur costs in terms of injury
and the commitment of time and energy to the contest. Such an investment may be worthwhile if the
resource is valuable, but not if the costs exceed the value of the resource. As a result, many animal
contests involve ritual displays so the contestants may assess their relative strengths before deciding
whether it is worth escalating the struggle.
7. Explain the difference between intrasexual and intersexual selection. (pp. 727–729)
Intrasexual selection occurs when individuals of the same sex compete for access to mates, as when
males fight to maintain exclusive access to a group of females. While it is often referred to as male–
male competition, there are cases where females compete with each other for access to males. For
example, female Mormon crickets compete for access to calling males, presumably because of the
nutritional gain from eating the remains of the spermatophore after fertilisation.
Intersexual selection occurs when individuals of one sex choose their mates on the basis of
characteristics of potential partners.
8.
Why is it usually the case that the male courts the female rather than the other way around?
(pp. 727–729)
In general, males are able to service many females, whereas females produce limited numbers of ova
and often make a considerable nutritional investment in them. Thus females are a limiting resource for
male reproductive success and males often compete for access to females. However, females generally
make the greatest investment in the offspring through nutritional investment in the ova and often
through parental care. They are therefore more likely to choose a male to ensure that he contributes
good genes to the substantial maternal investment. Courting males must convince the females of their
genetic quality, perhaps by a display that indicates health and vigour. Alternatively, they provide the
female with a nutritional gift that reflects the quality of their territory or their capacity to provide
(important if the male contributes to rearing the young).
9.
Why do helpers of co-operatively breeding birds remain with the parents rather than
attempt to breed on their own? (pp. 730–735)
There are several different systems of co-operative breeding in birds. The most common form occurs
when young do not disperse from the parental territory, but remain and assist in feeding further batches
of young or protecting them from predators. Thus co-operative breeding involves both delaying
reproduction and assisting in rearing the young of other individuals. Delaying of breeding can occur if
breeding territories are limited and an individual must wait for one to be vacated before it breeds.
While waiting, an individual may gain experience in caring for young by assisting resident birds in
rearing broods. Such assistance may also prevent the helper from being ejected from the territory.
10. Why is the naked mole-rat often referred to as a vertebrate analogue of termites? (pp. 730–
735)
Colonies of social insects centre on a sexually reproductive queen, while non-reproductive individuals
do the work of the colony. In the case of the social hymenopterans, the queen is fertilised before the
colony is established and her consort dies soon afterwards. Non-reproductive females perform the
colony labour. In the case of the termites, a reproductive male remains with the female throughout the
life of the colony and both male and female non-reproductives contribute to colony labour. The naked
mole-rat is closest to the termite organisation, because sexually active males remain with the
reproductive female and non-reproductive individuals of both sexes maintain the colony.