Living in the environment: behavioural and - SandyBiology1-2

9
Living in the
CHAPTER
● Earth
● Biosphere
● Biome
● Ecosystem
● Community
● Population
● Organisms
● Systems
● Organs
● Tissues
● Cells
● Organelles
● Molecules
● Atoms
environment:
behavioural and
reproductive
adaptations
Chapter 9 Behavioural
and reproductive
adaptations
Key knowledge
Behavioural adaptations: individual and group behaviours of animals, including rhythmic feeding
behaviours; communication; and social and territorial behaviours
● Reproductive adaptations: systems and strategies; development and life cycles
●
Introduction
Wander through the forests of the Dandenong Ranges at dusk, and you might be
surprised to hear the whirr of a camera, or the raucous sound of the kookaburra, or
even the buzzing of a chainsaw. Where have these sounds come from?
Investigation would reveal the court of a lyrebird. The shape of the tail gives the
lyrebird its name, and the sounds it produces, or mimics, are indistinguishable from
the real thing. Why invest so much time and energy in producing a perfect sound?
Making the ‘best’ sounds is showing other lyrebirds that you are the best. The male
that is able to entice the most receptive females into his court is the most successful.
Having the best court, along with the most splendid display, ensures the survival of
the species. The male lyrebird must perform at his best in a prime location.
The male lyrebird is exhibiting a particular kind of behaviour that increases his
chance of reproducing. But like all animals, lyrebirds have other behaviours that help
them to survive from day to day.
In order to survive as an individual and as a species, animals must meet their
requirements; these include the availability of food and water in sufficient quantities
and quality; shelter; protection from predators, and interaction with other members of
the same species.
Members of some species live a solitary
existence, at least for part of their lives.
Polar bears come together only during
the mating season and then only briefly.
Other species, such as termites, cannot
survive alone. Their survival depends on
the collaboration of individuals within the
group; group survival occurs at the cost of
individual survival, except for the female
egg layer – the queen.
Particular kinds of behaviour can
increase the chance of survival of the
individual or the group. The chance of
reproduction can be increased so that new
generations of individuals replace those
that are lost from the population by death
or emigration. These types of behaviour
are referred to as having adaptive value.
bioTERMS
adaptive value
behaviour that increases the
chances of survival of the
individual or the group
Figure 9.1 Male lyrebird displaying
to the female.
271
Differences in behaviour shown by different species are the result of interactions
between their structure, their physiology, their relationship with other living
things and the habitat in which they live. Much behaviour is linked to changes in
environmental conditions. These include rhythmic or cyclic behaviours that exploit
the best conditions at the best times; group and social behaviours that enhance the
survival and reproductive prospects of the individual; and migratory behaviours.
Rhythmic behaviours
bioTERMS
biological clock
an internal mechanism by
which many plants and animals
are able to keep a sense of time
Figure 9.2 The
Ulysses butterfly
determines the timing of its
activities using its biological clock.
The magnificent Ulysses butterfly is one of the species kept at the Butterfly House at
Melbourne Zoo. It settles when the light outside begins to fade during winter months,
despite the use of direct artificial lights within the enclosure. The artificial lighting
extends the time the Butterfly House is open to the public. The butterfly uses its
biological clock to determine the timing of its activities. However, when the insects
settle for the night, they are easy targets for the wandering hands of
little visitors to the zoo.
At any point in a 24-hour period, somewhere
in the world animals are actively searching
for food, sleeping, mating, hibernating, or
looking after young. What determines the
activity an animal undertakes at a particular
time? The common theme throughout this
chapter will be how an animal obtains the
resources needed to best survive. A range of factors is
considered when seeking answers. The environment –
including all biotic and abiotic factors – is vital. So just as
a variety of environments exist, so do a variety of behaviours,
among animals, that best exploit that environment. The active
time of an animal can be at any time in that 24-hour period. It
may be entirely in daylight hours; mostly at night; or at dawn or dusk.
Animal behaviours follow a rhythm or pattern in a specific timeperiod. If this rhythm occurs within a 24-hour period, it is called a circadian or daily
rhythm. Animals isolated from environmental cues, such as the Ulysses butterfly in the
Melbourne Zoo, are still capable of displaying these rhythms.
Circadian rhythms
The activity times of animals throughout the 24-hour period of a day will vary for a
range of reasons. Feeding time is one of the major driving forces. When animals feed
or collect food they are often at their most vulnerable, from either environmental
conditions or predators. Animals tend to be active at times that offer the lowest threat
to their survival.
Animals active during the main part of the day are diurnal; those active at night are
nocturnal, and those active at dawn or dusk, the twilight of each day, are crepuscular.
Each of these creatures will display physiological features that best suit them to these
activity times.
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Chapter 9 Behavioural
and reproductive
adaptations
Diurnal
The numbat (Myremecobius fasciatus) is active during daylight hours, and it spends its
time searching for food. It walks slowly, investigating the ground for termites, digging
and licking up the insects as they emerge, with its extremely long tongue. When active,
and therefore vulnerable to predators, one of the features that help it
survive best is its colouring, which makes it different from other
marsupials of Australia. Its shoulders and general colour are
reddish-brown, with several prominent white bars across
the rump. Given its preferred habitat – sclerophyll forest
and woodland – the coat provides it with camouflage
when out feeding. One behaviour thought to put off
potential predators or curious humans is its staccato
movement, running rapidly across the ground and
then freezing. The numbat nests in the hollows of
fallen branches on the forest floor at night.
Figure 9.3 Numbat foraging in
natural habitat.
Up late!
The desert hopping mouse (Notomys alexis) shelters in large groups, in deep burrows
during the heat of the day. They build elaborate, cool burrow systems that have several
vertical, circular entrance holes. The animals are seen bounding across open plains
on their hind feet, throughout the night. They are omnivorous and enjoy a
diet of seeds, most plant parts and arthropods. Their range takes in arid
areas of central and western Australia where they manage to avoid
extreme heat and desiccation by remaining underground during the
day. As seed-eaters, they are most vulnerable when collecting food
(mainly seeds but may also include some succulents). They feed
in their quiet and cool burrows, out of harm’s way.
Animals active during parts of the night and generally resting
or asleep during the day are nocturnal. These animals live in
areas such as deserts or places that offer extremes in environmental
conditions during daylight hours. Nocturnal animals are active
at night, greatly increasing their chances of survival. This lifestyle,
however, offers its challenges, and many have developed and evolved
characteristics and behaviours that allow them to survive and thrive.
9.4 The desert hopping mouse.
Figure
u detect a prominent survival feat
Can yo
ure?
Up at the crack of dawn!
The largest of the kangaroo species, the red kangaroo (Macropus rufus)
rests throughout the day, gathers in large family groups at dusk where
food is abundant, and feeds on grasses and herbs. Fading light and
increasing light and heat are the challenges faced by these crepuscular
organisms. Therefore, along with well-developed senses, these animals
have particular features that support their lifestyle. Sugar gliders
(Petaurus breviceps) produce a pungent aroma from scent glands
located on the head, on their chest or about the genital opening.
Members of a group are permeated by the scent of the dominant
male and therefore are able to locate each other quite
successfully in fading light. The scent marks
the territories of different groups.
Figure 9.5 The
red kangaroo rests
throughout the day.
273
REVIEW
1 When you fly non-stop from Melbourne to London, your body still remains on Melbourne time for a number of days.
Explain why this is so.
2 Complete the following table:
Activity time and conditions
Definition
Benefits
Features of animals
Diurnal
Nocturnal
Crepuscular
3 Explain the adaptive value of a nocturnal lifestyle.
BIOBOX 9.1
SURVIVING EBB AND FLOW
Vertical height (m)
A tide is the periodic rise and fall of oceanic waters resulting from the gravitational attraction of the Sun and the
Moon on the water and the Earth itself. Within one 24-hour period, there are usually two low tides and two high
tides. The low and high tides alternate on a continuous cycle and are experienced along shorelines. The area along
the shore between which the tide is experienced is the intertidal zone. The high water mark at high tide and the low
water mark at low tide are the boundaries of this zone.
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
rocky ledge
supralittoral
zone
highest tide
level
usual tidal
range
lowest tide range
sublittoral
zone
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intermittent splashing
periwinkles
algae visible in winter
splash zone
sea anenome, starfish, octopus,
brown algae with floats
rock pools
periodic wetting and drying out
algae (leafy green)
periwinkles, limpets, chitons,
rock crabs
wave pounding
kelps (brown algae)
with holdfast,
barnacles, sea squirts
Figure 9.6
Transect profile
of a marine rock
platform.
Chapter 9 Behavioural
and reproductive
adaptations
Interpreting behaviour
The red kangaroo (Macropus rufus) and the African lion (Panthera leo) spend most of
their lives in family groups. The adult males spend some of their time in solitude till
they have founded their own family. Termites, ants and honeybees live in groups of
thousands of related individuals. Emperor penguins and humans live in social groups.
A survey of the animal kingdom exposes a range of social behaviours. For example,
in some species individuals are typically found in groups, in others individuals are
solitary. Given such a variety, how might any type of group or individual behaviour
contribute to the survival of the individual or the species? Biologists often take a
cost–benefit approach in explaining why animals exhibit certain behaviours. That
is, they weigh up the advantages and the disadvantages of the behaviour in terms of
reproductive success. An individual that exhibits desirable features is more likely to
contribute its genetic information to the next generation.
The study of animal behaviour is ethology, and a person who studies behaviour is
an ethologist. It is very easy to interpret observations of particular kinds of behaviour
from a human point of view – interpretation that is described as anthropocentric. For
example, if you smile at the gorillas in the zoo, they feel you are actually threatening
them – exposing teeth is regarded as a threat by the primates, whereas as humans we
see this as a friendly acknowledgment or positive reinforcement.
Tides alternately submerge and expose the residents of these zones. A change in environmental factors twice
daily requires adaptive behaviour to survive these conditions. The higher organisms are along the intertidal zone,
the more they may dry out, freeze in winter, or bake in summer, and the less food comes their way. The lower they
are along the intertidal zone, the more they must compete for sheltered space and exposure to food. At low tides
birds, rats and other foraging animals move in to feed on them. High tides may bring in the predatory fish. The
occupants are mainly sedentary or limited to rock pools with an almost constant supply of water, albeit brackish.
Animals and plants are adapted physiologically to these conditions; otherwise they would not occupy
these habitats. But their behaviour, too, enables them to take advantage of a situation that is both unpredictable
and extreme. Physiological features enable them to survive the cyclic events that may bring with them extreme
conditions in temperature, salinity, food, fresh water and oxygen availability. However, they also feed at times that
allow for maximum intake.
Barnacles are often associated with the bottoms of sailing craft and pier supports. They also inhabit the
intertidal zone rock pools and rock platforms. During low water, they are exposed to the elements, but at high
water they are submerged and this is when they feed. They possess long, feathery appendages that emerge from
a well-protected ‘beak’. As the water immerses them, their appendages wave about and collect microscopic
material such as plankton and algae, which is quickly despatched to their digestive systems. The tide goes out,
and they slam shut and stay that way till the next high tide.
275
Living in groups
bioTERMS
social behaviour
the behaviour of animals
living in groups
Figure 9.7 Meerkats successfully
cooperate during feeding times. Here a
sentry watches for danger.
In some species, individuals acting socially are typically found in groups and exhibit
social behaviour. In others, individuals are solitary members of the population. Access
to resources such as food, shelter and a mate is often the underlying reason for living
in groups.
Observation of animals living in groups over many years has increased
ethologists’ understanding of the biological basis of social behaviour. This has
given rise to the understanding of various behaviours related to group living such as
communication systems, territorial behaviours and the demonstration of aggressive
and submissive behaviours.
Given the substantial costs to individual reproductive success, why should
individuals of any species live close to others in a particular environment? When they
do, it may be that the benefits of social life are great enough to overcome the costs.
Successful cooperation
Meerkats live in large communities. They are burrowing carnivores that spend
a great amount of each day with their heads in the ground searching for food.
This makes them vulnerable to attack by predators but one animal is usually
posted as sentry. When a threat is imminent, the sentry produces a series of
distinctive calls – a warning for all meerkats to be alert. The rest of the colony
responds by standing on their hind legs and scanning the area for predators.
Having more pairs of eyes increases the chance of detecting predators quickly.
Having a sentry means that the other animals can safely continue with their
feeding until the alarm is given.
The biologist Birgitta Sillen-Tullberg found tangible evidence of the
benefits of group living in Australian sawfly caterpillars, which live together
in clumps. When something disturbs the caterpillars, they collectively rear
up and writhe about, all the while regurgitating partially digested food.
Sillen-Tullberg suggested that individual sawfly caterpillars benefit from the
coordinated act of repelling bird predators. She predicted that birds are more
likely to consume a solitary caterpillar, not a cluster of them. To test her
prediction, she offered young, hand-reared great tits (Parus major) a chance
to feed on caterpillars either one by one or in a group of 20 per offering. Ten
birds offered one individual at a time consumed an average 5.6 caterpillars.
However, 10 birds each offered a clump of caterpillars only ate an average of
4.1. The results Sillen-Tullberg obtained supported her prediction.
Working together
Similarly, the members of a wolf pack show helpful behaviour, as they fend off
predators and share food. Only one male and one female wolf produce pups. Others
of the pack do not breed, but they bring back food to members that stay inside
the den and guard the pups. Therefore, even if a predator is successful in attacking
a group, each individual is safer in a larger group simply because the chance of
being the unlucky one caught by the predator is smaller. The larger the group, the
less probability that a particular individual will be taken. The enormous herds of
wildebeests and antelopes on the plains of Africa demonstrate this point. Baboons
will act cooperatively to ‘mob’ a potential predator to the point where the harassment
discourages the predator from continuing its assault on the troop.
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Chapter 9 Behavioural
and reproductive
adaptations
Figure 9.8 Lions work together to
Predators too may benefit from living in groups. Thus, some species are more
catch wildebeest prey.
successful at catching large prey when hunting in groups than when hunting on
their own. Classic studies in the African Serengeti have shown that this is so for
Figure 9.9 Spotted hyenas and
lions, spotted hyenas and wild dogs. They work cooperatively to single out and chase
vultures feeding on a giraffe carcass.
down prey.
Within the jungles of the Ivory Coast,
group living provides daily examples of
benefits to both the predators and the
prey. Savannah chimpanzees, though
predominantly fruit eaters, will also hunt
for meat at regular intervals. Their preferred
prey is small, agile monkeys such as the black
and white colobus. The monkeys are smaller
and able to move among the finest branches,
leaping and moving very quickly away from
the more cumbersome, larger chimpanzee.
In order to catch their prey the chimpanzees
must operate as a team. In order to escape, the
colobus must also communicate with each other.
A variety of vocal signals and screeches penetrate
throughout the forest. However, the chimpanzees
have assembled as a team with various roles such
as chasers, blockers and ambushers. In a short
bioBYTE
space of time, the chimpanzees have cornered
The letter home from school warning of
an individual and begun devouring the hapless monkey. The
another infestation of head lice is enough
colobus troop will continue to sound alarm calls while the
to make most people start scratching. In ancient
chimpanzees appear to ‘whoop up’ the feasting. In this case the
civilisations the act of nit-picking was a socially
predators working as a group have outwitted the prey. Group
important pastime. In fact it was held in such
high regard that in some societies live lice were
strategies were employed by both the colobus monkeys and the
put back into the hair so the community had a
chimpanzees, but the predators outsmarted the prey.
reason to pick nits out at a later date!
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BIOBOX 9.2
‘SUPERPACKS’
Dingoes traditionally live and hunt in small territorial packs, which defend their food and territory from other
packs. University of Queensland researcher Nick Baker has reported that dingoes on Fraser Island, Queensland, have
developed an uncharacteristic tolerance for each other.
Recent observations, however, indicate that the smaller groups are working together as one large pack. It is
thought that the formation of the ‘superpack’ evolved on the island due to the small territory and the abundance of
food. Visitors to the island have hand-fed the wild animals, which may have resulted in the animals becoming bold in
the presence of humans.
Honeybees build hives with an internal air-conditioning system created by thousands of worker bees fanning
with their wings. From late spring to autumn, this keeps the colony around 34.5–35.5°C. In winter, the energy
released by bees means that the temperature never falls below 17°C. Honeybees, being insects, are ectothermic but
collectively are endothermic. Group living allows individuals to do things they could never achieve on their own.
Wanting some alone time?
Figure 9.10 A penguin huddle. Each
penguin gets to spend some time in
the middle.
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Unit 2
The essentials of life in the real world are often in short supply. Animals need
food, shelter and, at some point in their lives, a mate. These essentials can be more
effectively delivered to those animals that live in a group but with the benefits of living
in groups come costs.
When lions hunt in groups, the first to feed are the large males, then the females
and young. Last of all are the adolescent males who, at best, pick through the leftovers.
These males, if they want a share of the best, must fight for it. This is when the vicious
cycle of survival begins. They are less fit, therefore they have less energy, thus when
they fight a well-fed large male, the chances of them winning the battle, for either the
food or the females, are greatly diminished.
The colonies of millions of penguins on the Antarctic continent face other
difficulties. Space is at a premium. In the winter months, where each individual is
located is the difference between life and
death. Male emperor penguins spend the
winter months on the continent incubating
eggs. They huddle in large groups and are able
to present a greatly reduced surface area to
the icy conditions. The lucky ones are in the
middle of the huddle. They benefit from the
heat generated by the other birds. The ones
on the outer edges are exposed to the elements
and therefore face death. Penguins overcome
this problem by a continual shuffling between
those penguins on the outside of the huddle
and those penguins on the inside. Each
penguin spends some time in the middle.
Chapter 9 Behavioural
and reproductive
adaptations
In large populations in particular environments, the benefits of social life can
come at great reproductive cost to the individual. Dangers to health are also prevalent
in large colonies in the form of the spread of contagious diseases promoted by
overcrowding, and depleted food resources when times are harsh. In the event that
competing for resources such as food and nesting sites occurs, those individuals that
are best able to survive the ravages of disease are those that can successfully compete
for the limited resources.
The flow-on effect is that they are the ones most likely to reproduce and pass
on their advantageous features to the next generation. These offspring will go on to
compete successfully and survive as long as these conditions persist.
REVIEW
4 List five advantages to humans of living in groups. List five
disadvantages to humans of living in groups.
5 For your answer to Question 1 on page 274, indicate
which relate only to the individual, and which relate to
the community.
6 Using the examples given in the text, describe two instances
where group living is of benefit to the group, but not to
the individual.
Getting the message across
When animals live together in groups, whether it is a pair of albatrosses (a very small
group of two) or a termite colony (a group of thousands) they need to be able to
attract others, repel threats, and establish and maintain some social organisation.
The ability of animals to communicate with one another is fundamental to animal
behaviour. Communication signals evolve or persist when they increase the survival
prospects of the group. Moreover, signals involve two aspects – signalling and
receiving. Signallers are individuals whose actions or cues can induce behavioural
changes in other individuals of the same species, which are designated signal receivers.
Narrow, brittle tunnels radiate out from a termite colony along the trunk of a dead
eucalyptus tree in far north Queensland. If you
chip a hole in a tunnel, pale worker termites
inside begin banging their head against the wall.
The vibrations alert soldier termites, which run
to the breach and make a defensive stand. Each
soldier has a swollen, eyeless head that tapers
to a point. Disturb a soldier, and it will shoot
thin jets of silvery ‘goo’ out of this point. These
strands of goo release volatile odours that attract
more soldiers to battle the invasion.
In order to communicate, where a spoken
language is absent, signals are given, interpreted
and then acted upon. These signals may take
many forms but predominantly within the
Figure 9.11 Termites respond to
acoustical signals when their colonies
have been breached.
279
animal kingdom they will be one of three kinds: an acoustic signal, such as that given
by a frog calling to attract a mate; a chemical signal, such as the release of distinctive
scent by the sugar glider alerting others to its territorial claim; or a visual signal such as
the display of the Victoria’s rifle bird (see Figure 9.29).
Table 9.1 Elements of communication.
Element
Description
Example
Context
The setting in which the communication
occurs
Courtship
Sender
The individual who transmits the signal
Male lyrebird
Signal
The message conveyed from one
individual to another
Come and check out my court – it’s the
best around
Code
Understanding the meaning of the signal
He’s making a pass at me
Channel
A medium in which the signal is
transmitted
Visual – dancing and prancing
Receiver
The individual who detects the signal and
responds
Female lyrebird
Acoustic signals
Figure 9.12 Siamang with enlarged
throat pouch when tree calling.
Termite head-banging is an acoustical signal – a sound with precise, species-specific
information. The ability to interpret the meaning of this signal is an innate behaviour;
it is programmed in the organism’s genes and does not need to be learnt.
The lyrebird’s song is one of the most complex with its array of natural imitations such
as the songs of other birds including the kookaburra. The lyrebird is also able to imitate
man-made sounds such as a lawnmower or the sound of an automatic camera winding.
Humpback whales vocalise when locating members of their pod by emitting sound
waves that travel through the oceans. Elephants and rhinoceroses make herd members
aware of impending threats by stamping the ground. The ground is firm enough
to transmit the shock waves created this way and the sensitive end of the elephants’
trunks detects the signals.
Siamangs (the largest gibbon) produce calls transmitted through the thickest of jungles.
The songs of birds in the morning act as a rollcall of all members of the flock. Gorilla
chest-thumping and calling are signs of aggression and are designed to warn off potential
aggressors to the family group. These aggressors may be other gorillas or predators.
Vocalisations are used by a range
bioBYTE
of animals to claim and defend their
territories. The strawberry arrowAquatic mammals have developed a method
poison frog of the Amazonian basin
of finding things under water – sonar. Their
eyes, similar in structure to land mammals, do
claims an area roughly 2 square
not function well in water, so their best chance
metres and then sits in the middle of
of locating pod members or food relies on
it. If an intruder enters this space the
their use of sonar – an acoustic signal. An
frog will call loudly, which is often
increasingly common occurrence is the
beaching of whales. A team of international
enough to scare off a rival.
scientists has gathered new evidence
implicating the use of military sonar in the
beaching of whales.
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Chapter 9 Behavioural
and reproductive
adaptations
Chemical signals
The odours released by the termites are called pheromones – chemical
signals between individuals of the same species. Ants will lay down a
chemical trail to a food source, allowing other members of the colony to
locate it. Ants also release pheromones when alarmed, warning of danger.
This pheromone is in the form of formic acid.
Chemical odours from potential food and danger are the most important
stimuli that animals have to deal with. Some, such as termite alarm signals,
stimulate or suppress aggressive or defensive behaviour. Others, such as
bombykol molecules released by the female silk moth, are sex attractants.
A chemical odour from the urine of some male mice will trigger and
enhance oestrus in female mice.
The lemurs of Madagascar mark out their turf by depositing scent from
glands on their wrists or beneath their tails. These markings, however,
occasionally require reinforcing. Lemurs cover their tail in the scent and
then fan their tails, forcefully spreading their distinctive odour throughout
their territory. The scent travels great distances and keeps many rivals at bay.
Visual signals
Both acoustic and chemical signals are effective in the absence of direct line of sight
with members of the group. However, for animals active during the day and in open
areas, visual signals are the most effective means of communication. A dominant male
baboon will yawn and expose his formidable canines if a rival for a receptive female
confronts him. His yawn, a threat display, may precede a physical attack on the rival.
However, suppose the rival backs down. The signaller benefits by retaining access
to the female without a fight. The signal receiver also benefits by avoiding a serious
beating, infection or death.
Along with exposing their teeth, many primate groups will use eyelid flashes
as a way of warning off others. Interestingly, eye contact among primate species is
often perceived as a threat. Primate keepers in zoos are therefore discouraged from
‘eyeballing’ their charges.
The most dramatic visual displays occur in bird species, the lyrebird having one
of the most elaborate dances. In other bird species, these displays are often associated
with position in the hierarchy within a group. The displays of the most senior birds in
the pecking order are quite exceptional, with the dominant
animal having the most dramatic plumage. The great
tits of northern Europe display their seniority by the
presence of a black stripe that runs through their
yellow breast. The wider the band, the more senior
the bird. When food is plentiful the need
for displaying is reduced. However, at
times when food resources are limited
and the tits gather in smaller areas,
the badge of seniority is flashed,
allowing the owner first access to
the available food.
Figure 9.13 Ants following a trail
and carrying food.
Figure 9.14 Exposing
canines is a threat
display by a male
baboon. This visual
signal of aggression
can resolve conflict
without the need for
a fight.
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BIOBOX 9.3
THE CASE OF THE HONEYBEE
Honeybees have one of the most exceptional communication systems of any animal species. When worker bees find
a rich food source within 80 metres of their hive, they perform a dance when they return to the hive. As it is dark in
the hive, the other bees cannot watch the dance; instead, they follow the worker around the comb as she dances.
When the workers then fly out of the hive, they locate the same food source almost immediately.
The round dance passes on information about the richness of the food source. The higher the quality of the
food source, the more often the dancing bees change the direction of their dances. If the food source is more than
80 metres away from the hive, on her return she performs a ‘waggle dance’. This conveys precise directions about
the distance of the food source. The worker signals the information in three ways:
 the speed at which the bee completes one circuit of
bioBYTE
the dance – the faster the dance the closer the food
The mandrill employs a subtle visual signal
 the number of abdominal waggles – more waggles,
to point out its authority. The adult male,
the nearer the food
on reaching maturity and the rank of dominant
 the pitch of sound burst during the dance – higher
male within the troop, develops physically to
such an extent that he is very different in
the pitch, the closer the food.
appearance to other members of the troop.
The waggle dance also conveys information about the
The facial and rump colouring of the male is
direction of the food source.
quite distinctive.
REVIEW
7 Illustrate, by means of a concept map, the elements of a
communication system. Use a different example to the one in
Table 9.1.
8 Explain why communication between members of a species
persists within that species.
9 In what situations is obvious communication between
animals advantageous?
10 Explain the advantages of chemical signals over acoustic signals
when trying to keep rivals away.
11 Many animals have evolved to blend in with their surroundings
so as to hide from predators. Explain why some birds are
brightly coloured and why this may be more important than
being camouflaged.
Why communicate?
Communication may be either intraspecific (occurring between individuals of the
same species), such as the sentry meerkat warning the rest of the colony of imminent
danger; or interspecific (occurring between individuals of different species), such as
that seen when a male baboon is defending his troop from predators. What is the role
of intraspecific or interspecific communication? What message is being conveyed? The
answer is twofold and includes both order (or social organisation) and boundaries
or territories.
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Chapter 9 Behavioural
and reproductive
adaptations
Getting the order right (social organisation)
In a baboon troop, individuals help one
another, but reproductive opportunity
is unequal. Some individuals give up
safe sleeping places, choice bits of
food, and even receptive females to
others upon receiving a threat signal
or a sign of aggressive behaviour from
another troop member. Social behaviour
increases the number of interactions
between individuals. These interactions
may not always be positive, and may
result in conflict. In conflict, there is by
definition a winner and a loser and this
is what sets up a dominance hierarchy.
These conflicts may be resolved
by fighting or by the submission of
some individuals to the stronger, and
therefore dominant, individual. For
the sake of group harmony, and access
to available resources, individuals will
act to appease the dominant animal as
described below. In return, the lower
ranked individuals benefit from the
strength and protection of the dominant
animal. An example is the antilopine
wallabies (Macropus antilopinus) of
northern Australia, which live in
large social groups watched over by a
dominant male who has mating rights
with all females within the group.
bioTERMS
dominance hierarchy
a set of levels in a society where
some members are subordinate
to others
CTIVITY
LA
9.1
Why do subordinate adults that do not breed remain in a social group and appear to
make sacrifices for dominant peers? First, challenging a strong member may result in
injuries that shorten a life. Second, it may not be possible to survive alone outside the
group. A solitary baboon surely whets the appetite of the first leopard that sees it. Selfsacrificing or submissive behaviour may even give subordinates a chance to reproduce
if they live long enough and if predation or weakness in old age removes dominant
peers. Some subordinate wolves and baboons do move up the social ladder if
dominant members slip down a rung or fall off. Therefore, acceptance of subordinate
status might pay off in the long term for the patient individual.
Aggressive and submissive behaviours are often the costs associated with living in
groups. Where a hierarchy exists, a dominant animal runs the show. Other animals
within the group benefit from the attributes that have placed this individual in that
position, whether it be protection for the group from predators or from individuals in
other groups.
Figure 9.15 The antilopine wallaby
lives in large social groups.
ACTICA
PR
Aggressive and submissive behaviour
283
Figure 9.16 Lions live in
social groups called prides.
bioTERMS
infanticide
the killing of young
Life in the pride
Lions live in social groups, called prides, which usually consist of about half a dozen
adult females, their dependent offspring and two to four adult males. Daughters born
into the pride commonly remain there for life, whereas sons leave before they reach
reproductive maturity. As a result, the females within a pride are quite closely related.
One noteworthy feature of life in the pride is that the cubs may suckle from any adult
female with milk. Such communal suckling is rare in mammals. In most species, each
female suckles only her own offspring. The close relationship of females within a lion
pride may explain the existence of communal suckling.
The adult males in a pride may be driven away by a new coalition of males. If a
pride is taken over, the new adult males kill as many of the young cubs as possible.
The reason for this infanticide is more subtle than might appear at first sight. In
common with many other mammals, female lions do not ovulate when they are
lactating. However, once their cubs have been killed, the females come back into
oestrus. Infanticide therefore allows the new males to sire their own cubs more
quickly. In the African Serengeti 25% of all cubs die from infanticide.
REVIEW
12 Using the examples in the text, give an example of a behaviour
that is submissive and one that is aggressive.
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13 Describe two benefits of dominant behaviour for an individual in a
baboon troop.
Chapter 9 Behavioural
and reproductive
adaptations
In primates such as gorilla families
and baboon troops, the highest ranked
animal is a male. Physical signs such as the
development of silver hair on his back or
enhanced facial structures and physical size
usually accompany the male’s status. This is
sexual dimorphism where there are obvious
differences, usually in size and colour,
between the sexes.
Figure 9.17 Silverback male gorilla.
BIOBOX 9.4
THE IMPORTANCE OF GROOMING
Amongst groups of primates an important social activity is grooming. Within certain groups such as baboons, the
hierarchical order is supported by the observation of grooming behaviour. The baboons offer an example of a highly
ordered group with one dominant male within the group consisting of a few adult females and their young. The dominant
male may be groomed for a number of reasons, the foremost being to establish his dominant position in the group. The
few occasions he may groom another animal occur when he would like to mate with a particular female. Subordinate
animals will groom animals higher in the ‘pecking order’. They will not, however, jump a rung in the hierarchy. It is a
privilege to groom the dominant animal, and not one easily conceded to another.
It is not uncommon to witness lines of chimpanzees grooming each other at any one time and deriving what has
sometimes been interpeted as pleasure. Apart from strengthening bonds and maintaining hierarchies, the behaviour
has the beneficial effect of enhancing the survival of the animal which may depend on the activity as for removing
potentially life-threatening parasites so that the individual remains healthy.
In insect societies, the
dominant females are queen
bees, ants or termites. In wasp
society, it is the queen that
selects the site for her colony.
She lays her eggs and gives rise
to her first workers, who get on
with the task of building the
nest, gathering food and caring
for the young.
Figure 9.18 In insect societies it is
the queen who rules the colony.
285
Whose place is this anyway? Territory
Figure 9.19 (a) The sugar glider
has a scent gland on top of its head
(b) Frogs use acoustic signals to
define their territory.
a
b
Finding prime real estate is a bonus at the best of times. An animal’s needs are
primarily ready access to food, shelter and, when the time is right, a mate. Animals
that locate these resources in one place do not give it up easily, and in fact fight to
defend their territory.
Defence of the ‘patch’ or ‘turf’ may take
many forms. Hummingbirds defend patches of
flowers; African antelopes defend their courts
by head-butting their rivals; even sea anemones
will defend the rock to which they anchor
themselves. Step one in defending a territory
is establishing the boundaries. Songbirds and
frogs use sound to proclaim their turf; dogs
and sugar-gliders use well-placed pheromones.
Different strategies work in different
environments. Sounds are appropriate where
visual signals would not be seen clearly, such
as in bushland, forests or lakes.
African antelopes establish courts and then
spend time displaying in an aggressive manner in
the centre. Any rivals that don’t get the message are
chased away quickly. In open areas, visual signals
are effective. If these signals do not deter intruders,
physical defence such as chasing and fighting
may ensue.
Territorial defence may also involve the
destruction of a rival’s area. The satin bowerbird of
southern Australia is renowned for the collection
of blue-coloured objects when building its mating
‘bower’. Woe betide any rival whose bower is located
within acoustic range of another. One male will
actively destroy the bower of a rival by pulling down
any structures and stealing any collected objects to
fortify his own bower. In this manner his chances of mating with a female are greatly
enhanced and those of his rival are miserly in comparison. Not all species have
territories, but in those that do, territories have a variety of functions which mainly
encompass a reliable food source and access to mating opportunities.
REVIEW
14 Give two more examples of sexual dimorphism (other than baboons and gorillas).
15 List the benefits of cooperation within a group.
16 Why do some animals go to a great extent to defend their territories? List some ways in which they
defend their territories.
286
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Chapter 9 Behavioural
and reproductive
adaptations
Migration
Australia has two distinct populations of humpback whales. Both spend the summer
months feeding on krill in the oceans off Antarctica, but in autumn and spring they
migrate up the east and west coasts to their breeding grounds. Off the west coast, they
migrate past Exmouth Gulf on their way to the waters off Broome, whereas on the
east coast they head for the Great Barrier Reef. At times, they have been sighted as far
north as Torres Strait.
b
Seasonal changes to the availability of food and competition for resources and the
need to breed have a direct impact on the populations of many animals. In order to
meet these needs two options exist: stay and make the most of what is available, or
move to where the resources being sought are more readily accessible.
Some animals will hibernate during the colder months when food is scarce;
however, an alternative to this is the seasonal movement of whole communities or
part of communities in migration. Triggered by the seasonal changes of autumn, the
humpback whale and many bird species that spend the summer months in southern
regions of the Southern Hemisphere migrate northwards to warmer latitudes in
winter. Movement in the opposite direction occurs in the Northern Hemisphere.
Thus, swallows migrate from Northern Europe to South Africa, and golden plovers
from Canada to the southernmost tip of South America.
Migration takes many forms and may involve distances of a couple of metres or
many thousands of kilometres. The behaviour is seen in many animals, from crabs,
butterflies and locusts to humpback whales, caribou and Canada geese. It may take
place on land, in the earth, in the seas or in the air. Migrations may occur seasonally,
daily or annually. Factors that influence these movements include food availability,
weather conditions and breeding seasons to name but a few. The paths followed by
migrating organisms may be predetermined genetically, reliant on navigational skills
or forced.
BIO
a
Figure 9.20 Humpback whales in
(a) Antarctic waters and
(b) tropical waters.
LIN
K
Animal migration
287
Land migrations
Figure 9.21 The orang-utan moves
around its territory looking for fruits.
Earthworms are able to avoid changes in temperature and water availability by
retreating deeper into the earth. Therefore, in winter months you would be hardpressed to find an earthworm within 1 metre of the surface. As ectothermic organisms
they rely on their environment for some body temperature and therefore in order to
be able to keep functioning they must avoid icy and dry conditions. They are able to
do this by burrowing deeper into the ground. In addition to this seasonal movement
earthworms have been observed coming to the surface at night to deposit the
equivalent of faeces or ‘worm poop’, a rich organic deposit.
More familiar migrations involve vast herds of caribou in the tundra and Northern
Hemisphere forests, or the wildebeests of Africa. The need for adequate food drives
these mass movements which, for the caribou, are influenced by the changes in
weather conditions. As winter approaches the feeding lands of the tundra will either
be frozen or covered in snow. Movement south into the forests provides both food
and some shelter from the climatic extremes of the Arctic winter. The paths taken
by the herds are the same for each herd each year and there is some
speculation as to how the animals find their way. Some scientists
believe that they rely on the younger animals learning the path, this
knowledge being passed on to the new members each year. With
such a great number moving at one time, it is an advantage that
the memory of the path is retained by many animals and not just
one individual.
bioBYTE
Not all migrations, however,
cover great distances across
The fruit bats that took up
residence in Melbourne’s
the globe. The orang-utan of
Botanic
Gardens were on their annual
Borneo and Sumatra will move
southerly migration from Queensland.
around its territory, following
Landing in the Gardens’ Fern Gully,
the availability of different
they led a relatively peaceful and
safe life – no predators, plenty of
fruits throughout the year.
BIOBOX 9.5
CHRISTMAS ISLAND CRABS
food. The human locals took offence
at their nightly cacophony, and
many attempts were made to scare
them away from roosting in the
gardens, including loud noises.
Christmas Island is located west of Australia’s coast within the tropic zone. It therefore experiences a wet and a
dry season rather than the four seasons observed in temperate regions. As well as the volume of water, another
phenomenon occurs every year at the beginning of the wet season. Christmas Island is the home to the endemic and
distinctively red Christmas Island crab, and at this time the crabs begin migrating from their habitat on the island’s
central plateau to the coast. The males begin to move first and, once they arrive, they commence building and
defending breeding burrows in the lower rocky terraces of the coast. The males are quickly joined by the females. The
timing is critical as the migration has to coincide with the least difference in depth between low and high tide. It is in
the first quarter of the Moon that the females release their eggs into the sea.
Crabs will follow the same migration paths each year, despite the presence of many man-made structures such
as roads and buildings. They tend to move in the morning and evening, avoiding the heat of the day and staying close
to shaded areas. If they are caught out in the open, and exposed to the Sun, they will dehydrate very quickly and die.
288
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Chapter 9 Behavioural
and reproductive
adaptations
Air migrations
The most spectacular migrations take place in the skies, such as monarch butterflies on
their annual pilgrimage from northern Canada to the forests of Mexico. The migration
begins in late August and the butterflies take till November to arrive. Despite their
status as insects and the many perils they encounter on their 5500 kilometre journey,
they are able to cover an average of 100 kilometres per day at a speed of about 25
kilometres per hour. Once they reach their destination the animals will roost quietly
till the start of the breeding season in February. By March the butterflies have begun
their journey back north. The migration can involve up to three generations of the
butterflies. Over 50% of the butterflies will die in Mexico. The journey is continued
by their offspring. But why do the monarchs migrate at all? This is open to speculation
but one predominant idea is that they escape the cooler weather in the northern
winter. But how do they know it is going to get cold? They don’t! One hypothesis is
based on the way butterflies are able to respond to changes in light intensity and it is
this that initiates the migratory behaviour in the first place.
The migration of locusts is not an annual event and in fact takes place only after
an enormous build-up in the locust population. Not all forms of the locust migrate;
in fact a particular migratory form develops called a nymph. The nymph will develop
only under specific environmental conditions. These conditions are unknown, but
hot weather is one possibility. When migration commences the sheer numbers of the
locusts blacken the skies. They will consume most vegetation in their path and are
a serious threat to agriculture. There is some solace to be taken in the fact that the
generation after a migratory phase is not migratory.
Canada geese are another species
that migrates when they detect changes
in light intensity. The change in light
intensity is the trigger for the release
of a particular hormone. If light
intensity decreases, the hormone levels
decrease and thus the birds begin their
migration. They begin their southerly
journey from Alaska and head as far
south as Mexico. The availability or
scarcity of food is one factor in the need
to migrate. They fly in a distinctive ‘V’
formation, travelling at speeds of up to
60 kilometres per hour.
bioTERMS
nymph
one stage in the life cycle of
an animal between larval and
adult stages
Figure 9.22 Canada geese flyin
g in
their distinctive ‘V’ formation.
Water migrations
Water migrations involve long-term and short-term movements. Daily movements
of plankton from deeper areas during the day to areas close to the surface at night are
common. The movement of these organisms has a follow-on effect on the animals that
feed on them. Longer-range migrations involve many organisms.
The great white pointer shark is a long-distance swimmer that covers thousands of
kilometres of Australia’s coastline in search of prey. Individuals have been tagged and
then electronically tracked. One individual was tracked from Neptune Reef in South
Australia to Rockhampton in Queensland and back again over a 7-month period.
289
CSIRO researchers have
developed a profile of
the movements of the
animals and know that
sharks go north in autumn
and return to southern
oceans in spring. Shark
locations are transmitted
via satellite whenever one
surfaces. Scientists receive
the information after 20
minutes and can then track
the animals in almost real
time. Other behaviours are
also noted, including stops
at seal colonies.
Migration patterns may
be in cycles that take longer
than one calendar year. The
green sea turtle, a long-lived
animal, will return to the
beach where it was born, to
reproduce and eventually
die. It may take up to 40
years to do so.
Figure 9.23 The path of the great white pointer shark along the coast
of Australia.
Figure 9.24 Sea turtle making
its way to the ocean after
laying eggs.
REVIEW
17 Explain the benefits of migration to an animal species.
18 Distinguish between local migration and large-scale migration,
giving examples of each.
290
Unit 2
19 List four factors that will trigger migratory behaviour in
some animals.
20 In what ways has technology aided the development of
appropriate ecological practices for great white pointers?
Chapter 9 Behavioural
and reproductive
adaptations
Reproductive behaviour
Figure 9.25 Male mandrill.
Finding the ‘right’ mate, reproducing and raising
young are all reproductive behaviours. Many
species have developed and practised very specific
behaviours to ensure time and energy are not wasted
in pursuing unsuitable partners.
Large breeding-age mandrill males prefer a
solitary, bachelor existence and are generally absent
from the stable, family groups called hordes. Only
during the breeding season do they return to
the group. Without the normal long-term social
bonds formed by being permanent members of the
group, these males need to gain the attention of
prospective mates in a hurry, and their bright blueand-red face will certainly do that! For organisms
that reproduce sexually, reproductive success
depends on finding a mate. During the course
of evolution an amazing diversity of patterns of
courtship, mating and parenting have arisen.
Meeting the right type –
courtship
Figure 9.26 Emperor penguins caring
for their young.
The night before the female Siberian dwarf hamster gives birth
to a litter, she marks the area around the entrance to her burrow
with pungent vaginal secretions. Males from some distance are
thus forewarned of her condition and gather. Immediately after
giving birth, the female leaves her litter and mates with a male.
She then returns to her burrow and to her young. The scent
sends two messages. One message informs prospective mates
of her species. The other message is that she is almost ready to
mate. At the most basic level, a mate must be an individual of
the same species but the opposite sex. In many species, what
ensures the ‘right’ individuals mate with each other is courtship,
the behavioural process whereby sexually mature individuals of
a species become mating pairs.
Group living offers close proximity to potential mates.
However, the probability of achieving this is dependent on the
social structure within the group. Elephant seals live in harems
with one dominant bull that has access to all females. Other
males wishing to mate must first challenge the bull successfully
in order to win the opportunity. The largest and the strongest
elephant seals will mate and pass on their traits to the next
generation. The male emperor penguin that survives the winter
caring for its young has characteristics that are invaluable to the
survival of the young, and the female Siberian dwarf hamster
produces litters continually to ensure that her genes persist.
291
Fig
ur
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.27
292
g to
ayin
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p
s
i
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aco
e
p
ale
Am
Unit 2
ale.
a fem
Each of these animal species displays a system for a range of social relationships in
which individuals of a species find and compete for mates. Other groups live entirely
without adult males, such as mandrills, till the breeding season. Male orang-utans live
a solitary existence till receptive females cross into their territory.
Courtship conveys a great deal more information than just the species and sex
of the performing individuals. It goes some way to explaining the effort and energy
invested by many males of the species. As females generally invest more time and
energy in their offspring than do males, choice of a mate is particularly important
for females. Male peacocks make themselves attractive to females (see Figure 9.27),
advertising their fitness-enhancing characteristics such as good genes, adaptive
behaviour and possession of valuable resources. Moreover, it is not always about the
parenting role. In the growling grass frog, the females’ eggs are fertilised and are left
to themselves. The females have to ensure the best chance of their offspring surviving
to reproduce themselves by selecting the ‘fittest’ mate available, judging the male by
his song or call. The genes of the ‘fittest’ male are passed on to the offspring, thus
ensuring a certain amount of genetic superiority.
Courtship behaviour tends to be specific to each species. Among birds, the males
of the species have employed some of the most elaborate devices. Displays of virility
include the highly decorative breeding plumage of the wood and mallard ducks, the
expanding and colourful throat pouches or lappets of pheasants, and the dancing,
preening and dramatically choreographed movements of the Victoria’s rifle bird and
lyrebird. The females seem to be putting prospective mates through a series of trials
so that they can ensure that the resulting offspring have a male parent that will offer
effective survival skills. In all of this, however, a number of trials are quite ineffective
for the bare survival of the animal, such as wonderful songs and dances, impressive
flying skills and magnificent plumage, which appear more of a hindrance than an
aid in survival. All, however, offer other animals the
information that the territory, no matter how
it is defined, belongs to a specific animal.
The dances are interpreted as
visual signals to other males to
stay away.
Some prospective
mates are more
practical by offering
food, as has been
observed with
doves and
grebes.
Chapter 9 Behavioural
and reproductive
adaptations
Figure 9.28 Plumage of a breeding male duck.
The satin bowerbird will prepare an elaborate nesting site as an enticement
to the selecting females. Sticklebacks prepare egg-laying areas and lure
females with strictly sequenced actions. The male blue-footed booby,
though it has dispensed with a nest, offers the female of its choice a twig
that is delicately placed on her foot. Whether the young are raised by one
or two parents (as is the case with albatrosses) is dependent on the role of
each in protecting the young and gathering food. As a rule if both parents
are involved in the rearing of the young, the parents pair for life. On the
other hand, if one parent cares for the offspring – usually the female – the
possibility of the other parent finding other mates is high.
Courtship and copulation is an all-in-one process for some animals.
It is particularly risky for animals who are hunters, such as spiders, where
approaching the female takes a lot of skill and luck. Even then there is no
guarantee that the male will walk away unscathed. The female in most
species of spider is larger than the male, so he goes to great lengths to ensure
she is aware he is a mate and not a prospective meal. If they have good sight,
as is the case with the wolf spider, the male uses visual signals to telegraph
who he is and his intentions. If she is not interested, she will charge at him as
she would for prey. If she is receptive to his overtures, she will demonstrate
this by vibrating her front legs as he advances towards her, but he still retreats
quickly after the deposition of the sperm, just in case. In the insect world,
food is offered as an enticement to mate. The courting male hanging fly will
release a scent near a female with which he would like to mate. As the female
locates the male and accepts the gift, he brings his abdomen forward in an
attempt to mate.
Spiders that weave webs are particularly sensitive to vibrations. The males
will approach the outer boundary of the web and make specific vibration
patterns that identify them to the female. In any case, the males of some
species do not survive the mating process. They make the ultimate sacrifice
for the survival of the species.
Figure 9.29 The Victoria’s rifle bird
is usually very shy. The male has an
iridescent triangular shield on its
breast. The shield is integral in the
courtship ceremony. His wings are
fanned and held vertically to frame his
head, which he moves dramatically
from side to side.
293
Raising the brood
bioTERMS
learnt behaviour
behaviour that changes, based
on past experience and trial
and error
Parenting behaviour varies among many species, if indeed it exists at all. Whether the
animals are social or solitary, a great deal of time is invested in ensuring the survival of
the young. Animals that do not display parenting behaviour have alternative strategies
to ensure that at least some offspring survive to continue the species. Usually this is
the production of many more offspring than can possibly survive. The green sea turtle
is one such example. The female will lay up to 200 eggs on the beach where she was
born. She will then cover the eggs and return to the ocean. Following the incubation
period, the eggs will begin to hatch and the young turtles will make their way to the
sea slowly. The hatchlings are easy pickings for hungry birds and other predators.
Making it to the ocean does not necessarily guarantee their survival, but just provides
different hazards to overcome. From the original clutch of 200 eggs, after 10 years it is
expected that two, possibly three, individuals have survived. Only one of the original
clutch will reach sexual maturity and the age of reproduction.
Parenting of the young provides the offspring with the best chance of reaching
sexual maturity. The time spent with the parent ensures the learning of a variety of
survival strategies from locating food sources to identifying friend or foe, to selecting a
partner and mating successfully with a member of the same species. Evidence collected
by the observation of animals in captivity has demonstrated this. The female orangutan will spend up to 10 years rearing a single young and does not mate again till the
young is independent of her.
Some individuals will exhibit a particular behaviour only after finding that the
behaviour is beneficial to their survival chances. This is learnt behaviour and can be
achieved only if the particular animal has the necessary physiological and anatomical
features to carry out that particular behaviour.
Mammals, and birds in particular, display a variety of parenting behaviours.
Usually the young are born in smaller numbers compared to arthropods or
amphibians, which rarely display any signs of looking after their young, though there
are always exceptions. The male seahorse incubates the fertilised eggs from a mating
and carries them in his body till they ‘hatch’. The midwife toad carries the young in
her mouth till they mature and hatch as fully formed young, not as tadpoles as seen in
other amphibians.
Development and life cycles
ACTICA
PR
294
Unit 2
9.2
CTIVITY
LA
The caterpillar feeds on leaves and pupates when it reaches a particular size and age.
The monarch butterfly emerges from its pale-green, yellow-spotted chrysalis with
soft, flexible wings. It rests as fluid pumps through its wings and they unfold to form
the familiar shapes. While the wings set and harden, it is vulnerable. The green tree
frogs from tropical Australia first appear in rainforest pools as tadpoles feeding on
insect larvae and water plants; occasionally these tadpoles will eat each other. During
their life in the water their form will change from a completely water-dependent
swimmer to a land-based leaper. This change from one form to another is known as
metamorphosis.
Chapter 9 Behavioural
and reproductive
adaptations
Figure 9.30 A tadpole changing into a frog.
Plants such as mosses and ferns exhibit different forms at different stages of their
life. Reproduction for these plants includes life as a separate sexually reproducing
form and a separate asexually reproducing form. Both forms occur on land; however,
their appearance is markedly different. In plants such as these, this is known as an
alternation of generations.
These are the sequential
stages that an organism
a
b
passes through during its life,
or its life cycle. Throughout
the life cycle of the animal
or plant, the need for basic
resources does not change
but what these resources look
like does. A caterpillar and a
butterfly need food to grow.
The caterpillar exploits the
leaves of the plants; these
are available throughout the
year. The butterfly requires
nectar and is unable to access
the nutrients in leaves at all.
The change in form throughout the butterfly’s life cycle is so remarkable that it results
in the larva and adult stages having different types of mouthparts.
Most mammals provide their young with a head start by not introducing them to
the hazards of the real world till they are fully formed. However, even here there are
variations. The echidna and the platypus, as monotremes, produce soft leathery eggs
that they guard till the young emerge. When they do, the parents will provide food,
from their own bodies, which contains all their basic nutritional needs till the young
are of an age to fend for themselves.
Figure 9.31 Mouthparts of
(a) a caterpillar and (b) a butterfly.
Each has different food requirements.
bioTERMS
monotremes
mammals that reproduce via the
production of soft-shelled eggs
295
Figure 9.32 Underbelly of an echidna
with eggs in her fold.
bioTERMS
marsupial
mammals that give birth to
underdeveloped young who
then spend time in a pouch till
they are fully formed
placental
describes mammals that
develop completely into
miniature forms of the adult and
are nourished during gestation
via a placenta
The common brush-tail
possum (Trichosurus vulpecular),
a marsupial, gives birth to very
immature young 10 days after
fertilisation. The undeveloped
young makes its way to the
mother’s pouch where it attaches
itself to a nipple for the next
16–20 weeks. After this time it will
ride on the mother’s back until it is
weaned, somewhere between 7 and
9 months of age.
Placental mammals provide
their young with the best possible
start by retaining the young within
the mother’s body till it is fully
formed. This time is called the
gestation period and its length
varies. The young of the wildebeest
(Connochaetes gnou) are able to stand
up and feed from their mothers
within 30 minutes of their entry into
the world.
The mammals will continue to
care for their young until they are
able to fend for themselves. This
must surely provide them with the
best opportunities of surviving to
adulthood and reproducing their
own offspring. Most other members
of the animal kingdom and the
plant kingdom are unable to provide
this level of care, and rely on other
Figure 9.33 Placental mammal giving birth.
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Unit 2
Chapter 9 Behavioural
and reproductive
adaptations
strategies to ensure that their line survives. Commonly, this is indicated by the number
of offspring produced. Frogs and toads produce hundreds of eggs and leave them in
pools of water, or close to pools. Fish use the same strategy. Reptiles will lay their eggs
and may guard them till they hatch, and even help the young reach water after they
hatch. That is, however, where their contribution to the next generation ends.
Courtship, mating and parenting of offspring occurs to ensure the long-term
continuation of a species. Considering the effect of the environment on continuing
the line shows that some animals must also be able to reproduce in the harshest of
conditions or suspend their reproduction processes until such time arises that allows
the young to flourish. Ferns and acacias produce spores and seeds that are able to
withstand the harsh conditions of the Australian bush. Kangaroos will carry a fertilised
egg that does not develop further till adequate food supplies are assured.
REVIEW
21 A great deal of energy and time is expended in life cycles that include metamorphosis. Detail the
benefits and the costs to the species of such a strategy.
22 Give a reason to explain why different foods must be consumed by the same organism at different
stages in its life cycle.
23 Explain why mammals produce only a small number of offspring at any one time.
Summing up
ACTICA
PR
CTIVITY
LA
9.3
The survival of living things relies on the availability of essential resources. These are
food, shelter and a mate. The structure and function of the organism are the first ways
to reach this. Fitting in and interacting with others and the environment are the next
steps. As we have seen, a range of forms exist, as do a range of behaviours. All work to
enhance the organism’s survival prospects. Methods of communication underlie and
enhance social behaviour. Signals within groups of the same species, and with other
living things, increase the knowledge the animal has about its environment.
Living in groups has both advantages and disadvantages, and the success of an
organism’s social behaviour is measured by the number of offspring it produces,
which then reach sexual maturity and reproduce themselves. Occasionally, in certain
circumstances, solitary animals are able to leave more offspring than social animals.
Ensuring the least waste of time and energy requires finely tuned senses to detect the
range of signals on display. Within social animals some order or hierarchy may be of
benefit to the species as a whole.
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Visual summary
land
air
water
life cycles
Reproductive Behaviour
migration
parenting
courtship
crepuscular
circadian
Environments
rhythmic
behaviours
ethologist
biological clock
nocturnal
diurnal
hierarchy
Ethology
Behaviour to Survive
territory
Organisation
aggressive and
submissive behaviour
signalling
acoustic
chemical
visual
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Unit 2
Group Living
grooming
cooperation
sheltering
feeding
Chapter 9 Behavioural
and reproductive
adaptations
Key terms
adaptive value
ethologist
nymph
alternation of generations
ethology
parenting behaviour
anthropocentric
infanticide
pheromones
biological clock
innate behaviour
placental
chemical signal
interspecific
sexual dimorphism
circadian
intraspecific
signallers
courtship
learnt behaviour
signal receivers
crepuscular
marsupial
social behaviour
diurnal
migration
territory
dominance hierarchy
monotremes
visual signal
dominant
nocturnal
Apply understandings
 The African peach-faced lovebird carries
nesting material to its nest by tucking it into
its feathers. This behaviour is not learnt from
a parent. What type of behaviour is this?
What is the adaptive value of this behaviour
to the species?
 Human societies generally invest a lot of
time and energy in caring for and raising
their young. Some bird species such as the
cuckoo do not care for their young at all.
The adult will lay her eggs in another bird’s
nest and leave the eggs to hatch and be raised
by other birds. Give one advantage and
one disadvantage of the different parenting
behaviours as shown by humans and birds.
 How is learning by imitation a useful strategy
among primate groups?
Investigate and inquire
 A large caterpillar in the tropics responds
 The period of parental care is non-existent
to being poked by partly letting go of its
substrate and puffing up part of its body.
a Propose a possible mechanism that
underlies this behaviour.
b Propose how the behaviour has
adaptive value.
c How would you test both hypotheses?
 A hyena releases specific chemicals from
certain glands in order to mark plants in its
territory. What evidence would you need to
demonstrate that this action is an evolved
communication signal?
in tortoises, fairly short in most birds, and
long in orang-utans and humans. What
relationship, if any, might there be between
the duration of parental care and the
development of survival skills in the young?
 What evidence might biologists have that
make them believe some migratory birds:
a have an instinctive ability to navigate?
b process information from their
surroundings internally?
c change the way that information is
processed as time passes?
299