Biology 1001A Final: Biology 1001 Notes Part 3
31 Oct 2018
School
Department
Course
Cycle 7
Lecture outcomes:
1.examples of genetic exchange/recombination without reproduction, and of reproduction
without genetic exchange/recombination
2.how recombination contributes to population genetic variation
3.meanings of monoecious, dioecious
4.difference between sequential and simultaneous monoecy
5.examples and predictions of size-advantage model of sex change
6.examples and predictions of adaptive sex ratio manipulation
7.reason why most populations have 1:1 sex ratios
8.prevalence of sexual vs asexual reproduction in animals, plants and other forms of life
9.costs of reproducing sexually as opposed to asexually
10.benefits of reproducing sexually as opposed to asexually
Lecture outcomes:
1.how environmental stability influences whether sexual or asexual reproduction is favoured
2.lottery principle and Red Queen principle as environmental (short-term) benefits of sex
3.how sexual reproduction places different selective forces on males vs. females
4.distinction between intrasexual selection and intersexual selection
5.why males usually compete for access to females (rather than vice versa), and why in some
species this pattern is reversed
6.which sex has higher potential fitness
7.which sex has higher average fitness
8.relationship between sexual selection and parental investment
Cycle 8: Chapter 47
Chapter 47.12
Social Behaviour
• Social behavior, the interactions that animals have with other members of their species,
has profound effects on an individual’s reproductive success.
• Some animals are solitary, getting together only briefly to mate (e.g., house flies and
leopards).
• Others spend most of their lives in small family groups (e.g., gorillas).
• Still others live in groups with thousands of relatives (e.g., termites and honeybees).
• Some species, such as caribou and humans, live in large social units composed primarily of
nonrelatives.
• In many species, the level of social interactions varies seasonally, usually reflecting the
timing of reproduction, which, in turn, is influenced by changes in day length.
African Lions May Commit Infanticide
• African lions (Panthera leo) usually live in prides, one adult male with several females and
their young.
• Males typically sire the young born to the females in their pride, achieving a high
reproductive output.
• Females benefit from the support of the others in the group, which includes caring for young
and cooperating in foraging.
• Female lions living in prides wean more young per litter than those living alone.
• The females in a pride are often genetically related, and their estrus cycles are usually
synchronized.
• Male lions are bigger (∼200 kg) than females (∼150 kg), and males fight vigorously for the
position of pride male.
• Males protect their females from incursions by other males.
• When a new male takes over a pride, he kills all nursing young, bringing the females into
estrus.
• At first, this infanticide seems counterproductive. However, it benefits the male because it
increases the chances of his succeeding at reproducing.
• Were he to wait until the females had raised their dependent young, his reproductive
contributions could be delayed for some time, perhaps as much as a year or more.
• Furthermore, in the intervening period he could lose the opportunity to sire any young at
all.
• Females are not large enough to protect their young from the male.
• If a female takes her nursing young and leaves the pride, her efficiency as a hunter declines,
and she is less able to protect her young.
• Her reproductive success plummets.
• Females can be more productive (measured by output of young) when they are part of a
pride.
• But why live in a group in the first place? By hunting together, lions are more efficient
foragers than when they hunt alone; therefore, they raise more young.
• Perhaps more important is the threat posed by spotted hyenas, which live in large groups
(clans).
• Although individually smaller (∼60 kg), when spotted hyenas outnumber lions, they can
chase lions from their kills.
• Furthermore, many of the lion’s main prey also live in groups, and group defenses affect
lions’ hunting success.
• The situation in lions exemplifies some biological realities.
• Males and females do not have the same strategies when it comes to reproduction.
• Understanding behavior means considering genetic relatedness and production of offspring,
as well as the setting in which the animals live.
Group Living Has Its Costs and Benefits
Social Behaviors
• Ecological factors have a large impact on the reproductive benefits and costs of social
living.
• Groups of cooperating predators frequently capture prey more effectively than they would
on their own.
• White Pelicans (Pelecanus erythrorhynchos) often encircle a school of fish before attacking,
so being part of a group provides a better yield to individuals than working alone.
• On the other hand, prey subject to intense predation may benefit from group defense.
• This can mean more pairs of watchful eyes or ears to detect an approaching danger.
• It may also translate into multiple lures so that when a predator attacks, it is more difficult
to focus on an individual.
• When you are part of a group that is attacked, it may be someone other than you that is
captured, diluting the risk to any one group member.
• When attacked by wolves, adult muskoxen form a circle around the young, so attackers are
always confronted by horns and hooves (Figure 47.32).
• Insects such as Australian sawfly caterpillars also show cooperative defensive behavior
(Figure 47.33).
• When predators disturb the caterpillars, all group members rear up, writhe about, and
regurgitate sticky, pungent oils.
• The caterpillars collect the oils from the eucalyptus leaves they eat. The oils do not harm the
caterpillars but are toxic and repellent to birds.
• Living in groups can also be expensive.
• One cost can be increased competition for food.
• When thousands of royal penguins crowd together in huge colonies (Figure 47.34), the
pressure on local food supplies is great, increasing the risk of starvation.
• Communal living may facilitate the spread of contagious diseases and parasites.
• Nestlings in large colonies of Cliff Swallows (Petrochelidon pyrrhonota) are often stunted in
growth because the nests swarm with blood-feeding, bedbuglike parasites, Oeciacus
vicarius(Figure 47.35). The parasites move readily from nest to nest in crowded
conditions.
• Some social animals learn to recognize and avoid diseased group members.
• Caribbean spiny lobsters live in groups but avoid conspecifics infected by a lethal virus
(PaV1). It is no surprise that most animals live alone.
• Group living brings both costs and benefits.
• Not all animals that live in groups are social, a term implying some organization of the
group.
• The 10 million Brazilian free-tailed bats emerging from a cave roost near San Antonio, Texas,
are no more a social group than the dozens of people leaving a high-rise apartment or
university residence.
• Within the aggregation, there may be social units, but the aggregation itself is not
necessarily a social unit.
• Social animals usually live in groups characterized by some form of structure.
• Some individuals may dominate others (a dominance hierarchy), manifested in access to
resources.
• Dominant (alpha or α) individuals get priority access to food (or mates or sleeping sites).
• In some situations, only dominant individuals (a male and a female) reproduce.
• Dominance hierarchies may be absolute, such as when the same individual always has
priority access to any resource.
• In relative dominance hierarchies, an individual’s status depends on the circumstance.
• One individual may dominate at a food source, while another may dominate in access to
