Notes are written on Reproductive Animal Strategies from the Grade 12 IEB Life Science syllabus. These notes are very clear and easy to understand and are really helpful.
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IEB Gr 12 Biology Population Dynamics and Community Ecology
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REPRODUCTIVE ANIMAL STRATEGIES
Reproduction = the production of a new generation of organisms from an existing generation
THE GOALS OF EACH SPECIES:
To produce the maximum number of surviving offspring while using the least amount of
energy = reproductive effort
Asexual reproduction is energy efficient (low reproductive effort) because it only involves a
single animal
Sexual reproduction is more complex needing a much higher energy input (high reproductive
effort)
Unique reproductive strategies have therefore developed that will ensure maximum
reproductive success in different environments = it enables species to breed successfully and
then survive to a reproductive day
Strategy = genetically determined behaviour -COURTSHIP
-EXTERNAL VS FERTILISATION
STRATEGIES:
-OVIPARY, OVOVIVIPARY
A. COURTSHIP
AND VIVIPARY
- these strategies are used to select partners for reproduction
- these strategies can be simple/complex -PARENTAL CARE
1.SIMPLE STRATEGIES
Simple strategies such as chemical, visual or auditory stimuli are used for mates to find each other –
they can be used singly or in combination
Eg:
moths produce species-specific pheromones that guide males towards them
frogs have to return to the water for mating and breeding, once the males reach the
breeding ground they sting (grunt, croak) to attract females
male birds advertise when they are ready to mate by singing a species-specific song that
attracts females, once they mate the male then impresses and stimulate the female sexually
often by special plumage
2.COMPLEX STRATEGIES
The more elaborate forms of courtship are unique to each species
The females usually favour males that are:
- larger
- have more elaborate physical features
- display more energy in courtship activity than other males
This helps the female to choose the better male, which can reinforce pair bonding (important for
parental care) and promises healthier offspring
Eg:
the blue cranes courtship displays include:
o a complex and extended series of calls
o elaborate dances by the males
springbok have an annual rut (a period of sexual excitement), usually when the animals,
males defend territories with loud grunts, attack vegetation with their horns and deposit
middens of urine and dung in a ritualized display. Most young are born 6 months later in the
spring, shortly before the rainy season begins. The timing of this display ensures that:
, o the mothers are in good condition
o the young are born when there will be enough food to enable them to reach
reproductive stage
the rutting strategy results in breeding only taking place if conditions are favourable
the male African hoopoes (bird) exhibit courtship feeding by feeding insects to their mates =
it allows for the female to save her energy for incubating and brood
HOW COURTSHIP MAXIMISE REPRODUCTION:
courtship mechanisms ensure that males and females find suitable mates eg: the strongest
male
sexual behaviour in courtship is timed so that the male and female are ready for mating at
the same time
energy expenditure is usually by the male, the female conserves her energy for breeding
as a result of these factors, it is more likely that strong healthy offspring will be produced
B. EXTERNAL VS INTERNAL FERTILISATION
Fertilization = the joining of the nucleus of an egg and sperm. The sperm are motile as they are able
to swim but eggs do not movie
1.EXTERNAL FETILISATION
It takes place in water and occurs in most aquatic vertebrates eg: fish & frogs
Not an ideal process as:
it is wasteful as huge numbers of eggs are produced – most of the eggs are eaten
fertilisation is not certain
HOW THEY MAXIMISE EXTERNAL FERTILISATION
As fertilisation is not certain in water, to maximise reproductive strategies success, aquatic animals
must use various strategies. Some of the strategies include:
Huge numbers of eggs and sperm are released into the water. A male frog sheds millions of R-strategy
sperm and a female sheds 2000 to 3000 eggs in the water. This increases the probability of
fertilisation. With the large number of fertilised eggs there are enough to grow into adults
even though many are lost to predation.
Courtship rituals eg: many fish side by side when releasing their eggs and sperm which
ensure that the male and female gametes are close to each other
It is important to note the reproductive energy expenditure goes almost totally into producing the
large number of eggs
2.INTERNAL FERTILISATION
This occurs in terrestrial vertebrates eg: reptiles, birds and mammals. With no external water for the
sperm to swim in, the male gametes are released directly into the body of the female (during
mating) and fertilise the eggs inside the body.
most birds and reptiles mate using a cloaca – a single opening located in the lower
abdomen. During mating, the males and females line up their cloacae for the transfer of
sperm
the males of virtually all mammals have a penis to introduce sperm into the female. This
process is known as copulation. The penis ensures that sperm is transferred successfully
without being destroyed by any environmental conditions.
, HOW DOES INTERNAL FERTILISATION MAXIMISE REPRODUCTION
K-strategy
Fertilisation is more certain as the gametes are placed as close together as possible therefore fewer
gametes are needed.
INTERNAL FETILISATION EXTERNAL FERTILISATION
k-strategy r-strategy
Land animals Water animals
Care taken for gametes to meet safely. Release gametes directly into water – sperm
Fertilisation happens inside female’s body swim to ova
Few ova produced Large number of ova produced
Complex mating organs Non-complex mating organs
Specialized eggs Non-specialised eggs
Parental care No parental care/protection
C. OVIPARY, OVOVIVIPARY AND VIVIPARY
- terms for reproductive strategies that describe the moment at which the future offspring separates
from a parent. These strategies indicate:
where the embryos develop
how the embryo and foetus are nourished
1.OVIPARY
In oviparous animals, eggs develop outside of the parent. This may be fertilised externally or
internally.
The majority of animals are oviparous. Egg yolk is the only food that the developing embryos receive
until; they hatch from the egg.
HOW THEY MAXIMISE REPRODUCTION IN AQUATIC ENVIROMENTS
- most fish and amphibians are oviparous
- the eggs are released into the water and are fertilised externally.
- a large amount of eggs is needed as the developing embryos are vulnerable to predation
- the vast number ensures the survival of species but it requires a high input from the female
Eg: Catsharks
- they are oviparous
- the females lay egg cases that are known as mermaid purses
- these eggs contain the embryo and yolk supply, and the young shark eventually hatches out
of the case
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