Explore the reproductive strategies of animals with this IEB-aligned Grade 12 Life Sciences summary, covering courtship, competition, fertilization methods, and development types (ovipary, ovovivipary, and vivipary). This document explains how these strategies maximize reproductive success across s...
Animal Reproductive Strategies
Reproduction: the production of a new generation (o!spring) of organisms from an existing generation
What is the goal of each species?
- produce the maximum number o! surviving o!spring while using the least amount of energy di!erent
environments, this is known as reproductive success
1. Reproduction/ copulation occurs
2. O!spring are produced
3. O!spring reach reproductive age
I. COURTSHIP AND COMPETITION
Types of competition:
‣ Direct male competition:
- Occurs often between males over a potential mating partner. This competition occurs when
females can only mate with a single male, which is typically the winner of the competition
- Often includes aggression ("ghting) between males, but can take on other forms.
‣ Female choice:
- Females chose ‘best’ male to mate with based on observing the male completion.
- Usually leads to selection for very ‘showy’ traits, that don’t appear to provide any bene"t to the
individuals survival, and might even make it more likely for the animal to be attacked by a predator
(I.e peacocks tail), however sometime the trait can improve likeliness of successful reproduction
Courtship behaviours: Behaviour and/or signals that are designed to attract animal for mating and
breeding
Simple strategies
‣ Includes chemical (pheromones), visual (brightly coloured body parts) or auditory stimuli which can
be used singly or in a combination.
- Female moths can release species-speci"c pheromones that attract males towards them
- Once male frogs reach breeding grounds they a species speci"c sing to attract females.
- Male birds signal when they are ready to mate by singing a species speci"c song that attract
females. Once they meet, male must stimulate the female sexually, often by special plumage.
Complex strategies
‣ elaborate forms of courtship that are unique to each species
‣ 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 promise healthier o!spring (more will survive).
, ‣ Springbok have an annual rut (period of sexual excitement), usually when animals re in peak
condition. To attract females, males defend territories with loud grunts, attack vegetation with their
horns and deposit middens of urine and dung in a ritualised display.
‣ Most young are born six months later in the spring, shortly before the rainy season begins. The timing
of this dimly ensure that:
- The mothers are in good condition
- The young are born when there will be enough food to enable them to reach reproductive age.
Rutting strategy results in breeding only taking place if conditions are favourable
‣ Lekking is a specialised form of courtship ritual where many males gather together in one place
and “display” at the same time, allowing females to choose amongst them.
II. EXTERNAL VERSUS INTERNAL FERTILISATION
EXTERNAL FERTILISATION
Takes place in water and occurs in most aquatic vertebrae’s, e.g "sh, and frogs
It is not an ideal process as:
‣ A huge number of eggs are produced, but many are eaten and lots of young do not reach maturity
(wasteful)
‣ Fertilisation is not certain.
How can external fertilisation maximise reproduction
‣ Huge numbers of eggs and sperm are released into the water. This increases the probability of
fertilisation, the large number of fertilised eggs will ensure there will be enough to grow into adults even
though they are lost to predation
‣ Courtship rituals: many male and female "sh swim close together to ensure male and female gametes
are close together
Note: reproductive energy expenditure goes almost totally into producing the large number of eggs.
INTERNAL FERTILISATION
‣ Occurs in terrestrial vertebrae’s e.g reptiles, birds and mammals.
‣ Gametes are released directly into the body of the female during mating/copulation 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 cloacas
‣ Most male mammals have penises to introduce the sperm into the female. ( penis ensures that sperm is
transferred successfully without being destroyed by any environmental conditions.
How does internal fertilisation maximise reproductive success.
‣ Fertilisation is more certain as gametes are placed as close together as possible. (Fewer gametes are
therefore needed)
‣ Energy is saved in producing gametes and thus can be used for other purposes to maximise
reproduction. (e.g a protective shell and increased yolk can be produced or development can be internal
via placenta)
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