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Life Science/ Biology grade 11-12 summary of animal strategies (IEB)
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A comprehensive summary of animal strategies from the mind action series textbook (IEB) from an A (80%+) student
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BIOLOGY PRELIMINARY NOTESKIARA DURKIN
REPRODUCTIVE ANIMAL STRATEGIES
The goal of each species
• Produce the maximum number of surviving offspring while using the least amount of energy
= reproductive effort
• Asexual reproduction found in lower and microscopic organisms have a low reproductive
effort
• Sexual reproduction in all vertebrates requires a higher reproductive effort
Strategy: genetically determined behaviour
1. Courtship (behaviour/ signals that are designed to attract another animal for mating and
breeding)
• Simple strategies: chemical (pheromones), auditory or visual (bright colours) stimuli
- Females emit pheromones that indicate that they are ready to mate
• Complex strategies: elaborate and unique to each species
- Females prefer larger, elaborately featured, energetic males
- Females choose better male = reinforces pair bonding (important for parental
care)
How will courtship maximise reproduction?
- Ensure that males and females find suitable mates
- Sexual behaviour timed – both male and female are ready to mate
- Energy exerted by male; females have more energy for breeding
- Increases likelihood of offspring surviving to sexual maturity
2. External vs internal fertilisation
• External fertilisation:
- Most aquatic vertebrates
- All reproductive energy goes to producing eggs
- Not ideal: fertilisation is uncertain; large number of eggs eaten
Strategies to maximise reproduction from external fertilisation:
- Huge numbers of eggs and sperm released (many survive, many are lost to
predators
- Courtship to ensure male and female gametes are close together
• Internal fertilisation:
- Terrestrial vertebrates
- Birds + reptiles breed using their cloaca
Strategies to maximise reproduction from internal fertilisation:
- Gametes placed closely together
Fewer gametes needed – effort can be placed into parental care/ elaborate
gestation/ incubation
3. Ovipary, ovovivipary and vivipary
• Ovipary: eggs develop outside of the parent
- Could be fertilised internally or externally
- Majority of animals are oviparous – egg yolk is the only food source that
developing embryos receive
, - How does ovipary in aquatic environments maximise reproduction?
Embryos well protected
High amount of effort placed into producing and laying eggs
- How does ovipary in terrestrial environments maximise reproduction?
Few eggs produced = more energy to protect + incubate; produce nutrient rich
eggs; allows offspring to be fully formed when hatched
Shell protects against predators, pathogens, damage, and dehydration
• Ovovivipary: eggs are fertilised internally and are kept inside female’s body until
ready to hatch
- Not dependent on mother except for physical protection and gaseous exchange
- Egg richly supplied with yolk
- Occurs in many sharks
- How does ovovivipary maximise reproduction?
Fewer eggs produced, mother expends less energy
Developing embryo much less vulnerable to predation, cold temperatures, and
damage
Young are born fully developed: able to get own food and escape predators
• Vivipary: fertilisation is internal and eggs do not have a shell
- Young are born live
- Obtains nutrition from mother through placenta
- How does vivipary maximise reproduction?
Embryo is nourished and protected
Further energy is expended on parental care
- Chances of offspring surviving = high
4. Amniotic egg
• Amniotes (reptiles & birds/ mammals – do not lay eggs) produce eggs that, after
fertilisation, develop extra-embryonic membranes (amnion, allantois, yolk sac &
chorion) – allow embryo to survive + develop on land
• How does amniotic egg maximise reproductive success?
- Embryonic membranes maximise development of embryo and foetus; allows
offspring to survive harsh conditions more easily
- Fluid filled amnion surrounds embryo: protects embryo from dehydration and
mechanical injury
- Allantois: reservoir for nitrogenous waste in birds + reptiles
- Yolk sac: nutritious food that develops embryo
- Chorion surrounds all membranes:
Birds + reptiles – allows for gaseous exchange
Mammals – forms placenta with endometrium to allow foetus to move safely
5. Precocial and altricial development
• Strategies of development, to increase likelihood that offspring will reach
reproductive age, evolved to:
- Provide nourishment to embryo
- Protect them from predation
• Precocial development:
- Hatch/ are born when fully developed
- Parental energy goes into prenatal care; females less involved after birth
- Precocial species at birth/ hatching:
1. Open eyes and hair
2. Large brains
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