Strategy

How it works?

What is its advantage?

External Fertilisation

The sperm fertilises the egg outside the body of the female, usually in water.

Water prevents the eggs from drying out and allows the sperm to swim towards the egg.

Internal Fertilisation

The male deposits its sperm inside the reproductive organs of the female and fertilisation occurs inside the female’s reproductive organs.

Allows terrestrial animals to reproduce in a dry environment without the need for water.
Internal fertilisation is more certain than external fertilisation.

Ovipary

Eggs are laid and hatching takes place outside the mother’s body.

Egg provides nutrition for the developing embryo and protects the embryo. A shelled egg frees these animals from the need to reproduce in water.

Vivipary

The young develop inside the uterus of the mother after the eggs are fertilised internally.

More efficient development of the embryo as nutrients are received for a longer period from the mother’s blood through a placenta. Embryo is protected in the body of the mother.

Ovovivipary

Young develop from eggs that are fertilised internally and retained within the mother's body after fertilisation until they hatch.

Embryos obtain their nutrients from the egg yolk. The eggs are protected from predators until hatching occurs.

Amniote Egg

Embryo protected by the shell of the egg; egg consists of many extraembryonic membranes that serve different functions.

Amniote egg protects embryo from dehydration. Yolk sac provides nutrition, Allantois for excretion, chorion for gas exchange.

Precocial Development

Hatchlings are quite well-developed when they hatch - eyes open, able to move, able to feed. Brain size and intelligence remains the  same throughout their lives.

Hatchlings are more prepared to handle the challenges of the environment; More independent.

Altricial Development

Hatchlings are poorly-developed when they hatch. Unable to feed on their own, cannot move. Brain size and intelligence increases a lot after hatching.

Parental care afforded to protect the young from predators.

Parental Care

Parental care offered through building of nests, protecting the eggs, protecting the young, teaching the young.

Increases chances of survival of the young.

COLUMN I

COLUMN II

1. Oviparous

A  Eggs are produced

B  Eggs are always incubated by the female

2. Ovoviviparous

A  Eggs incubated in nests

B  Eggs incubated in the female’s body

3. Precocial

A  Small, helpless offspring born

B  Intense parental care required

4. Viviparous

A  Gestation period required

B  Live offspring born

5. Altricial

A  Intense parental care required

B  Offspring can look after themselves