Advantages & Disadvantages of Internal and External Reproduction

Internal Reproduction.

Advantages:

1. Increase chance gametes meet
2. greater change of successful fertilisation
3. More protection against outside environments and predators, and therefore a higher chance of surviving until birth.
4. More selective of their mates 
5. Less chance of desiccation of gametes

Disadvantages:

1. Harder to bring both male and female into intimate contact
2. Limited amount of offspring being produced at any given time. 
3. Higher risk of sexually transmitted diseases being passed on.

External Reproduction.

Advantages:

1. Results in the production of a large number of offspring
2. Easier to find mates as the gametes released can drift (wind, water etc).
3. More genetic variation

Disadvantages:

1. Environmental hazards such as predators reduce the change of surviving into adulthood.
2. Large amounts of gametes go unfertilised and wasted.
3. Not guaranteed that sperm will come in contact with eggs
4. Greater chance of desiccation of gametes/zygotes.

http://adarwinstudygroup.org/sexuality/internal-external-fertilization/