2.4 a - parental investment

• sperm is produced in much larger numbers than eggs but each egg has a larger energy store
• females make large investments in the egg structure in non-mammals or in the uterus and during gestation in mammals
• parental investment is costly but it increases the probability of production and survival of the young
• r-selected species give limited parental care so most offspring wont reach adulthood
• k-selected species give a high level of parental care so many offspring have a high probability of surviving to adulthood
• classification of r and k selected organisms is based on the level of parental investment in offspring and number of offspring produced
• r-selected species are smaller, have a shorter generation time, mature more rapidly, reproduce earlier in their lifetime and produce a larger number of smaller offspring which receives a smaller energy output
• k-selected species are larger, live longer, mature slower, can reproduce many times in their lifetime and produce relatively few, larger offspring
• r-selection tends to occur in unstable environments where the species has not reached its reproductive capacity
• k-selection tends to occur in stable environments
• external fertilisation allows very large numbers of offspring to be produced, but many gametes are predated or not fertilised
• in external fertilisation there is no or very limited parental care so few offspring survive
• using internal fertilisation increases the chance of successful fertilisation and fewer eggs are needed
• in internal fertilisation offspring can be retained internally for protection and/or development, and there's a higher survival rate