Life history is a collection of hypotheses that explain why animals differ in so called life history traits which includes size at birth, growth and developmental schedules, age and size at maturity, number, size, and sex ratio of offspring, reproductive schedules, mortality schedules. These traits are explained as a result of the specific properties of the ecologies the species evolved in.
r/K-selection[edit | edit source]
r/K selection was the predecessor of the life history theory which superseded it, adding additional mechanisms explained in the sections below (tbd). At the core of r/K selection is a distinction between two kinds of ecologies on the opposite of a spectrum:
- Unpredictable, but easy ecologies, e.g. tropical regions are full of competing animals, but food is readily available. Animals in such ecologies are said to be r-selected, where r is the growth rate and r-selected means maximizing growth rate. This means making as many offspring as possible and not investing much in it, hoping it will make its way through the unpredictable but easy, i.e. requiring little guidance on part of the parents (r-strategies). R-strategists have a fast life history (speed).
- Predictable, but harsh ecologies, e.g. cold regions have relatively low population counts as food is hard to attain through the winter. Animals in such ecologies are said to be K-selected, where K is the carrying capacity of the environment. In harsh ecologies this capacity is low, so species produce few offspring and care for them, and maintain the population size near the maximal carrying capacity. K-selected species evolve "K-strategies" that emphasize high levels of parental care, resource acquisition, kin provisioning, and social complexity. The K-strategy requires more complex nervous systems and larger brains. K-strategists have a slow life history.