Life Histories

All the events that affect an organism's survival and reproduction make up its life history. The pattern of these events varies across species, even among organisms living in the same habitat.

For example, a small snail matures quickly and produces thousands of eggs.

Most of these offspring die early in life, so producing many eggs increases the chance that a few survive to adulthood.

This pattern reflects an r-selected strategy, a term used to describe species that produce many offspring and provide little parental care.

Species with this strategy often show a Type III survivorship curve, characterized by high mortality early in life. Individuals that survive the early stages have a much higher chance of reaching adulthood.

On the other hand, howler monkeys follow a K-selected strategy. They mature slowly, have only a few offspring over a long lifespan, and provide years of parental care to help ensure their survival.

These primates show a Type I survivorship curve, characterized by high survival rates during early and middle life and high mortality in old age.

The final survivorship curve, Type II, shows an equal probability of survival and mortality throughout an organism's life cycle.

For example, many songbirds face similar threats from predators, disease, and environmental stress at every age. Because of that, their survivorship curve forms a steady diagonal line.

These survivorship curves show how different species adopt different strategies to balance their survival and reproduction.