Summary of Chapter Concepts

Life history traits represent the schedule of an organism’s life. Species differ in a wide range of traits that help determine their fitness throughout their life including the birth or hatching of offspring, the time required to reach sexual maturity, fecundity, parity, and longevity. These traits are under the influence of natural selection and often evolve in particular combinations.

Life history traits are shaped by trade-offs. Trade-offs can occur because of physical constraints, time or energetic constraints that affect allocation, or genetic correlations that cause selection favoring one trait to come at the cost of another trait. Common trade-offs include offspring number versus offspring size, and growth versus reproduction.

Organisms differ in the number of times that they reproduce, but they all eventually become senescent. Semelparous organisms breed once in their life whereas iteroparous organisms breed more than once. Regardless of how many times an organism breeds, it ultimately experiences a decay in physiological function followed by death. In semelparous organisms, this decay in function occurs rapidly after reproduction. In iteroparous organisms, the decay in function can be very gradual.

Life histories are sensitive to environmental conditions. As with all phenotypes, life history traits are the product of genes and environments interacting. Some of the most common environmental influences on life history traits include variation in resources and predators, both of which can induce substantial changes in the life history of organisms. Current anthropogenic changes in the environment can also affect life history traits by altering environmental cues—such as temperature—that induce life history changes.