Introduction

A life history can be defined as the timing of and relative investment of energy in survival, growth, and reproduction (Figure 1). However, such a simple definition belies the complexity of life-history patterns we observe in nature. For example, trees may survive for hundreds of years while many insects live for only days. Marine mammals may have only a few offspring in a lifetime while some marine fish can produce hundreds of thousands of eggs every time they reproduce. This is the diversity of patterns that the study of life histories attempts to explain.

Ecological and evolutionary processes interact to produce variation in life history. For example, predator-prey interactions depend on the population dynamics of both predators and prey. Yet predation, as a source of mortality, influences the evolution of traits affecting body size and reproduction in prey. Prey reproduction will in turn affect prey population growth rate and thus the biomass of prey available to predators affecting predator

size growth at maturity and future reproduction -Time -

Figure 1 An organism's life history can be represented by its survival, growth, and reproduction through time. However, a life history is actually a composite of many individual traits (such as initial size) and is influenced by multiple life-history tradeoffs (such as between offspring size and number). This figure presents one possible life-history pattern where each circle is a different age and the size of the circle represents body size. Arrow width represents survival between age classes and the contribution through reproduction to future generations. In this example, the hypothetical organism has an equal probability of survival across all age classes, does not grow following maturity, and total reproductive effort (offspring size and number) increases with age.

size growth at maturity and future reproduction -Time -

Figure 1 An organism's life history can be represented by its survival, growth, and reproduction through time. However, a life history is actually a composite of many individual traits (such as initial size) and is influenced by multiple life-history tradeoffs (such as between offspring size and number). This figure presents one possible life-history pattern where each circle is a different age and the size of the circle represents body size. Arrow width represents survival between age classes and the contribution through reproduction to future generations. In this example, the hypothetical organism has an equal probability of survival across all age classes, does not grow following maturity, and total reproductive effort (offspring size and number) increases with age.

reproduction and population size. When thinking about life-history patterns, it is impossible to disentangle evolution from ecology and ecology from evolution.

The study of life-history patterns has a long history of theoretical and empirical research. We generally understand the selective pressures that determine basic life-history traits such as age at first reproduction, number of reproductive bouts, partitioning of reproductive effort, and longevity. Yet many questions remain unanswered, such as how environmental variation and climate change may affect life histories and how the details of life-history variation affect ecological communities. In addition, new methods (such as novel genetic techniques and modeling approaches) continue to advance our knowledge and raise new questions.

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