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Chapter 9

Chapter 9.docx

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Melody Neumann

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9.0 Life Histories and Evolutionary Fitness o The schedule of an individual’s life – age at maturity, number of offspring, life span- makes up what ecologists call the life history of the individual. Life histories include all the behavioral and physiological adaptations of organism, and all the individual response of organisms to their environments because all of these ultimately contribute to reproductive stress. Life histories are complex phenomena influenced by physical conditions, food supply, predators, and other aspects of the environment Chapter Concepts  Trade-offs in the allocation of resources provide a basis for understanding life histories  Life histories vary along a slow-fast continuum  Life histories balance trade-offs between current and future reproduction  Semelparous organisms breed once then die  Senescence is a decline in physiological function with increasing age  Life histories respond to variation in the environment  Individual life histories are sensitive to environmental influences  Animals forge in a manner than maximizes their fitness o Ecologists have used observation, mathematical modeling, and experimentation to explore why life histories differ so much among species. In 1947, David Lack of Oxford University was the first person to recognize that these differences in reproductive strategy had evolved in response to differences between tropical and temperate environments. Lack made three important points: 1. stated that because life history traits, such as the number of eggs in a clutch(the set of eggs laid together in a nest), contribute to reproductive success, they also influence evolutionary fitness 2. demonstrated that life histories vary consistently with respect to factors in the environment, such as the length of time available for feeding young. This observation suggested that life history traits are molded by natural selection. 3. Proposed a hypothesis that could be subjected to experimental testing o Selection favours individuals with the highest fitness relative to other individuals in the same population 9.1 Trade-offs in the allocation of resources provide a basis for understanding life histories o Tradeoff: a consequence of devoting limited time, energy or materials to one structure, function or behavior at the expense of another o Allocation: The division of limited time, energy, or materials among competing functions or requirements o Parity: the number of episodes of reproduction in an individual’s lifetime o Reproduction involves many allocation problems: when to begin to breed, how many offspring to have at one time, how much care to bestow upon them. How the resolution of these problems influences and individual’s survival and reproduction at each age governs the evolution of the life history. Each life history has many components, the most important of which are age at maturity, parity, fecundity and longevity 9.2 Life Histories vary along a slow-fast continuum
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