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BIO120H1 (305)
Chapter 7

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University of Toronto St. George
James Thomson

Chapter 7Life Histories and Evolutionary Fitness132144 A 148155 A remainder CLife history the schedule of an individuals lifewhen it reproduces how many young in raises how long it lives etc includes all behavioral and physiological adaptations Life histories vary extremely between species though ultimately each has about the same reproductive chances ie having one offspring survive to maturity Specific modifications of form and function are thought to be adaptive of an individual to increase its reproductive chances These modifications are frequently linked to environmental factors and resource availability eg birds can raise fewer young when food is limited Generally the number of young that a species rears is specific to how many will likely survive adding more or few will detrimentally affect with compromise of efficiency Behaviors which lead to increased reproductive fitness also add to evolutionary fitness ie organisms which successfully reproduce will pass on their genes Despite this no one species gains a particular advantage over the long term as all species are in perpetual competition for resources In any environment resources are limited and individuals must adapt appropriate to either increase the range resources they may use or improve the efficiency with which they use resources These modifications either behavioral or biological are essentially tradeoffs ie when you devote more resource to a particular structure or function you decrease resource availability for other structure or processes Allocation using available resources in such a way as to achieve maximize fitness To understand specific modifications it is generally necessary to examine an individuals entire life history as tradeoffs obviously affect other systems Some very important components of life history are maturity ie first reproduction parity number of reproductive episodes fecundity number of offspring produced per reproductive episode longevity life expectancy Components of an individuals life history are generallyrelated by time frame Some organisms have accelerated time frames ie they quickly mature have many offspring and short longevity there individuals are often small in size and serve as prey for many other creatures On the opposite end of the spectrum are individuals with slower time frames ie take many years to reach maturity and have few offspring over their long lives often large in size and have few predators
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