BIOB50 Ch.7

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Biological Sciences
Marc Cadotte

Chapter 7 Life History Analyses Introduction y Life history a record of events and landmarks relating to its growth development and reproduction and survivaly Characteristics that define the life history of a organism Age and size at sexual maturity Amount and timing of reproductionSurvival and mortality ratesLife History Diversityy Life history patterns vary within and among speciesy Study of life histories is concerned w categorizing variation in life history traits and analyzing the causes of that variationIndividuals within species differ in their life historiesy These differences members of a species growing and maturing at different rates may result from genetic variation or from differences in environmental conditionsy However most variation results from a combo of genetic and environmental factorsIndividual variation y Life history strategy of a species is the overall pattern in the timing and nature of life history events averaged across all the individuals in the species It is shaped by the way the organism divides its time and energy bw growth reproduction and survivaly Genetically influenced traits often can be recognized as those that are more similar within families than bw them Eg siblings often are similar in appearance and reach similar heights and weightsy Natural selection favours individuals whose life history traits results in having a better chance of surviving an reproducingy How and why have particular life history patterns evolved Some describe life histories as optimal that is resulting in a maximization of fitness Life history strategies are not necessarily perfectly adapted to maximize fitness particularly when environmental conditions changePhenotypic plasticityy Phenotypic plasticity a single genotype may produce different phenotypes for a particular trait under different environmental conditions Eg growth and development may be faster in higher temperaturesy Plasticity in life history traits can be a source of plasticity in other traitsy Callaway et al 1994 showed that ponderosa pines grown in cool moist climates allocate more biomass to leaf growth relative to sapwood production than do those in warmer desert climates resulting in different tree shapesy Phenotypic plasticity that responds to temp variation often produces a continuous range of growth ratesOther types of phenotypic plasticity produce discrete types or morphs w few or no intermediate formsy This particular type of phenotypic plasticityin which a single genotype produces several distinct morphs is called polyphenism Eg spadefoot toad tadpoles in Arizona ponds contain both omnivore morphs and larger carnivore morphsy Carnivore tadpoles grow faster and are more likely to metamorphose before the ponds where they live dry up
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