lect 10 - Biology 5C, Spring 2008 April 21 - Walton LECTURE...

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Biology 5C, Spring 2008 April 21 - Walton LECTURE 10: Life Tables and Unregulated Population Growth What factors determine how fast a population grows? Factors which add individuals: births and immigration Factors which subtract individuals: deaths and emigration We will restrict most of our discussion of population growth to closed populations : no immigration or emigration. ..or the rates are so small to be inconsequential! How fast a population will grow depends on the composition of the population. One with a high proportion of females in a reproductive age range will grow more rapidly than one composed mostly of post-reproductive and pre-reproductive individuals. Age structure is important . Death rates and fecundity rates vary with age and sex. Two statistics in particular summarize the vital statistics of a population, and allow calculation of potential population growth rates. l x : survivorship, or the probability of a newborn individual surviving to age x . Three types of survivorship ( l x ) curves observed in organisms (see Fig 52.3). Note that the curves are plotted on a semi-logarithmic scale! 1
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Biology 5C, Spring 2008 April 21 - Walton 0 1 2 3 4 5 6 Average # of offspring per female Age-specific fecundity: an m x (or b ) curve Age m x : age-specific fecundity; the average number of female offspring per female of age x. Parameters that are important: 1) age at first reproduction 2) fecundity: average number of offspring per episode (clutch size) 3) survivorship: how many females of a particular age, x , are reproducing In addition to the mean number of offspring per reproductive episode, the number of reproductive episodes/lifetime (parity: semelparous vs. iteroparous ) is important.
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lect 10 - Biology 5C, Spring 2008 April 21 - Walton LECTURE...

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