Biology lecture 7.docx

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18 Apr 2012
Biology lecture 7
October 3rd
Last lecture(put into last note)
Population overshoot- population quickly increases until carrying capacity and once
there pop quickl falls.
- tau in equation provides time delay
- -increasing delay creates large overshoot
allee effects was interests in social benefits hel in pop growth.
-low threshold. If number fall below it, pop goes to extinction. Above it is ok. If were
above carrying capacity, trouobles also occurs
Age structure:
On pop pyramid, we look at ages of sexes
Age structure pop groeth
- 1 population
- fecundity anf survivorship vary by age
- age structure has age classes
age class intervals
- arbitrary unitsof time chosen to five a reasonable # of age classes for the
organism in question
Life tables
- statsitacl average for an individual in a population
survivorship schedule
- age class as X
- l(x)= probaaility of beng alive a age X
- L0=1. By definition
- Lx declines with x
- Lxcurve representative of a species
- Exponential decay. Probability of death constant through life. Taking log of
exponential line gives straight line
- Three types of life curves.
- Type1: humans where risk of death small in early life higher in later life. Type
III: detah higher in early life as many eggs made
- Lx by X(age class) has infant mortality, it flattens out at mid age and then line
Fecundity schedules
- age class deonted by subscript x
- bx=# of daughter born of age x during interval x to x+1
- shape of bx curve characteristic of species
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