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Biology 1001A- Lecture 21.docx

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Western University
Biology 1001A
Tom Haffie

Biology 1001A Lecture 21: Population Ecology II November 23, 2011 Read text section 46.1, 46.4 Population Ecology:  Age structure and population growth  Life tables and survivorship curves  Life history strategies Characteristics of Populations can affect population growth rates  Ex. Age Structure o A larger ‘base’ will have a larger younger population  Potential for rapid future population growth o A Stable or equal base will maintain it’s population (Zero Population Growth) o A narrow base will have negative growth. Not enough young population. Future growth will decline. Life Table Analysis  Summarize survival and reproduction for a cohort of individuals Survivorship Curves  Type 1: Vey little risk of mortality, until you get really old (a fraction of total lifetime). Happens to larger animals, small numbers of offspring, and larger body size. Humans have similar characteristics. (looks like negative exponential)  Type 2: For small body animals (birds, mice, etc…) most things are not dying from old age, instead due to nothing with age, for example, dying in a flood. (Graph looks like a negative steady decline).  Type 3: Produces a large number of offspring. Most die early in age. Life History Characteristics  Life history: balancing energy or resources given competing demands o Growth o Reproduction o Self-maintenance (repair)  Different environments favour different life histories Quantity vs. Quality… r and k  R-selected Species: o Don’t live very long o Produce a large number of offspring o Unstable environments  K-selected species: o Invests more in offspring o Smaller number of offspring o Able to compete for limited resources Modeling Population Growth  ∆N = [# Births (and immigrations)] – [# of deaths (and emigrations)]  B, D, I, E (total # of births, deaths, immigrations, emigrations per unit time)  ∆N/∆t = (B+I) –(D+E), per unit time  Per capita birth and death rates:  b = B/N, d =D/N Intrinsic Growth Rate = r  R = (Births/N) – (deaths/N) o Example: A small town in Kenya  Starting N= 1000  60 babies born each year (b= 60/1000 =0.06)  30 deaths each year (d= 30/1000 = 0.03)  r = (0.06 – 0.03) = 0.03 (3%)  Net change of +30 people/ yr  In the exponential model of growth…. Exponential Population Growth  dN/dt = rN o Grows if r > 0, shrinks if r < 0 o Doubling time = 7/r (in %)  But often unrealistic to assume growth is independent of N L
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