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Lec 21.docx

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Biology 1001A
Tom Haffie

Lec 21: Population Ecology 2 • read text sections 45.3-45.5 • Age structure and population growth • Life tables and survivorship curves • Life history strategies • Models of population growth Characteristics of populations can affect population growth rates - Age structure valuable to know because knowing the proportion of individuals that - are young or can reproduce tells us how fast the population has been growing in the past/ the potential for reproductive success . - We can tell what is going to happen to the population in the future, - Left (Zero Growth)- the population in not growing- there are enough prereproductive individuals to eventually replace the reproductive individuals. - Middle (negative population growth)- more individuals dying the being added by new births Life table analysis • summarize survival and reproduction for a cohort of individuals • Population ecologists summarize the rates of population growth in the form of life table analysis. • Take individuals of the same age and follow their lives • See who is alive at the beginning, see who makes it to the following age interval. Then calculate the age specific mortality rate/ survivorship rate. • - Used by insurance companies to adjust their premiums Survivorship curves - Plots the porportion of individuals alive at the beginning of the cohort with the percentage of life span - Type 1- (very large vertebretes + humans)- Low risk of dying throughout most of the lifetime- mortality speeds up at the end of the lifetime (speeds up with old age: monesence) - Type 2- constant risk of dying throughout your whole life (happens when mortality is independent of age: natural disaster, predators) - Type 3- Vast majority of mortality happens early in life (once individuals reach a favourable body size they are likely to survive) - Illustrates variation in life history characteristics. Life history characteristics • Life history: balancing energy or resources given competing demands – growth – reproduction – self-maintenance (repair) • Different environments favour different life histories • No matter what kind of organism you are, you go through growth, reproduction, and self maintenance (requiring energy) • Even within a species we can see that differeent environments favour different life history patterns Quantity vs quality… r and K Dicotomy- all organisms will fall between r-selection and k-selected R stratigists – (ex. Fruit fly) Maximizing amount of offspring produced- often have a single reproductive cycle- they invest relatively little in one offspring K stratagists- (ex human)- generation time is slower- the typically produce fewer larger offspring and invest a lot of care into those few offspring. Sometimes animals can fall in between the 2 classifications Modeling population growth • DN = # births (and immigrations) - # deaths (and emigrations) • B, D, I, E (total # of births, deaths, immigrations, emigrations per unit time) • DN/Dt = (B + I) – (D + E), per unit time Per capita birth and death rates: - These predict how fast a population is going to grow in size - Birth, Immigration- increase N - Death, Emigrations- decrease sizes
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