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Biology Lecture 21.docx

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Biology 1001A
Tom Haffie

Biology Lecture 21:Population Ecology 2  Characteristics of populations can affect population growth rates: o Age Structure: the proportion of individuals that are pre reproductive (too young to reproduce) versus reproductive ages versus too old to reproduce  Life table analysis: o Life table analysis: we choose a large number of individuals that are the same age o Looks at and classifies the typical lifespan for the species or the population we are looking at, into different age classes. o Analyzes how many are alive at the beginning of the age interval and what proportion of those individuals successfully survive to the start of the next age interval  Survivorship curves: o Survivorship curves make use of the same information life tables o Allow us to analyze when most of the mortality occurs in a life span o There are three main types of survivorship curves:  Type 1: short risk of death until old age (typically large animals like humans)  Type 2: the risk of mortality is usually constant, usually nothing to do with old age (typically small vertebrae animals like lizards)  Type 3: most die in early life and do not make it to adulthood, thus an older individual has a larger chance of survival than a young one (typically in animals that produce many offspring like fish)  Life history characteristics: o All organisms must partition their energy into a combination of these three processes:  growth  reproduction  self-maintenance (repair) o The way an organisms balances these demands above is called their life history strategy  Quantity vs. quality...r and K: o r-selected species: focus on quantity of offspring (Example: mice) o K-selected species: focus on quality of offspring (Example: humans)  Modeling population growth: o ∆N= # births (and immigrations)- # deaths (and emigration)  Represents the increase or decrease in population over some unit of time. o B, D, I, E (total # of births, deaths, immigrations, emigrations per unit time) o ∆N/∆T = (B+I) - (D+E), per unit time o Per capita (per individual) birth and death rates: b= B/N, d=D/N  Intrinsic growth rate = r : o r = (births/N) - (deaths/N) o In the exponential model of growth, we are going to assume r is independent of population size  Exponential population growth: o According to the exponential model of growth the rate of change in population is equal to: dN/dt = rN o When r >0 the population is going to increase over time o When r<0 the population is going to decrease over time o Doubling time = 70/r (in %) o Assumes population size is not going to influence the value of r (in most natural populations this is not a good assumption to make)
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