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Population Studies

Population Studies. Chapter 5 Sections 1 and 2. Defining Populations. The researcher must define the population’s geographic boundaries Ex: Edges of a lake for a trout study, a state for coyote, a Petri dish of bacteria, etc. Population Density.

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Population Studies

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  1. Population Studies Chapter 5 Sections 1 and 2

  2. Defining Populations The researcher must define the population’s geographic boundaries Ex: Edges of a lake for a trout study, a state for coyote, a Petri dish of bacteria, etc.

  3. Population Density The number of individuals of a particular species per unit area or volume • Ex: In a forest measuring 50 km2, a researcher counted 1000 birch trees. What is the population density? PD = 1000 birch trees = 20 trees/km2 50 km2 Population density is useful measurement to compare populations in two or more locations.

  4. How to Calculate Growth Rate Growth Rate is the change in population size over time elapsed. Ex: A population of sea lions decreased from 10,000 to 8,500 from 1995 to 2005. What is the growth rate? GR = 8500-10000 = -1500 = -150 sea lions/year 2005-1995 10

  5. Population Growth can be Positive, Negative, or Zero Positive Growth Rates • Birth Rate (number of births per year) • Immigration (number moving IN per year) Negative Growth Rates • Mortality or Death Rate (deaths per year) • Emigration (number moving OUT per year) Zero Population Growth • No change in population size

  6. EXPONENTIAL Population grows at a constant rate Represented with a J-curve LOGISTIC Population may grow exponentially at first, but eventually one or more factors will limit its growth Represented with an S-curve Types of Growth

  7. Exponential Growth Doubling Time: The time it takes for a population to double in size The larger the population gets, the faster it grows!!

  8. Logistic Growth A limiting factor is a condition that restricts a populations growth. Ex: food, space, disease, etc. The carrying capacity is the number of individuals an environment can support for a period of time with no net increase or decrease. (Zero Population Growth)

  9. DENSITY-DEPENDENT Limits the population more as density increases Typically BIOTIC factors (predators, competitors, parasites) except for space which is abiotic DENSITY-INDEPENDENT Limits growth, but is unrelated to density Typically ABIOTIC factors (rain, wildfires, temperature, ice, etc.) except for human disturbances which are biotic (ex: pesticides) Types of Limiting Factors

  10. Population Growth Cycles • Populations of predators and prey “boom & bust” in a staggering fashion to keep numbers in check • Some populations do this on their own (possibly controlled by hormones)

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