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Chapter 5 Populations

Chapter 5 Populations. 5.1 How Populations Grow. Describing Population Geographic Range : area inhabited Density and Distribution : Population Density - # of individuals per unit area Distribution – individual spacing in a population (random, uniformly, clumping

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Chapter 5 Populations

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  1. Chapter 5 Populations

  2. 5.1 How Populations Grow • Describing Population • Geographic Range: area inhabited • Density and Distribution: • Population Density - # of individuals per unit area • Distribution – individual spacing in a population (random, uniformly, clumping Wild Flowers King Penguin Striped Catfish • Growth Rate: size of population over time (increase, decrease, stay the same) • Age Structure: # and age of males/females

  3. Population Growth • Birthrate & Death Rate: influence whether pop grows, stay the same or decreases • Immigration: moving into range (increased good supply) • Emigration: moving out of range (food shortage)

  4. Exponential Growth: occurs with unlimited resources; # of offspring increases with each new generation • Organisms that reproduce rapidly : (bacteria reproduce very 20 minutes) • J–curve: slow growth first then faster • Organisms that reproduce slowly: • Organisms in new environment: (invasive species: no natural predators)

  5. Logistic Growth • Phases of Growth: • Phase1: Exponential w/initial unlimited resources (few die; many reproducing) • Phase 2. Slows: pop. grows at slower rate • Phase 3. Stops: zero growth rate (curve levels off; pop. can remain here indefinitely)

  6. Logistic Growth Curve: • S-shaped curve • Exponential growth slows, then stops • Decreased birthrate; increased death rate • Decreased immigration; increased emigration

  7. Carrying Capacity: • Max # of species individuals environment can support • Birthrate = death rate; immigration = emigration • Slight pop. change over time; stabilizes at that approx #

  8. 5.2 Limits to Growth • Limiting Factors: (ie: limiting nutrient controls productivity) • Control the growth of populations • Determines carrying capacity of envirnmt for species • Shaped history of life on earth (Darwin)

  9. Density Dependent Limiting Factors • Operate when # of org/unit area reach certain level • Competition: for limited essential resources w/ pop • Within species: some thrive/reproduce; some starve (can lower birthrate/increase death rate) • Between diff species: can drive evolutionary change

  10. Predation and Herbivory: • Predator-prey Relationships • Pop. cycle up or down (or fluctuate) over time • Isle Royal: Wolves and moose • Herbivore Effects: herbivores/plants pop. also fluctuate • Isle Royale: Moose and Balsam Fir (overgrazing) • Humans as Predators • Cod birthrate can’t keep up w/Hi death rate • Biologists use birthrate/age structure data est. limits

  11. Parasitism and Disease: • Both weaken/kill host; spread easier w/high population • Isle Royale Canine Parvovirus left 3 breeding females • Stress from overcrowding: • Too much fighting: ↓ birthrates, ↑ death/emigration CPV is life threatening and can affect the heart or intestinal tract with symptoms of vomiting/ diarrhea

  12. Density-Independent Limiting Factors: • Unusual weather/natl disasters affect all pops similarly • Hurricanes, floods/wildfires • Can cause pop to “crash” (be decimated) then rebound • True Density Independence? • Moose pop exploded after CPV – pop crashed with harsh winter=effects greater w/unnaturally dense pop • Controlling Introduced Species • Artificial measures (removal) temporary/expensive • Best to find/introduce natural predator=sterilize for minimal adverse effects

  13. 5.3 Human Population Growth • Historical Overview: Slow past growth w/limiting factors: scarce food/predators/disease=↑ death rate=multiple offspring w/few surviving • Exponential Human Population Growth • Industrial revolution improved nutrition/medicine = ↓ death rates w/birthrates remaining hi • The Prediction of Malthus • Exponential growth can’t last • Growth limited by competition-war; scarce resources-famine; parasitism-disease • Density Dependent Limiting Factors • World Population Growth Slows • Exponential Growth through mid-sixties; then slowed

  14. Patterns of Human Population Growth • Demography: study of human growth (birth/death rates and age structure) • The Demographic Transition • Shift from High birth/death rates (Phase 1) to low birth/death rates (Phase 3) = U.S, Japan, Europe; J to S curve • Age Structure and Population Growth • A higher % of young people = growing population; equal age group # = slower, steady growth • Future Population Growth • Approx. 9 billion by 2050; but grow more slowly than last 50 years

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