Chapter 5 Populations 2.pdf
Chapter 5 Populations 2.pdf
Chapter 5 Populations 2.pdf
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<strong>Chapter</strong> 5 <strong>Populations</strong>
5.1 How <strong>Populations</strong> Grow<br />
A.Describing Population<br />
1. Geographic Range: area inhabited<br />
2. Density and Distribution:<br />
‣ Population Density - # of individuals per unit area<br />
‣ Distribution – individual spacing in a population<br />
(random, uniformly, clumping<br />
Wild Flowers King Penguin Striped Catfish<br />
3. Growth Rate: size of population over time (increase,<br />
decrease, stay the same)<br />
4. Age Structure: # and age of males/females
B.Population Growth<br />
1.Birthrate & Death Rate: influence whether pop<br />
grows, stay the same or decreases<br />
2.Immigration: moving into range<br />
(increased good supply)<br />
1.Emigration: moving out<br />
of range (food shortage)
C.Exponential Growth: occurs with unlimited resources;<br />
# of offspring increases with each new generation<br />
1.Organisms that reproduce rapidly :<br />
(bacteria reproduce very 20 minutes)<br />
‣ J–curve: slow growth first then faster<br />
2. Organisms that reproduce slowly:<br />
3. Organisms in new environment:<br />
(invasive species: no natural predators)
D.Logistic Growth<br />
1. Phases of Growth:<br />
‣Phase1: Exponential w/initial unlimited resources<br />
(few die; many reproducing)<br />
‣Phase 2. Slows: pop. grows at slower rate<br />
‣Phase 3. Stops: zero growth rate (curve levels off;<br />
pop. can remain here indefinitely)
2. Logistic Growth Curve:<br />
‣S-shaped curve<br />
‣Exponential growth slows, then stops<br />
‣Decreased birthrate; increased death rate<br />
‣Decreased immigration; increased emigration
3. Carrying Capacity:<br />
‣Max # of species individuals environment can<br />
support<br />
‣Birthrate = death rate; immigration = emigration<br />
‣Slight pop. change over time; stabilizes at that<br />
approx #
5.2 Limits to Growth<br />
A.Limiting Factors: (ie: limiting nutrient controls productivity)<br />
‣Control the growth of populations<br />
‣Determines carrying capacity of envirnmt for species<br />
‣Shaped history of life on earth (Darwin)
B.Density Dependent Limiting Factors<br />
‣ Operate when # of org/unit area reach certain level<br />
1. Competition: for limited essential resources w/ pop<br />
‣ Within species: some thrive/reproduce; some starve (can<br />
lower birthrate/increase death rate)<br />
‣ Between diff species: can drive evolutionary change
2. Predation and Herbivory:<br />
‣Predator-prey Relationships<br />
Pop. cycle up or down (or fluctuate) over time<br />
Isle Royal: Wolves and moose<br />
‣Herbivore Effects: herbivores/plants pop. also fluctuate<br />
Isle Royale: Moose and Balsam Fir (overgrazing)<br />
‣Humans as Predators<br />
Cod birthrate can’t keep up wHi death rate<br />
Biologists use birthrate/age structure data est. limits
3. Parasitism and Disease:<br />
‣Both weaken/kill host; spread easier w/high<br />
population<br />
‣Isle Royale Canine Parvovirus left 3 breeding<br />
females<br />
4. Stress from overcrowding:<br />
CPV is life threatening and can affect the heart or<br />
intestinal tract with symptoms of vomiting/diaharia<br />
‣ Too much fighting: ↓ birthrates, ↑ death/emigration
C.Density-Independent Limiting Factors:<br />
‣ Unusual weather/natl disasters affect all pops similarly<br />
‣Hurricanes, floods/wildfires<br />
‣ Can cause pop to “crash” (be decimated) then rebound<br />
1.True Density Independence<br />
‣Moose pop exploded after CPV – pop crashed with<br />
harsh winter=effects greater w/unnaturally dense pop<br />
2. Controlling Introduced Species<br />
‣Artificial measures (removal) temporary/expensive<br />
‣Best to find/introduce natural predator=sterilize for<br />
minimal adverse effects
5.3 Human Population Growth<br />
A. Historical Overview: Slow past growth w/limiting factors: scarce<br />
food/predators/disease=↑ death rate=multiple offspring w/few surviving<br />
1. Exponential Human Population Growth<br />
‣ Industrial revolution improved nutrition/medicine = ↓ death rates<br />
w/birthrates remaining hi<br />
2. The Prediction of Malthus<br />
‣ Exponential growth can’t last<br />
‣ Growth limited by competition-war; scarce<br />
resources-famine; parasitism-disease<br />
o Density Dependent Limiting Factors<br />
3. World Population Growth Slows<br />
‣ Exponential Growth through mid-sixties; then slowed
B. Patterns of Human Population Growth<br />
‣ Demography: study of human growth (birth/death rates and age structure)<br />
1. The Demographic Transition<br />
‣ Shift from High birth/death rates (Phase 1) to low birth/death rates<br />
(Phase 3) = U.S, Japan, Europe; J to S curve<br />
2. Age Structure and Population Growth<br />
‣ A higher % of young people = growing population; equal age group # =<br />
slower, steady growth<br />
3. Future Population Growth<br />
‣ Approx. 9 billion by 2050; but grow more slowly than last 50 years
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