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