Transcript Chapter 5 Populations

Chapter 5 Populations
5.1 How Populations Grow
A.Describing Population
1. Geographic Range: area inhabited
2. 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
3. Growth Rate: size of population over time (increase,
decrease, stay the same)
4. Age Structure: # and age of males/females
B.Population Growth
1.Birthrate & Death Rate: influence whether pop
grows, stay the same or decreases
2.Immigration: moving into range
(increased good supply)
1.Emigration: moving out
of range (food shortage)
C.Exponential Growth: occurs with unlimited resources;
# of offspring increases with each new generation
1.Organisms that reproduce rapidly :
(bacteria reproduce very 20 minutes)
 J–curve: slow growth first then faster
2. Organisms that reproduce slowly:
3. Organisms in new environment:
(invasive species: no natural predators)
D.Logistic Growth
1. 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)
2. Logistic Growth Curve:
S-shaped curve
Exponential growth slows, then stops
Decreased birthrate; increased death rate
Decreased immigration; increased emigration
3. Carrying Capacity:
Max # of species individuals environment can
support
Birthrate = death rate; immigration = emigration
Slight pop. change over time; stabilizes at that
approx #
5.2 Limits to Growth
A.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)
B.Density Dependent Limiting Factors
 Operate when # of org/unit area reach certain level
1. 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
2. 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
3. Parasitism and Disease:
Both weaken/kill host; spread easier w/high
population
Isle Royale Canine Parvovirus left 3 breeding
females
CPV is life threatening and can affect the heart or
intestinal tract with symptoms of vomiting/ diarrhea
4. Stress from overcrowding:
 Too much fighting: ↓ birthrates, ↑ death/emigration
C.Density-Independent Limiting Factors:
 Unusual weather/natl disasters affect all pops similarly
Hurricanes, floods/wildfires
 Can cause pop to “crash” (be decimated) then rebound
1.True Density Independence?
Moose pop exploded after CPV – pop crashed with
harsh winter=effects greater w/unnaturally dense pop
2. Controlling Introduced Species
Artificial measures (removal) temporary/expensive
Best to find/introduce natural predator=sterilize for
minimal adverse effects
5.3 Human Population Growth
A. Historical Overview: Slow past growth w/limiting factors: scarce
food/predators/disease=↑ death rate=multiple offspring w/few surviving
1. Exponential Human Population Growth
 Industrial revolution improved nutrition/medicine = ↓ death rates
w/birthrates remaining hi
2. The Prediction of Malthus
 Exponential growth can’t last
 Growth limited by competition-war; scarce
resources-famine; parasitism-disease
o Density Dependent Limiting Factors
3. World Population Growth Slows
 Exponential Growth through mid-sixties; then slowed
B. Patterns of Human Population Growth
 Demography: study of human growth (birth/death rates and age structure)
1. 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
2. Age Structure and Population Growth
 A higher % of young people = growing population; equal age group # =
slower, steady growth
3. Future Population Growth
 Approx. 9 billion by 2050; but grow more slowly than last 50 years