Chapter 5 Populations

5.1 How Populations GrowA.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 Growth1.Birthrate & Death Rate: influence whether pop

grows, stay the same or decreases

2.Immigration: moving into range

(increased good supply)

3.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 Growth1.Phases of Growth:Phase1: Exponential w/initial unlimited resources

(few die; many reproducing)Phase 2. Slows: pop. grows at slower ratePhase 3. Stops: zero growth rate (curve levels off;

pop. can remain here indefinitely)

2.Logistic Growth Curve:S-shaped curveExponential growth slows, then stopsDecreased birthrate; increased death rateDecreased immigration; increased emigration

3.Carrying Capacity:Max # of species individuals environment can

supportBirthrate = death rate; immigration = emigrationSlight pop. change over time; stabilizes at that

approx #

5.2 Limits to GrowthA.Limiting Factors: (ie: limiting nutrient controls productivity)

Control the growth of populationsDetermines carrying capacity of envirnmt for speciesShaped 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 populationIsle Royale Canine Parvovirus left 3 breeding females

4.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

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 SpeciesArtificial measures (removal) temporary/expensiveBest to find/introduce natural predator=sterilize for

minimal adverse effects

5.3 Human Population GrowthA. 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-diseaseo 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