Population Density

The number of organisms per unit area

United States or New York City?

Which has a higher population size?

Which has a higher population density?

3 Types of Dispersion

Fig. 4.2UniformClumpedRandom

What type of dispersion….?

White-tailed deer?Black bear?Bison?Mountain lions?Seeds dispersed by wind?Caribou?

What is a limiting factor?

Density-dependent limiting factors

a) Affect large, dense populations more than smaller, less- crowded populations

“Depends” on “density”

Density-dependent limiting factors

i. Predation: Fig. 4.5 Wolves & Moose on

Isle Royale

Isle Royale

In addition to the predator/prey relationship, the moose and wolf population were affected by:The amount of food for the mouse

Disease among the wolf population

THE “PREY” ALWAYS INCREASES FIRST.

Predator - Prey

Density-dependent limiting factors

ii. Disease & Parasites: Easily spread in

large, dense populations

Density-dependent limiting factors

iii. Competition: Fig. 4.6 - Compete

for available resources

Food, water, space

iv. Crowding & Stress: The higher population density, the more crowding and stress on individual organisms

Density-independent factors

a)The density of the population DOES NOT MATTER

b)It doesn’t matter if the population is 5 or 5,000, they will be affected

Density-independent factors

i. Hot/Cold Weatherii.Firesiii.Floods/Hurricanes/

Tornadoesiv.Human Activities – toxic

waste spills, pesticides, deforestation

Population Growth Rate

How fast a population grows

It depends on 4 major factors

Population Growth Rate

a) Natality = birthrate

b) Mortality = death rate

Population Growth Rate

c) Emigration – “exit” or leaving population

d) Immigration – “in” or moving into a population

Population Growth Rate

Population growth =

Natality – Mortality + Immigration - Emigration

If natality is 10, mortality is 6, immigration is 3, and emigration is 2……

1.What is the net effect on the population size?

2.If the original population consisted of 10 individuals, what is the new population size?

Population Growth Rate

If birth rate > death rateThe population will…..

If birth rate < death rateThe population will….

Exponential Growth (J–shaped curve)

a)If ideal conditions (have everything!) continue, the population will continue to grow rapidly

b) Doubling and re-doublinga) 1, 2, 3, 8, 16, 32, 64, 128……..

c) Does NOT last long in nature – WHY?

Exponential Growth (J–shaped curve)

d) This is current human population growth worldwideHow long can it last?Discuss

e) Draw graph*Industrial revolution

Boom and Bust

a)As ideal conditions continue, population grows exponentially until it reaches a “peak” size (boom) and then crashes (bust)

b)Ex: Rabbit populationc)Draw graphs

Yeast Population Growth

Logistic Growth (S-shaped curve)

a) Exponential growth at first, eventually the population size levels off as the growth rate slows down

b) Carrying capacity: Largest number of individuals that the environment can support

Logistic Growth (S-shaped curve)

c)Draw graphd)Things that prevent the

population from getting too big:

c) Lack of food or waterd)Home/shelter availability

Reproductive Patterns

r-strategy: rate strategyGenerally are smallShort life spansProduce many offspring

rat, fruit fly, locusts (Fig. 4.9)

Reproductive Patterns

k-strategy: carrying capacity strategyLarger organisms, long life spanProduces few offspring –better chance of survival Take care of the offspring, usually for a long time

Kangaroo, elephant

Demography

The study of human population size, density, distribution, movement, and birth and death rates

Demographic Transition

A change in a population from high birth and death rates to low birth and death rates

(Read pg 102)

Demographic Transition

Stage 1: birth rate & death rateStage 2: birth rate & death rateStage 3: birth rate & death rateStage 4: birth rate & death rate

Discuss & answer questions on Notes handout

Zero Population Growth

Birth rate = Death rate

Age-Structure Diagram

# of males & females in 3 age groups:Pre-reproductive stageReproductive stagePost-reproductive stage

Age-Structure Diagrams

Fig. 4.14 – predict future population sizes…

Pyramid shaped (pre-reproductive larger)

Smaller at the bottom (pre-reproductive #’s smaller)

Education & Demographic Transition

1.What does the first graph tell us?

2.What does the second graph tell us?

3.What is a key factor in reducing the overall worldwide population growth?