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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?
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