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**The number of organisms per unit area**

Population Density The number of organisms per unit area

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**United States or New York City?**

Which has a higher population size? Which has a higher population density?

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3 Types of Dispersion Fig. 4.2 Uniform Clumped Random

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**What type of dispersion….?**

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

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**What is a limiting factor?**

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**Density-dependent limiting factors**

a) Affect large, dense populations more than smaller, less- crowded populations “Depends” on “density”

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**Density-dependent limiting factors**

Predation: Fig. 4.5 Wolves & Moose on Isle Royale

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**The amount of food for the mouse Disease among the wolf population**

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

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**The “prey” always increases first.**

Predator - Prey The “prey” always increases first.

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**Density-dependent limiting factors**

ii. Disease & Parasites: Easily spread in large, dense populations

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**Density-dependent limiting factors**

iii. Competition: Fig Compete for available resources Food, water, space

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

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**Density-independent factors**

The density of the population DOES NOT MATTER It doesn’t matter if the population is 5 or 5,000, they will be affected

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**Density-independent factors**

Hot/Cold Weather Fires Floods/Hurricanes/Tornadoes Human Activities – toxic waste spills, pesticides, deforestation

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**Population Growth Rate**

How fast a population grows It depends on 4 major factors

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**Population Growth Rate**

a) Natality = birthrate b) Mortality = death rate

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**Population Growth Rate**

c) Emigration – “exit” or leaving population d) Immigration – “in” or moving into a population

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**Population Growth Rate**

Natality – Mortality + Immigration - Emigration

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

What is the net effect on the population size? If the original population consisted of 10 individuals, what is the new population size?

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**Population Growth Rate**

If birth rate > death rate The population will….. If birth rate < death rate The population will….

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**Exponential Growth (J–shaped curve)**

If ideal conditions (have everything!) continue, the population will continue to grow rapidly Doubling and re-doubling 1, 2, 3, 8, 16, 32, 64, 128…….. Does NOT last long in nature – WHY?

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**Exponential Growth (J–shaped curve)**

d) This is current human population growth worldwide How long can it last? Discuss e) Draw graph *Industrial revolution

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Boom and Bust As ideal conditions continue, population grows exponentially until it reaches a “peak” size (boom) and then crashes (bust) Ex: Rabbit population Draw graphs

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**Yeast Population Growth**

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**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

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**Logistic Growth (S-shaped curve)**

Draw graph Things that prevent the population from getting too big: Lack of food or water Home/shelter availability

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**Reproductive Patterns**

r-strategy: rate strategy Generally are small Short life spans Produce many offspring rat, fruit fly, locusts (Fig. 4.9)

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**Reproductive Patterns**

k-strategy: carrying capacity strategy Larger organisms, long life span Produces few offspring –better chance of survival Take care of the offspring, usually for a long time Kangaroo, elephant

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

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**Demographic Transition**

A change in a population from high birth and death rates to low birth and death rates (Read pg 102)

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**Demographic Transition**

Stage 1: birth rate & death rate Stage 2: birth rate & death rate Stage 3: birth rate & death rate Stage 4: birth rate & death rate Discuss & answer questions on Notes handout

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**Zero Population Growth**

Birth rate = Death rate

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**Age-Structure Diagram**

# of males & females in 3 age groups: Pre-reproductive stage Reproductive stage Post-reproductive stage

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**Age-Structure Diagrams**

Fig – predict future population sizes… Pyramid shaped (pre-reproductive larger) Smaller at the bottom (pre-reproductive #’s smaller)

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**Education & Demographic Transition**

What does the first graph tell us? What does the second graph tell us? What is a key factor in reducing the overall worldwide population growth?

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Population Biology CHAPTER 4. Population Dynamics Population Dynamics is the study of change in populations including growth, decline, births, deaths,

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