The number of organisms per unit area 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. 4.2 Uniform Clumped Random

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 Predation: Fig. 4.5 Wolves & Moose on Isle Royale

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

The “prey” always increases first. Predator - Prey The “prey” always increases first.

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

Density-independent factors Hot/Cold Weather Fires Floods/Hurricanes/Tornadoes 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 Natality – Mortality + Immigration - Emigration

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?

Population Growth Rate If birth rate > death rate The population will….. If birth rate < death rate The population will….

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?

Exponential Growth (J–shaped curve) d) This is current human population growth worldwide How long can it last? Discuss e) Draw graph *Industrial revolution

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

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

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

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

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 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

Zero Population Growth Birth rate = Death rate

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