1. Chapter 19
Populations

2. Do Now Which of the following are possible causes of extinction?
I. climate change
II. catastrophic events
III. biological factors
IV. human impact
A. I, III, and IV only
B. I, II, III, and IV
C. II, III, and IV only
D. I, II, and IV only
Answer: B

3. Understanding Populations
Population-a group of organisms that belong to the same species and live in a particular place at the same time.
Population size-the number of individuals that the population contains.
Size is a fundamental and important population property that can be difficult to measure directly.
Population Density-measures how crowded a population is.
Always expressed as the number of individuals per unit of area or volume.

4. Dispersion-the spatial distribution of individuals within the population.
Clumped distribution-individuals are clustered together.
Uniform distribution-individuals are separated by a fairly consistent distance.
Random distribution-each individual’s location is independent of the location of other individuals in the population.

5. Population Dynamics
All populations are dynamic-they change in size and composition over time.
Birth (Natality) rate-the number of births occurring in a period of time.
Death (Mortality) rate-the number of deaths in a period of time.
Life expectancy-how long on average an individual is expected to live.

6. Age structure-the distribution of individuals among different ages in a population

7. Patterns of Mortality
Survivorship curve-show the probability that members of a population will survive to a certain age.
Type I-mortality increases rapidly later in life.
Type II-mortality stays the same throughout life
Type III-mortality is great in early life

8. Do Now
In any ecosystem, the basic resources that organisms need for survival are always in limited supply.
Which of the following are examples of limited resources in an ecosystem?
A. food
B. sunlight
C. water
D. all of these
Answer: D

9. Population Growth Rate
Demographer-scientists who study population dynamics
Growth rate-the amount by which a population’s size changes in a given time.
Growth rate depends on four processes:
Birth
Death
Immigration-the movement of individuals into a population
Emigration-movement of individuals out of the population
Growth rate=birth rate-death rate

10. Exponential Model
As long as the birth rate exceeds the death rate, the population size will continue to increase.
Exponential Growth-a pattern of increase in number due to steady growth rate
Does not account for limiting factors.
At times following the logistic population growth model.
Limiting Factor-Any factor that restrains the growth of a population.
Ex. Space, food, water, nutrients
Can be biotic or abiotic

11. Logistics Model
Birth rates and death rates are not constant: birth rates decline and death rates rise as the population grows.
Logistic Model-builds on the exponential model but accounts for the influence of limiting factors.
Carrying Capacity-the number of individuals the environment can support over a long period of time.
Small population= high birth rate/ low death rate
Large population= low birth rate/ high death rate

12. Population Regulation
Density-independent factors-reduce the population by the same proportion regardless of the population’s size
Ex. Weather, floods, and fires
Density-dependent factors-an individual’s chance of surviving or reproducing depends on the number of individuals in the same area.
Are triggered by increasing population density.
Ex. Resource limitations, shortages of food or nesting sites

13. Perils of Small Population
The rapidly growing human population has caused extreme reductions in the populations of some other species and subspecies.
Ex. 200 Siberian tigers remain in the wild because of hunting and habitat destruction.
Factors that can kill entire population
Ex. Storms, fires, floods, disease outbreaks
Inbreeding-mating with relatives
Leads to decreased genetic variability.

14. Do Now
Which of the following events would most likely contribute to lowering the carrying capacity of a population?
A. an increase in the water supply in the habitat
B. a decrease in the number of females in the population
C. a loss of habitat due to human development or natural disasters
D. an increase in the number of predators who eat the animal
Answer: C

15. History of Human Population Growth
Homo sapiens originated 500,000 years ago and exhibited slow growth until 10,000 years ago.
Hunter-gatherer lifestyle-small nomadic groups that obtained food by hunting animals and gathering roots, berries, nuts, shellfish, and fruits.

16. Agricultural revolution-occurred 10,000 years ago when humans began to domesticate animals and cultivate certain plants for food.

17. Population explosion-began after 1650 due to better sanitation and hygiene, control of disease, increased availability of food and improved economic conditions.
Mortality rates fell sharply again after WWII.

18. Population Growth Today
Growth rate peaked in the late 1960s and leveled off due to declining birth rates.
Developed Countries-modern, industrialized countries
Some populations are declining due to death rates exceeding birth rates (ex. Russia, Germany, Italy)
Developing Countries-poorer, faster growing populations

19. Demographic Transition
Demographic Transition Model-shows how population changes happen.