Limiting Factors

Mrs. Harlin

How Populations Grow

• What is a population?– Consists of all the individuals of a species that live together in

one place at one time.– A species is a group of individuals that can successfully

interbreed to produce fertile offspring.

Population Size

• Considered growing if the birth rate exceeds the death rate.

• Declining if the death rate exceeds the birth rate.

• If it’s about the same, then the population is in equilibrium.

Population Growth

• Populations experience exponential growth. This is known as a J-curve.

Limiting Factors of Growth• Availability of food• Competition within a species

and with other species• Predators• Disease• Lack of space• Sunlight• Sanitation• Medicine• Clean Water

Limiting Factors of Growth• These pressures may

cause a population to stabilize. Graphed the population would look like a S-shaped curve (logistic model). This means the organisms have reached the carrying capacity (K) of their environment.

Reproductive Patterns• Reproductive patterns are factors in determining population

growth. • R-strategists– Organisms have a small body size, mature rapidly,

reproduce early, and have a short life-span. (mosquitoes)• K-strategists– Large organisms that live in stable environments,

reproduce and mature slowly, and are long-lived. (humans)

Predator/ Prey Relationships

• Due to reproductive patterns, there is a perfect balance in nature that keeps species from becoming extinct.

• Ex: Snow shoe hare are r-strategists; lynx which prey upon the hare are K-strategists.

Predator/Prey Relationships

What IF?

• Snow shoe hare did not reproduce fast enough….

• Lynx reproduced as fast as the snow shoe hare…..

Threats to Population Growth

Caused by humans:– Over hunting by humans.– Habitat Destruction/Deforestation (cutting down

trees).– Exotic Species; ex: lionfish, kudzu, zebra mussels– Ozone destruction– Acid rain caused by factories– Burning of fossil fuels- climate change.– Not following Sustainable Use Policy.

Threats to Population Growth

• Not caused by humans:– Disease ( AIDS, influenza, tuberculosis, Dutch Elm

Disease Pfiesteria)

HIV• Infection of white blood cells• Infected cells still function normally, so

a person may not appear sick.• People with HIV eventually get AIDS

because more white blood cells are infected and produce new viruses.

• Eventually people lose their white blood cells because the viruses enter a lytic cycle and die.

• Without white blood cells, your body cannot fight disease causing organisms.

AIDS Epidemic

• Already, more than 30 million people around the world have died of AIDS-related diseases.

• In 2010, 2.7 million people were newly infected with HIV, and 1.8 million men, women and children died of AIDS-related causes.

• 34 million people around the world are now living with HIV.

Think the flu is no big deal?- Think again…- In 1918, a particularly

deadly strain of flu, called the Spanish Influenza, spread across the globe

- It infected 20% of the human population and killed 5%, which came out to be about 100 million people

Tuberculosis• Airborne bacteria that affect the

lungs.

• Became an epidemic in 1993 and peaked in 2004. The number of cases is currently declining.

• In 2010, an estimated 12.0 million people were living with TB, including 8.8 million new cases, and there were an estimated 1.4 million TB deaths.

Dutch Elm Disease

• Caused by a fungus that only affects Elm trees.

• Enters the xylem cells through passive transport then affects all other cells.

Pfiesteria

• Protist that causes fish kills.

• Killed 1000s of fish in NC in 1997.