Limiting Factors Ms. Cuthrell

How Populations Grow What is a population? 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 A population is considered growing if the birth rate exceeds the death rate. A population is 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 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.

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

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. (Pathogens)

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.