Lesson 4.3 Population Growth From 1800 to today, the human population has grown from about 1 billion to more than 6.8 billion—an exponential rate of increase.

Lesson 4.3 Population Growth Birth and Death Rates A population’s relative birth and death rates (mortality and natality) affect how it grows. Survivorship curves show how the likelihood of death varies with age.

Immigration and Emigration Lesson 4.3 Population Growth Immigration and Emigration In addition to births and deaths, population growth is affected by immigration and emigration—individuals moving into and out of a population. Migration, seasonal movement into and out of an area, can temporarily affect population size.

Calculating Population Growth Lesson 4.3 Population Growth Calculating Population Growth Determined by the following equation: (birth rate + immigration rate) – (death rate + emigration rate) Growing populations have a positive growth rate; shrinking populations have a negative growth rate. Usually expressed in terms of individuals per 1000 Did You Know? Immigration contributes more than 1 million people to the U.S. population per year.

Lesson 4.3 Population Growth Exponential Growth Population increases by a fixed percentage every year. Normally occurs only when small populations are introduced to an area with ideal environmental conditions Rarely lasts long

Logistic Growth & Limiting Factors Lesson 4.3 Population Growth Logistic Growth & Limiting Factors Growth almost always slows and stops due to limiting factors. Limiting factors: Environmental characteristics slow population growth and determine carrying capacity. Density-dependent: Influence changes with population density. Density-independent: Influence does not change with population density.

Population Control Concept Map Use the following words or phrases: temperature limiting factors competition habitat distribution density-dependent parasitism disease more intense as population increases food supply same regardless of population size predation

Canadian Lynx vs. Snowshoe Hare Rudolfo's Usenet Animal Pictures Gallery Study done by Charles Elton. Hare population underwent regular cycle, with 10 years between population peaks. Peaks in lynx population cycle occurred near peaks of hare cycle. Conclusion: -More hares = More lynx -Hare population decreases due to predation -Lynx population decreases due to less prey -Hare population rebounds as lynx population decreases Problem: Hare populations on islands without lynxes still undergo regular cycles Possible explanation: Lynx population depends on hare population, but hare population depends on other factors. adapted from Odum, Fundamentals of Ecology, Saunders, 1953

Lesson 4.3 Population Growth Biotic Potential An organism’s maximum ability to produce offspring in ideal conditions Many factors influence biotic potential, including gestation time and generation time. Organisms with high biotic potential can recover more quickly from population declines than organisms with low biotic potential.

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What to Turn In I will randomly collect one set from each group. Procedure page with graph on back Spread sheet Limiting Factors table Follow-up Questions and Conclusions I will randomly collect one set from each group.

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