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Chapter 5 Populations Group of individuals that belong to the same species and live in the same area California Biology Science Standards B1 6.b. Students know how to analyze changes in an ecosystem from changes in climate, human activity, introduction of nonnative species, or changes in populations size. B1 6.c. Students know how fluctuations in population size in an ecosystem are determined by the relative rates of birth, immigration, emigration, and death. Characteristics of Populations 1. Geographic distribution: - area inhabited by a population - can range in size and shape 2. Population Density: - the # of individuals per unit area - # can vary 3. Population Growth: - how a population grows or decreases in size Factors that affect population size 1. 2. 3. # of births # of deaths # of individuals that enter or leave a population Scenarios: If population grows? If population decrease? If population stays the same? Immigration Movement of individuals into a population Cause population to increase in size Emmigration Movement of individuals out of a population Causes population to decrease in size Population Growth Concept Map Section 5-1 Population Growth can be Logistic growth Exponential growth characterized by No limits on growth Unlimited resources represented by Constant growth rate J-shaped curve characterized by Limits on growth which cause a Falling growth rate Go to Section: represented by S-shaped curve Exponential Growth - Occurs when the individuals in a population reproduce at a constant rate - in the beginning #’s increase slowly - over time the pop. becomes so large it is exponential (VERY BIG !!!!!!!!) - Only can happen when the pop. has: 1. abundant space & food 2. protection from predators & disease 3. the ability to reproduce *** does not continue for a long time*** Examples of Exponential Growth Find graphs on internet Logistic Growth - Occurs when a populations growth slows or stops following a period of exponential growth Caused by: 1. resources become less available 2. birthrate ↓ deaths ↑ or they are equal 3. immigration ↓ emmigration ↑ or they are equal - Figure 5-4 Logistic Growth of Yeast Population Section 5-1 Carrying Capacity • The largest # of individual that a given environment can support Carrying capacity Time (hours) Go to Section: Limits to Growth Limiting Factor: - a factor that causes population growth to decrease - can be Density Dependent or Density Independent Density – Dependent Factors Limiting factors that depend on population size Become limiting only when the population density (# of individuals) reach a certain level Affect very large populations only Types of Density Dependent Factors 1. Competition – when populations become crowded, they start to compete for: food, water, space & sunlight - can be among the same species or different species 2. Predation – often controls populations in nature ** predator/prey relationships** 3. Parasitism & Disease – take nourishment from the host causing death or disease. Density-Independent Factors Affect all populations regardless of size Types: 1. unusual weather 2. natural disasters 3. seasonal cycles 4. human activities How populations respond to the factors Populations size crashes But most will build up again or may stay low for some time Always Remember…. 1. Environments are always changing 2. Most populations can adapt to the changes 3. Population will grow & shrink in response 4. Major upsets can lead to long term decline (usually caused by human activity) Human Population Growth Like other organisms, human population tends to increase with time For most of human existence – population has grown slowly (limited food source/incurable disease) About 500 years ago – population began growing more rapidly Causes: agriculture & industry (easier & safer) food supply more reliable goods shipped around the world improved sanitation Result: decreased death rate & birthrate increase So….. Humans experienced EXPONENTIAL GROWTH Human Population Growth Section 5-3 Industrial Revolution begins Agriculture begins Plowing and irrigation Go to Section: Bubonic plague