Populations Group of individuals that belong to the same species and live in the same area Chapter 5 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. # of births 2. # of deaths 3. # 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 Movement of individuals into a population Cause population to increase in size Cause population to increase in size

Emmigration Movement of individuals out of a population Movement of individuals out of a population Causes population to decrease in size Causes population to decrease in size

Population Growth can be represented bycharacterized by represented by which cause a Exponential growth Logistic growth Falling growth rate S-shaped curve Limits on growth No limits on growth J-shaped curve Constant growth rate Unlimited resources Section 5-1 Go to Section: Population Growth Concept Map

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

Carrying Capacity The largest # of individual that a given environment can support Number of Yeast Cells Time (hours) Carrying capacity Section 5-1 Figure 5-4 Logistic Growth of Yeast Population Go to Section:

Limits to Growth Limiting Factor: Limiting Factor: - a factor that causes population growth to decrease - can be Density Dependent or Density Independent Density Independent

Density – Dependent Factors Limiting factors that depend on population size Limiting factors that depend on population size Become limiting only when the population density (# of individuals) reach a certain level Become limiting only when the population density (# of individuals) reach a certain level Affect very large populations only 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 Affect all populations regardless of size Types: Types: 1. unusual weather 2. natural disasters 3. seasonal cycles 4. human activities

How populations respond to the factors Populations size crashes Populations size crashes But most will build up again or may stay low for some time 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 Like other organisms, human population tends to increase with time For most of human existence – population has grown slowly (limited food source/incurable disease) For most of human existence – population has grown slowly (limited food source/incurable disease) About 500 years ago – population began growing more rapidly About 500 years ago – population began growing more rapidly Causes: agriculture & industry (easier & safer) Causes: agriculture & industry (easier & safer) food supply more reliable food supply more reliable goods shipped around the world goods shipped around the world improved sanitation improved sanitation Result: decreased death rate & birthrate increase Result: decreased death rate & birthrate increase So….. Humans experienced EXPONENTIAL GROWTH So….. Humans experienced EXPONENTIAL GROWTH

Agriculture begins Plowing and irrigation Bubonic plague Industrial Revolution begins Section 5-3 Go to Section: Human Population Growth