CHAPTER 5Populations

By PresenterMedia.com

Ch 5 Sec 1

CHARACTERISTICS OF POPULATIONS:

1. geographical distributution2. density3. growth rate4. age structure

How Populations GrowRelationships along a food chain set the

stage for population growth

& decline.

To better understand changes in

populations, we study population

Biology.

•Geographic distribution, or range, is the area inhabited by a population.

- may vary in size from a few cubic centimeters, to millions of square kilometers.

•Density is the number of individuals per unit area.

# of individuals POPULATION = unit area

POPULATION GROWTH

•Three factors affect population size:1. # of births2. # of deaths3. # of individuals that enter and leave a

population- Examples: immigration and

emigrationimmigration – movement of

individuals into an areaemigration – movement of

individuals out of a population

EXPONENTIAL GROWTH

•If a population has abundant space and food, and has protection from predators and disease, that population will grow exponentially.

- Example: A bacterial colony in a petri dish, with a doubling time of 20 min. Some bacteria have the fastest reproduction rate among all living things.

•Exponential Growth occurs when the individuals in a population reproduce at a constant rate

- under ideal conditions, with unlimited resources, a population will grow exponentially.

LET’S LOOK AT FIGURE 5-3 ON PAGE 121!

LOGISTIC GROWTH

•As resources become less available, the growth of a population slows or stops. •Logistic Growth occurs when a population’s growth slows or stops following exponential growth. •This may happen if...

- birthrate decreases- death rate increases- both occur at the same time- immigration decreases- emigration increases

•The largest number of individuals that a given environment can support is the carrying capacity.

LET’S LOOK AT FIGURE 5-4 ON PAGE 122

***complete the Guided Reading packets for Ch 5 Sec 1***

5:2 Limits to Growth

• Limiting factors are factors that cause population growth to decrease

- Examples: competition, predation & parasitismThese affect a population more strongly as a population grows larger.

- Drought, climate extremes & human disturbances limit a population’s growth regardless of the population’s size.

Density-Dependent Factors

• Factors that depend on population size•There at three main types of density-dependent factors

1. competition2. predation3. parasitism & disease

COMPETITION

• The more individuals that live in an area, the sooner they will use up available resources, so they must compete.

- Example: The Atlantic puffin lives in large colonies along the coast of eastern North America from Maine north into the Arctic. Puffins nest in burrows dug into the sides of cliffs. Because nesting sites are limited, puffins MUST compete for space.

PREDATION

• In nature, populations are often controlled by predation.• Predator-Prey relationships are one of the best known mechanisms of population control.

- Example: The interaction between moose & wolves on Isle Royale, an island in Lake Superior. Periodic increases in the moose population, the prey, is quickly followed by increases in the wolf population, the predators. As the wolves prey on the moose, the moose population falls. Then, there is a decline in the wolf population because there is less food.

• The cycle of predator & prey populations can be repeated indefinitely.

PARASITISM & DISEASE

• Parasitic organisms range in size from microscopic, disease-causing bacteria to tapeworms 30cm or more in length.

- Example: The larval sphinx moth are attacked by parasitic wasps. The wasp inserts its eggs beneath the moth’s skin. After hatching, the wasp larvae feed on their host internally until they appear as white cocoons on its back.

Density-Independent Factors

• Factors that affect all populations in similar ways regardless of the population size. • Unusual weather, natural disasters, seasonal cycles, and some human activities are density-independent factors. • In response to these factors, many species’ populations will crash and then eventually build up again.

- Example: A severe winter frost can kill giant saguaro cacti in the Arizona desert.

***COMPLETE Guided Reading packet for 5:2 AND Ch 5 Sec 2

Assessment page 127***

5:3 Human Population Growth

• Like the populations of many other living organisms, the size of the human population tends to increase with time. • About 500 years ago the human population began growing more rapidly due to agriculture & industry. • Human population is growing exponentially.

Patterns of Population Growth• Demography is the scientific study of human populations and attempts to explain how those populations will change over time.

• Birth rates, death rates & age structure of a population help predict why some countries have high growth rates while other countries grow more slowly.

•Scientists have identified a variety of social & economical factors that can affect human populations.

- Example: Medical advances can lead to a dramatic drop in a population’s death rate.

Demographic Transition

• This occurs when there is a dramatic change in birth and death rates.

Age Structure

• age-structure diagrams, or population profiles, graph the number of people in different age groups in a population.

- Helps demographers predict future growth of a population

- Current projections suggest that by 2025, the world’s population may reach more than 9 billion!

***Complete the Guided Reading packets for 5:3 and the Section Assessment on page 132***