4.1 Lesson

Lesson 4.1: Population Dynamics

Essential Question: What are characteristics of populations and what limits a population’s size?

Summary:
Students will begin learning more about characteristics that all populations share: density, distribution, and range.
They will explore factors that limit the growth of populations.
As students review these topics, they will examine specific ways in which population size influences the ecological relationships in an ecosystem and affects ecosystem stability.

TEKS 13.A Investigate and evaluate how ecological relationships, including
predation, parasitism, commensalism, mutualism, and competition,
influence ecosystem stability.

4

Lesson 4.1 Vocabulary

• population dynamics
• population density
• dispersion
• population range
• density-independent factor
• density-dependent factor

4

Population Characteristics 1

• A population is made up of organisms of a single species that share the same

geographic location at the same time.

• Population dynamics is the study of factors that influence changes in a

population size.

• All species occur in groups called populations.

• All populations have certain characteristics, such as population density,

spatial distribution, and population range.

• Ecologists use the characteristics of populations to compare one population to

another.

Ask Yourself Identify three characteristics all populations have.

5

Multiple Choice

All of the humans that reside in Terrell, TX are called a what?

• Species

• Population

• Ecosystem

• Cohort

Multiple Choice

Ecologists study and compare what?

• populations

• diasease

• parasites

• competition

Population Characteristics

Population density

• One characteristic of a population is population density, which is the number of organisms per unit area.

• Population density is often related to resource availability.
• Human populations tend to be denser around resources.
• Populations of organisms may decrease as people outcompete them for resources.

• Sometimes populations increase because of human activity, and the results aren’t positive.

• When cycles of matter are disrupted, ecosystem stability decreases.

Spatial distribution

• Another characteristic of a population is dispersion—the pattern of spacing of a population in an area.

• In a uniform dispersion, individuals tend to be spaced fairly equally due to competition for resources like mates or space

• Clumped dispersion often occurs in animals that move in herds or other sorts of groups, such as in pods of whales or flocks of birds.

• Random dispersion occurs when there is no pattern in a population’s distribution.

8

Population ranges

• No population, not even the human population, occupies all habitats in the biosphere.

• Each species has a population range, or distribution where it can be found throughout its lifetime.

• If an animal migrates, the area to which it migrates is considered part of its range.

• A species’ range can change due to abiotic and biotic factor

• Because human activities have the power to change these factors, they have the ability to influence a population range.

9

Multiple Choice

The places where an organism can be found throughout its lifetime is its...

• home range

• population range

• ecosystem range

• resource range

Population-Limiting Factors

Limiting factors are biotic or abiotic factors that keep individuals from continuing to increase indefinitely.

• Changing a limiting factor, such as the available food supply, often changes the number of individuals that are able to survive in a given area.

• More food/resources = bigger population = less competition
Less food/resources = less population = more competition

SURVIVAL OF THE FITTEST!

12

Match

Match the following

• Abiotic

• Biotic

• Competition

• Ecology

Non-Living

Living

Organisms use the same resources

Study of interactions among organisms and their environment

• Non-Living

• Living

• Organisms use the same resources

• Study of interactions among organisms and their environment

Population-Limiting Factors

Density-independent factors
• Any factor in the environment that does not depend on the number of members in a population per unit area is a density-independent
factor.

• These factors usually are abiotic and include natural phenomena such as weather events like drought, flooding, tornadoes, extreme temperatures.

13

Population-Limiting Factors

Density-dependent factors
• Any factor in the environment that depends on the number of members in a population per unit area.

• Density-dependent factors are often biotic factors such as predation, disease, competition and parasites.

14

Population-Limiting Factors

Density-dependent factor examples:

• Outbreaks of disease occur when population sizes and density are high.

• Population density is high = easier spread of disease among individuals

• Through hunting, humans interfere with predation by decreasing populations of predators like wolves.

• The use of pesticides to control large numbers of nuisance insects may be beneficial to humans, but it also deprives predators of the energy they need to reproduce successfully, leading to a decline in ecosystem stability.

14

Population-Limiting Factors

Density-dependent factors
• Any factor in the environment that depends on the number of members in a population per unit area.

• Competition increases when the population density increases.

• When population density is high, disease is transmitted easily from one individual to another. If resources are less than the population density, organisms will compete.

THINK- ONE PIZZA for 20 STUDENTS
Less organisms=less competition
More organisms=more competition

14

Match

Match the following

• Density Dependent

• Density Independent

• More organisms

dependent on population size

not dependent on population size

More competition for resources

• dependent on population size

• not dependent on population size

• More competition for resources