Population GrowthChapter 20

Population Growth1950’s – fish

farmer introduced hydrilla into a canal in Florida.Out of control

growth!

Geographic Range

The area inhabited by a population is called its geographic range.

Population DensityPopulation density refers

to the number of individuals per unit area.

Population DistributionDistribution refers to how

individuals in a population are spaced out across the range of the population—randomly, uniformly, or mostly concentrated in clumps.

Random DistributionPurple lupines grow

randomly in a field among other wildflowers.

The dots in the illustration represent individual members of a population with random distribution.

Uniform DistributionAn example of a

population that shows uniform distribution is the king penguin.

Clumped DistributionAn example of a

population that shows clumped distribution is the striped catfish. These fish organize into tight groups.

Growth RateA population’s

growth rate determines whether the population size increases, decreases, or stays the same.

Population GrowthA population will

increase or decrease in size depending on how many individuals are added to it or removed from it.

Birthrate and DeathrateA population can grow

when its birthrate is higher than its death rate.

If the birthrate equals the death rate, the population may stay the same size.

If the death rate is greater than the birthrate, the population is likely to shrink.

Which of the following is NOT one of the factors that play a role in population growth rate?

a. immigrationb. death ratec. emigrationd. demography

The movement of organisms into a range is called

a. immigration.b. emigration.c. population shift.d. carrying capacity.

Which of the following could describe a population that is decreasing in size?

A) The birthrate and the death rate remain the same.B) The death rate is becoming lower than the birthrate.C) The death rate is constant and the birthrate is increasingD) The death rate is becoming higher than the birthrate.

Exponential GrowthUnder ideal conditions with unlimited resources, a

population will grow exponentially. In exponential growth, the larger a population

gets, the faster it grows.

If you plot the size of this population on a graph over time, you get a J-shaped curve that rises slowly at first, and then rises faster and faster.

Exponential Growth

Logistic growth occurs when a population’s growth slows and then stops (most populations experience this type of growth)follows a period of exponential growth.

Logistic Growth

3 Phases of Population Growth

Carrying capacity is the maximum number of individuals of a particular species that a particular environment can support.

Carrying Capacity

A) The birthrate and the death rate remain the same.B) The death rate is becoming lower than the birthrate.C) The death rate is constant and the birthrate is increasing.D) The death rate is becoming higher than the birthrate.

Which of the following could describe a population that is decreasing in size?

The graph in Figure 5–1 shows the growth of a bacterial population. Which of the following correctly describes the growth curve?

A) logisticB) limitingC) demographicD) exponential

Suppose that a species of toads is introduced into a new environment in an attempt to reduce the population of insects. The toad has no natural predators in the new environment. The toad population would most likelyA) increase exponentially.B) increase logistically.C) decrease rapidly and die out.D) remain the same.

If a population grows larger than the carrying capacity of the environment, which of these is most likely to happen?

A) The death rate may rise.B) The birthrate may rise.C) The death rate must fall.D) The birthrate must fall.

Limiting FactorsA limiting factor is a

factor that controls the growth of a population.

Some depend on population density and others do not.

Density Dependent FactorsDensity-dependent

limiting factors include competition, predation, herbivory, parasitism, disease, and stress from overcrowding.

CompetitionWhen populations

become crowded, individuals compete for food, water, space, sunlight, and other essentials.

CompetitionCompetition is a

density-dependent limiting factor. The more individuals living in an area, the sooner they use up the available resources.

The effects of predators on prey and the effects of herbivores on plants are two very important density-dependent population controls.

Predation and Herbivory

This graph shows the fluctuations in wolf and moose populations on Isle Royale over the years.

Predator Prey Relationships

Herbivore Effects Herbivory can also

contribute to changes in population numbers.

From a plant’s perspective, herbivores are predators.

Humans as PredatorsIn some situations,

human activity limits populations.

Fishing fleets have raised cod death rates so high that birthrates cannot keep up. As a result, cod populations have been dropping.

Parasitism and DiseaseParasitism and disease

are density-dependent effects, because the denser the host population, the more easily parasites can spread from one host to another.

This graph shows a sudden and dramatic drop in the wolf population of Isle Royale around 1980.

At this time, a viral disease of wolves, canine parvovirus (CPV), was accidentally introduced to the island.

Parasitism and Disease

Stress from OvercrowdingOvercrowding

causes stress in populationsLowers ability to

fight diseaseCauses some

females to neglect or even eat their young

Density Independent FactorsDensity-independent

limiting factors affect all populations in similar ways, regardless of population size and density.

Unusual weather such as hurricanes, droughts, or floods, and natural disasters such as wildfires, can act as density-independent limiting factors.

A) competition.B) temperature.C) crowding.D) disease.

Each of the following is a density-dependent limiting factor EXCEPT

A) a small, scattered populationB) a population with a high birthrateC) a large, dense populationD) a population with a high immigration rate

Which would be least likely to be affected by a density-dependent limiting factor?

A) earthquakeB) diseaseC) emigrationD) parasitism

Which of the following is a density-independent limiting factor?

Controlling Introduced SpeciesHydrilla in its

natural environment has natural predators, but in Florida they don’t exist.

Efforts have been made to control their population.

Controlling Introduced SpeciesThe best means of

control so far seems to be an imported fish called grass carp, which views hydrilla as an especially tasty treat.

Grass carp are not native to the United States. Only sterilized grass carp can be used to control hydrilla.