LIMITING FACTORS IN A POPULATION

TURN IN YOUR LESSON 21 to the HOMEWORK TRAY NOW

STANDARD 16 Identify density-dependent and density-

independent limiting factors that affect populations in an ecosystem.

POPULATION SURVIVAL IN ECOSYSTEMS Ecologists often study the Earth’s

Biomes at the ecosystem level. An Ecosystem is the abiotic and biotic

factors of the environment. Together, those factors provide

organisms with all the resources they need for survival.

POPULATIONS A Population is all of the organisms of

the same species that inhabit an ecosystem at the same time.

Density= mass per unit area

So, put them together, what is population density?The number of organisms in a population per

unit area.

POPULATION GROWTH Population size is determined by 4 factors:1. Birth rate2. Death rate3. Immigration = the movement of

individuals into an area4. Emigration= movement of individuals

out of an areaWhich two cause the population to decrease? Death rate & EmigrationWhich two cause the population to increase? Birth rate & Immigration

CHECKS & BALANCES OF EXPONENTIAL GROWTH Populations are regulated by specific

limiting factors in the ecosystem. Carrying capacity is the largest

population that a given ecosystem can support over time.

Limiting factors are both biotic (such as food, parasites and predators) and abiotic factors such as space, sunlight, water supply, temperature, etc.

LIMITING FACTORS IN A POPULATION FIT INTO ONE OF TWO CATEGORIES1. Density Dependent limiting factors

2. Density Independent Limiting factors

Density Dependent Limiting Factors The size of the population determines if

these factors will limit it or not. Is only a problem when the population is

too big or too small Examples:

Competition for Limited Resources Like Food, Water, Shelter, Nesting sites, mates

Predation/Prey balanceDisease & Parasitism

DENSITY INDEPENDENTLimiting factors DENSITY INDEPENDENT limiting factors do NOT

rely on the number of organisms present.

Examples1. Natural Disasters- fires, floods, tornadoes, etc.2. Human Impact- examples- clear cutting a

forest to build a shopping center, over fishing/hunting

3. Climate – Natural temperature/rainfall in the area

4. Innate behaviors- examples- migration, instincts, social behaviors of animals, etc.

LIMITING FACTORS

Density-dependentDoes matter number of organisms in the area

Food Living area Disease Predators

Density-IndependentDoes not matter number of organisms in the

areaWeather

Natural disasters

Which situation is caused by a density-independent limiting factor?

A The influenza outbreak of 1918–1919 killed over 20 million people.

B The cones of the jack pine need heat from a fire to help release seeds.

C A parasite alters reproduction in a woodpecker population causing fewer births.

D A queen bee regulates the number of eggs she lays according to the amount of food available.

Which statement BEST describes the relationship between natural disasters or human-caused disasters and population size?

A Natural and human-caused disasters are density-dependent factors.

B Natural and human-caused disasters are density-independent factors.

C Human-caused disasters are density-independent whereas natural disasters are density-dependent.

Which relationship BEST identifies a density-dependent limiting factor?

A A bobcat population declines due to disease.B A fish population declines due to a severe

drought.C A bird population declines due to pollution.D A wolf population declines due to a cold

winter.

Which statement BEST explains why a disease may

affect one population more than another population? A Because disease is a density-dependent limiting

factor, a larger population makes it easier for the virus to spread from person to person.

B Because disease is a density-independent limiting factor, a larger population makes it easier for the virus to spread from person to person.

C Because disease is a density-dependent limiting factor, climate can influence the disease, making it more or less affective.

D Because disease is a density-independent limiting factor, climate can influence the disease, making it more or less affective.

LIMITING FACTORS

Density-dependentDoes matter number of organisms in the area

Density-IndependentDoes not matter number of organisms in the area

WeatherNatural disasters

Food Living area Disease Predators

Which situation is caused by a density-independent limiting factor?

A The influenza outbreak of 1918–1919 killed over 20 million people.

B The cones of the jack pine need heat from a fire to help release seeds.

C A parasite alters reproduction in a woodpecker population causing fewer births.

D A queen bee regulates the number of eggs she lays according to the amount of food available.

Which statement BEST describes the relationship between natural disasters or human-caused disasters and population size?

A Natural and human-caused disasters are density-dependent factors.

B Natural and human-caused disasters are density-independent factors.

C Human-caused disasters are density-independent whereas natural disasters are density-dependent.

Which relationship BEST identifies a density-dependent limiting factor?

A A bobcat population declines due to disease.B A fish population declines due to a severe

drought.C A bird population declines due to pollution.D A wolf population declines due to a cold

winter.

Which statement BEST explains why a disease may affect one population more than another population?

A Because disease is a density-dependent limiting factor, a larger population makes it easier for the virus to spread from person to person.

B Because disease is a density-independent limiting factor, a larger population makes it easier for the virus to spread from person to person.

C Because disease is a density-dependent limiting factor, climate can influence the disease, making it more or less affective.

D Because disease is a density-independent limiting factor, climate can influence the disease, making it more or less affective.