1. Limiting Factors in a Population
TURN IN YOUR LESSON 21 to the HOMEWORK TRAY NOW

2. Standard 16
Identify density-dependent and density- independent limiting factors that
affect populations in an ecosystem.

3. 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.

4. 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.

5. Population growth Population size is determined by 4 factors:
Birth rate
Death rate
Immigration = the movement of individuals into an area
Emigration= movement of individuals out of an area
Which two cause the population to decrease?
Death rate & Emigration
Which two cause the population to increase?
Birth rate & Immigration

6. 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.

7. Limiting factors in a population fit into one of two categories
Density Dependent limiting factors
2. Density Independent Limiting factors

8. 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 balance
Disease & Parasitism

9. DENSITY INDEPENDENT Limiting factors
DENSITY INDEPENDENT limiting factors do NOT rely on the number of organisms present.
Examples
Natural Disasters- fires, floods, tornadoes, etc.
Human Impact- examples- clear cutting a forest to build a shopping center, over fishing/hunting
Climate – Natural temperature/rainfall in the area
Innate behaviors- examples- migration, instincts, social behaviors of animals, etc.

10. Limiting Factors Food Living area Disease Predators Density-dependent
Density-Independent
Does not matter number of organisms in the area
Weather
Natural disasters
Density-dependent
Does matter number of organisms in the area
Food
Living area
Disease
Predators

15. Which situation is caused by a density-independent limiting factor
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.

16. 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.

17. 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.

18. 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.

19. Limiting Factors Food Living area Disease Predators Density-dependent
Density-Independent
Does not matter number of organisms in the area
Weather
Natural disasters
Density-dependent
Does matter number of organisms in the area
Food
Living area
Disease
Predators

24. Which situation is caused by a density-independent limiting factor
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.

25. 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.

26. 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.

27. 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.