Population Growth

Do Now• Algae live inside a species of hydra. Both organisms are found

in an aquatic environment. The hydra uses the products of the alga's photosynthesis. Ammonia resulting from the hydra's metabolism contributes to the alga's nutrition. What type of relationship is this?

1. What are two abiotic factors and two biotic factors you can identify in this story?

2. What type of relationship exists between the algae and hydra?

3. What limiting factor in the story might limit the size of the algae?

Limiting Factors• Density-independent

limiting factor: Affects all populations in similar ways, regardless of the population size.

• (Size DOESN’T matter)

• Examples: – Natural Disasters– Weather– Human disturbances– Drought, Freezes, Fires

• Density- dependent limiting factor: DEPENDS on the population size. Affects the population if the population density, or number of organisms, reaches a certain level.

• (Size MATTERS)

• Examples: – Disease/Parasites– Predation– Competition– Amount of resources– Symbiosis

• Read the descriptions below and identify as Density-Independent OR Density-Dependent limiting factors:

1. Rainbow trout and yellow perch occupy the same territory and compete for food.

1. A severe flood brings a lot of sediments and silt into Lake Norman. Less sunlight can now get into the lake.

1. Many fish die due to an increase in water temperature.

1. A population of mice are growing quickly until parasites cause a disease to spread quickly through the mice population.

Population Growth: Population can grow in 2 patterns

2. Logistic Growth = “S” Curve• Levels off due to limiting

factors• Reaches carrying capacity =

largest # of organisms the ecosystem can support

1. Exponential Growth = “J” Curve • Grows at a fast, increasing rate• Examples: human growth,

bacterial growth• No limiting factors

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Human Population Growth• Human population has been growing

exponentially for the last ~30 years, putting great strain on the environment

• We underwent a demographic transition: throughout history we had high birthrates and high death rates, so populations remained stable

• With advances in medicine, nutrition and sanitation, we now have low death rates so the population is growing exponentially

Four things can affect the size of a population:

1. Number of births (increases growth)2. Number of deaths (decreases growth)3. Infant Mortality (# of babies that die)

(decreases growth)4. Number who enter (immigrate) or leave

(emigrate) the population

Where does it belong?Increases Stays the Same Decreases

High Birth, Low Death High Birth, Low Infant Mortality

Low Birth, Low Death Low Birth, High Death

High Birth, High Death High Infant Mortality, High Death

Scenario Population will…

Low birth rate, high death rate

High infant mortality rate, low birth rate

High birth rate, high emigration rate

Age Structure Diagrams: Used to see how many people there are in a country if the population is growing, decreasing or is stable.

Increasing Stable Decreasing

Which one ….Is growing rapidly?Has a low birth rate and low death rate?Is stable and growing slowly?Has a high birth rate and high death rate?

Guided Practice

• Read the first scenario and answer questions #1-3

• Read the second scenario and answer questions #4-8

Population Growth and Graphing Practice

• Directions: Using the graph paper provided, represent the data set below as two separate graphs. Be sure to label your axes and title your graphs, including all necessary information! Then, using your knowledge about population growth and limiting factors, interpret the graphs and explain the relationship you see. All questions must be answered in complete sentences below your graph.

• See “Hints” to help determine your X and Y axis.

• Graph the data for both data sets (fruit fly and rabbit)

• Answer analysis questions for both.

• Homework: Part II Graphing Human Population Growth AND reading “The Earth’s Carrying Capacity”

Exit Ticket

1. Which one of the following is a density-dependent limiting factor that might cause a population to reach carrying capacity?

a. Competition for resourcesb. A floodc. A severe droughtd. Humans building new factories