Your “Do Now” 5/14

• Fill out a pre-test from up front• Try your best and pay attention!– This is the material we’ll be learning this week

Agenda 5/13

• Quizzes back– Retakes Wednesday

• Notes #3 on Populations• Practice

Learning Target #3 5/13

3) I can explain how multiple factors affect population sizes

• Population: all the members one species that live in the same place at the same time

• Limiting factor: anything that can slow/limit the growth of a population

• Carrying capacity: the maximum population of a species that a habitat can support

• The carrying capacity depends on the limiting factors so it can change

Example: a habitat supports 10 mice while food is a limiting factor. Add more food and carrying capacity goes up

Types of limiting factorsBiotic Abiotic

Food supplyCompetition# of matesPredators

SpaceClimate Oxygen WaterLight

Summarizing how biotic and abiotic factors can affect a population

• A change in one or both of these factors can affect a population

CFU

• Popcorn questions:– Look at your notes– Pick a person and ask them a question from the

notes– If you get picked, pick the next person

• Population density: the number of individuals in a certain area

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• The resources available to support a population of organisms is mostly finite (there is a limited amount of them)

• As the number of individuals in a space increases, resources are limiting and the organisms compete

• Density-independent: Factors that could affect any population, no matter how many individuals are in the area

Example: Weather. A tornado could kill individuals in any population, no matter what size/density

• Density-dependent: factors that affect populations differently depending on how many individuals are in the area

Example: Predator-Prey Relationships

• Predator and prey population sizes are often closely related

1. If there are too many prey in one area, the predators will reproduce more and eat more prey, making prey population go down

2. If there are too few prey in one area, the predators will starve, allowing the prey to reproduce and go up.

Factors that can increase the size of a population

• Birthrate: number of individuals produced in a population over time

• Immigration: new organisms moving into a population

Factors that can decrease the size of a population

• Mortality (death rate): number of individuals that die in a population that over a certain period of time

• Emigration: organisms leaving a population

Population Growth

• Rate of change: how fast/slow a population is changing at one point in time

• Zero population growth: time when a population’s size stays constant

Note: This only happens when # births = # deaths

Phases of Population Growth

1. Lag phase: time when a population grows very slowly (small size)

2. Exponential phase: time when a population grows exponentially (very quickly)

3. Stabilization phase: time when a population grows slowly (close to carrying capacity)

J Curve

• Exponential growth

• Population does not reach carrying capacity

S Curve

• Population has all 3 phases

• Has reached carrying capacity

Measuring the size of a population

• Mark re-capture method (common with mammals): Catch some animals, mark/tag them, then catch more and see what percentage are marked

• Quadrant sampling (common with large plants): Use a grid to count the number of plants in a certain area, then use that to predict how many are in a bigger area