Agenda

-Group activity: Studying Populations

Bell Ringer Week of 4/19-4/23

Q: Describe the niche of a fox in its habitat.

Learning Target

I will determine the cause of population change and identify

factors that limit population growth.

TuesdayApril 21, 2015

Group Activity

Determining Population Size

• Direct observation- count all of its members. Ex: Try counting all crabs in a tide pool.

• Indirect observation- Observe signs of organisms rather than the organism itself. Ex: counting the holes in a mud nests built by cliff swallows

• Sampling (estimate method)- Not always possible for direct observation due to very large population or spread over a large area. Scientists estimate population by counting number of organisms in a small area (sample) and multiple to find number in larger area.

• Mark-and- Recapture Studies (estimate method)- turtles are caught, counted, and marked with paint. Weeks later scientists go to the same location to caught turtles and count how many unmarked turtles vs. marked turtles they have. Using formula, they can estimate total population.

Changes in Population Size

• The main reason for an increase in population is birth rate.• The main reason for a decrease in population is death rate.• If birth rate > death rate, population size increases• If death rate > birth rate, population size decreases• If food/water source is scare, some members of a species may wander off in search of

better grassland (Emigration)• Best way to graph changes in population is a line graph (Use line graphs to show

change over time)• Population density= # of individuals

Unit area

Example: Population density= 20 monarch butterflies

102 m

Limiting Factors

• Food and water• Ex: a giraffe must eat 10 kg of leaves per day to survive and the surrounding trees

provide 100 kilograms of leaves a day. How many giraffes could safely inhabit the space?*

• Space• Ex: Pine seedlings spout and must have room for their roots to grow. If the

seedlings are too close together they could run out of room and branches could block sunlight the seedlings need.

• Weather• Ex: temperature and the amount of rainfall and limit population growth. What do

you think happened to Florida’s orange crops this year?

*Carrying capacity- largest population that an area can support*