Populations

Population DynamicsLearning Objectives

What characteristics are used to describe a population?Lesson 1

What factors affect population size?Lesson 2

What are exponential and logistic growth?Lesson 3

Organisms in Your EnvironmentLesson 1

See Handout Elicit 1-1Take the Pre-assessment to see what you

know.

Activity: List organisms that live on your property.

Calculate the population density of the organisms that live on your property.

PopulationsLesson 1

Information ecologists need to study populations1. Geographic Range is the area which is inhabited by a

species. Ecologists need to determine the geographic range of a species to study its populations.

For instance bacteria in a rotting log may inhabit only a few square centimeters.

Hydrilla is an aquatic plant native to the warmer regions of Asia. The plant was introduced in Florida and is now an invasive species found in many of our lakes, rivers, and spring systems. In fact, the range of this plant has expanded and it is now found in many places throughout the world and United States.

Characteristics of PopulationsLesson 1

Geographic Range

This map shows the geographic distribution of killer whales. Killer whales move from the coast of California to the Aleutian Islands During their migrations.

Geographic Distribution Maps of Pythons invading Florida help scientists learn about their populations.

Lesson 1

PopulationsLesson 1

Information ecologists need to study populations2. Population Density: The number of individuals of a

population in a given area. Population density is the number of individuals in a measurable region.

The members of the population can be spread out or can be clustered throughout the area. Population densities can be small or large.

If there are no limiting factors, population densities can be larger than if limiting factors are present. Limiting factors are things like lack of resources, predators, natural disasters and lack of space.

Characteristics of PopulationsLesson 1

Population Density Equation

Population Density = # of individuals/given area

This saguaro cactus in a desert community has a low density.

How many Populations of Species can you find?

(Lesson 1)

We will be investigating areas on our campus in groups.

Please read the Instructions first. You will list each species that you find. You will list each abiotic factor in your area; this

would be any non living thing, like a rock or water. List what effect it has on the living organisms in the area.

You will list the numbers of individuals of a species you find. (10 ants, 2 strands of grass)

You will make a drawing to represent the area of your transect.

Context Word MapsLesson 2

Population DensityImmigrationEmigrationExponential GrowthLogistic GrowthCarrying Capacity

You will create a context word map for each of the terms.I’ll show you an example, and you will work on creatinga context word map for each of the above terms.

There are 4 main characteristics of Populations Lesson 2

Geographic Distribution or Range √

Population Density √Now we will look at two more

characteristics Population Growth Rate

Age Structure

Characteristics of Populations (Lesson 2) Population Growth Rate

Population growth can remain constant over time. Population growth can increase rapidly over time.(Examples would be the Pacific Sea Otters once protected

from hunting, and the Burmese Pythons in Florida.)Populations can also see a decrease in size, just as theotter populations can due to predation by killer whales.Native populations can decrease due to invasive species. The question arises, how do these types of interacting factors shape and influence population growth?

Three Factors Can Affect Population Size Lesson 21. The Number of BirthsA population will grow if the births out number the deaths2. The Number of DeathsA population will shrink if the deaths out number births3. The Number of Individuals that Enter (Immigration)

or that Leave (Emigration) the PopulationImmigration: The movement of individuals into an area,which can cause an increase in the population size.Emigration: The movement of individuals out of an

area,which can cause a decrease in the population size.*Population size will not change and will remain fairly

constant, if the birth rate is the same as the death rate AND immigration is the same as emigration.

Some Causes of Immigration and Emigration (lesson 2)

For many species, when the young reach maturity, they leave their birth area to seek mates and immigrate to new areas to establish a territory. Wolves and bears are some examples.

Destruction of habitat (for example building of a housing development) can cause animals to emigrate from an area and immigrate into an area with intact habitat

Food shortages can also cause animals to emigrate. They will leave an area and go out searching for food. Thus the animals end up immigrating into new areas.

Natural disaster can affect both immigration and emigration rates, as well other limiting factors.

Exponential Growth (Lesson 2)Exponential Growth happens when the

individuals in the population reproduce at a constant rate. At first the number of individuals in a growing population increases slowly, but over time the population grows infinitely large. If a population has abundant space and food, and is protected from disease, predators, and natural disasters, the organisms in the population will multiply and increase, thus under ideal conditions, with unlimited resources, a population will grow exponentially.

How is the population growth rate of pythons affecting the population of mammals in the Everglades National Park?

Lesson 3 Link: http://www.youtube.com/watch?featureplayer_detailpage&v=rwRdqkEcmbs

Click on the picture to watch a short video

Exponential Growth Rate Examples….

1 2 3 4 5 60

50000

100000

150000

200000

250000

Growth of Bacterial Population

Time (hours)

Num

ber o

f Bac

teriaBacteria reproduce ex-

ponentially.

In just one day millions of bacteria will be pro-duced.

Notice the J Shaped Curve

Logistic GrowthLogistic Growth happens when a population’s

growth decreases or ceases following a period of exponential growth.

Imagine a few animals are introduced to a new area plentiful in resources, the growth rate would increase exponentially, but as resources become less available, the growth of a population slows or stops.Factors that may cause population growth to

slow down.Birthrate decreases, or deathrate increases,

or both events occur at the same rate. Immigration rates decrease and the rate of emigration increases, or both.

Logistic Growth continued….Most normal populations follow a logistic growth curve.

Carrying Capacity

Note that even when the population growth is said to stop, the population is still slightly fluctuating.

Growth levels off as a population reaches what is called the carrying capacity.

The carrying capacity represents the largest number of individuals that a given environment can support. Note the S shaped curve for Logistic Growth

- - - - - - - - - - -

Logistic Growth

Review of Exponential & Logistic Growth

(Click on either picture to use an applet simulation of exponential or logistic growth.)

It’s your turn to Analyze the DataDays # of Fruit

Flies5 10

10 100

15 200

20 400

25 600

30 620

35 640

40 640

1. Make a graph utilizing the data in each table. Table 1 will be used to show the growth rate of a fruit fly population. The other graph will utilize data from Table 2 on the next slide to show the growth rate of a populations of rabbits.

Make sure to title your graphs and label the x-axis and the y-axis.

Table 1

Analyzing Data continued….

Generations

# of Rabbits

1 100

2 105

25 1000

37 1600

55 2400

72 3350

86 8000

100 13,150

Table 2

2. What type of growth do you find in the fruit fly population? Is it the same type of growth seen in the rabbit population?

3. Is there a carrying capacity on either graph, and if so, when does the population reach it? What is the maximum number of individuals supported at this time?

4. What would happen, if during the rabbits’ 20th generation, predators moved into the rabbits’ habitat and began eating rabbits?

Age StructureAge Structure: Age structure diagrams are

useful in predicting future population growth rates. Population profiles graph the numbers of individuals in different age groups within a population.

If there are higher numbers of teens, the population will increase in future years!

Here they are again… The 4 main characteristics of Populations

Geographic Distribution or Range

Population Density

Population Growth Rate

Age Structure

Review of Key TermsPopulation Density:

The number of individuals in a given areaImmigration:

The movement of individuals into an areaEmigration:

The movement of individuals out of an areaExponential Growth:With unlimited resources, growth can be infinite

Logistic Growth:Rapid growth followed by growth slowing down

Carrying Capacity:The maximum number an environment can

support

The EndReferences

Biology by Miller & Levine, Prentice Hall, 2002Guided Reading and Study Workbook, 2002

http://www.pbs.org/wnet/nature/episodes/invasion-of-the-giant-pythons/video-alligator-vs-python/5541/

http://www.otherwise.com/population/

Images from various sources using Google Images doing a search on public domain and royalty free images