Investigation 6, Part 1Reproductive Potential

Warm upWhat is a population?

All the individuals of a species that are living in an area at one time.

Reproductive PotentialEvery population has the potential to

increase in size. Some have potential to grow slowly and

steadily while others have the potential to grow rapidly.

If you have the proper information, you can calculate the potential for population growth for any organism.

The theoretical unlimited growth of a population over time is called reproductive potential.

Milkweed BugsLook on lab sheet 27. Look over the data silently. Entomologists (People who study bugs) have

discovered some general information about the lives of milkweed bugs living in the wild.

That information is written on the question and answer chart on your lab sheet.

Based on this information, you should be able to figure out the population after one month, two, four, etc, as long as nothing is limiting their population growth.

Get out your calculators!Lets complete the first one together. You will now do the rest on your own. Go in 2 month intervals. 2, 4, 6, 8, one year

(12).

Think…..Who has children/offspring?

Only females.How many children/offspring are female?

Half.Who are the parents in each generation?

The offspring from the previous generation. How long do they live?

4 monthsPopulation reduction?

Calculate the new generation of offspring and add to it only the number of parents who produced them.

Bugs older than the parents of that generation will be dead. (The grandparents)

ResultsWithout any limitation on population growth, every egg

produces a new individual in the population and every individual lives out its natural life, 4 months.

Only females produce eggs. Half the population is female.Both males and females are 2 months old when they reach

maturity and mate, and the females produce 100 eggs. (Or you could say 50 eggs per bug.)

When a generation reaches maturity, their parents are 4 months old and die. Dead bugs must be subtracted from the population.

The population at any time is the number of immature milkweed bugs and their parents, minus their grandparents.

So….. How many is that?A pair of milkweed bugs has the potential to

produce a population of almost:32 BILLION!

This number of bugs would:Circle the earth 8 times. Nose to tail.Covered about 8 football fields, but not stand

on top of each other. Have a mass equal to 30,000 average middle

schoolers. Fill about 12 average middle school classrooms

floor to ceiling.

What’s the problem?Clearly milkweed bugs do not increase in

population at the rate we calculated. What prevents this rate of growth from

occurring?Discuss….

Limiting FactorAny biotic or abiotic factor that acts in some

way to limit the number of individuals that survive and reproduce in a population.

What are some factors that might limit milkweed bugs in nature?

ReviewWhat happened on lab sheet 27? What was our data?Example: how many bugs did we start out with? How

long did they live? How many eggs were produced?Mature in 2 monthsLifespan of 4 monthsProduced 100 eggs per female100% of eggs hatched and produced offspring32BILLION bugs!

What would happen if ONE variable was changed? What if they laid 150 eggs?

SimulationWe can use the computer to calculate the

reproductive potential of the milkweed bugs with different characteristics than the one we investigated.

What happens when we limit size?

Now you try. Use lab sheet 29 to investigate different limiting factors.

What were your results. We will discuss as a class.

InvestigationOne critical factor in the reproductive cycle

of the milkweed bug is the successful hatching of eggs.

If eggs do not hatch, the population will not increase.

I have data from an experiment in egg hatching.

We have a record of the experimental procedure and the data collected.

Review DataReview the purpose and design on page 31.Study the data on page 32 to see what effect

each variable had on egg hatching.Summarize the results on page 33.Write in complete sentences. Use EVIDENCE

from the experiment to support your conclusions. Be specific.

Example: The environment best for egg hatching is______. It produced ______ more eggs than the other environments.

Analyze the DataHumidity and light? Do they limit the

hatching?There is not data to support that.

Temperature?Yes.Below 10 degrees C and over 40 degrees C

seem to prevent hatching. Eggs at 20-40 degrees C hatch in large

numbers. Cooler temps can extend the time.

Wrap UpEcologists use many different methods to get

information about ecosystems.One way is through lab experiments. They bring some of the natural world into the

lab and focus on one part of it.Variables can be carefully controlled in the

lab to determine cause and effect relationships.

They can also use field observations and computer models.