Why Do Animals Survive or Die?

Natural selection means that there are random differences in characteristics that organisms inherit from their parents. These characteristics may give individuals an advantage or disadvantage compared to others in surviving and reproducing. The advantaged offspring are more likely to survive and reproduce. In this way, there will be more of the organisms with advantageous characteristics. When an environment changes, characteristics that give an organism an advantage may change.

Natural Selection

Natural selection exists everywhere. If you are into sports, then you already know that you have to be a good team to win the Super Bowl, NBA Finals, or the NCAA Championship. From your everyday experiences, you know that the stores in East Cleveland will only survive if they do good business. The stores that have prices that are too high, things to buy that are of low quality, or are not well maintained will fail.

Sports teams and stores on the street are both excellent examples of natural selection, even though it may not seem like it at first! You may think that some scientist came up with some very complicated and hard to understand theory, but natural selection is actually the simplest explanation of what has been going on for billions of years. If you do well, you survive – if you don’t, then you die.

Natural Selection in Football

Going back to sports, if the Cleveland Browns (magically) won the Super Bowl this year, that would mean that they were a good team. It doesn’t matter what you think, but because they out-competed all of the other teams, that means that they played the game better than those teams. It’s important to realize that natural selection isn’t about what scientists think should happen, it’s about noticing what does happen. So, if the Browns win the championship, they are a good team. Furthermore, if they win, then companies will want to give them money so that the company can be associated with a “winner”. With this money, the Browns can improve their training, their stadium, or go out and get better players. This means that because they won, they will be better prepared for the future.

Natural selection says that the best organisms will survive and reproduce more individuals like themselves. The weakest individuals die and do not get to reproduce. In a population of wild cats, the cats that are able to hunt the most birds survive and produce kittens; the cats that are unable to hunt birds die.

Going back to the stores, if Bob’s Discount Gas offers gas for $3.00 a gallon, even though it costs them $3.50 a gallon, then they will eventually go out of business. This means that the other gas stations will benefit and get more money that people aren’t spending at Bob’s. The weakest die off, leaving the strongest with the rewards.

When scientists are talking about living things and natural selection, there are a few key terms that are used in order to make things easier. The individuals that have characteristics which make them stronger than the others are the advantaged offspring (in the example, this would be the Browns). The characteristics that make them stronger are called advantageous characteristics. Again, it doesn’t matter what you think is a better characteristic – it all depends on what ends up helping an organism survive and reproduce!

Natural Selection on the Street

Even more importantly, what happens when the environment changes? In other words, what happens if the NFL decides to make the field 20 yards longer, the NBA decides to move the 3-point line to half-court, or the NCAA decides that the shot clock should be 24 seconds instead of 35 seconds? You can imagine that different teams would do better under these circumstances. The same thing would happen to Bob’s Discount Gas if all of the other gas stations went out of business; all of a sudden, they would be doing very well because they could set whatever price for gas that they wanted! If the environment changes, then some characteristics that did not help the organism before may now be advantageous. If suddenly there are no birds for our wild cats to hunt, then the cats that are better mouse hunters will survive better and reproduce more good mouse-hunters.

1. Define natural selection in your own words.
2. Which are the advantaged offspring out of any population of offspring?
3. Why doesn't it matter what scientists think about natural selection?
Put it together
4. Describe an advantageous characteristic using an example of your own.
5. Select one sports team that you think will win this year. Explain why!
Think about it
6. Create a change in the environment East Cleveland. Predict at least three stores that will survive and three stores that will go out of business because of this environmental change. Explain why they would survive or go out of business.

London’s Peppered Moths


Predominant In the majority
Fitness Ability to survive; well-adapted to the environment
Textile Cloth and other materials to make clothing
Catalyze To help to bring about
Agriculture Farming
Soot Ash, the remains of things that have been burned
Lichen A combination of a fungus and an algae that help each other (mutualism)
Mechanism Way that something works
Genetic Diversity The amount of differences in characteristics within a population
Directional Selection Natural selection moves characteristics in a particular direction

A Case Study in Natural Selection

By Laura Klappenbach


In the early 1950’s, H.B.D. Kettlewell, an English physician with an interest in butterfly and moth collecting, decided to study the unexplained color variations of the peppered moth. Kettlewell wanted to understand a trend that had been noted by scientists and naturalists since the early nineteenth century. This trend, observed in the industrialized areas of Britain, revealed a peppered moth population—once primarily made up of light gray-colored individuals—that now consisted primarily of dark gray individuals. Kettlewell was intrigued. Why had this color variation taken place in the moth population? Why were dark gray moths more common only in industrial areas while light gray moths were still predominant in rural areas? What do these observations mean?

Why Had This Color Variation Taken Place?

To answer this first question, Kettlewell set about the task of designing several experiments. He hypothesized that something in industrial regions had caused the dark gray moths to be more successful than the light gray individuals. Through his investigations, Kettlewell established that dark gray moths had greater fitness in the industrial areas than light gray moths. He was able to attribute this increased fitness to the dark gray moths’ ability to better blend into their habitat and avoid predation by birds.

Why Were Dark Gray Moths More Common in Industrial Areas While Light Gray Moths Were Still Predominant in Rural Areas?

Once Kettlewell had completed his experiments, the question remained: what had changed the moth’s habitat in industrial regions enabling darker colored individuals to blend in to their surroundings better? To answer this question, we can look back into Britain’s history. In the early 1700’s, the city of London—with its well-developed property rights, patent laws, and stable government—became the birthplace of the Industrial Revolution.

Advancements in iron production, steam engine manufacturing, and textile production catalyzed many social and economic changes that echoed beyond the city and altered the future of what had been, until then, a primarily agricultural workforce. Great Britain’s plentiful coal supplies provided the energy resources needed to fuel the fast-growing metalworking, glass, ceramics, and brewing industries. Because coal is not a clean energy source, its burning released vast quantities of soot into London’s air which settled as a black film over the city.

In the midst of London’s newly industrialized environment, the peppered moth found itself in a difficult struggle to survive. Soot coated and blackened the trunks of trees throughout the city, killing lichen that grew on the trees and turning the bark from a light gray-flecked pattern to a dull, black film. The light gray, pepper-patterned moths, that once blended into the lichen-covered bark, instead stood out as easy targets for birds and other hungry predators.

Lichen attached to a rock

About Natural Selection

The theory of natural selection suggests a mechanism for evolution and gives us a way to explain the variations we see in living organisms and the changes evident in the fossil record. Selection processes can act on a population to either reduce genetic diversity or to increase genetic diversity. The types of natural selection (also know as selection strategies) that reduce genetic diversity include: stabilizing selection and directional selection.

The selection strategies that increase genetic diversity include diversifying selection, frequency-dependent selection, and balancing selection. The peppered moth case study described above is an example of directional selection: the frequency of color varieties changes dramatically in one direction or another (lighter or darker) in response to the predominating habitat conditions.


  1. What did H.B.D. Kettlewell observe?
  2. Why was there a difference in fitness between the two colors of moths?
  3. Why were dark-colored moths surviving better than light-colored moths?
  4. What are the five types of natural selection mentioned in the article?
  5. Why is this an example of directional selection?
  6. In the 20th century, London began to clean up its industrial pollution, to the point where the trees returned to their normal colors. What effects do you think this had on the moth and bird populations? Be specific!
Leaves & Evolution

Get five different dead or live leaves. They should all be from different kinds of trees and plants, not just different colors: keep in mind that anything that a plant uses for photosynthesis is a leaf! Organize them in some way, as you will hand in the leaves with your homework assignment. Answer the following questions:

  1. Homeostasis is the balance of an organism with its environment. Examples of homeostasis include a human sweating on a hot day, shivering on a cold day, and eating food in order to maintain the same amount of energy. Now think about the plants that you got these leaves from. How do these leaves demonstrate the homeostasis of the plant? Keep in mind that I am asking you about information you already know: plants need water, sunlight and carbon dioxide.
  2. Natural selection is an evolutionary process that results in the fittest organisms surviving. Using any of the characteristics of these leaves (such as shape, size, color, shininess, etc.), what are two ways that these plants have found to survive better than other plants around them?
Beans and Birds

Natural selection is the main way that evolution works. It is the process that creates populations that are adapted to their environments. Organisms with favorable variations tend to survive and pass their variations to offspring while those with unfavorable variations die. In this activity, your group will design and conduct a simulation experiment to answer a question concerning the evolution of seed coloration in bean seeds.

  1. What is the main idea behind natural selection?

It is important to a population of bean plants that its seeds survive and grow into a new generation of plants. Mutations may have produced many seed color variations such as red, blue, brown, orange, and white. Since the seed colors that actually exist in pinto bean plants are brown and white, it seems reasonable to conclude that these colors are an advantage to the bean plants’ survival and were selected over many generations. The problem you will investigate using pinto bean seeds is: “How does natural selection change the frequency of genes or traits in a population over many generations?

  1. Get the following materials:
    1. One container of each of the colors of bean seeds
    2. Three different habitats (construction paper)
  2. Using the materials on the above list, design an experiment that answers the question posed by the problem: ”How does natural selection change the frequency of genes or traits over many generations?” In other words, how can natural selection change the numbers of certain colors of bean seeds? In your experiment, you will:
    1. Have a “bird” (a member of your group) eat half of the beans every generation.
    2. Reproduce the beans that survive after each generation by doubling their numbers, repeating for at least five generations.
    3. Record how many beans were eaten and survived every generation.
    4. Use the different habitats to show what happens to the numbers and colors of the beans when the habitat changes. For example, you could do the experiment three times, once with a black habitat, once with a brown habitat, and once with a green habitat.
  3. In designing your investigation:
    1. State a hypothesis
    2. Describe a procedure
    3. Determine what data to collect and create a data table for each habitat
  4. Get your procedure approved by the teacher before you start!
  5. Do the experiment and record the data.
  6. Make a graph to illustrate your data. This can be a bar, circle, line graph or something else of your choice. Compare the different color beans.
  7. Study your survivor populations for each generation. These are the beans that are not eaten by the bird. What changes occurred in the frequencies (totals) of colors between each generation?
  8. Compare the original and survivor populations. Is there any seed color or colors from the original population that are not represented in the survivor population?
  9. How do the colors of the survivors relate to their habitat?
  10. What do you predict would happen to the frequencies of colors if you continued the simulation activity for several more generations?
  11. How might a change in the habitat or in the animals (herbivores) eating the seeds affect the frequencies of seed colors?
  12. Have you confirmed your hypothesis? Explain.
  13. Explain how natural selection changes the frequency of genes over many generations.
  14. How would you improve this experiment? Comment on seed color, habitat, seed eating herbivores, number of repetitions, season of the year, etc.
Homologous Structures

Homologous Structures

This diagram shows the arm, leg, flipper and wing of four mammals. All four mammals eventually descend from a common mammal ancestor, and show similar bone structures. The upper bone (that connects to the body of the animal) is called the humerus. The bones that connect the humerus to the “fingers” are the radius and ulna. The radius is found on the “thumb” side of the arm, the ulna on the little-finger side. (As an experiment, you can feel them in your own arm by holding your forearm and twisting your wrist.) The carpals form the wrist (or ankle) and the phalanges form the “fingers” or “toes.”

  1. The phalanges of the whale and human are different. Why? Include in your response the environments in which the two live.
  2. Using the above diagram and your knowledge of animals, explain why the cat and bat have different leg / wing structures.
  3. These are called homologous structures because they have similar bones but different functions. Think of two animals that have the same structure, but the animals use it for different reasons.
    1. What are the two animals?
    2. What is the structure?
    3. What are the different uses they have?


When a sperm fertilizes an egg for any animal, the beginning of this new life looks very similar, no matter what the animal. The above diagram (which is not completely accurate) shows the embryology for eight different animals. Animals that are highly related show more similarities in their development from an egg to a mature adult.

  1. What do you notice that is suggested that humans have during their development that, when born, we do not have? Why is this?
  2. What structures do you see that all the eight animals have in common in the:
    1. First stage (I)?
    2. Second stage (II)?
    3. Final stage (III)?
  3. From looking at this embryology chart, describe what type of organism could be the common ancestor of all of these animals.


This diagram shows different strains of bacteria (the dots) and how resistant they are to antibiotics. The strains of bacteria are different because of mutations (changes in DNA) that cause differences in offspring.

  1. According to the diagram, how many bacterial strains from the original population survive when an antibiotic is used?
  2. What is the difference between the original and final population of bacteria?
  3. What does resistance to antibiotics mean?
  4. Why did the low resistance bacteria die?
  5. Antibiotics that kill bacteria are being developed all of the time. In terms of mutations, why can’t scientists just find an antibiotic that kills all bacteria all of the time?
Geographic Separation

Geographic Separation

The diagram shows how “greenish warblers” (a type of bird) started in the Himalayas, but, over thousands of years, migrated to Siberia by two different paths, one through China and one through Kazakhstan. Due to changes in the warblers over those thousands of years, this geographic separation made it impossible for the two types of warbles to breed with each other when they met again in Siberia.

  1. Can the populations in squares “A” and “B” interbreed? What about “A” and “F”? “D” and “E”? Why?
  2. What causes geographic separation to create different species?
  3. Let’s say that in an experiment, scientists brought birds from populations D, E and H together. Assume that each population is a different color. Draw what this looks like if there are four birds of each population and each bird has one offspring. Think about which populations will breed with each other and which won’t!
Analogous Structures

Analogous Structures

This diagram shows the wing structure of four different animals: insect, dinosaur, bird and bat.

  1. Differentiate in two ways the wings of the bird and the insect.
  2. “Batman” is a fictional character, but humans are capable of flight with structures like hang-gliders. Explain why, if he were real, “Batman” would have to have wings many times bigger than they are in the movies.
  3. Wings are examples of analogous structuresbecause they have the same function, but very different bone structures (and sometimes, no bones at all). Think of two animals that have parts which do the same thing, but have very different structures.
    1. What are the two animals?
    2. What do they do that is similar?
    3. What structure does each one have that is different?
Adaptive Radiation

Adaptive Radiation

Galapagos finches are often called “Darwin’s finches” because he was the first scientist to try and explain why there were so many different kinds of finches on the Galapagos Islands. He explained that the beaks of the finches were different because of adaptive radiation, when a species of organism adapts to different environments.

  1. How are the beaks of finches that eat mainly insects and mainly seeds different?
  2. According to the diagram, all of these finches began as a type of finch that ate seeds. Why would they start to eat things other than seeds?
  3. Create a map of one of the islands which has a large fruit tree, a cactus, a beach and plants that give off seeds. Place each of the finches on the map, depending on what they eat.
  4. Using your map, why did the one ancestor finch evolve into all of these different descendants?
  5. Think of another example of adaptive radiation, using animals that you are more familiar with.
The Great Fossil Find

Answer all questions on a separate sheet of paper, in groups of 3 – 4!

In this activity, you and the members of your team will play the roles of paleontologists working in the field in Ohio, near the town of Canton. One clear crisp afternoon in October, you find four well-preserved and complete fossil bones.

  1. Withdraw four fossil bones from your envelope. Make sure you take them out without looking at the ones remaining in the envelope!

It is too late in the day to continue with the dig, so you return to camp with your find. That night, in camp, after dinner, around a lantern, you and your colleagues begin to assemble the 4 bones you found earlier. Since the bones were all found together and in an undisturbed layer, you assume that they are all from the same animal. You spend the rest of the evening trying different arrangements of the bones in hopes of identifying the animal

  1. Use the next 3-5 minutes to try various combinations

As the night wears on, you get weary and decide to retire and begin anew in the morning.

  1. What kind of animal do you think it could be?

Ohio mornings are marvelous. They are clear, cool, and clean. Just the kind of day you need to get work done at the dig. The rock layers that hold your fossils are very hard and only grudgingly give up three more specimens. With the day at an end, you make your way back to camp for another try at assembling this mystery animal.

  1. Withdraw 3 more bones from the envelope. Use the next 3-5 minutes to incorporate your new finds in your fossil reconstruction.

It’s getting late, and you are getting weary. Maybe tomorrow you will find the answer to the puzzle.

  1. What kind of animal do you think it could be now?

The next day is cold. It is the last day of the digging season. Winter lurks behind the hills, and you must leave. Just as the day is about to end in disappointment and defeat, one member of the group cries out “I’ve got them! I’VE GOT THEM!”

  1. Withdraw 3 more bones from the envelope. Use the next 3-5 minutes to incorporate these latest finds. Record what you think it is now.

Back in the lab at East Cleveland, you go searching in the resource library, and you find some partial skeleton drawings from another group working at a different location but dealing with the same geological period. They have found a skeleton similar to yours, but with some additional bones that you don’t have. You use this information to add to your own data.

  1. Take the next 3-5 minutes to compare your findings with those of a team near you, looking for clues that might help you in your reconstruction, and possibly even suggest an entirely different animal than your earlier ideas. Apply these latest clues to the assembly of your skeleton as best you can. Record the type of animal suspected now. Be as specific as you can.

Once you are back in your own laboratory at Shaw High School, you find a Skeletal Resource Manual with drawings of the skeletons of some existing animals. You notice some interesting similarities between some of the drawings and your unknown fossil.

  1. Use any resources you can find to assist you in your final assembly of the fossil skeleton. Record your final interpretation:
  2. Be sure that all envelopes (with their bones) and Skeletal Resource Manuals get returned.
  3. Is there agreement on what the creature was? If so, discuss what the most telling clues were. If not, what was the main source of conflict?
  4. Did the discovery of new bones cause any conflict within your group? Explain.
  5. Did any of your group members resist changing in light of the new information? Explain.
  6. If this “Fossil Find” scenario is typical of the work of scientists, what features of the nature of science does it demonstrate?
  7. From looking at the fossil and the resource manual, what could you say about how and where this animal lived?
  8. Is it possible for scientists to do studies about things that happened millions of years ago? Explain.
Population of Pill Bugs


Estimating the size of a population is difficult because animals like to move around and hide from you! But if we tag a population, release that population, then look for that same organism again later, then we can get a good estimate as to the total size of the population.
Think about it this way: if we wanted to find out the population of East Cleveland, we could walk around the entire city and stamp everyone’s hand that we see. Assuming that stamp won’t just wash off, we could walk around the city again a week later and see how many new people we meet. If you don’t meet very many people with the stamp, that means the population is bigger than if you meet mostly stamped people.
Of course, we have to bring math into this. It’s not that hard, and a calculator will help us tremendously. Here’s how we figure out the total population of animals:

# collected the first time x # collected the second time

# that were already marked the second time

Let’s make up some numbers using the previous example. Let’s say we met 500 people on the first walk through East Cleveland. The second walk, one week later, we met 700 people. Out of those 700 people, 20 of them had stamps on their hands. After doing the math (500 x 700 divided by 20), we estimate that East Cleveland has 17,500 people. And we only had to count 1200 of them! Well, okay, 1200 people is a lot. So what if we were a little bit lazier? It turns out that if we met 100 people the first time and 175 the second time, and 1 of them had a stamp on their hand already, we would end up with the same result.

What’s the point of all of these numbers? Well, it turns out that you only had to talk to 275 people in order to estimate a population of 17,500. Animals are even harder to find, so when we count natural populations of animals, it turns out to be very convenient to only have to find a small percentage of the population.

In this experiment we will be working with pill bugs (woodlice, rolly-polly, or potato bug; scientific name Armadillidium vulgare) and figuring out what their population is at Shaw High School. Since they are easy to find in the ground, this will allow us to have a large sample size when we look for them both times. They tend to be attracted to dark, moist places, so we will create a pill bug “trap.” Once pill bugs find a dark and moist place, they tend to wander less freely and stay in more or less the same place.


  • White-out
  • Trowel
  • Meter stick
  • Pencil & paper
  • Clipboard
  • 2 beakers
  • 4 stakes


  1. Measure out an area that is 25 cm wide by 25 cm long. Place one stake in each corner. This is the area that you will be investigating in order to count the pill bugs.
  2. Using wet newspaper, paper towels, or vegetable matter, cover the staked area. Place a sign that reads “Experiment in progress. Do not disturb.” This will sit for 2 to 3 days.
  3. Using the trowel, dig up the area between the stakes, placing any pill bugs in the first beaker. You should be counting how many pill bugs are collected. Also, record how wet or dry the soil is, and any other observations that you can make.
  4. Once you have finished digging up the area and have removed all of the pill bugs that you could find, you will need to mark the pill bugs. Place a stripe of white out on the pill bug, then put it into the second beaker.
  5. Once all of your pill bugs have been marked put them back into the area that you dug up.
  6. Four days later, you will return to this area to repeat steps #1 and 2. This time, however, you will be making two tallies: the number of pill bugs with a white stripe and the number of pill bugs without a white stripe.


  1. Fill in the data table below:

Day 1

Number of pill bugs found

Day 2

Number of total pill bugs found

Day 2

Number of marked pill bugs found


  1. Calculate the estimated population size by:
    1. The number of pill bugs found on day one multiplied by the number of pill bugs found on day two
    2. Divide that by the number of marked pill bugs found on day two
  2. Since you now have the estimated population size for the area that you looked in, get the estimated population sizes for the entire class. Find the average of those population sizes.
  3. Given the average population sizes, let’s find out about how many pill bugs there are in one acre (about the size of Shaw High School’s yard). Since one square meter has 16 of your squares in it, multiply your population by 16. One acre has about 4000 square meters in it, so multiply that number by 4000.
    1. How many pill bugs should there be in one acre of land?
    2. Are these reasonable assumptions to make, that every section of this one acre will have the same number of pill bugs? Why or why not?
Coat Color in the Rock Pocket Mouse
Predator-Prey Dynamics


When something is dynamic, that means it is always changing. A predator and prey relationship is dynamic. For example, a growing population of mice can support a growing population of owls. But, as an owl population increases, it will need more and more mice.


The graph models a typical relationship between predator and prey populations. The lines are called population growth curves.




Analyze and Conclude


  1. What does the x-axis show? What does the y-axis show?
  2. Describe the pattern of the growth curves over time. What does this pattern tell you about population size?
  3. Identify two characteristics of predator-prey growth curves other than the general pattern.
  4. When the predator population starts to increase in size, what begins to happen to the prey population? How can you tell?
  5. Compare the drop in a prey’s population curve to that of a predator. What do the curves suggest about what happens to each population?






Build Science Skills



Suppose a long period of cold weather destroys almost the entire predator population at point B on the graph. Briefly describe what you think will happen to the prey population. Assume the predator population does not recover until point D. Think about what factor, other than a predator, could affect the size of the prey population. Then, extend the lines on the graph from point B to beyond point D to model your predictions. Give the graph a new title.



Extinctions Through Time

The graph shows the percentages of genera (singular: genus) that have gone extinct during different geologic periods. The periods are shown along the top of the graph. Genera are groups of related species. For example, cat species belong to the genus Felis.

The most important extinction event for you, as a mammal, comes with the mass extinction that occurred at the end of the Cretaceous Period. At that time, the dinosaurs disappeared and mammal species rose in number. Use the graph to answer the Analyze and Conclude questions on the next page.


Analyze and Conclude

  1. What is plotted on the y-axis?
  2. What do the text balloons in the graph point to?
  3. Which mass extinction killed off the highest percentage of genera?
  4. Describe the overall pattern of extinction shown on the graph.
  5. Can you conclude from the graph alone the percentage of species that became extinct during different periods? Why or why not?

Build Science Skills

What evidence is this graph probably based on? Why does the graph use percentages instead of actual numbers? How would data from the earlier periods be different from data available from more recent periods? Explain your reasoning.


How Competition Affects Growth

You may think the term competition refers only to interactions that occur between species. However, members of the same species also compete for resources in the environment. This competition is a density-dependent factor. It depends on how many members of a species occupy the same area. Too high a density will limit growth of a population. The limit depends on the species.


  • 2 small paper cups
  • 18 bean seeds
  • tray
  • water
  • potting soil


  1. Label two paper cups 3 and 15. Use a pencil to punch several small holes in the bottom of each cup. Place the cups on a tray.
  2. Fill each cup two-thirds full with potting soil.
  3. Plant 3 bean seeds in cup 3 and 15 bean seeds in cup 15. Push the seeds into the soil until they are just covered by the soil.
  4. Slowly add water to both cups until the soil is moist but not wet. Try to add about the same amount of water to each cup.
  5. Put the tray in a location that receives bright indirect light. Each day for two weeks, add an equal amount of water to the cups to keep the soil moist.
  6. Count and record the number of seedlings in each cup every other day. Describe any differences you see in the seedlings.

Data Table


Number of Seedlings


Cup 3

Cup 15








Analyze and Conclude

  1. What was the difference in the number of seedlings growing in each cup after two weeks?
  2. What differences other than number did you observe about the seedlings growing in the two cups?
  3. What resources are the seedlings competing for?

Build Science Skills

Write a hypothesis that describes what happened in your experiment. Include details about the design of the experiment in your hypothesis. Hint: Use the words if and then in your hypothesis.

Caterpillar Carrying Capacity

From: https://docs.google.com/document/d/1qZ8xFT2t2cu4IJrB4BQQLJKyXv7MfDVNJqcdJ_aNtGY/edit#heading=h.bvcp4kfhevc9


Carrying capacity is the highest population of a particular organism that can survive in an ecosystem sustainably. More simply, carrying capacity is the number of living things that can survive in one place. Carrying capacity depends on a lot of different factors, and can change due to many factors. It depends on how much food, water, space and shelter are available in the ecosystem; carrying capacity changes based on the population of other organisms, changes in the environment, availability of food sources, and more!

Manduca sexta, as a caterpillar, requires a large amount of food and a small amount of space in order to survive. Even though it doesn’t require that much space, how much is not enough? Since it requires a large amount of food, how much is not enough?



  • Tobacco or tomato leaves
  • 12 caterpillars per group
  • 3 habitats per group of varying sizes
  • Materials for making new habitats
  • Diet



Your objective will be to determine the minimum amount of space OR the minimum amount of food that one caterpillar needs in order to survive. Given the materials that you have available, you need to:

  1. Choose whether you will be testing for the amount of space or food
  2. Determine the details of the experiment: how many caterpillars in each habitat? How much food in each habitat? How large is each habitat?, etc.
  3. Once your experiment is approved by your teacher, start the experiment!
  4. Mass the amount of food that you are using in grams.
  5. Get the volume of the habitat that you are using in mL. If the habitat will hold water, you can fill it up with water, then calculate how much water you used. If the habitat will not hold water, then you will need to measure, in centimeters, the width, height and depth of the habitat.



  1. Based on your question that you answered, make a table with the following columns: Habitat, # of Caterpillars, Amount of Food, Volume of Habitat, Food / Caterpillar, Space / Caterpillar, Caterpillars Survived.
  2. For the “amount of food” column, you will need the mass of the food in grams. For the “volume of habitat” column, you will need the volume in mL. If you have the width, height and depth of the habitat, you will multiply those three numbers to get cubic centimeters (cm3).
  3. Divide the amount of food by the number of caterpillars to get the next column; divide the volume of the habitat by the number of caterpillars to get the next column.
  4. Determine which habitat showed the minimum amount of either space or food (depending on your question) in order for the most amount of caterpillars to survive. Why do you think this is the appropriate amount of space or food?
  5. Compare your results with other groups. Did other groups find similar results? Why or why not?
  6. If you wanted to fit the most amount of caterpillars in the same place, with the least amount of food, how much space would you give each caterpillar, and how much food would you give each caterpillar? Show your work!