How Do Ecosystems Change Over Time?

Remember that a change in gene frequency in a population over the course of years is evolution. Explain that the genetic differences of organisms within a species increases the chances that at least some members of a species will survive under changing environmental conditions.

Ecosystems and Evolution

In biology, we talk about organisms alone and in groups. So far, we’ve been concerned mainly with individual organisms, which together form populations. Those populations of organisms combine with other populations in order to form communities, and those communities come together with abiotic factors to form entire ecosystems. As we’ve already seen, those ecosystems can be grouped together as a biome when they exhibit similar climates. So, when we study ecosystems and evolution, we are concerned with how the populations in those communities change.

Example of a butterfly

When you look at a population of humans, there are always certain similarities and differences that you notice. For instance, skin color, hair type and color, eye color, average height are all genetic characteristics that are the easiest to notice about people. Biologists don’t just study humans; we study all sorts of living things.

Imagine that you were looking in a field of butterflies: you see thousands that have yellow and black coloring and also a few dozen that have blue and black coloring. You also notice that there are hundreds of birds hunting the butterflies. Before we look at the behavior of the birds, we can make a conclusion about the gene frequency of the yellow color among the butterflies. Specifically, we can say that the gene frequency of yellow is around 99%, because 99% of the butterflies have yellow instead of blue. Similarly, we can say that the gene frequency of blue is about 1% for this population of butterflies.

Gene frequency, or the percentage of individuals in a population that have a certain characteristic, is a way to measure evolution. Going back to the butterflies and the birds, you notice that the birds are only hunting the yellow and black butterflies. For some reason, they are leaving the blue and black butterflies alone. You leave and come back a week later to the same field to find that there are only a few hundred butterflies; what’s more, half of them are now blue and black butterflies!

This is an example of evolution – in this case, the population of butterflies has changed. The gene frequency of yellow coloring has decreased to about 50% because of changing environmental conditions. What were the “changing environmental conditions”? The birds that were hunting the butterflies made the change in the butterfly population. Even though the total number of butterflies has decreased, the blue and black butterflies are surviving better because of the hunting patterns of the birds.

We have seen that there are many factors that go into making a biome: temperature, precipitation, animals, plants, mountains, rivers, oceans, etc. All of these factors affect the evolution of the living things within the biome.

1. What is the biotic relationship between the yellow and black butterflies and the blue and black butterflies that feed on the same plants? Explain.
2. What is the biotic relationship between the butterflies and the birds? Explain.
3. Calculate the gene frequencies if there were 150 yellow and black butterflies and 100 blue and black butterflies in the field.
Put it together
4. List at least two reasons that the birds could be only eating the yellow and black butterflies.
5. Predict what would happen if the climate became mostly cloudy, changing the birds' vision so that both types of butterflies appear to be the same. What type of interaction is this, in terms of biotic and abiotic factors?
Think about it
6. Consider the Forest Hills ecosystem. Inside the ecosystem, among other things, are bushes, trees, and rabbits.
a) Come up with any genetic characteristic for the rabbits that has two forms (in the butterfly example, this was the yellow and blue colors). This can be something like the color of fur, type of nose, length of ears, etc.
b) Come up with genetic frequencies for these two forms, as percentages. Keep in mind that all percentages need to add up to 100%.
c) What do you think will happen to these gene frequencies if snakes are introduced to Forest Hills? Assume that evolution will happen, and list the gene frequencies after the snakes are introduced.
7. What are the four major biotic roles in an energy pyramid?
8. What would you tell someone who asked you, "Is it true that you can travel to the center of the Earth?" Explain!
9. What does it mean that an ecosystem recycles materials?
10. Differentiate biotic from abiotic.
  1. Choose three genetic characteristics in you and the people you know to study. Write these down!
  2. You will examine three members of your family/friends and three students. If you choose characteristics that depend on gender, make sure you only talk to people who are the same gender. Make a table showing your results and calculate the gene frequencies for each characteristic. You can use the table below:
    First name of person Characteristic 1:_______________ Characteristic 2:________________ Characteristic 3:________________
    Family / Friends
  3. Looking at this characteristic in your family, what trends do you notice?
  4. Looking at this characteristic in other students, what trends do you notice?
Choose an Animal
  1. Take an animal card and describe 3-5 features of the animal that make it unique
  2. What is an environment that the animal lives in?
  3. What characteristics does the animal have that makes it fit for this environment?
  4. Choose another environment. What characteristics does the animal have that help it in future generations?
  5. Write a two-paragraph article about how one of these animals evolved into the animal that it is today.
Beetles, Part 2

Take your 16 beetles from part one (ask me or another student if you do not have any beetles) and separate the four beetles that survived. At random, take two of the beetles and “breed” them by creating sixteen more beetles in the second generation. Make sure to only include characteristics from the two parents, and try to mix up those characteristics in each member of the second generation. Hand in your two parents, sixteen children and responses to the following questions:

  1. What are three observations that you can make about the children?
  2. Are all of these children well suited for their environment? Why or why not?
  3. Choose one of the aspects of your environment and change it. Which beetles in the second generation are best suited for this new environment? Why?
  4. Think about what beetles will be around in ten generations. What would you expect them to look like?
Gene Frequency

In this activity, you will be reproducing bacteria in a biome of your choice. You will figure out which bacteria survive and which die depending on the environment that you choose. Finally, you will calculate the gene frequencies and see if they changed from the beginning to the end. Below, you will find a table which shows the three genes, and the descriptions of their alleles (“D” means dominant, “R” means recessive).

Gene Allele Description of the Allele
1stGene:Temperature Dom. Able to withstand temperatures below 0°C
Rec. Able to withstand temperatures above 100°C
2nd Gene: Water D Can survive under water
R Cannot survive under water, but can survive in ice
3rd Gene: Sunlight D Uses sunlight for energy
R Doesn’t use sunlight for energy, but requires very little food

You will start with a total of 10 bacteria that all have this gene. Some bacteria are dominant for some genes and recessive for others. In the table below, I have started you off by telling you which alleles (Dominant or Recessive) each bacteria (A - J) will have for each gene.

P1 Generation Bacteria Name
1st Gene: Temperature Dom. D D D R R R R D D
2ndGene:Water Rec. D D R D D R R D D
3rdGene:Sunlight Dom. R D R D R D R D R
  1. Is bacteria #1 dominant or recessive for the 1st gene? Is bacteria #6 dominant or recessive for the third gene?
  2. Choose a biome for these bacteria and write it down.
  3. Right now, calculate the initial gene frequency for each dominant and recessive allele and record it in the chart below. The first gene has been calculated for you: 6 out of the 10 bacteria are dominant for the first gene, so the gene frequency is 60% dominant and 40% recessive.
Gene Allele Initial Gene Frequency
1stGene:Temperature D 60%
R 40%
2nd Gene: Water D
3rd Gene: Sunlight D

You are going to simulate evolution by deciding which 5 bacteria in the P1 generation survive to the F1 generation. Once you decide which five will survive, you will then reproduce each bacteria to make a total of 10 bacteria in the next generation. For example, if you choose that bacteria A, D, E, I and J should survive to the F1, then you will have:

F1 Generation Bacteria Name
1st Gene: Temperature D D D D R R D D D D
2ndGene:Water D D R R D D D D D D
3rdGene:Sunlight D D R R D D D D R R
  1. Go ahead and make the F1 generation. For each bacteria that you selected, why did you pick it? Fill in the table below with your choices.
F1 Generation Bacteria Name
1st Gene: Temperature
  1. Make the F2 generation by taking 5 of the above bacteria and making copies of each one.
F2 Generation Bacteria Name
1st Gene: Temperature
  1. Make the F3 generation by taking 5 of the above bacteria and making copies of each one.
F3 Generation Bacteria Name
1st Gene: Temperature
  1. Calculate the final gene frequencies:
    Gene Allele Final Gene Frequency
    1stGene:Temperature D
    2nd Gene: Water D
    3rd Gene: Sunlight D
  2. Compare the initial and final gene frequencies:
    1. Which allele made the biggest jump in frequency from the P1 generation to the F3 generation?
    2. Did evolution happen? Why or why not? Use the definition of evolution in your response.
    3. Was this an example of directional selection? Why or why not?
    4. Choose another biome. Which bacteria do you think would have done the best in this new biome?
Saving the Golden Lion Tamarin

Zoos are no longer just a place to house animals for display and public education. Many zoos participate in programs to assist in the survival of endangered species, such as the golden lion tamarin. This primate is native to the coastal regions of the Amazon rain forest. The tamarins are threatened because their habitat is being split into small pieces and destroyed.

In the early 1970s, there were 91 golden lion tamarins in 26 different zoos. Biologists made a plan to help the species survive. The goal was to increase the number and genetic diversity of golden lion tamarins. As of 2007, there were 496 golden lion tamarins in 145 zoos around the world. Further, about 153 tamarins from the program have been reintroduced to the wild since 1984. These tamarins are part of a healthy wild population of more than 650.

Analyze and Conclude

    1. Use this data table to help you organize the data from Build Connections.

Number of Captive Golden Lion Tamarins

Number of Participating Zoos



  1. Use the formula below to find the percent by which the captive population of golden lion tamarins has increased since 1970.

percent increase = ( (new population – original population) / original population) × 100

  1. Until the captive population had reached a target size, biologists limited the number of tamarins that were reintroduced into the wild. What do you think the target size for the captive population is? Use the graph to explain your answer.


  1. Only 153 golden lion tamarins have been reintroduced from captivity. However, there is now a reintroduced population of about 650. Where did the other 497 come from?

Build Connections

When populations of wild animals become very small, do you think that they should be removed from the wild and brought into zoos? Why or why not?