Habitat Fragmentation and Species Diversity

Background

Every organism needs a certain space in which to search for food, nest, search for mates, and fulfill the myriad other requirements of life. Species that are adapted to large continuous home ranges will suffer when the size of that range is restricted. If that habitat size is reduced past a certain critical level it will not be able to support the species which live there.

When a group of species occupies an area these pressures are increased as each species competes with the others for limited resources within that area. This leads to a relationship between the area available and the number of species that area will support. Larger areas support more species than smaller areas.

As the human population grows we require more space. That requirement often comes at the expense of other organisms. Human encroachment into wilderness areas such as forests and wetlands has resulted in the degradation or destruction of these habitats. Loss of habitat and habitat fragmentation are areas of major concern in species conservation. Road construction, deforestation, draining of swamplands, etc. result in large areas of habitat being broken up into a series of smaller areas, each of which will support fewer species.

Lab Outline

This lab will illustrate visually and graphically the effects of habitat destruction on hypothetical populations of amphibians living in a wetland. Using this model you will be breaking a large, continuous habitat into increasingly smaller fragments (or patches). You will then see how this affects the diversity and species composition of the wetlands.

These effects are also important in determining the size of areas set aside for conservation of wetlands. Is it better to have several small refuges, or one large refuge? This is referred to as the SLOSS (Single Large Or Several Small) debate in conservation biology.

This lab will allow you to see how habitat fragmentation affects species diversity and help determine the best conservation strategy for these hypothetical amphibians.

The Lab

Habitat Fragmentation-Part One

In this simulation we will be looking at a community of insectivorous amphibians. These eight (8) species all compete for one resource (aquatic insects). When you begin the simulation, these will be a lag time before the amphibians appear; this allows the insect population to reach a level where they will sustain the amphibians.

Since these amphibians do not eat each other, the only interaction they have is competition for food. Therefore, any effects on population sizes will be a result of loss of habitat and food.

  1. Run EcoBeaker (double-click on its icon).
    2.
  2. Open the Habitat Fragmentation Situation File (use the Open command on the File menu). The window at the top left is the habitat grid. The next window to the right is the line graph representation of the Simpson Diversity Index, below that is the numerical value for the Simpson Diversity Index at the present time. To the left of this window is the Control Panel. Use this panel to start, stop, and reset the simulation. In the lower right is a line graph representing the population levels of each species over time. In the lower left is the Habitat control window. You can use this to change the size of the roads, and the frequency with which they are built.
    3.
  3. Press the GO button on the Control Panel.
    4.

    In the habitat grid you should see the wetland (green) divided by two roads (gray). Aquatic insects (lighter green) should settle in the wetland for the first ten timesteps (days). On the tenth day the amphibians will be introduced at random onto the grid. Amphibians introduced onto roads will either move out of the road or die.

  4. Pause the model at 100 day increments (press STOP, record your data, then press GO). Record the Simpson Diversity Value. Stop the model at 500 days, record the final data (Simpson Diversity Value and the amphibian with the highest population level) and press RESET to clear this run. Repeat this process 5 times.

Things to notice:

Are all species represented equally in all patches?

Do larger patches have more or fewer species than small patches?

Data Table 1. Simpson Diversity Values

Run

100 Days

200 Days

300 Days

400 Days

500 Days

Who ‘won’?

1

            

2

            

3

            

4

            

5

            

Questions:

What is the overall trend in diversity and population size over time?

Is the amphibian that ‘wins’ always the same?

 

Habitat Fragmentation-Part 2

The next part of the lab will increase the frequency of road-building. What effect do you think this will have on the diversity values and their rate of change?

  1. Double-click on ‘N/S Road’ in the Habitat window. Single click on ‘Add on timesteps’ and change the values from 50 to 25.
    2.
  2. Double-click on ‘E/W Road’ in the Habitat window. Single-click on ‘Add on timesteps’ and change the value from 50 to 25.
    3.
  3. Follow the same procedure as in Part 1, Steps 2, 3, and 4 above.

Data Table 2. Simpson Diversity Values

Run

100 Days

200 Days

300 Days

400 Days

500 Days

Who ‘won’?

1

            

2

            

3

            

4

            

5

            

Questions:

What effect did increasing the frequency of road building have on diversity?

Were the changes in diversity slower, the same, or more rapid than before?

As urbanization increases, do you expect to see the same problems in the real world as we did in this lab?

How would you manage these amphibians? Reduce or increase road building? Increase or decrease the size of undisturbed patches? Provide some way for amphibians to cross the roads?

Additional Investigations

What effect does adding complexity to the trophic dynamics of these amphibians have on the rate of diversity change? Food Chains? Food webs? -Look at HF Food Webs.sit

Can you alter species characteristics to make them less susceptible to extinction?