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Succession: How Much Change in a Year?

Objective: Analyze quantitatively the changes between two photos of a plot of land. An evaluation of the relative amount of change will be generated.

Every landscape undergoes change all the time. However, there are sometimes that it is stable enough for humans to say, "This is a climax community." That means the plants and animals fit well enough together to keep the whole community in check. If an area is traumatized by either flood, fire, drought, volcanic eruption, earthquake, stampede or housing development, then a characteristic group of plants and animals recolonize or "invade" the bare earth. Invaders typically have a short life span, a high metabolism, a high reproductive rate, and they are easily transported. Conversely, climax communities are slow growing, long lived and when among the ecology they adapted to, they have a low reproductive rate which keeps their population in check. Actually, when you think about it, all organisms have the built in ability to reproduce enough to take over the entire world. What keeps most organisms in check are other organisms. When the checks and balances are taken away, a species starts to get a more gluttonous share of the resources. This throws our nice little "climax community" out of balance. We could look to the Malelucha in Florida, the tumbleweed in the Desert Southwest, but I think the most worrisome invader is me. I'm typing on a computer that was made from resources taken from thousands of others of my species. I am burning the energy locked up in the coal produced by quintillions of plants millions of years ago. I've been vaccinated and sanitized so the checks and balances that would have taken me out a long time ago are all gone. It is therefore my duty not to reproduce. My genes are staying with me.

The articles to read about the desert environments are

The photos are of my lichen sites and are attempts at being in the same place one year apart. You can easily see the invasion of other plants as well as the general well being of the desert in July 1998. I don't think they difference of color is entirely due to the lack of my photographing skills.

See A-6 for assessment.

Outline: Digitalize photos taken of the same area but at different times. Using NIH Image program, compare the plant's sizes and coverage using the measuring tools. Some manipulation of the images will be necessary. A number value of the amount of change will be discovered and then compared to other plots.

Open up the program NIH Image by double clicking on the microscope icon Â.

Navigate to and Open up the two images that you are assigned. They will digitized images of 3x4 photos taken from the same site at different times. Most of them will be a year different. If there is a measuring tape, use your measure tool ‡ and measure what ever it is. It could be a cactus, a measure tape or a rock. If it is a tape measure, Go to Analyze/Set Scale and set the scale.

Look at the photo for a while and see if you can determine what has changed between the two. Is there more lichen, more moss, more bushes, more ground covered by grass? When you have determined what has changed you need to isolate that part of the image from the rest. You have two ways to do this and it depends upon which you think has less error.

First try drawing around the part of the image that has changed with the selection tool fi. Then either to Analyze/Measure or hold down the ü key and hit 1. Hold down the ü and hit 2 to show your results.

Second try to use Options/Density Slice. It will turn an area on the LUT table red. Using your LUT tool Ê to move the red area up and down the table until an outline of that part of the image has become red. Get the magic wand tool Î and click on the item that you want. If you have two things, hold down the shift key, and click with the magic wand until both images are selected. hold down the ü and hit 1. Then hold down the ü and hit 2.

Write down five things: 1) The photo's name 2) the object measured 3) the number and units you came up with. 4) the method you used to get that number (free hand outline or density slice) and 5) which number you're more confident in.

Example of a data table:

Look at the images again and determine if there is anything else that has changed. You need to use your "Find Waldo" skills. If there is something else, measure its area in both pictures and determine if there is a difference.

Compute the percentage of change between each image by using the following formula:

% of change = (Larger Item Image Area * 100) / (Larger Item Image Area + Smaller Item Image Area)

Questions (2pts each)

1) What are the differences between the two years?

2) To what could you attribute this change?

3) Which plants or organisms are increasers?

4) Which organisms are decreasers?

5) Which organisms stayed the same?

6) Does one organism interfere with the other? If so, who does what to whom?

7) Does man play a role in the change?