Activity 5: Teaching Tips
This is a good opportunity to remind students of the importance of controlling variables in any experiment.
You may wish to substitute the seeds suggested for this activity with rapid-growing plant seeds.
You may wish to have the students make quantitative observations by measuring the height of the plants. If you do, this is also an excellent chance to introduce
or remind students of the uncertainty in measurements.
Factors that students might consider include such things as temperature, nutrients, light, soil characteristics (other than nutrients), and moisture.
The text states that “Competition among individuals of the same species is a very important factor in evolutionary change.” This concept is dealt with in greater depth in the next chapter. However, you may wish to direct students’ attention
to the statement at this time. Ask them to explain in their own words what the sentence means. Ask them to speculate how competition within a species can lead to evolutionary change.
In 1934 Soviet ecologist G. F. Gause completed a classic series of experiments
to study the competition between two species. He used the single-celled Paramecium. He grew species in culture under two different conditions.
Under one condition a species of Paramecium was grown alone in a culture containing a limited amount of bacterial food. Under the second condition
the two species were grown together in the same vial. Whereas the population survived if grown separately, only one species survived when grown together
with another. These and other similar experiments led ecologists to propose the principle of competitive exclusion. It states that two species cannot live together
at the same time in the same place if they are limited to one or more limited resources. Stated in another way, no two species can occupy the same niche.
It is interesting to note that when Gause grew the two different species of Paramecium in the same tube, both species survived. One species fed on the bacteria at the bottom, and the other species fed on the bacteria suspended
in solution.
The government maintains extensive databases on invasive species that are easily accessible by the Internet. Some of these databases are regional in scope.
Take some time to familiarize yourself with invasive species in your region.
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Whether students actually carry out the experiment, this Inquiring Further
provides excellent practice in designing an experiment. It could provide an opportunity to assess if students understand the idea of variables and the need
for controls in an experiment. |