Question

During a hiking trip in northern Minnesota, you pull out your pocket microscope and notice that one lake with high acidity levels has a high abundance of water fleas (Daphnia) and a low abundance of a species of zooplankton predator, while another lake with low acidity has few water fleas and many of the predator. You note that Minnesota has many lakes with different acidity levels. You hypothesize that zooplankton do worse in high acidity, allowing Daphnia to flourish. Design tests of this hypothesis using 1) an experimental manipulation, 2) a natural experiment, and 3) a microcosm experiment.

Answer 1

(1) Experimental Manipulation:

Select a set of lakes in Minnesota.

Divide the set into 2 halves.

First half of samples of lakes: make the water less acidity. (This is Control Group)

Second half of Samples of lakes: make the water high acidity (This is Experimental Group).

Measure the Daphnia in both the samples.

H0: Null Hypothesis: 1 = 2 (Zooplankton do not make worse in high acidity in allowing Daphnia to florish)

HA: Alternative Hypothesis: 1 < 2 ( Zooplankton make worse in high acidity in allowing Daphnia to florish)

(2) A Natural Experiment:

Observe all the lakes in Minnesota.

Among the available lakes:

Select 2 sets of lakes as follows:

First set of samples of lakes: where the water is less acidity. (This is Control Group)

Second set of Samples of lakes: where the water is high acidity (This is Experimental Group).

Measure the Daphnia in both the samples.

H0: Null Hypothesis: 1 = 2 (Zooplankton do not make worse in high acidity in allowing Daphnia to florish)

HA: Alternative Hypothesis: 1 < 2 ( Zooplankton make worse in high acidity in allowing Daphnia to florish)

(3) A Microcosm Experiment:

Create articicially through simulation two sets of samples as follows:

First set of samples of lakes: with the water less acidity. (This is Control Group)

Second set of Samples of lakes: with the water high acidity (This is Experimental Group).

Measure the Daphnia in both the samples.

H0: Null Hypothesis: 1 = 2 (Zooplankton do not make worse in high acidity in allowing Daphnia to florish)

HA: Alternative Hypothesis: 1 < 2 ( Zooplankton make worse in high acidity in allowing Daphnia to florish)