Practice questions: the hypothesis-testing approach

NOTE: this question is challenging because of the nature of the subject, but also because of the level that I would like you to reach in terms of interpreting data and critiquing experiments. Being able to critically evaluate data allows us to draw justified conclusions in science, but also to make truly informed decisions in life (you will also require this skill for your assignment and for many courses that you may take in the future).

Study the experiment described in your text, figure 1.12 (this is the experiment about capsaicin). You should be able to briefly describe the experimental set up.

a) What is the research question?
Does the presence of capsaicin (in chilies) deter some predators (mice) but not others (thrashers)?

b) What is the overarching hypothesis (or the Ha, or the “hypothesis with a name”)?
Capsaicin deters cactus mice (and other organisms that feed on chilies and destroy their seeds) but not thrashers (and other organisms that eat chilies and disperse their seeds).

c) What is the purpose of using the hackberry as one of the food options for the mice and the thrashers?
They act as a “standard” or a control.
First, they allow us to determine whether the mice and/or the thrashers might avoid the chilies just because they are avoiding foods that are round and have the size and texture of chilies. (If we just had the two types of chilies, and mice did not eat either, one could argue that they did not eat them because those mice were avoiding food and/or avoiding small round berries-nothing to do specifically with the chilies or with the capsaicin).
Second, they allow us to get a sense of whether mice and thrashers respond differently or not (or how differently they respond) to small round berries. If mice ate a much smaller % of hackberries than thrashers, then one could argue that they also ate fewer chilies because they generally are less attracted than thrashers to small round berries.

d) What is the purpose of having two types of chilies (pungent and non-pungent)?
We want to test whether the capsaicin, which is present in the pungent, but not in the non-pungent chilies, deters mice but not thrashers. If we only had non-pungent chilies, we could not test the effect of the presence of capsaicin. If we had only the pungent chilies, and the mice did not eat them (but ate the hackberries), we could not conclude that this is due to the capsaicin: one could argue that it is the colour (or some other property) of the chilies that deter the mice, not the capsaicin. Having the two different types of chilies allows us to really isolate and test the variable of interest: the presence of capsaicin.

e) You will notice that the predictions don’t match with the hypotheses very well. Recall that a prediction is a result/outcome that we expect to see if the hypothesis is correct.
Write a better, stronger and more specific prediction for the dispersal hypothesis.
If the dispersal hypothesis is correct, then when presented with non-pungent and pungent chilies, mice are expected to consume non-pungent chilies (but not pungent chilies), while thrashers are expected to eat the two types of chilies in equal amounts.
(Both organisms are expected to eat hackberries, but this isn’t part of the hypothesis).

f) List all the possible outcomes of the experiments that would not match your prediction.
(This is a pretty tedious exercise because of its length, but it is very good to do. You won’t have to do such tedious things on your exams).
Possible outcomes that do not match the prediction:
1. All situations where there are no differences between mice and thrashers; e.g. neither organism eats any of the berries, both organisms only eat hackberries, both organisms eat hackberries and non-pungent chilies, etc.
2. Mice do not eat non-pungent chilies or hackberries, but eat