The following challenges have arisen:
Here are some examples of hypothesis that students of mine or others have tested:
Since my lab is not tied into a lecture, I find it helpful to discuss mechanisms of soil invertebrate diversity with students before this lab. I try to have students read beforehand and discuss what they found. The best kinds of questions to ask should be “explain how...,” “what if...,” and “how does _____ affect...?” types. Some examples: “How does litter quality typically affect functional types in the soil invertebrate community?”; “What would happen if a pasture was plowed to plant corn?”; “How does succession from an old field to a forest affect the community structure?”; “Explain why the litter community differs from the soil community.” With the levels of students I have, I find the “bounded inquiry” method works the best. Here, the research question can be either generated by the student or by the instructor. I try to get students to do this, but I guide the discussion so that they are likely to come up with a testable hypothesis. In bounded inquiries, the study system and methods can be either student-generated or given by the instructor. Again, I try to have them generate this, with my guidance. Both the data collection and analysis and presentation steps are done by the students.
Guided inquiry differs in that the research question and the study system and methods are given by the instructor, and the data collection can be either done by the students or given by the instructor. With highly motivated and well-prepared students, the instructor can use the “open-ended inquiry” model, where the research question is either student-generated or given by the instructor (ideally, it is student-generated with guidance from the instructor). Representative readings are listed in the Introduction; I would suggest any of the following as good places to start: Behan-Pelletier and Newton 1999, Hooper et al. 2000, Kalisz and Powell 2000, Six et al. 2002, Wardle and Lavelle 1997, and Wolters et al. 2000. For sampling methods, I suggest Brower et al. (1998), chapter 3d, or Southwood and Henderson (2000), chapter 6. You may also find many resources on the Internet. For example, using the phrase “soil biodiversity” at http://scholar.google.com will yield many useful hits.
Although I have not done this, it would be interesting to include measurements of soil and parameters, such as soil moisture, temperature, organic matter (loss on ignition), texture, chemistry, and an index or litter quality or quantity, and site parameters such as light levels and air temperature. In that case, you should give the students a reading from an ecological methods source that will help them. Brower et al. (1998) has quite a few suggestions for assessing soil properties such as parent material, soil moisture & temperature, soil organic matter and density, and soil texture in Chapter 2c, and soil chemistry measurements are outlined in Chapter 2e. However, both Hach and LaMotte1 make inexpensive soil test kits, which might also be included. Site parameters, such as light, temperature, etc. could also be measured; again, Brower et al. (1998), chapter 2b has some good suggestions.
This lab has a lot of room for variation and local adaptation. The actual sampling could be fairly quantitative or it could just be a grab sample. You could have students focus on the effect of different wattage of light bulb on their results. Diversity indices other than Shannon can be used; Brower et al. (1998) has a good summary of them. Even if you use the Shannon index, you can use the t-test in Brower et al. (1998) or Zar (1999) instead of the Komolgorov-Smirnov test described here, provided that you replicate a fairly large number of times. It would also be possible to include visual ways of presenting diversity. This would include a species-area curve (really a taxa-area) curve and a log-normal curve. Note that Brower et al. (1998) describes both of these curves well in Chapter 5a. If you decide to go this route, you should have students measure the area and/or volume that they sample.
For #1, you want students to see that both richness and evenness contribute to overall diversity.
For #2, my goal is to get students to see that, in ecology, many factors co-vary, making it hard to see which one is driving the process you are interested in. It can take a lot of imagination to design an experiment that separates these different factors.
Question #3 will hopefully get students to dive into the literature and figure out what the functions are of the critters they have found. This may also get them to think about the quality of the litter these animals are feeding on, which will lead to them to see how vegetation can drive invertebrate communities.
Question #4 will lead students to think about the limitations of their sampling techniques, introducing the idea of bias. Perhaps they can come up with a better design than I have outlined here!
Concerning Question #5, I haven’t done anything with succession in this experiment, so I don’t have a lot of guidance to offer on this point. It also looks like few other ecologists have thought about, based on the paucity of references I could find in this area. Nonetheless, what we think of as plant succession is actually two different processes from the invertebrate community’s perspective. Ecology has a long history of lumping multiple processes together under one name. This question will illustrate another example of that occurrence; it may also potentially lead some students down a path that may make an important contribution to ecology someday!
Question #6 is trying to illustrate feedback loops, showing that not only does litter quality affect the invertebrate community and thus the litter decay rate, but the invertebrate community itself can also affect the litter decay rate.
The purpose of Question #7 is to link the soil food web with the vertebrate food web in the same community.
A variety of assessment schemes are possible in addition to the written report. See the comments under #4 of Challenges to Anticipate and Solve. Oral or poster presentations, either individually or by a group, are also possible. I have not tried this with students in an ecology class before, but I have seen it work well in other types of courses. These kinds of presentations will take at least one lab period. Students in my program actually get this kind of experience in a research methods course, so I don’t have to do a lot of preparation in this area. If your students are unlikely to have this background, I highly recommend the in Pechenik (2001).
I think a formal written evaluation, similar to course evaluations, could be designed and given to students after they have been assessed in this lab, in order to evaluate the effectiveness of the lab.
This lab is essentially a number of modules that can be mixed and matched as needed. For hypothesis generation, you may give hypotheses to students if they are not prepared or motivated enough to come up with their own. The sampling methodology can be as quantitative or qualitative as judged appropriate. The same is true for counting taxa; you may simply have students note presence or you may have them count numbers of individuals of each taxon. For evaluation, you may use the form of written report given here, or you may use another. If you wish to train students in oral presentation, you may use that instead or in addition to written work.