Challenges to Anticipate and Solve

The following challenges have arisen:

  1. Developing testable hypotheses: Since my lab is in a course separate from ecology lecture, students often don’t have the background—or they’ve forgotten it—needed to easily come up with a good hypothesis. In this case, you may want to prepare them well with references and/or discussions beforehand. The references and web sites listed are a good place to start—you might also want to give a mini-lecture beforehand on soil communities to prime the pump for a discussion leading to testable hypotheses. On the other hand, you may find that giving students readings ahead of time constrains their creativity in designing their experiments. Also, if students think that we already know the correct answer, they may become less engaged in the exercise, and they may think they got the “wrong” answer if they find something different.
  2. Here are some examples of hypothesis that students of mine or others have tested:

    • How do invertebrate communities vary under a hardwood vs. hemlock canopy?
    • What is the effect of soil pH on invertebrate diversity?
    • What is the effect of an invasive plant on invertebrate diversity?
    • In an agricultural setting, how do different tillage systems affect invertebrate diversity?
  3. Identifying invertebrates: Most students think this is going to be impossible. I wondered myself, being a plant ecologist. However, at the level described here, it really is pretty straightforward! As long as you can identify the organism to phylum or class, the name of the species doesn’t matter in a biodiversity study—mite #1 works just as well as the Latin name.
  4. Manipulating large data sets with a spreadsheet: Student familiarity with Excel is all over the map. In my course, students have generally had a good deal of experience with Excel by the time we get to this lab. If they haven’t, you may want to consider an “Excel 101” workshop before doing this lab. See some of the Excel Tutorial websites for pointers.
  5. Writing a research-style paper: Again, students in my course have had experience by the time we get to this. If your students haven’t done this before, give them an example of a well-written paper from a previous class. For their first effort, have them hand in a draft that you write comments on. I’ve found that students really appreciate this and learn a lot quickly if you give them a chance on a draft. It also makes subsequent reports a lot easier to read and grade.


Lab Description

Introducing the Lab to Your Students:

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.

Activities in the Lab:

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.



Questions for Further Thought

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.



Assessment of Student Learning Outcomes

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).



Evaluation of the Lab Activity

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.



Translating the Activity to Other Scales

  1. Translating this experiment to larger scales: I generally teach this to a class of 11—14 junior and senior biology majors. With a larger class, it would certainly be possible to ask more quantitative questions. I suspect that it would be harder to find the time to have students come up with their own hypotheses. I also suspect that you will need to dispense with the oral/poster presentations, and you may need to cut back on the written part as well.
  2. Translating this experiment to pre-college settings: You may want to dispense with most of the diversity calculations. Simply showing students the tremendous diversity of animals in the soil will be educational. Calculating and e might be sufficient at the high school level.

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.