Lab Exercise III:  Plant competition

 

            Competition can be a major factor restricting the growth in individual plants, the structore of populations, and diversity and function of communities.  There is no doubt that some species are better competitors than others, yet when we look outside we do not see a world dominated by a single dominant species.  Why hasn’t the “best” competitor replaced all the other species?  Clearly, a species’ competitive ability, as well as the population/community level effects of competition will be dependent upon numerous ecological and environmental factors.  The intensity of effects of competition can be influenced by plant density, spatial arrangement, soil nutrient heterogeneity, intensity of other ecological factors (e.g. herbivory), resource availability, and numerous other factors and processes.

 

Goals: 

 

  1. Learn the basics of experimental design, from concept to implementation to analysis.
  2. Explore how one factor/process influences the strength of competition experienced either by individual plants, or whole populations.
  3. Learn the skills necessary to give an effective oral presentation of the research project.

 

Unlike the other labs in this course, this one is relatively unstructured.  Rather than telling you what to do and when to do it, you and your lab partner will be responsible for developing a testable hypothesis, designing an appropriate experiment, conducting the experiment, analyzing the data, and interpreting the results.  It is worth spending some time at the beginning of the lab talking with each other, ensuring a strong project.  Like the other labs, this one will require you and your partner to maintain the plants outside of regular class hours.

 

This assignment is worth 10% of your final grade.  One-half of this mark will be allocated by the TAs for overall effort and rigor of the experimental study, with the remaining half allocated specifically for the quality of the oral presentation you and your partner will give in the last week of lab.  Details of the oral presentation will be provided at a later date.

 

The following is a list of supplies available to your group.  No group will likely use them all, and other common equipment is available as well.  The constraints around us (e.g. teaching lab, short time frame, etc.) will require a good deal of creativity. 

 

Common Equipment:

 

Greenhouse pots (a few different sizes)

Potting soil

Sand

Seeds of Brassica rapa (control and two GA mutants (short/long internode lengths)

Seeds of other, slower growing, weedy species.

Scissors

Fertilizer

Miscellaneous chemicals

Rulers

 

A general game plan:

 

  1. Choose a TESTABLE hypothesis
    1. There are many great ideas, but not everyone can be tested.  Accept the constraints of the lab (little budget, little space, little time), and work to find the best question in this setting.
    2. The “best question” here is the one which your whole group is interested in, and which you can test.  It is not necessarily a question which will get you into Science or Nature.  If you have those sorts of questions in mind, feel free to talk to me about doing a 499!
  2. Design the experiment
    1. Figure out how to isolate the variable of interest while keeping all other potentially confounding effects constant across treatments.
    2. Determine what your dependent variable(s) will be. 

                                                               i.      Will you be measuring something about the population (e.g. size structure), or something about individual plants (e.g. biomass), or both? 

                                                             ii.      Will you measure these things only at the end of the study, or in the middle as well?

    1. A good experimental design would let you draw the figures that you will use in your talk BEFORE you have even filled the first pot with soil.  Although you won’t know the “answer” at the start, you should know what each axis will be, and what the different possible answers would indicate about your factor/process and competition.

                                                               i.      If you are unable to do this before you have all the messy data, you definitely won’t be able to do it after you have the data.

  1. Create a timeline of the experiment.
    1. What needs to happen when?
    2. Who is going to be responsible for each step of the study? 
    3. Who is going to water?
    4. Where is the data going to be kept?
  2. Implement the study.
    1. Follow your timeline.
    2. Take detailed notes of each step.
    3. Take pictures of each step (digital camera is available).
  3. Get ready for analysis and presentation
    1. Do not wait until the end to start getting the analysis ready.

                                                               i.      Set up a spreadsheet as soon as possible

    1. Start working on the introduction/methods sections of the talk BEFORE the data comes in.

                                                               i.      Once the data is here, things will get real busy real fast.

 

When you have questions/concerns TALK TO YOUR TAs and ME.  Don’t let problems grow – they just get much harder to fix later.