Principal Ecological Question Addressed

Does host plant vigor or physiological condition (as measured by plant size) influence the oviposition decision of an ovipositing gall-forming herbivorous insect? What are the effects of these oviposition decisions and gall formation on subsequent host plant growth and reproduction? Why might the physiological condition (as measured by plant size) of a host plant matter to an herbivore?


What Happens

Students test competing hypotheses to explain: 1) why galling herbivores choose the goldenrods they do, and 2) the effects of herbivores on plant reproduction. Students conduct a field study involving goldenrod plants and galls formed by one of two common gall-forming insect species. After measuring plant size and reproductive attributes of plants with and without galls in the field, students analyze the results using statistical tests to evaluate the competing hypotheses regarding plant susceptibility to attack and herbivore effects on plant reproduction. Students then communicate the concepts they have tested, the results of their tests, and their conclusions for the comparisons they performed.


Lab Objectives

  1. To learn to identify tall goldenrod and the galls formed by herbivores that oviposit on and feed on this plant.
  2. To use a transect technique to survey the frequency of herbivores on plants in the plant population studied and to practice measurement and data collection skills.
  3. To understand primary concepts of herbivore responses to plant vigor and plant reproductive responses to herbivory.
  4. To test hypotheses about herbivore responses to plant vigor and plant reproductive responses to herbivores using appropriate statistical methods.
  5. To effectively communicate the purpose, results, and conclusions of this study by writing a Brief Communication.
  6. To examine the biology of the plant and insect species studied and the adequacy of the hypotheses tested to explain the attack of plants by herbivores and the reproductive response of plants following herbivory.

Equipment/Logistics Required

Tape measures (35m or 50m), meter sticks, 150cm rulers, tally meters (hand-held 'clicker' used for counting), and wire flags or flagging tape are all needed. A 0.5m x 0.5m or a 1m x 1m PVC square sample quadrat frame may be useful.


Summary of What is Due

At the end of the first lab period, I conduct a brief formative assessment in which students write a one minute paper to address misconceptions about plant-herbivore interactions that they had prior to the classroom discussion.

In a timely way, each group of students must prepare and submit a spreadsheet that contains the raw data they collected in the field. This task may be completed upon return to the lab if time permits; if not completed in the lab, students must e-mail the spreadsheet with their data to the instructor and to other students in the class.

Students will produce a Brief Communication; which is a short report that includes all sections of a traditional lab report except no abstract is expected. Students must include at least two citations to support the ideas in their Introduction or Discussion, and a figure and table of statistical results for each test they perform.


Keyword Descriptors

Ecological Topic Keywords:

coevolution, galls, herbivores, parasites, plant ecology, plant-herbivore interactions, plant vigor hypothesis, plant stress hypothesis, oviposition decisions, habitat selection, foraging decisions, herbivore impact, plant tolerance, plant overcompensation

Science Methodological Skills Developed:

collecting and presenting data, data analysis, evaluating alternative hypotheses, field work, graphing, scientific writing, statistics, use of primary literature

Pedagogical Methods Keywords:

formative evaluation, guided inquiry, misconceptions, minute paper, rubric (for Brief Communication)