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Animals Can Run Away, but Plants Must Stay

Responses to Herbivory

Co Authors:

Nicole D. Tunbridge
Department of Biology
Kwantlen Polytechnic University

Carol Pollock
Department of Zoology
University of British Columbia

Joan Sharp
Department of Biological Sciences
Simon Fraser University


In this PowerPoint-driven case study, students consider the many challenges faced by plants and discuss which of these might induce a morphological response. Examples of phenotypic variation within a plant species are presented and students discuss in small groups how to determine whether the observed variations have a genetic basis. The concept of a "common garden" experiment, in which plants are grown in a common environment and variation is measured, is elucidated and discussed. A specific example of phenotypic variation is introduced: Plectritis congesta from islands without herbivores (deer) are taller than the same species from islands with deer. An experiment with simulated herbivory is described and students are asked to predict results, assessing whether modification of pattern of growth is an induced response or a constitutive defense. A field experiment involving deer predation is introduced. The morphological response of Plectritis to predation is presented as an evolutionary tradeoff. The case is appropriate for introductory general biology (majors and non-majors), ecology, and plant biology courses and, with some modification, introductory evolution courses.

  • Explain how biotic and abiotic factors can act as agents of selection.
  • Distinguish between constitutive defenses and induced responses and explain the conditions under which each may be adaptive.
  • Explain how a common garden experiment can distinguish between genetic and environmental causes of phenotypic variation in plants.
  • Plan common garden and field experiments, and identify dependent and independent variables from these experiments.
  • Interpret data from common garden and field experiments.
Keywords: Natural selection; adaptation; evolution; evolutionary fitness; phenotypic variation; common garden experiment; experimental design; plant defenses; constitutive defenses; induced responses; herbivory; plasticity
Topical Area: Scientific method
Educational Level: Undergraduate lower division
Formats: PDF, PowerPoint
Type/Method: Clicker, Discussion, Interrupted
Language: English
Subject Headings: Biology (General)   Ecology   Genetics / Heredity   Evolutionary Biology   Botany / Plant Science   Science Education  
Date Posted: 5/2/2018
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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Answer Key

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Supplemental Materials

The PDF document below is a pre-case assignment on Plectritis congesta. Students will also need access to the journal article: Mondor and Addicott (2003) “Conspicuous extra‚Äźfloral nectaries are inducible in Vicia faba,” Ecology Letters 6 (495–497), Please note that this article, for copyright reasons, is not provided with the case; instructors wishing to use it will need to acquire it through their library.


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