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Evolution 2nd Edition

Evolution (2nd Edition)

Book Edition2nd Edition
Author(s)Bergstrom, Dugatkin
PublisherW. W. Norton
Section 18.1: Coevolution and Mutualism
Section 18.2: Antagonistic Coevolution
Section 18.3: Mosaic Coevolution
Section 18.4: Gene-Culture Coevolution

Chapter 18, Section 18.1, KEY CONCEPT QUESTION, Exercise 18.1

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Aim: Examine the hypothesis which suggests that the trees would produce lesser resources [liquid rich in proteins and carbohydrates] when they are not under predation pressure.



  • The trees under study are protected from their predators by creating a special barricade, such as cage-like structure. This reduces the stress on the plant to generate responses for its protection from predation [action of mammals and insects].
  • A control group is taken, wherein the predation pressure is not decreased for the trees. As a result, the trees are not protected neither from insects nor mammals.


  • In the non-control experimental group, lesser amounts of resources are produced by the trees for the insects A because of the absence of potential predators.
  • In the control experimental group, significant amounts of resources are produced by the trees for the insects A in order to protect themselves from mammals or insects.



The trees are more prone to the predation in their natural environment. For this reason, they form a mutualistic relationship with the insects A, wherein the insects A provide protection to the trees from predators, such as mammals or insects. In return, the insects A get food from the trees in the form of carbohydrate-rich liquid. However, in a condition, wherein the trees are not vulnerable to the predators, lesser resources for the insects A are produced.

Additionally, less production of resources for insects A would also be favored by the natural selection because of low energy-cost at the plant's end and high benefits.

Verified Answer

Aim: Examine the production of resources [liquid rich in carbohydrates] by the trees when the predation pressure is reduced.



In order to predict the outcome, the trees are provided protection from the predators. Additionally, a control is taken where trees are not protected from the predators. This is to ensure that there is normal production of resources that the insects A are utilizing.


Observation: The resources are produced in a lesser amount when trees do not need protection from insects or mammals [predators]. In contrast, normal amounts of resources are produced in the control trees that are not given protection from predators.


Results: The trees produce normal amounts of resources for insects A in order to protect themselves from predation. However, these trees do not form enough resources when there is no requirement of protection.

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