topic 8 optimal defense theory

Question 1

what is OPT DEF theory? assumes?

Answer 1

• Organisms evolve defenses in a manner that optimizes fitness
• ASSUMES:
○ Defenses are beneficial: enhance plant fitness, relative to undefended
plants, when herbivores are present.
○ Defenses are costly: reduce plant fitness, relative to undefended plants,
when herbivores are absent.

Question 2

• Investment in defense by plants is based on:

Answer 2

1. risk of herbivory
2. tissue value (fitness)
3. cost of defense

Question 3

5 predictions of the theory?

Answer 3

1. Because defense are costly, organisms evolve defenses in direct
   proportion to their risk of herbivory (all else equal)
2. Within organisms, valuable & frequently attacked tissues will be the
   best defended.
3. poorly defended individuals will have higher fitness than well defended
   individuals when herbivores are absent (because defenses are costly)
4. Well defended individuals will have higher fitness than poorly
   defended individuals when herbivores are present (otherwise defense
   wouldn’t have evolved)
5. `Costly defences are more effective

Question 4

• Support for theory / exs

Answer 4

1. induced defense in basal shoots only (repro structures) - supports prediction 3
2. soybeans w investment in toxis - supports prediction 4
3. white clover with cyanogenic and acyanogenic morphs - supports predictions of the theory - acyanogenic have high performance than cyanognic in the absence (but not presence) of herbivores