This preview shows page 1. Sign up to view the full content.
Unformatted text preview: taste bad
alkaloids - potent poisons
- Source of our pesticides, drugs and spices. Inducible Nature Of Plant Defenses
- Always present/produced e.g tannins
- Energetically expensive.
- Made when needed.
- Toxins increase dramatically in many plants following
defoliation by herbivores.
- in area of wound or systemically throughout plant
- response in minutes -> next growing season
- Can substantially reduce subsequent herbivory. Responses of Herbivores To Plant Defenses
1. Evolve methods to counteract plant toxins
e.g. containment, break-down
- Leads to:
a. specialization of insect herbivore to particular plant
b. evolutionary arms race.
2. Some herbivores use chemicals to their advantage preferentially feed on plants with high concentrations and
sequester chemicals to use against own predators.
Ex. Interactions between cottonwood trees, beavers, and
leaf beetle (Chrysomela confluens) (text)
***cost of inducible defense --> energetic cost to producing more chemical which would result in less seed production
because there is less energy available for other things*** “Why Don’t Herbivores Eat More Plants”?
- Levels of herbivory low in terrestrial ecosystems.
1. Top-Down Control Hypothesis
- herbivore populations limited by predation and disease. 2. Bottom-up Limitation Hypothesis
- plant tissues poor food sources (low N) and well
limits herbivore densities/growth and reproduction
Limits herbivore densities/growth and reproduction * Both important factor in limiting impact of herbivory.
- Depends on plant species. MUTUALISM (+/+)
Mutualisms = relationships that beneﬁt both parties
View Full Document