Lecture Notes: Module 4 - Predation, Herbivory, and Parasitism

Chapter 14: Predation and Herbivory

Key Learning Objectives

• Predators and herbivores limit the abundance of other species.
• Populations of predators and prey fluctuate in regular cycles.
• Predation and herbivory drive the evolution of various defenses.

Consumer-Resource Interactions

• Types of Heterotrophs:
  • Detritivory
  • Herbivory
  • Predation
  • Parasitism
  • Parasitoids
  • Hyperparasitoids
• Species obtain energy by consuming other organisms.
• Species interactions can change over life stages, as seen with saguaro and palo verde.

Predation

• Predators consume and kill prey, removing individuals from populations.
• Herbivores can act as predators by consuming and killing plants.

Parasitism

• Parasites do not kill hosts directly but consume them in a way that can increase the host's mortality.
• Parasites depend on the extent and duration of their association with their hosts.
• Parasitoids eventually kill their hosts after development.

Parasitoids

• Unique predators that kill their host after full development.
• Example: Cotesia glomerata (wasp) ovipositing in caterpillar larvae.
• Can manipulate host behavior to increase their reproductive fitness.

Brood Parasitism

• Example: Cuckoos lay eggs in the nests of other bird species.
• Cuckoo chicks mimic host chicks and are raised by host parents.

Predator-Prey Cycles

• Examples: Snowshoe hares and Canada lynx cycles.
• Predator-prey cycles demonstrate top-down and bottom-up control.
• Top-down control: Predators limit prey population.
• Bottom-up control: Resource availability limits prey population.
• Experimental laboratory settings reveal complex interactions that affect population stability.

Lotka-Volterra Models

• Continuous-time model predicting predator-prey cycles.
• Key Variables:
  • N = number of prey
  • P = number of predators
  • c = capture probability
  • a = assimilation efficiency
  • m = mortality rate of predators
• Key Insights:
  • Prey populations are stable when additions and consumption are balanced.
  • Predators' populations are stable when mortality and additions are balanced.
  • Joint equilibrium points indicate stability in predator-prey interactions.

Functional Response Curves

• Type I: Linear increase in prey consumption.
• Type II: Slows as prey density increases, then plateaus.
• Type III: Low consumption at low prey density, increases at high density due to factors like prey refugia and switching.

Evolution of Defenses

• Structural Defenses: Reduce predator ability to capture prey.
• Chemical Defenses: Often energetically costly but deter predators.
• Aposematism and Mimicry:
  • Mullerian Mimicry: Unpalatable species share warning signals.
  • Batesian Mimicry: Palatable species mimic unpalatable ones.
• Coevolution: Reciprocal evolutionary adaptations, e.g., predators adapting to prey defenses.

Evolution of Herbivory

• Plant chemical defenses (secondary metabolites) reduce herbivory but at fitness cost.
• Plants may produce alkaloids, terpenoids, and phenolics as defense mechanisms.
• Example: Nicotine production in tobacco plants is a trade-off with seed production.

Honors and Recognition

• Dr. May Berenbaum recognized for studies on chemical coevolution and insect-plant interactions.

These notes summarize the key concepts and examples discussed in Module 4 on predation, herbivory, and parasitism, providing insights into consumer-resource dynamics and evolutionary adaptations.