Lecture 15

Coevolution Overview

  • Definition: Coevolution involves the evolution of interacting species that exert selection pressure on each other, resulting in changes in gene frequencies within populations.

Mutualisms and Interactions

  • Types of Interactions:

    • Mutualism (+/+)

    • Parasitism (+/-)

    • Competition (-/-)

    • Predation (+/-)

Mutualism Details

  • Mutualism:

    • Organisms provide compensatory benefits via resource exchanges.

    • Most organisms on Earth are involved in mutualistic relationships.

  • Key Examples:

    • Coral and zooxanthellae

    • Lichens (fungi + photosynthetic partner)

Categorization of Mutualisms

  • By Exchange of Goods:

    • Resource acquisition (nutrients, food)

    • Dispersive (movement)

    • Defensive (protection)

  • Intimacy and Dependency:

    • Facultative (not essential for survival)

    • Obligate (necessary for survival)

Resource Acquisition Examples

  • Plants:

    • Legumes and rhizobia: (Plants receive fixed nitrogen, Rhizobia receive carbohydrates)

  • Animals:

    • Termites and protists/bacteria: assist in cellulose digestion.

Dispersive Mutualisms

  • Pollination: Involves a pairing between pollinators (e.g., bees, birds) and flowering plants.

  • Seed Dispersal: Large seeds dispersed by animals, aiding plant reproduction while providing food for animals.

Defensive Mutualisms

  • Example of ants and acacia trees:

    • Acacia trees provide shelter to ants, ants defend against herbivores.

  • Cleaner wrasse fish remove parasites from larger fish, benefiting both parties.

Implications of Coevolution

  • Coevolution outcomes include:

    • Positive reinforcement in mutualisms

    • Increased competitive abilities in competitors

    • Arms race dynamics between consumers and resources

  • Example: Acacia providing thorns and nutrients to attract ants.

Character Displacement

  • Definition: Phenomenon where sympatric species exhibit more distinct traits to reduce competition than when they are allopatric.

Coevolutionary Arms Race

  • Adaptations can impact the Lotka-Volterra parameters affecting predator-prey dynamics.

    • Equations:

    • Prey: dNdt=rN−cNP\frac{dN}{dt} = rN - cNP

    • Predator: dPdt=acNP−mP\frac{dP}{dt} = acNP - mP

  • Explains the cyclical nature of predator-prey interactions.

Dynamics of Coevolution in Consumer-Resource Relationships

  • Adaptations change population dynamics and can alter equilibrium stability:

    • Lower capture rates and better consumer adaptations could lead to diverse outcomes.

Population Growth Cycles

  • Changes in parameters (c, a, r) influence cycles' amplitude and population minimums.

  • Amplitudes affected by predator adaptations improving capture efficiency.

Conclusion

  • Mutualisms are a critical aspect of ecological interactions with diverse outcomes in population dynamics and adaptations.

  • The joint evolution of species through coevolution shapes ecosystems and influences biodiversity.