Species Interactions and Coevolution

Topic 16: Species Interactions Continued

Relationships Between Species in a Community

• Interspecific interactions consider how the interaction affects each species.
• The interaction can have one of three outcomes for each species:
    - Positive (+)
    - Negative (-)
    - Neutral (0)

Types of Interspecific Interactions

• Species A and B interactions:
    - + - 0
    - Mutualism (+/+)
    - Predation (+/-)
    - Grazing (+/-)
    - Parasitism (+/-)
      - Types of Parasitism:
        - Endoparasitism
        - Ectoparasitism
        - Behavioral Parasitism
    - Parasitoidism (+/-)
    - Interspecific Competition (-/-)
    - Commensalism (+/0)
    - Amensalism (-/0)
    - Neutralism (0/0)

Learning Objectives

• After completing this lecture, you should be able to:
    1. Understand the different categories of interspecific interactions, including subtypes:
       A. Grazing
       B. Predation
       C. Parasitism (endo, ecto, behavioral)
       D. Parasitoidism
    2. Explain the ecological and evolutionary effects of +/- interactions:
       A. Lotka-Volterra predator-prey models
       B. Adaptations of predators and prey
    3. Define coevolution and the Red Queen Principle
    4. Understand how coevolution occurs in response to:
       A. Mutualistic interactions
       B. Antagonistic interactions
    5. Contrast exponential, logistic, competition, & predator-prey models
    6. Recognize the different types of mutualism (obligate and facultative), commensalism, and amensalism

Classification of +/- Interactions

• Classifications based on two factors:
    - Duration of interaction
    - Extent of lethality
• Categories:
    1. Grazer:
       - Consumes part of prey non-lethally in a short interaction
    2. Predator:
       - Kills and consumes prey lethally in a short interaction
    3. Parasite:
       - Harms a host non-lethally over a long period
    4. Parasitoid:
       - Long-term relationship that is lethal to the host

Types of Interactions

Grazing (+/-)

• One species quickly consumes another in a non-lethal manner, often involving plants or algae as prey.

Predation (+/-)

• One species quickly consumes another lethally.
• Predator and Prey dynamic is characterized by a predator actively hunting and killing its food.

Parasitism (+/-)

• One species harms the other non-lethally, often over an extended period.
• Types of Parasitism:
    1. Endoparasitism:
       - Examples include heartworms, tapeworms, and Plasmodium (malaria).
    2. Ectoparasitism:
       - Examples include ticks, lice, and lampreys that feed on external surfaces of hosts.
    3. Behavioral Parasitism:
       - The parasite harms the host without residing on or in it.
       - Example: Brood parasites like the European Cuckoo and Brown-headed Cowbird manipulate host behaviors for their benefit.

Parasitoidism (+/-)

• One species harms another lethally over a long period.
• Typically involves a parasitoid, which lays eggs on host organisms.

Remaining Species Interactions

• Commensalism (+/0):
    - One species benefits while the other is neither helped nor harmed.
    - Example: Sea cucumber and crab; cattle egret with cattle.

• Amensalism (-/0):
    - One species is harmed while the other is unaffected.

Effects of +/- Interactions

• Example of predator-prey dynamics between snowshoe hares and lynx over years.
    - Years: 1850, 1875, 1900, 1925
    - Hare Population (Thousands): 160, 120, 80, 40
    - Lynx Population (Thousands): 9, 6, 3, 0
• Ecologically: These interactions create cycles in predator-prey dynamics.
• Evolutionarily: Adaptations arise to increase survival and reproductive success.

Modeling Predator-Prey Dynamics

• Lotka-Volterra equations help model these interactions.

• Prey Growth:
  $dN_{prey}/dt = rN_{prey} - (cN_{prey}) P$
    - Where:
      - $N_{prey}$: prey population
      - $P$: predator population
      - $c$: capture efficiency (per capita death rate of prey per predator)

• Example of Prey Growth:
    - Given values: $N_{prey} = 100$, $r = 2$, $P = 10$, $c = 0.01$
    - $dN_{prey}/dt = (2 * 100) - (0.01 * 100) * 10$
    - Calculation:
  $dN_{prey}/dt = 200 - 10 = 190$

• Predator Growth:
  $dP/dt = b(cN_{prey})P - dP$
    - Where:
      - $b$: conversion efficiency
      - $d$: death rate (per capita death rate of predator)
    - Example: If $N_{prey} = 100$, $P = 10$, $b = 1.25$, $d = 0.1$, then:
  $dP/dt = 1.25(0.1 * 100) * 10 - (0.1 * 10)$
  $dP/dt = 12.5 - 1 = 11.5$

Adaptations to +/- Interactions

• Adaptations occur to enhance success rates in these interactions, such as:
    1. Hiding: Cryptic coloration examples include caterpillars and ptarmigans.
    2. Countershading: Provides camouflage in both land and aquatic environments.
    3. Deception/Mimicry: Mimicking features to confuse predators or prey.
    4. Mechanical Defenses: Physical adaptations such as armor or spines.
    5. Agility: Enhancing speed for evasion or pursuit.
    6. Living in Groups: Increased survival probability through flocking behavior.
    7. Masting: Synchronizing reproduction in prey to overwhelm predator consumption.
    8. Alarm Calls and Mobbing: Warning calls or collective deterrence of threats.
    9. Chemical Defenses: Use of toxins for both offensive and defensive purposes.

Coevolution

• Defined as the process where two species respond to each other's adaptations over time.
• Mutualism: Benefits both species involved through specific adaptations (e.g., pollinators and plants).
• Antagonistic Interactions: Each party adapts to counteract the other's advantages, such as predator-prey dynamics leading to natural selection.

The Red Queen Principle

• States that species must continually adapt to maintain their relative fitness due to constant competitive pressures.
• Example: The adaptation in coloration in mimicry, where a non-toxic species evolves to resemble a toxic one, requiring both species to continue to evolve to retain their survival strategies.