Ecological Interactions and Community Dynamics

Energy Flow and Interactions

• Ecosystem Energy Flow:
  • Predation, herbivory, and parasitism are essential interactions in ecosystems.
  • Energy transfer is negative (the prey dies), leading to ‘plus-minus’ relationships in these interactions.

Types of Species Interactions

• Predation:

  • Animals consuming other animals.

• Herbivory:

  • Animals consuming plants.

• Parasitism:

  • One species lives within another, benefiting while harming the host, e.g., microbes infecting plants.

• Competition:

  • Interaction where both species are negatively affected; both would benefit more separately.

• Commensalism:

  • One species benefits while the other is unaffected, e.g., cattle egrets feeding on insects disturbed by musk ox.

• Mutualism:

  • Both species benefit significantly from the interaction, often evolving traits for this purpose – an example is the symbiotic relationship between yucca plants and yucca moths.

Specific Examples of Interactions

• Predatory Specialization:

  • Predators may evolve specialized properties to aid in hunting, e.g., wolves hunting in packs or snakes detecting prey via heat signatures.

• Optimal Foraging Theory:

  • Theory explaining how animals assess costs versus benefits in food searching. Research shows predators, like bluegills, exhibit preferences for larger prey when assessing food availability.

• Prey Defenses:

  • Defensive adaptations in prey can include:
  • Chemical defenses: Examples include plants producing toxins, like milkweed.
  • Physical defenses: Thorns and spines on plants.
  • Mimicry: Prey might mimic appearances of unappealing or dangerous items to deter predators.

• Aposematism vs. Mimicry:

  • Aposematism: Bright coloration warning predators of toxicity.
  • Müllerian Mimicry: Toxic species display similar warning coloration to reinforce predator avoidance.
  • Batesian Mimicry: Non-toxic species mimic toxic species to avoid predation.

Community Dynamics

• Competition and Niche:

  • Competitive exclusion principle explains how two species competing for the same resources will push one to extinction if resources are limited.
  • Niche: The ecological role of a species, including its habitat and resource use.
  • Fundamental niche: All potential habitats and conditions species can occupy.
  • Realized niche: Actual conditions and resources used due to competition with other species.

• Resource Partitioning:

  • Organisms will adapt their behaviors and resource preferences when competing to decrease overlap in niches, leading to different root depths in plants, e.g., Pennsylvania smartweed, Indian mallow, bristly foxtail.

Community Structure

• Equilibrium vs. Individualistic Communities:

  • Equilibrium communities: Species found consistently in certain environments, clear boundaries between different community types.
  • Individualistic communities: Species distribution depends on various environmental conditions, leading to overlapping species in habitats.

• Species Richness:

  • Refers to the number of different species within a community; varies across environments.
  • Examples:
  • Low richness: Arctic tundra, due to harsh environmental conditions.
  • High richness: Tropical rainforests with high diversity.

• Conservation Considerations:

  • Focus on preserving species-rich environments to best support biodiversity.