Ecosystem Interactions

Interactions in Ecosystems

Competition

  • Definition: Competition occurs when two organisms fight for the same limited resource.

Types of Competition

  • Intraspecific competition: Competition within the same species.

  • Interspecific competition: Competition between different species.

Examples of Competition

  • Interspecific or intraspecific?:

    • Two red squirrels race up a tree to find a hidden pile of nuts. (Intraspecific competition)

    • A hyena chases off a vulture to feast on an antelope carcass. (Interspecific competition)

    • Shrubs and grasses on the forest floor compete for sunlight. (Interspecific competition)

    • Brown bears hunting for fish on a river’s edge fight over space. (Intraspecific competition)

Habitat vs. Niche

  • Habitat: The area in which an organism lives.

  • Niche: The role that the organism plays in the environment, encompassing all its interactions with biotic and abiotic factors.

Niche Types

  • Fundamental niche: The entire range of conditions an organism is potentially able to occupy.

  • Realized niche: The part of the fundamental niche that a species actually occupies due to competition and other interactions.

Example: Barnacle Competition

  • Competition between two species of barnacles (Chthamalus and Balanus):

    • Observation: To determine the realization and fundamental niches of barnacles, observe their growth in competitive settings.

    • High tide vs. Low tide:

    • Diagram shows the locations of Chthamalus and Balanus in the intertidal zone.

Determining Realized Niche

  • Question: How can we determine the realized niche of each barnacle?

    • Observation: Note where they grow when allowed to compete.

    • Results: Balanus realized niche; Chthamalus realized niche may differ based on competition.

Determining Fundamental Niche

  • Experiment: Conduct removal experiments to test niches.

    • Procedure: Remove each species and observe where the other species grows.

    • Results:

    • Balanus fundamental niche

    • Chthamalus fundamental niche

Example: Planaria Species

  • Streams with only Planaria species A

  • Streams with only Planaria species B

  • Streams with both Planaria species

    • Question: What are the fundamental and realized niches for each species?

Predicting Outcomes of Interspecific Competition

  • Competitive Exclusion Principle:

    • States that two species cannot occupy the same niche indefinitely.

    • Study Example (Gause, 1934): Two species of Paramecia, P. caudatum and P. aurelia, were studied; results indicated competitive exclusion.

Predator-Prey Interaction Model

  • Diagram Interpretation: Shows the population dynamics between predators and prey over time.

    • Entities: Rabbits (prey) and Wolves (predators).

    • Graphical Data:

    • X-axis: Generational time

    • Y-axis: Number of organisms (e.g., 200 for rabbits, 180 for wolves).

Symbiosis

  • Definition: Symbiosis is any relationship where two or more species live closely together.

  • Types of Symbiosis:

    • Mutualism (+/+): Both species benefit from the interaction.

    • Commensalism (+/0): One species benefits while the other is neither helped nor harmed.

    • Parasitism (+/-): One species benefits at the expense of the other.