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Chapter 38: Communities and Ecosystems (Species Interactions I)

Learning Objectives (Ch 38, sections 38.1 - 38.5)

  • Describe the different types of species interactions in communities.

  • Describe the processes that allow some species to coexist in the same habitat by reducing competition.

  • Explain the positive or negative effect on each species involved in a symbiotic relationship.

Communities and Ecosystems: Overview

  • Definition of a Community:

    • A community includes all populations, representing multiple species, in the same region.

  • Definition of an Ecosystem:

    • An ecosystem is the biotic (living) community plus the abiotic (nonliving) environment.

Species Interactions in Communities

  • Types of Species Interactions:

    • Species interactions have varying effects on survival and reproductive success of the participants.

    • Competition: harms both participants.

    • Mutualism: benefits both species.

    • Commensalism: benefits one species and does not affect the other.

    • Parasitism, Herbivory, and Predation: harm one species and benefit the other.

Summary of Species Interactions (Table 38.1)

Interaction

Effects on Species 1

Effects on Species 2

Competition

–

–

Mutualism

+

+

Commensalism

+

0

Parasitism

+

–

Herbivory

+

–

Predation

+

–

Competition

  • Definition of Competition:

    • Occurs when two or more species try to obtain the same limited resource.

    • Consequences of Competition:

    • Negative consequences for both species involved as neither obtains all the resources it needs, leading to:

      • Reduced growth

      • Reduced survival

      • Reduced reproduction, especially for weaker competitors.

    • Niche Principle:

    • Therefore, two species cannot coexist indefinitely in the same niche.

Niche

  • Definition of Niche:

    • Includes all resources required for survival, growth, and reproduction.

    • Each organism has a unique niche, that includes:

    • Interactions with other organisms.

    • Interactions with abiotic aspects of the environment, such as light, water, temperature, salinity, and chemicals.

    • Niche Principle Recap:

    • Two species cannot coexist indefinitely in the same niche.

Competitive Exclusion Principle

  • Definition:

    • According to the competitive exclusion principle, the species that acquires more resources will eventually “win,” and the less successful species will die out.

Example: Battle between Two Species of Barnacles

  • Species Involved:

    • Balanus barnacles and Chthamalus barnacles.

  • Interaction Observations:

    • In the absence of Balanus, Chthamalus occupies the entire intertidal zone.

    • However, with Balanus present, Chthamalus is confined to the high-tide zone.

Resource Partitioning

  • Definition & Process:

    • Sometimes, multiple species with similar requirements coexist in the same habitat through resource partitioning.

    • Example: Penguins in the southern Indian Ocean feed at different times or locations, which reduces competition.

  • Conclusion on Competition:

    • Competition can lead to resource partitioning instead of competitive exclusion.

Example: Resource Partitioning in Warblers

  • Species:

    • Blackburnian warbler, Bay-breasted warbler, Cape May warbler, Black-throated green warbler, Myrtle warbler.

Symbiotic Relationships

  • Definition of Symbiotic Relationships:

    • Occur when two species share a close (often lifelong) relationship where one typically lives in or on the other.

  • Types of Symbiotic Relationships:

    • Mutualism (+/+):

    • Improves the fitness of both partners.

    • Example: Clownfish and anemone protect each other from predation.

    • Commensalism (+/0):

    • One species benefits, while the other is not significantly affected.

    • Example: Mosses on tree trunks gain sun exposure without affecting the tree.

    • Parasitism (+/−):

    • One species benefits at the expense of another.

    • The organism feeding off another is termed a parasite, while the prey is the host.

    • Example: Roundworms in humans cause elephantiasis.

Feeding Relationships

  • Definition:

    • Feeding relationships link species within ecosystems.

  • Examples of Feeding Relationships:

    • Herbivory:

    • Herbivores consume plants (e.g., nutria feeding on marshland plants).

    • Predation:

    • Predators eat prey animals (e.g., wolves working cooperatively to capture elk).

Coevolution

  • Definition:

    • Reciprocal evolutionary change between interacting species, driven by natural selection.

Conditions for Coevolution:

  1. Two or more interacting species must exist in the same place and time.

  2. The actions of one species impose differential survival or reproduction in the other species and vice versa.

Example of Coevolution

  • In the Rocky Mountains:

    • Crossbills eat lodgepole pine seeds, selecting for pine cones with thick scales, leading to birds evolving larger and stronger bills.

Geographic Context: Grand Teton National Park

  • Locations Involved:

    • Includes areas in Montana, Wyoming, and Idaho.

    • Plant Characteristics:

    • Lodgepole pine exhibiting larger, open, fewer seeds versus smaller, closed, more seeds based on coevolution with crossbills.