Species Interactions

Interactions Among Species

  • Species interactions significantly influence community structure.

Learning Outcomes

  • Describe the various types of interactions among species in a community.

  • Understand how disturbances and the passage of time change communities.

Niche

  • Definition:

    • The set of physical and biological conditions a species requires for survival, growth, and reproduction.

  • Examples of Niche Components in Tropical Tree Lizards:

    • Temperature range.

    • Size of branches for perching.

    • Time of day when active.

    • Size and kinds of insects it consumes.

    • Preference for sunny versus shaded surfaces.

  • Concept of Competitive Exclusion:

    • Two species cannot permanently coexist if their niches are identical.

    • They can coexist if they start using slightly different resources—termed resource partitioning.

Types of Interactions Between Species

  • Antagonism:

    • One species benefits while the other is harmed.

  • Mutualism:

    • Both species benefit from the interaction.

  • Competition:

    • Neither species benefits; negative impact on both.

  • Commensalism:

    • One species benefits while the other is unaffected.

  • Amensalism:

    • One species is harmed while the other is unaffected.

Predation

  • Nature of Interaction: Antagonistic.

  • Traits of Predators:

    • Fast, strong, equipped with sharp claws and teeth.

  • Traits of Prey:

    • Big eyes and ears, high rate of reproduction, cryptic coloration.

  • Adaptive Strategies in Both:

    • Both predators and prey evolve adaptations to increase success in their interactions.

Protective Traits in Prey

  • Types of Defense:

    • Cryptic Coloration and Object Resemblance:

    • Example: Grasshopper resembling a leaf for camouflage.

    • Escape Behavior:

    • Adaptations that allow prey to detect and evade predators (running, flying, jumping, swimming).

    • Toxins and Defensive Chemicals:

    • Prey may contain toxic compounds; many have bright warning coloration to advertise their toxicity.

    • Example: Brightly colored poison dart frog.

    • Schooling/Flocking Behavior:

    • Predators can become confused by groups of prey.

    • Example: Dense school of fish.

    • Defense Armor and Weapons:

    • Protective structures such as sharp thorns or shells.

Aposematism

  • Definition: Producing toxins as a defense mechanism has drawbacks.

    • Even if a predator is repelled, the prey can still be killed.

  • Warning Coloration: Bright coloration serves as a warning to predators about toxicity.

  • Mimicry Types:

    • Batesian Mimicry: A harmless species mimics the appearance of a toxic species.

    • Examples include the poison dart frog and the Monarch butterfly vs. the Viceroy butterfly.

    • Müllerian Mimicry: Two or more toxic species resemble each other, reinforcing avoidance behavior by predators.

    • Example: Heliconius butterflies in South America, where each population varies morphologically yet resembles another toxic species.

Impact of Predation on Community Structure

  • Predation can significantly alter community dynamics.

  • If predators are overly efficient:

    • They can lead to the extinction of prey populations.

    • Subsequent predator extinctions may follow, shown by the example of Didinium preying on Paramecium.

Herbivory

  • Definition: Consumption of plants by animals.

  • Plant Defense Mechanisms Against Herbivory Include:

    • Toxins.

    • Thorns.

    • Hairs.

    • Waxy cuticles.

    • Silica in cell walls.

    • Production of attractants for predators of herbivores once attacked.

    • Example: The tobacco hornworm feeds on jimsonweed, and the plant responds by producing chemicals that attract parasitoid wasps. The wasps lay eggs on the caterpillar, whose larvae then consume the caterpillar, ultimately stopping herbivory.

    • Location Example: Honey locust in Cedar County, Iowa.

Parasitism

  • Definition: A parasite extracts nutrition from its host without killing it.

  • Types of Parasites:

    • Microparasites:

    • Include bacteria, viruses, and protists that dwell inside the host, reducing its vigor.

    • Macroparasites:

    • These may live inside or outside the host, examples include worms, fleas, ticks, and lice.

    • Some plants can also be parasitic.

  • Co-evolution:

    • Hosts evolve defenses against parasites, which leads to parasites coevolving traits to overcome host defenses.

Mutualism

  • Definition: Both species benefit from the interaction, although not always equally.

  • Examples of Mutualism:

    • Angiosperms and Pollinators:

    • Approximately 75% of angiosperms rely on pollinators. The pollinator receives food (pollen, nectar), while the plant has its male gametophytes directly delivered.

    • This leads to co-evolution between flowers and insects.

    • Angiosperms and Frugivores:

    • Seeds are dispersed by frugivores.

    • Legumes and Rhizobium:

    • The plant fixes carbon while the bacteria fix nitrogen, leading to a mutual exchange.

Competition

  • Nature of Competition:

    • Different species may depend on the same resources, leading to an unstable ecosystem.

  • Competitive Exclusion Principle:

    • If two species compete for the same resources, one will usually become locally extinct.

    • Example: In cultures where Paramecium aurelia and P. caudatum are grown together, P. caudatum becomes extinct.

Resource Partitioning Among Competing Species

  • Resource partitioning occurs as a result of selection pressures, driving changes in predation.

    • Example: Owls hunt at night while hawks hunt during the day, reducing competition and allowing coexistence.

Types of Competition

  • Interference Competition:

    • One species directly interferes with another's access to resources.

  • Exploitation Competition:

    • One species is more effective in utilizing a resource, leading to potential resource allocation differences.

  • Competition can be equal for a resource, but results may be skewed if one species is preferentially preyed on by a shared predator.

Commensalism

  • Definition:

    • One partner benefits, while the other partner is neither harmed nor helped.

  • Example:

    • Orchids living on branches of a large tree, gaining access to sunlight without affecting the tree.