16 - Species Interactions 1

Species Interactions

  • Key Concepts:

    • Competition

    • Predation, Herbivory, and Parasitism

    • Mutualism and Commensalism

    • Bottom-Up and Top-Down Control

Ecological Hierarchy

  • Biosphere: The global sum of all ecosystems.

  • Biome: Large regions characterized by specific climate conditions and types of flora and fauna.

  • Ecosystem: An ecological community of organisms and their physical environment interacting as a system.

  • Community: A collection of different species living together in one area.

  • Population: A group of individuals of the same species living in the same area.

  • Individual: A single organism.

Ecosystem Interactions

  • Definition: All organisms in a particular region and their environment interact and depend on each other.

  • Interconnectedness: Ecosystem elements interact either directly or indirectly.

Biological Communities

  • Community Definition: All species in a common environment that interact.

  • Ecological Processes: Interactions govern the evolution and ecological dynamics within the community.

  • Characterization:

    • Species Richness: Variety of species present.

    • Relative Abundance: Proportion of each species in the community.

    • Primary Productivity: Rate of generation of biomass in an ecosystem.

    • Biomass: Total mass of organisms in a given area.

Types of Species Interactions

  • Nature of Interaction:

    • Competition: −

    • Amensalism: −, 0

    • Predation, Herbivory, Parasitism: +, −

    • Mutualism: +, +

    • Commensalism: +, 0

    • + = Positive effect; − = Negative effect; 0 = No effect.

Competition Overview

  • Intraspecific Competition: Competition among individuals of the same species.

  • Interspecific Competition: Competition among individuals of different species.

  • Types of Competition:

    1. Exploitation Competition: Indirect competition through resource consumption.

    2. Interference Competition: Direct interaction by intimidation or aggression.

  • Competition Inequality: Competition can lead to extremer asymmetric competition, observable in plants via allelopathy.

Detailed Examples of Competition Types

  • Intraspecific Competition: Individual caterpillars compete for leaves.

  • Interference Competition: Beetle intimidates caterpillar, limiting its resource use.

  • Exploitation Competition Example: Aphids and caterpillars vying for leaves.

Frequency of Competition

  • Field studies show competition is common (55% in Joseph Connell's study of 215 species).

  • Higher likelihood of competition when species pairs utilize the same resources.

  • Degree of competition varies by species and habitat (marine vs. terrestrial).

Species Coexistence

  • Concept: Similar species can coexist by occupying different niches.

    • Gause's experiment with Paramecium illustrates competitive exclusion principle: complete competitors cannot coexist.

  • Resource Partitioning: Differentiation of niches allows similar species to coexist, as exemplified by warblers feeding at different tree heights.

Niches Definition

  • Fundamental Niche: Full range of conditions under which a species can survive.

  • Realized Niche: Actual conditions occupied by a species when accounting for competition.

Connell's Barnacle Experiment

  • Examined two barnacle species to understand fundamental vs. realized niches.

  • Findings: Competitive exclusion was demonstrated as Chthamalus was excluded by Semibalanus in lower intertidal zones.

Character Displacement

  • Definition: Morphological differences that promote coexistence between species due to competition.

  • Notable Example: Galapagos finches show size specialization when sympatric (in the same area).

Predation and Herbivory

  • Classification: Types of predation are categorized by lethality and duration of interaction.

  • Antipredator Strategies:

    1. Chemical Defense: E.g., Bombardier beetle's hot spray.

    2. Aposematic Coloration: Warning colorations indicating toxicity (e.g., tropical frogs).

    3. Camouflage: Cryptic coloration for hiding (e.g., stick insects).

    4. Mimicry:

      • Müllerian Mimicry: Noxious species mimic each other.

      • Batesian Mimicry: Harmless species mimic harmful ones (e.g., scarlet king snake).

    5. Displays of Intimidation: Deceptive strategies to deter predators (e.g., porcupine fish).

    6. Armor and Weaponry: Physical means of defense (e.g., tortoises shells).

Biological Interactions in Herbivores

  • Herbivory Effects: Can be lethal to small species but mostly non-lethal to larger species.

  • Hypotheses for Low Plant Consumption:

    1. Natural enemies keep herbivore numbers in check.

    2. Plants have developed defenses against herbivory.

Plant Defenses against Herbivores

  • Mechanical Defenses: Thorns, spines, and hard fibers (e.g., rose thorns).

  • Chemical Defenses: Secondary metabolites including:

    • Alkaloids: Toxic compounds like nicotine.

    • Phenolics: Compounds imparting bitterness (e.g., tannins in tea).

    • Terpenoids: Compounds with defensive properties (e.g., in peppermint).

Secondary Metabolites Overview

  • Definition: Non-essential compounds with specialized functions in plants.

  • Examples of Uses: Medicinal uses (e.g., morphine from poppies, caffeine from coffee).

  • Natural Sources: Predominantly from plants, but also found in bacteria, fungi, and marine organisms.

Human Uses of Secondary Metabolites

  • Used as medicines and flavorings, including:

    • Codeine, Morphine: Pain relief.

    • Nicotine: Stimulant from tobacco.

    • Penicillin: Antibiotic from fungi.

  • Sources: Various plants and marine creatures provide unique compounds.