Learning Module 13 A&B

Big Idea 4: Ecology

  • Organisms evolve as a result of interactions with one another and with their environment.

  • These interactions change over time.

Community Ecology Module 13A

  • Variations in the abiotic (non-living) and biotic (living) environment determine the distribution of organisms and their physical and behavioral adaptations.

Learning Outcome 13

  • Biological community structure is shaped by diverse interactions among species, including trophic interactions.

  • Community composition can change after disturbance, and species may gradually replace each other in succession.

Key Points:

  1. Interspecific Interactions

    • Examples of types of interspecific interactions:

      • Competition

      • Predation

      • Herbivory

      • Parasitism and parasitoids

      • Mutualism

    • Determination of community structure based on these interactions.

  2. Primary Producers

    • Identification of primary producers in a community (e.g., plants, algae).

    • Examples of adaptations found in consumers:

      • Predators: Hunting strategies, anatomical adaptations.

      • Parasites: Strategies for infiltration into hosts.

      • Herbivores: Adaptations for feeding on plants.

    • Defense mechanisms in food sources (prey, hosts, plants).

  3. Niche and Niche Partitioning

    • Description of a species’ niche and how it facilitates coexistence of species within a community.

    • Niche Partitioning: Differentiation in ecological niches allows for coexistence.

  4. Community Composition and Disturbance

    • Explanation of disturbances leading to primary or secondary succession.

Outline of Interspecific Interactions

  • Competition: (- -)

  • Predation: (+ -)

  • Herbivory: (+ -)

  • Parasites and parasitoids: (+ -)

  • Mutualism: (+ +)

  • Symbioses: (+ +), (+ -), (+ 0)

  • Species Diversity

  • Species with Large Impacts

  • Community Organization

  • Disturbance and Succession

Interspecific Interactions

  • Definition: Relationships between species in a community.

  • Classified by their effects on each species:

    • Competition: Both species are negatively impacted: (- -).

    • Trophic Interactions: One benefits, the other doesn’t: (+ -).

    • Mutualisms: Both species benefit: (+ +).

Competition (- -)

  • Interspecific Competition: Occurs when species compete for a resource in short supply.

  • Differentiates from intraspecific competition (competition within the same species).

  • Strong competition can lead to Competitive Exclusion:

    • Local elimination of a competing species.

  • Competitive Exclusion Principle: Two species competing for the same limiting resources cannot coexist in the same place.

Ecological Niches

  • Definition: The sum of a species’ use of biotic and abiotic resources is called the species’ ecological niche.

  • An ecological niche also reflects an organism’s ecological role within the ecosystem.

  • Similar species can coexist if there are significant differences in their niches (resource partitioning).

Competition and Niche Partitioning

  • Competition leads to spatial or temporal niche partitioning illustrated by:

    • A. distichus perching on sunny surfaces.

    • A. insolitus usually perching on shady branches.

Fundamental and Realized Niches

  • Fundamental Niche: The potential niche occupied by a species.

  • Realized Niche: The niche actually occupied, impacted by interspecific competition:

    • Example: The realized niche of Chthamalus barnacle is smaller than its fundamental niche due to competition.

Evolutionary Change from Competition

  • Character Displacement:

    • An evolutionary change observed when two similar species' distributions overlap; characteristics become more divergent in sympatric populations than in allopatric populations.

Predation (+ -)

  • Definition: An interaction where one species (predator) kills and eats another species (prey).

  • Examples of predator adaptations:

    • Speed, camouflage, hunting strategies (e.g., cheetah, bald eagle).

  • Examples of prey adaptations to avoid predation:

    • Behavioral defenses, morphological defenses, physiological adaptations (e.g., camouflage, warning colors).

  • Includes Müllerian Mimicry: Several harmful species resemble each other.

Herbivory (+ -)

  • Definition: Interaction where an herbivore eats parts of primary producers (plants or algae).

  • Defense adaptations in plants include:

    • Mechanical defenses (thorns).

    • Chemical defenses (toxins).

Parasitism and Parasitoids (+ -)

  • In Parasitism, a parasite derives nourishment from a host, which is harmed without being killed.

  • Parasitoid: Organism whose young develop inside or on its host, eventually killing it.

Mutualism (+ +)

  • Definition: Interaction where both species benefit.

  • Examples of mutualisms that are symbiotic:

    • Mycorrhiza: Fungi and plant roots.

    • Rhizobia: Nitrogen-fixing bacteria in legumes.

    • Gut microbiome: Bacteria aiding in digestion.

  • Not all symbiotic relationships are mutualistic, and not all mutualistic relationships are symbiotic.

Symbiosis (+ +) or (+ -) or (+ 0)

  • Definition: Close and direct interactions between species.

  • Types of symbiotic relationships include:

    • Parasitism: (+ -)

    • Mutualism: (+ +)

    • Commensalism: (+ 0)

Community Ecology Module 13B

  • Reiteration: Abiotic and biotic variations influence organism distribution and adaptations.

Outline of Community Structure

  • Interspecific Interactions

    • Types: Competition, Predation, Herbivory, Parasitism, Mutualism, Symbiosis.

  • Species Diversity and Impact

    • Dominant species, Foundation species, Keystone species, Invasive species.

  • Community Organization

    • Trophic Structure, Bottom-Up and Top-Down control.

  • Disturbance and Succession

Species Diversity

  • Species diversity is the variety of organisms in a community.

  • Consists of two components:

    • Species Richness: Number of different species.

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

  • Important note: Diversity is not the same as richness.

Species with Large Impacts

  1. Dominant Species:

    • Most abundant, or highest biomass. Hypotheses: most competitive in resource exploitation or most adept at avoiding predators.

  2. Foundation Species (Ecosystem Engineers):

    • Cause significant physical changes affecting community structure (e.g., beaver dams altering landscapes).

  3. Keystone Species:

    • Exert strong control on community structure via their ecological roles. Not necessarily abundant (e.g., Pisaster sea star).

  4. Invasive Species:

    • Defined as alien species likely to cause economic, environmental harm or harm to human health.

    • They typically dominate because they lack natural predators and negatively impact native biodiversity.

Invasive Species Examples in the US

  • Categories of invasive species include:

    • Terrestrial Plants

    • Terrestrial Vertebrates

    • Aquatic Plants

    • Fish and other Aquatic Vertebrates

    • Terrestrial Invertebrates

    • Terrestrial Pathogens and Diseases

    • Aquatic Invertebrates

    • Aquatic Pathogens and Diseases

Trophic Structure (Emergent Property)

  • Definition: The network of feeding relationships between organisms in a community.

  • Food Chains:

    • Link trophic levels from producers to top carnivores.

Food Webs

  • Definition: Complex interconnections of food chains depicting multiple feeding relationships.

  • Organisms can occupy multiple trophic levels.

Community Organization: Bottom-Up and Top-Down Controls

  1. Bottom-Up Model:

    • Unidirectional influence from lower to higher trophic levels (e.g., agricultural models).

  2. Top-Down Model (Trophic Cascade Model):

    • Control originates from higher trophic levels, where predators limit herbivores, potentially affecting vegetation and nutrient levels (e.g., wolves in Yellowstone National Park).

Application of Trophic Cascade: Biomanipulation

  • Example of biomanipulation: Addition of pike perch controlling roach fish populations, allowing zooplankton to thrive, subsequently ending cyanobacterial blooms.

    • Cyanobacteria bloom results from unregulated primary consumers (zooplankton eaten by roach fish).

Disturbances & Succession

  • Definition: A disturbance is an event that changes a community, removing organisms and altering resource availability.

    • Types of disturbances:

    • Natural: storms, fires, flooding.

    • Human-induced: deforestation, pollution (light, noise, chemicals).

  • Ecological Succession: Sequential change in community composition during colonization following disturbance.

    • Primary Succession: Occurs where no soil exists (e.g., after glacier retreat).

    • Secondary Succession: Begins in areas where soil remains (e.g., after a forest fire).

Primary Succession Process

  • Stages involve:

    • Pioneer Species (e.g., lichens, mosses) colonizing bare rock.

    • Transition to small annual plants and then to perennial grasses, and eventually intermediate species (shrubs, trees).

Secondary Succession Process

  • Stages involve:

    • Starting with pioneer species (e.g., grasses) soon after a disturbance and transitioning to intermediate and climax communities involving varied forest types.

Impact of Disturbance on Species Diversity and Composition

  • Historical perspective: Climax Community notion.

  • Current understanding: Community dynamics are non-equilibrium models with communities constantly changing post-disturbances.

  • Intermediate Disturbance Hypothesis: Proposes that moderate disturbance levels can lead to higher species diversity.

Summary of Learning Outcomes

  • Reinforces the understanding that community structure is shaped by various interspecific interactions and the capacity of communities to change over time through succession, illustrating resilience and adaptation in ecosystems.