Community Ecology, Biodiversity, and Disruptions Exam Notes

Community Ecology

  • Community: A group of populations of different species living closely and capable of interacting.

Niche

  • Habitat: A specific place or part of an ecosystem occupied by an organism.
  • Ecological Niche: The role and position a species has in its environment.
    • Fundamental Niche: The niche potentially occupied by the species without limiting factors (e.g., predators, competitors).
    • Realized Niche: The portion of the fundamental niche actually occupied by the species.

Interspecific Interactions

  • Interspecific Interactions: Interactions of individuals from one species with individuals of another species.
    • Types:
    • Competition
    • Predation
    • Herbivory
    • Symbiosis (parasitism, mutualism, commensalism)
    • Facilitation

Competition

  • Competition: A -/- relationship where different species compete for limited resources.
    • Competitive Exclusion Principle: Two species competing for the same resource cannot coexist permanently; the competitor with even a slight advantage will eliminate the inferior competitor.
    • Niche Partitioning: Natural selection drives competing species into different patterns of resource use or niches.

Predation

  • Predation: A +/− relationship where one species (predator) kills and eats another species (prey).
    • Adaptations from natural selection include:
    • Cryptic Coloration: Camouflage.
    • Batesian Mimicry: Harmless species mimics a harmful one.
    • Mullerian Mimicry: Two or more bad-tasting species resemble each other.

Herbivory

  • Herbivory: A +/− relationship where one organism eats parts of a plant or alga.

Symbiosis

  • Symbiosis: When two or more species live in direct contact.
    • Types:
    • Parasitism: (+/−) One organism (parasite) derives nourishment from another (host).
    • Mutualism: (+/+) Both organisms benefit.
    • Commensalism: (+/0) One organism benefits, and the other is neither harmed nor benefited.

Facilitation

  • Facilitation: (+/+ or 0/+) One species has a positive effect on the survival and reproduction of another without intimate association of symbiosis, commonly seen in plant species.

Species Diversity

  • Species Diversity: Variety of different organisms within a community.
    • Species Richness: Number of different species.
    • Relative Abundance: Proportion each species represents of all individuals in the community.
    • Importance of biodiversity: Increases ecosystem productivity, resilience, and stability.

Simpson’s Diversity Index

  • A metric to calculate biodiversity based on species richness and relative abundance.
    • Formula: D=N(N−1)∑n<em>i(n</em>i−1)D = \frac{N(N-1)}{\sum n<em>i(n</em>i-1)}
    • Where $N$ is the total number of organisms of all species and $n_i$ is the number of organisms of a particular species.
    • High diversity index indicates high biodiversity.

Invasive Species

  • Invasive Species: Non-native species that can occupy a wide range of habitats and competitively exclude native species.
    • Example: Insects introduced unknowingly via commercial shipping.

Keystone Species

  • Keystone Species: Not typically abundant, but crucial because other organisms in the ecosystem depend on them.
    • Examples:
    • Coral: Provides food and protection to many marine species.
    • Honey Bees: Essential pollinators.
  • Removal impacts the ecosystem significantly, potentially leading to collapse.

Disturbances

  • Disturbance: An event altering community composition by removing organisms or changing resource availability (e.g., fires, droughts, human activities).
  • Ecological Succession: Gradual changes in species composition following a disturbance.
    • Primary Succession: Changes in a previously lifeless habitat.
    • Secondary Succession: Changes that clear an existing community but leave the soil intact.

Human Disturbances

  • Major threats to biodiversity:
    • Habitat Loss: Primarily due to agriculture and urbanization.
    • Invasive Species: Non-native that disrupts local ecosystems.
    • Overharvesting: Unsustainable harvesting rates, e.g., ivory poaching, overfishing.
    • Global Change: Climate change, pollution, and ecological disruptions.
    • Result: Increased endangered species and the potential for a mass extinction event.

Biogeographical Factors

  • Factors affecting diversity:
    • Latitude: Higher species diversity in tropics as compared to poles due to climate.
    • Area: Larger areas support more diversity due to varied habitats.

Pathogens

  • Pathogens: Disease-causing organisms that may have a significant impact on ecosystems with less diversity.

Practice Question

  • Consider a forest where a dominant plant species has been infected by a virus disrupting thylakoid membranes:
    • Photosynthesis Process Affected: Light-dependent reactions would be severely impacted.
    • Effects on Plants: Reduced production of ATP and NADPH, leading to decreased glucose synthesis and plant stress.