Community Ecology, Biodiversity, and Disruptions

Community and Ecosystem Interactions

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

Niche Concepts

• Habitat: A place or part of an ecosystem occupied by an organism.
• Ecological Niche: The role and position a species has in its environment.
  • Fundamental Niche: Potential niche if there were no limiting factors (predators, competitors, etc.).
  • Realized Niche: The portion of the fundamental niche that the species actually occupies.

Interspecific Interactions

• Interspecific Interactions: Interactions between individuals from different species.
  • Competition: -/- relationship where different species compete for limited resources.
  • Predation: +/- relationship where one species (predator) kills and eats another (prey).
  • Herbivory: +/- relationship where one organism eats parts of a plant or alga.
  • Symbiosis: Direct contact relationships between species.
  • Parasitism: (+/-) one organism benefits at the expense of another.
  • Mutualism: (+/+) both organisms benefit.
  • Commensalism: (+/0) one organism benefits; the other is neither helped nor harmed.
  • Facilitation: (+/+ or 0/+) one species benefits another without direct contact.

Competition and Resource Use

• Competitive Exclusion Principle: Two species competing for the same resource cannot coexist permanently; the stronger competitor will eliminate the weaker.
• Niche Partitioning: Natural selection drives competing species into different patterns of resource use or niches.

Predator-Prey Relationships

• Adaptations in Predation:
  • Cryptic Coloration: Camouflage to evade capture.
  • Batesian Mimicry: Harmless species mimics a harmful one.
  • Mullerian Mimicry: Bad-tasting species resemble one another.

Biodiversity

• Species Diversity: Variety of different organisms within a community.
  • Species Richness: Total number of different species.
  • Relative Abundance: Proportion of each species compared to the total number of individuals in the community.

Simpson's Diversity Index

• Simpson’s Diversity Index: A measure that considers both species richness and relative abundance to assess biodiversity.
  • High Diversity Index: Indicates high biodiversity.
  • Low Diversity Index: Indicates low biodiversity.

Keystone Species

• Keystone Species: Not always abundant but play a crucial role in maintaining the structure of a community.
  • Examples:
  • Coral: Forms reefs that provide habitat and protection for many species.
  • Honey Bees: Serve as pollinators important for ecosystem function.

Disturbances in Ecosystems

• Disturbance: An event that alters a community, typically by removing organisms or changing resource availability (e.g., fires, droughts).
• Ecological Succession: Gradual process in which species composition changes after a disturbance.
  • Primary Succession: Occurs in a new habitat that has not been colonized previously.
  • Secondary Succession: Follows disturbances that leave soil intact but remove organisms.

Human Disturbances and Biodiversity Threats

• Human Activity: The strongest force disrupting ecosystems.
  • Major Threats:
  • Habitat Loss: Most significant risk to biodiversity (e.g., urbanization, agriculture).
  • Invasive Species: Non-native species that can outcompete natives.
  • Overharvesting: Unsustainable harvesting reducing populations (e.g., overfishing).
  • Global Change: Climate alterations that impact ecosystems (e.g., pollution, CO2 emissions).

Biogeography

• Biogeographical Factors: Large-scale factors influencing biodiversity.
  • Latitude: Greater diversity in tropical regions than polar regions.
  • Area: Larger areas tend to support more species due to habitat variety.

Effects of Pathogens

• Pathogens: Organisms causing disease have pronounced effects in less diverse ecosystems.

Practice Questions

1. Species Richness and Abundance: Analyze differences between two communities with the same species richness but varying relative abundance.
2. Photosynthesis Disruption: Identify processes affected in a dominant plant species infected by a virus hindering its ability to photosynthesize.