Community Ecology Overview and Invasive Species Effects

Species Composition:
  - Richness: The number of different species in a community.
  - Evenness: The relative distribution of different species in a community.
  - Diversity: A combination of species richness and evenness, representing the complexity of a community.
Intraspecific Interactions: Interactions within the same species.
Interspecific Interactions: Interactions between different species, categorized as follows:
  - Neutral: 0/0
  - Mutualism: +/+
  - Commensalism: +/0
  - Parasitism: -/+
  - Predation: -/+
  - Competition: -/-
  - Facilitation: 0/+ or +/+

Types of Interspecific Interactions:
  - Neutral (0/0): Neither species affects the other.
  - Mutualism (+/+): Both species benefit from the interaction.
  - Commensalism (+/0): One species benefits while the other is unaffected.
  - Parasitism (-/+): One species benefits at the expense of the other.
  - Predation (-/+): One species kills and consumes the other.
  - Competition (-/-): Both species are harmed due to their struggle for resources.
  - Facilitation (0/+ or +/+): One species benefits while the other is helped or unaffected.

Competitive Interactions in Invasive Species:
  - Exploitative (Indirect) Competition:
    - Competitors consume the same limited resource.
    - Competing individuals adapt towards the limited resource rather than directly interacting with each other.
    - Also known as Competition Scramble.
  - Interference (Direct) Competition:
    - Limited resources lead to direct interactions that inhibit the use of resources.
    - Referred to as Contest Competition.

Reduction of Native Plant Species Richness:
- Example: Iceplant (from South Africa) in California
Reduction of Native Species Density (Evenness):
   - Examples:
     - Zebra mussel
     - Quagga mussel (Levine et al., 2003)
Reduction of Fecundity in Natives:
   - Example: Rhamnus cathartica (Buckthorn):
     - Produces emodin (a laxative for birds)
     - Increases susceptibility of nests to predators
     - Increases local coyote populations

Reduced Native Bird Species:
- Including reductions in abundance, species richness, and food availability.
- Example: Old World Bluestems (OWB) influence on bird populations.

Species Richness Calculation:
   - Analyzed through metrics like:
     - Number of species per location
     - Number of individuals per sample
     - Arthropod biomass per sample (g/sample)
Impact of OWB on local bird species, as per Hickman, Farley, Channell & Steier (2006).

Higher Earthworm Densities:
   - Correlation with Japanese barberry:
     - Increased nitrate concentration in soils under barberry trees
     - Decreased litter layer compared to native trees.
   - Example: Myrica faya (Faya Tree):
     - Increased earthworm activity contributes to feral hog activity and nitrogen mineralization rates.

Africanized Honey Bee:
   - Competes with native flower visitors for floral resources.
   - Competes with native organisms for nesting sites.
   - Transmits parasites/pathogens to native organisms.
   - Alters seed set in native plants.
   - Pollinates exotic weeds, impacting local ecosystems.
European Green Crab:
   - Competes with native species for refugia space.
   - Increased susceptibility of native crabs to predation.
   - Predator behavior alterations may drastically modify native species arrays, disrupting ecological balance.
   - Potential for long-lasting changes to aquatic systems.
   - Identified as very aggressive in both foraging and burrowing behaviors.