Invasive Species

Community Level Effects Continued

• Measuring at Community versus Population Level
    - Definitions of Community Level:
      - Evenness: This refers to how equal the abundances of different species are within a community. High evenness means species have similar population sizes.
      - Abundance: Denotes the total number of individuals of all species within a community.
      - Diversity: Combination of species richness (the number of different species) and evenness within a certain area.
    - Exam Note: Know the definitions and differences among evenness, abundance, and diversity.

• Community Level Interactions:
    - Types of interactions include:
      - Commensalism: One species benefits, while the other is neither helped nor harmed.
      - Competition: Both species are negatively affected due to competition for resources.
      - Predation/Herbivory: One species benefits by consuming another.

• Effects of Community Level Interactions:
    - Effects include:
      - Reduced richness
      - Reduced fecundity (reproductive success)
      - Reduced abundance
    - These effects are classified as Stage 4 impacts based on severity.

Specific Examples of Invasive Species

• Northern Snakehead
    - Interaction: Competes aggressively with native species for food.
      - Classed as either interference (direct competition) or exploitation (resource consumption).
    - Ecological Impact:
      - Acts as a voracious predator, detrimental to native species and their ecological balance.
      - Has the potential to drastically modify aquatic ecosystems.
    - Protection of Young: Exhibits aggressive behavior to protect its offspring.

• Round Goby
    - Precise Effects:
      - Reduces population of macroinvertebrates through consumption impacting abundance and biomass.
      - Detrimentally affects species richness and overall diversity in ecosystems.
      - Reduces recruitment of smallmouth bass due to nest predation.
    - Additional Notes:
      - Acts as a predator while competing with other species.
      - Serves as a food source for native birds but also introduces avian botulism, which lowers chick growth and reproductive success due to lower nutritional value.

• Brown Tree Snake in Guam
    - Impact on Native Species:
      - Caused significant declines in native bird populations.
      - Shifted dietary habits leading to decreased populations of native flying foxes and lizards.
    - Effect: The introduction of the snake has created an “empty forest” scenario, altering food availability and changing ecological functioning (e.g., zoochory, pollination).
    - Interactions: Largely predatory, with some competition involved.

• Nutria in the US
    - Disease Vector: Carries diseases such as Giardia, ringworm, salmonella, and toxoplasmosis.
    - Ecosystem Effects:
      - Rapidly impacts native plant communities by outcompeting native herbivores and degrading marsh structures (leading to flooding).
      - Interactions: Engage in herbivory, competition, and facilitate disease propagation.
    - Measurable Impacts: Results in reduced abundance of native plants, decreased biodiversity, and altered fecundity across specialist species.

• Rabbits in Australia
    - Destruction of Native Flora:
      - Engaging in overgrazing which leads to the demise of native marsupials and degradation of aquatic ecosystems due to soil erosion.
    - Pasture Plant Impact: It is noted that 7-10 rabbits can graze equivalent to one livestock unit.
    - Interactions: Primarily herbivory and exploitative competition.
      - Resulting effects include alterations in plant communities.

• Black Rats
    - Global Distribution: Present in numerous regions worldwide; impacts various taxa including birds, reptiles, and other small vertebrates.
    - Contributing Factors:
      - Acts through competition and serves as a vector for diseases, damaging native plants and crops alike.

Homework Assignment (Due April 2)

• Task Outline:
    - Identify a selected invasive species that hasn't been discussed.
    - Provide a brief overview including: name, native region, and details of introduction into non-native areas.
    - Identify community-level effects and describe the interplay of interactions that caused them.
    - Discuss the filters passed through by the species to achieve those effects.
    - Be explicit in providing details and note specific affected species, with at least two peer-reviewed references required.
    - Extras: Photos encouraged.

Understanding Invasive Success Factors

• Enemy Release Hypothesis
    - Describes how invasive species succeed after “removing” natural enemies or escaping them in new territories.
      - Native enemies impose lower impact on invasive species compared to local species.
    - Results in reduced or eliminated needs for defense mechanisms.
      - Energy conservation leads to enhanced growth and reproductive rates.
    - Example Illustrations:
      - Comparison between native and introduced Senecio species (fireweed) in New Zealand, wherein the magpie moth preferred the native species, demonstrating competition facilitated by enemy release.
      - Example: European starling as an instance of this phenomenon.

Tables of Hypotheses Regarding Invaders

• Hypotheses that Explore Factors Affecting Invader Success:
    - Highlights include:
      - Enemy Release
      - Evolution of Increased Competitive Ability
      - Biotic Resistance From Enemies
      - New Associations & Mutualist Facilitation
      - Invasional Meltdown
      - Biotic Resistance from Competitors
      - Empty Niche Hypothesis

For each hypothesis, key connections are drawn between mutualism, competition, enemies, and abiotic conditions that could influence invasive species' demographic success.