Invasion Biology Quiz

Invasive Species Introduction Criteria

• Invasive species must be exotic (not native)
• They must cause significant economic or ecological damage
• Only about 10% of exotic species are invasive

Factors Causing Invasion

• Many factors, often unique to each case
• Common factors include:
  • Human facilitation
  • Lack of natural enemies
  • Interactions with other invasive species

Intentional Introduction of Exotics

• Deliberately introducing species to a new habitat
• Negative consequences may not be anticipated at the time of release

Biological Control

• Introducing the natural enemy of a pest to control it.
• This can sometimes backfire if the introduced species becomes a pest itself

Accidental Releases

• Inadequate screening of imports
• Stowaways during transport of goods
• Gross negligence (e.g., bait bucket introductions)

Indirect Influences on Exotic Species Expansion

• Human activity can facilitate expansion via these factors:
  • Climate change
  • Natural enemy reductions (e.g., overfishing)
  • Habitat modification

Importance of Ecological Theory

• General ecological mechanisms impact biological invasions in a testable way.
• Examination of these mechanisms can predict invasion processes.
• Predictive ability supports proactive strategies for managing invasions

Importance of Case Studies

• Case studies provide empirical data for testing theoretical principles.
• Exceptions to established rules can lead to paradigm shifts in understanding invasions

Corridors of Invasion: The Spongy Moth

• Lymantria dispar (spongy moth) introduced by Etenne Leopold Trouvelot
• Rapid spread since introduction, causing significant deforestation (> 80 million acres by 1970)

Invasion Stages

• Transport
• Introduction
• Establishment
• Spread
• Impact (low to high, based on human perception of impact)

Two Key Concepts: Vectors and Pathways

• Vectors: The mechanisms for transporting organisms from their native habitat to a new habitat (e.g., wind, water, animals)
• Pathways: The routes between the source and novel habitat

Extra-Range Dispersal (ERD)

• Movements beyond a species' current range, including natural (wind, animals) and human-mediated dispersal
• Human-mediated ERD deposits species at a faster rate than natural dispersal mechanisms

Theory of Island Biogeography

• Species richness in isolated habitats results from two processes:
  • Immigration
  • Extinction

Natural Immigration Rate in Hawai'i

• Hawai'i's indigenous flora arrived at a rate of about one new colonization every 100,000 years.

Types of Transportation Vectors

• Intentional Vectors (e.g. food, biocontrol, pet trade): species deliberately introduced for a defined purpose
• Unintentional Vectors: species moved unintentionally as a byproduct, such as by hitching a ride in transported materials or cargo holds

Transport Vectors: The Role of Food

• Many exotic plant and animal species used for food were intentionally introduced.
• Some have escaped cultivation and established in natural areas
• Examples include St. John's Wort and Kudzu

Intentional Vectors: Non-food

• Biofuel crops are examples of species purposefully introduced (for ease of production or higher yields).

Ship Ballast and Nursery Plants as Vectors

• Ship ballast (water or solids) can transport plants and insects.
• Nurseries can unintentionally propagate exotic pests and species.

Strength of Transport Pathway Determinants

• Numbers of transported species
• Conditions of transported organisms at arrival

The "Tens Rule"

• Probability of an introduced species progressing to the next stage of invasion and establishment is approximately 1 in 10

Invasive Species Trends

• Species introduction rates tend to increase over time in a given area
• The total number of exotic species present in a particular location generally increases over time

Invasion Delays

• Changes in vector strength don't always immediately result in an increase in introduced species
• Delays exist in relationship between factors like GDP and established exotic species.

Species Accumulation Curves

• Ecologists use plots to study biodiversity
• Newly sampled plots find new species and existing ones
• Rate of discovery of new species declines as more places are sampled

Major Geographic Trends

• Higher number of invasive species in islands compared to mainland areas
• Reversal of latitudinal trends from baseline between old and new world areas

Critical Assumptions of Approach

• Trade volume must not increase in a way that increases deposited species
• There should be no change in the types of goods transported
• Inspections and regulation must remain consistent