WK 1: Magnitude transcipt notes

INTRODUCTION TO INVASIVE SPECIES

  • Magnitude
    • Overview of the lecture
    • Topics will cover general trends in invasion magnitudes.
    • Focus on quantifying numbers of invasive species, trends over time, and the concept of invasion debt.

HOW MANY INVASIVE SPECIES?

  • Challenges in Quantifying Introductions

    • Difficulty in quantifying introduced and naturalized invasive species.
    • Many introduced species do not survive or persist long enough to be observed.
    • Initial observation often occurs after a species has already become invasive.
    • Examples: Certain flashy birds or plants might be noticed, but most undocumented species may already be invasive.
    • Lack of comprehensive analyses on trends in invasive species introductions.

  • Estimates for Specific Taxa

    • Example: Freshwater fishes in Great Britain.
    • Native species: 38
    • Introduced species: 12
    • Approximately 25% of species are introduced; 10-20% of those are invasive.

  • Studies on Coastal Communities

    • Pioneering work by Prof. Jim Carlton and colleagues (Ruiz et al., 2000).
    • Review of introduced species in estuaries.
    • High numbers in San Francisco Bay: 157 introduced species.
    • Comparison with recent data revealing fewer introduced species in other areas: 2 in Argentina, 14 in the Netherlands.

THE TENS RULE

  • Introduction to the Tens Rule

    • The "tens rule" states that only 10% of introduced species transition through each stage of the invasion process (actual percentages can range from 5% to 20%).
    • 10% of introduced species become naturalized.
    • 10% of naturalized species become invasive.
    • 10% of invasive species have significant impacts.
    • Conclusion: Approximately 1 in 1000 introduced species may result in an invasive pest.

  • Examples of the Tens Rule Applying

    • Introduced plants in the U.S.:
    • California: 6% invasive
    • Florida: 10% invasive
    • Tennessee: 13% invasive
    • Williamson and Fitter (1996) graphs show various groups of introduced species adhering to the tens rule.

  • Exceptions to the TENS Rule

    • Hawaiian birds often exceed 40-60% establishment rates.
    • Bio-control agents can show similar unexpected results.

CRITIQUE OF THE TENS RULE

  • Empirical Data and Limitations
    • Jeschke and Strayer (2005) showed higher percentages of establishment and spread than predicted by the tens rule.
    • Findings:
    • 2-11% taxa were transported and released between continents.
    • 10-80% of introduced insects established populations, with 30-45% becoming invasive.
  • Mean Establishment Success
    • North America to Europe: 52%
    • Europe to North America: 60%
    • Spread significantly above 10%: 65% and 54% respectively.
  • Misapplication of the Rule
    • The tens rule should not be used for quantitative predictions or risk analyses, as it focuses solely on numbers rather than character and impact of invaders.