WK 1: Magnitude

Introduction to Invasive Species: Magnitude

Overview of Topics

  • The following topics are covered regarding the magnitude of invasive species:

    1. Magnitude and Geography
      1.1. How many introduced species exist?
      1.2. Trends in time regarding invasions.
      1.3. The concept of invasion debt.

How Many Introduced Species Are There?

  • Accurate estimates of introduced species are hard to obtain.

  • Example: Great Britain freshwater fishes:

    • 38 native species

    • 12 introduced species (24% of total species)

    • An approximation of 10-20% of introduced species are considered invasive (Simberloff, 2013).

Data on Introduced Species in Estuaries

  • The following data presents the overlap of established nonindigenous species in various estuaries:

Estuary

SFB

CB

PS

PWS

ChB

PPB

San Francisco Bay, CA

157 (100)

51 (32.5)

37 (23.6)

6 (3.8)

20 (12.7)

20 (12.7)

Coos Bay, OR

51 (89.5)

57 (100)

31 (54.4)

5 (8.8)

9 (15.8)

13 (22.8)

Puget Sound, WA

37 (64.9)

31 (54.4)

57 (100)

5 (8.8)

5 (8.8)

11 (19.3)

Prince William Sound, AK

6 (60.0)

5 (50.0)

5 (50.0)

10 (100)

0 (0.0)

1 (10.0)

Chesapeake Bay

20 (40.8)

9 (18.4)

5 (10.2)

0 (0.0)

0 (0.0)

49 (100)

Port Phillip Bay, Australia

20 (22)

13 (14.3)

11 (12.1)

1 (1.1)

5 (5.5)

91 (100)

Note on Table:

  • Diagonal entries reflect the number of nonindigenous species in each estuary.

  • Values below diagonal indicate the overlap as a percentage of species at the row site that also occur at the column sites.

  • Values above the diagonal indicate overlap as a percentage of species at the column site that also occur at the row site.
    (Reference: Ruiz et al. 2000, Ann Rev Ecol Syst).

Example Data on Species Composition

Estuary Data Examples:

  • NW Atlantic (New Hampshire) Data Overview:

    • Native:

    • Annelids: 227

    • Molluscs: 0

    • Crustaceans: 10

    • Bryozoans: 0

    • Exotic: 0% for all taxa.

  • SW Atlantic (Argentina) Data Overview:

    • Native:

    • Annelids: 5

    • Molluscs: 5

    • Crustaceans: 6

    • Cryptogenic: 0

    • Exotic: 2, giving % Exotic = 11%.

  • NE Atlantic (The Netherlands) Data Overview:

    • Native:

    • Annelids: 79

    • Molluscs: 56

    • Exotic: Various taxa, giving % Exotic = 7% (Preisler et al. 2009 in Rilov and Crooks (eds.)).

The TENS Rule

  • Definition: The TENS rule states that from a large number of introduced species, a small percentage will establish successfully and become invasive.

  • Data Examples showing established plants that have become invasive in the US:

    • California: 5.8%

    • Florida: 9.7%

    • Texas: 13.4%

Success Rates by Category (Simberloff, 2013)

  • British angiosperms, British Pinaceae, British edible crops, Australian pasture plants, U.S. high impact, Hawaiian birds, and biocontrol insects show varying success in establishment, becoming pests, etc. Success rates are given as percentages.

Establishment and Spread Correlation

  • The proportion of introduced animals that establish themselves (termed Establishment) and of these established animals that spread (termed Spread) varies:

    • Establishment vs. Spread percentages show differing rates across various taxa (planarians, insects, birds, etc.).

Temporal Trends in Exotic Species

Cumulative Number of Exotic Species Established in San Francisco Estuary

  • The number of established exotic species has significantly increased from the 1850s onward.

  • Graph Data:

    • Year range increases correlated to rising numbers of euros.

    • There is a clear upward trend line.

    • Reference: Cohen & Carlton 1998 Science.

Regional Trends in Marine Biology Invasions

  • Cumulative number of established exotic marine and estuarine species in the Northeast Pacific shows a dating trend from first records onward, represented through cumulative numbers, demonstrating the increasing concern of invasions.

  • Reference: Wonham & Carlton 2005 Biol. Inv.

Invasive Species in Coastal Communities of North America

  • Number of invasions recorded per decade shows a marked increase throughout the periods 1790-1999.

  • Various graphs detail species numbers corresponding to decades.

Mediterranean and Global Information on Invasive Species

Invasive Species Data Recorded

  • Non-native marine plant species reported in European coasts from before 1900 to 2008 show significant percentages.

  • The trend illustrates growing invaders in waters from prior to 1900 onset to modern times.

Longitudinal Data on Introduced Species

  • Example Graphs: Cumulative numbers of fish, phytoplankton, zoobenthos over the years reveal steady increments of non-native species.

Drivers of Invasion Increase

Rationale Behind Trends

  • Increase in studying efforts and trade activities drives the increase in reported invasive species.

    • Graph Data: Merchandise exports as a percentage of GDP for various countries, alongside increased shipping traffic data, exemplify this correlation.

Invasion Debt Concept

  • Definition: Invasion debt refers to the concept that the historical accumulation of introduced species will lead to future invasions that have not yet manifested, suggesting a lagged response in ecological systems.

Key Conclusions

  • Overall increase in number and rates of species introductions signals an urgent need for monitoring.

  • There is a lack of straightforward rules to predict the future number of invasive species, indicating the complexity of invasions.

  • Historical legacies strongly influence future invasions, demonstrating the long-lasting impacts of past introductions.