Invasive Species

I.  What is an invasive species?

A.  Introduction of non-indigenous species to habitats beyond their native range

B.  Focus is on those that become established in the wild and become a problem

C.  Stages of invasion:
1. Introduction
2. Establishment
3. Spread
4. Consequences detectable


II.  Impacts of invasions

A.  Impacts of invasive species on Biodiversity

1.  Predation by the Brown Tree Snake



2.  Nile Perch and cichlid fish



3.  Implications for global diversity


4.  Impacts on communities: case study with fire ants


5.  Impacts on ecosystems
       -- invasive grasses and fire

       -- Myrica faya, an invasive species in Hawai’i
            Nitrogen-fixing, and grows on lava flows
            Increases N inputs to the ecosystem
            Facilitates colonization of other invasive species


4.  Economic impacts
    -50,000 invasive species in the US
    -Cause environmental damage and loss of ~$137 billion/yr (Pimentel et al. 1999)
    -Damage caused as pests, weeds, and disease


III.  What are the characteristics of exotic species?  Can we predict invaders?



1.  Unique Life History Traits


        Fast population growth
        Short reproductive cycles
        Plants have small seeds that spread easily
        Generalists
        Human commensalists


        --  Predicting fish introductions into the great lakes   Kolar and Lodge (Science, 2002)


       -- Predicting pine invasions   Rejmanek and Richardson (1996)


2.  Release intensity


        - Invasion success related to species range   Bender, McAllister, and Fahrig (1999)

        - Invasion success related to number of attempts  Kolar and Lodge 1999


3.  Natural enemies hypothesis

        -- 88% fewer fungi and 24% fewer virus species infect each plant species in naturalized v. native ranges



4.  Evolution of novel traits, including rapid adaptation to local environment
    Phillips et al example with Cane Toads


IV. Which areas are invasible?

A.  Biotic resistance

1.  Diversity and invasibility

Elton (1958) proposed that diverse communities are less invasible
One hypothesis is that, in diverse communities, there are fewer resources available


2.  Open niches

B.  Physical environment
1.  Disturbance

2.  Other abiotic factors



V.  How do we control non-native species?

1.  Prevent entry

2.  Eradication

Fish removal and rapid recovery of rare frog    Vredenberg (2004)

Witchweed in NC

Trout removal in NC

3.  Maintenance

4.  Biological control