AEC 360  Ecology

Invasive Species

I.  What are invasive species?
    A.  Species introduced into habitats where they are not native

    B.  Weeds, ornamental, game, crops, pests, diseases, Ö

    C.  Also called exotics, aliens, non-indigenous species

    D.  Species that have escaped control

II.  How did species invade?
    A.  Natural pathways (wind, currents, transport by animals)

        1.  Natural colonization isnít easy

    B.  Human created pathways
        1.  Intentional (for profit, recreation, conservation)

        2.  Accidental (movement of people, soil from plant nurseries, ballast water)

    C.  Itís not easy for an invader to get established
      1.  Low establishment success rate

      2.  problems of small populations
         -extinction from chance events
          -individuals may not find mate

    D.  What are characteristics of successful invaders? 

    E.  Examples from NC:
        1.  Fire ants

        2.  Kudzu
              - Imported from Japan for erosion control and as an ornamental

               - Grows as much as a foot a day

                - acts as competitor with native plants, blocking all sunlight

                - entire root system must be destroyed to eliminate plant, otherwise constant mowing or herbicide application is required (~$500 million/yr on control)

       3.  Cane Toads (not from NC.....)

        -- Cane toads may be evolving to tolerate a greater range of environments

       --  Cane toad invasion added by their evolution

        -- Toads on the road:  roads as dispersal corridors for cane toads

       --  Predators are evolving in response to cane toads

       --  Snakes now have:
            Smaller mouth gape
            Resistance to toxins
            Behavioral avoidance

III.  What are the consequences of invasion?
    A.  What makes ecosystems prone to invasion?
        1.  Early successional
        2.  Disturbed
        3.  Productive
        4.  Absence of predators, pathogens
        5.  Simple (= low diversity)?

    B.  Consequences of invasions
        1.  50,000 invasive species in the US
        2.  Cause environmental damage and loss of ~$137 billion/yr (Pimentel et al. 1999)
        3.  Damage caused as pests, weeds, and disease
        4.  Threaten rare species

            -- examples: brown tree snake,  cichlids, zebra mussels

IV.  How do we turn back invasive species?
    A.  Eradication
         1.  Examples: witchweed and Brook trout in N.C.

    B.  Biocontrol

    C.  Prevention
        1.  Ban traffic in exotic species
        2.  Exchange ballast water at sea