BIO 360   Ecology

Lecture 22:  Predation and Biocontrol

I.  Biocontrol
    A.  What is biological control, or biocontrol?
        1.  Use of natural enemies (parasites, predators, and disease) to control pest population sizes
             a.  Invasive species
             b.  Pests that have increased due to agricultural use

        2.  Alternative to pesticide use or the use of toxins.

    B.  What are characteristics of a good biocontrol organism?
         1.  Adapted to similar habitats where pests are present
         2.  Host-specific
              - Attacks the pest
              - Does not attack other species
              - Does not harm humans
         3. Abundant
         4.  High per capita growth rate (r)
         5.  Does not drive its prey and itself to extinction
        NOTE: These characteristics are more common in parasites than in predators

    C.  Examples
        1.  European rabbit in Australia, and myxomatosis virus used to control it (Figure 14.4)

        2.  Prickly pear cactus, and moth (Cactoblastis tactorum) used to control it

        3.  Control of hemlock wooly adelgid in the southern Appalachians

    D.  Typical chronology with biocontrol
        1.  Pest introduced
        2.  Pest exponential growth
        3.  Biocontrol species introduced
        4.  Pest and biocontrol agent live together at low population sizes, or coexist

III.  Predator-prey interactions in nature:  Oscillations in population sizes

Key question is: how do predators and prey coexist?

    A.  Case 4: Natural predators can regulate pests

    B.  Natural fluctuations in lynx and hare (Figure 14.7)

    C.  Fluctuations in disease (measles) and host (human) infections (Figure 15.14)


    D.  Oscillations and coexistance in a classic predator-prey experiment: Gause 

        1.   Spatial variation in the environment may provide hiding places for prey

    E.  Oscillations and coexistance in a classic predator-prey experiment: Luckinbill 

        1.    Predator and prey live together longer if prey have less food, slower population growth rate

    F.  Conditions for predator-prey coexistance
        1.  Limited resources for prey

        2.  Spatial variation in the environment