NAU Biology BIO 326
NAU
Syllabus The Class Communicate Library Instructor
HelpGet Started
BIO326 : Predation/Competition : Competition : Lesson

Competition: Lesson


elk competing Glossary terms that are important in this lesson:

Allelopathy, asymmetry, competition coefficient, competitive coexistence, competitive exclusion, equilibrium, exploitation competition, interference competition, interspecific competition, intraspecific competition, isocline, keystone predator, Liebig's law of the minimum, limiting factors, Lotka-Volterra equation, parasitoid.



Use the outline below to guide your study of the material in this lesson. The outline follows the book, but indicates those topics the instructor feels are most important for you to learn in the course. You should read all the pages that are assigned, but the outline will help you focus your study.

Competition occurs when individuals share a resource which is in short supply. Sometimes competition is a head-to-head confrontation, but more often one individual uses a resource before another individual gets to it and deprives the other of something it needs.

I. Competition

  1. Introduction

  2. Resources

  1. Limiting resources
    • (Justus von) Liebig's law of the minimum: population is restricted by the resource which is most limiting
    • Limiting factors
      • A. A single factor is limiting when growth is directly proportional to the supply of that factor
      • B. Factors interact synergistically when more than one factor simultaneously restrict growth
      • C. The population is saturated with this factor when it does not respond to changes in supply
      • D. The population is inhibited when there is too much of the resource
      • Examples: Cyclotella meneghiniana, Impatiens parviflora
Limiting factors

  1. Early Experiments with Competition

II. Theory of Competition

  1. Intraspecific competition represented by the logistic equation

  2. Interspecific Competition: Lotka-Volterra equation, modified logistic

  1. Equilibrium Conditions
    • Equilibrium occurs when dN/dt = 0
    • Then Ni = Ki - aijNj  (Note that, when dN/dt = 0, the differential equation simplifies to an equation for a straight line.)
      • Ni = Ki when Nj = 0 (intercept on the x-axis)
      • Nj = Ki/aij when Ni = 0 (intercept on the y-axis)
      • Connect the two intercepts to obtain the equilibrium line for Population i
    • Population i will grow to a density somewhere on its equilibrium line (its isocline)
Equilibrium for Population i

  1. Predictions

III. Competition in Nature

  1. Parasitoids

  2. Plants

  3. Nutrients

  4. Barnacles, voles, and lizards

IV. Mechanisms of Competition

  1. Classification
    • Exploitation competition: some individuals consume resources before other individuals do; expressed through differential survival and reproduction
    • Interference competition: some individuals directly inhibit others; interference competition is relatively frequent within species
      • Allelopathy: Salvia (sage) use chemicals which inhibit the growth of other vegetation
Salvia sonomensis; Sonoma sage
  1. Asymmetry: response to competition by only one species
    • Chthamalus and Balanus
    • Predators and herbivores often involved
    • Patch reefs in the Caribbean Sea
      • Habitat of reef flat, reef slope and sand plain
      • Asymmetrical competition resulted when species that shared one resource (e.g. space or food) were differently specialized for other aspects of the environment (e.g. physical conditions or consumers)
  1. Distantly related species
    • Sharing resources provides potential for competition
  1. Influence of predation: keystone predator shapes the structure of biological communities
    • High diversity of grassland plant communities are maintained by grazing animals which prefer to eat superior competitors
    • Rocky coast of Washington: Sea star (Pisaster) predators limit populations of superior competitors resulting in high diversity of prey
    • Predatory newts preferred rapidly growing Scaphiopus tadpoles, resulting in survival of the inferior competitors as well as more food and better growth for all survivors
When you have completed this lesson, go on to Review Questions


E-mail Professor Gaud at William.Gaud@nau.edu
or call (520) 523-7516
NAU Copyright 1999 Northern Arizona University
ALL RIGHTS RESERVED