Lecture 21

Topics

• Continue discussion of competition models.

• Discuss the assumptions of the logistic model.

Study Sources

• Chapter 21 in Ricklefs; especially pp. 403-414.

• Study Guide: Competition

The Main Points

• We continued discussion of the three models remaining from the previous lecture: Species 2 always wins, coexistence, and the case where either species can win.

• Study Figs. 21-7 and 21-8 in Ricklefs. He does a great job of presenting the models. Make sure you understand the intercepts (on each axis) and the meaning of the vectors in each sector of the graph.

• The Assumptions of the logistic model
  1. No immigration nor emigration. All changes in the sizes of the populations are due to density dependent variables.

  2. All individuals are equal. Note that we multiply the biotic potential by N (the population size).

  3. dn/dt changes instantaneously with changes in N and/or K. No lag times.

  4. b and d vary linearly with population size (N).

  5. The negative effect on each species from its competitor is a linear response over all densities.