Answers to Review Questions

1. Immediately after application of the fertilizer, it is likely that the intensity of competition for nitrogen will drop because soil nitrogen levels will not be as limited in supply.

2. Four general features of competition, with an example of each, are (1) competition can be direct (as in allelopathy) or indirect (as in both pitcher plants and bedstraws), (2) competition is often asymmetrical (as in Tilman's diatoms), (3) competition can occur between closely (as in bedstraws) or distantly (as in ants and rodents) related species, and (4) competition is a common feature of natural communities.

3.

a. Possible reasons why these meadows harbor one or the other (or both) of these two plant species include the following: (1) both species could persist at all locations, but one species (or the other) has yet to disperse to some meadows; (2) the physical conditions of the meadows differ such that in some meadows species 1 is favored, while in others species 2 is favored, and in still others, the species can partition resources such that both persist; (3) the abundances of herbivores or pathogens that feed on species 1 or 2 may vary between the meadows, causing the outcome of competition to differ from meadow to meadow; (4) the rates of a periodic disturbance such as fire may differ among meadows (if one of the species is an inferior competitor but is more tolerant of fire).

b. Addition and removal experiments would help to evaluate these possible explanations for the observed distributions of the species. For example, in meadows where only species 1 is found, individuals of species 2 could be planted next to some individuals of species 1, but not others. Similarly, in meadows where both species are found, removal experiments could be performed in which individuals of species 1 would be removed from the vicinity of some species 2 individuals, but not others (and vice versa).