Answers to Hone Your Problem-Solving Skills Questions
1. Results from laboratory experiments, field observations, and mathematical models all suggest that competing species are more likely to coexist when they use resources in different ways.
For example, in Gause's experiments with Paramecium, P. caudatum coexisted with P. bursaria, most likely because one species fed primarily on bacteria, the other on yeast. Likewise, in the case of four species of Anolis lizards that lived together on Jamaica and ate similar food, Schoener's field observations indicated that these species used space in different ways (an example of resource partitioning). Finally, graphical analysis of the Lotka-Volterra competition model indicates that competing species can coexist when the inequality shown in Equation 14.4 holds. That inequality is more likely to hold when competing species use resources in very different ways (e.g., when α and β are not close to 1).2. Because β = 1.6 and there are 140 individuals of species 1, it would take 1.6 ? 140 = 224 individuals of species 2 to reduce its own growth rate by the same amount that the 140 individuals of species 1 do. Therefore, because there are 230 individuals of species 2 present, species 2 is having a slightly greater effect on its own growth rate than is species 1.
3. The statement is not correct. For example, if α = 0.5 and β = 1, Equation
14.4 predicts that both species will persist when 0.5 < K1∕K2 < 1. Thus, for example, if K1 = 100 and K2 = 150, both species should persist when α = 0.5 and β = 1. (The statement can be shown to be false in many other ways; for example, in Figure 14.14B, values for α, β, K1, and K2 can be selected such that species 2 always drives species 1 to extinction, even though α < β.)