Two competing species of grass occur in upland and lowland habitats in Minnesota

Question

Two competing species of grass occur in upland and lowland habitats in Minnesotan prairies; their isoclines are depicted on the above (upland on top; lowland on bottom). In both graphs, N1 is on the x-axis and N2 is on the y- axis. Use this information to answer the following questions:

1. In the upland system (top graph), point A in the phase plane represents a situation in which:

a) Grass species 2 is much more abundant than grass species 1.

b) Grass species 1 is much more abundant than grass species 2.

c) Grass species 1 is growing much faster than grass species 2.

d) It's impossible to tell without seeing the phase plane graph over time.

2. Which of the two systems above, upland or lowland, is characterized by a stable equilibrium?

a) Upland

b) Lowland

c) Neither

d) Both

3. Consider the stable equilibrium you identified in the previous question. According to the Lotka-Volterra model, how do the relative strengths of intraspecific and interspecific competition impact equilibrium stability?

a) A stable equilibrium results when intraspecific competition is weaker than interspecific competition.

b) A stable equilibrium results when intraspecific competition is the same strength as interspecific competition.

c) A stable equilibrium results when intraspecific competition is stronger than interspecific competition.

d) The relative strengths of intraspecific and interspecific competition have no effect on equilibrium stability.

4. In the system characterized by an unstable equilibrium, the outcome of competition depends on what?

a) The carrying capacities of the two species.

b) The competition coefficients (?) of the two species.

c) The initial population sizes of the two species.

d) The relative strength of competition between the two species.

5. Observe initial conditions at points A and B (upland, top), and C and D (lowland, bottom). Which TWO of the points on the graphs represent initial conditions that will result in one of the species being driven to extinction?

a) A and B

b) A and C

c) C and D

d) B and D

N,-N, Phase Plane N. Upland K, Lowland K,12 K. K, K,lo Zero growth isoclines for two hypothetical systems of two competing species of prairie grass

Explanation / Answer

b) Grass species 1 is much more abundant than grass species 2. b) Lowland c) A stable equilibrium results when intraspecific competition is stronger than interspecific competition. c) The initial population sizes of the two species. a) A and B

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