Ecology - Interspecific Competition using Lotka-Volterra Model

Homework #3 (50 points)

Due November 14, 2014

Review Questions and Problems: 10.2, 10.4

Interspcific Competition: Graph the following zero isoclines using the Lotka-Volterra model: (a) (b) (c) (d) K1 = 200 K1 = 200 K1 = 200 K1 = 200

!12 = 0.8 !12 = 0.8 !12 = 1.2 !12 = 1.5

K2 = 180 K2 = 180 K2 = 180 K2 = 180

!21 = 1.5 !21 = 0.6 !21 = 0.8 !21 = 1..8

Describe the predicted outcome of interspecific competition for each. (Can use the figures provide below or graph your own using a graphing program. (a) (b)

N1

N2

K1

K2

N2

K1

K2

N1

(c) (d)

N1

N2

K1

K2

N2

K1

K2

N1

Reading Assignments for Homework 3(a-c). a) Food-web theory predicted that omnivory would be rare because omnivory would decrease the stability of the food web (see Polis 1991). Polis (1991) found omnivory common in the Coachelle Valley community. Find a recent paper in the scientific literature after Polis (1991) that is studying the effect of omnivory on food web(s). What conclusions does the paper draw about how common omnivory is in food webs? Does the paper support food-web theory or the conclusions of Polis (1991) about the effect of omnivory on stability? Explain. b) Fire is a physical disturbance affecting diversity (heterogeneity) of a tallgrass prairie community (Collins 1992). Describe the community and disturbance. How does the disturbance affect the community and diversity? Do the results support or not support the the intermediate disturbance hypothesis? What factor(s) are important to explain why it supports or not supports the theory? c) Seastars (i.e., starfish) are predators affecting a kelp-dominated community (Duggins 1983). Describe the community and predator. Compare the results in this community to the predator-mediated coexistence hypothesis. Does the seastar predator affect the coexistence of sea urchins in the community? Do the results support or not support the theory? Explain. How does seastar predation effect other species in the kelp community? Explain.

Literature Cited

Collins, S. L. 1992. Fire frequency and community heterogeneity in tallgrass prairie vegetation. Ecology 73:2001-2006.

Duggins, D. O. 1983. Starfish predation and the creation of mosaic patterns in a kelp- dominated community. Ecology 64:1610-1619.

Polis, G. A. 1991. Complex trophic interactions in deserts: An empirical critique of food-web theory. American Naturalist 138:123-155.