Assignment 3

Predators develop abilities to locate and capture prey, and prey can evolve to develop mechanisms designed to minimize predation. However, if predators are more effective at capturing prey than prey species are at avoiding predation, then the population of prey species will be affected. Conversely, for some species, too little predation can also affect population numbers in a negative way if the prey species population exceeds its carrying capacity. Working within PopulationEcologyLab and referring to the detailed instructions on Assignment 3, answer the questions below.


1 .		Set the initial number of blue sparrows to zero. We will focus on the population growth of the brown sparrow and the hawk. Set the initial population number for the brown sparrow equal to 200 birds and for the hawk equal to 20 birds. Design experiments to test the effects of increasing flight speed of the brown sparrow. Try several different flight speeds. What happens? How does increasing flight speed affect the population numbers of sparrows and hawks?

2 .		Design experiments to test the effects of decreasing flight speed of the brown sparrow. What happens to the population numbers of the sparrow and hawk?

3 .		Design an experiment to test the effects of changing sparrow clutch size on the predator-prey dynamics. What happens to the population numbers of the sparrow and hawk as sparrow clutch size increases? What happens when sparrow clutch size decreases? What happens to the population numbers of the sparrow and hawk as hawk clutch size increases? What happens when hawk clutch size decreases?

4 .		Design experiments to test the effects of changing hawk clutch size on the predator-prey dynamics.

5 .		Rosenweig (1972) identified a phenomenon he called the "paradox of enrichment." He discovered that increasing the carrying capacity of a species—for example, by adding nutrients to a pond—can destabilize the system when the species is at risk of predation. Design experiments to test this idea. What did you discover? Explain your answers.