Assignment 2

Interactions between populations of two more different species (interspecific interactions) can affect population size and population density in a number of ways that can benefit or harm one or several species. These assignments are designed to help you learn about interactions that result in competition by following the population growth of both the brown and blue sparrow. Working within PopulationEcologyLab and referring to the detailed instructions on Assignment 2, answer the questions below.


1 .		Set the initial number of hawks to zero. Set the initial population numbers for both the brown and blue sparrow equal to 200 birds. Set the relative insect consumption by the brown sparrow equal to zero, and set the relative seed consumption by the blue sparrow equal to zero. Keep the remaining parameters at their default values. Run several simulations and get an estimate of the carrying capacity of each species. Note: You can run ten independent simulations by going to the Initial Population view and clicking the Multiple Run Mode button. With this mode, set the number of runs to 10, then run the experiment. What did you observe for the carrying capacity of each species?

2 .		Go to the Competition view and use the slider to increase the relative insect consumption by the brown sparrow, then run this experiment. What happened to the density of the two sparrows? Is there a point at which one of the two species goes extinct?

3 .		Now reverse the situation and keep the relative insect consumption by the brown sparrow equal to zero while increasing the relative seed consumption by blue sparrows. Before you run this experiment, formulate a hypothesis to predict the results of this experiment.

4 .		Is there a threshold clutch size needed to keep the population from going extinct? What happens to the variability in population numbers as clutch size gets smaller? If you were a conservation biologist, what would you say about your ability to predict population numbers when clutch size decreases?

5 .		What happened to the density of the two sparrows? Is that what you expected? Explain your results.

6 .		Keep the two consumption rates of resources equal, but gradually increase both. Make sure you run several simulations for each set of consumption rates. What happens as you increase the amount of competition between the two species of sparrows? Explain these results.

7 .		Set both of the relative consumption rates back to their default value of 0.50. Design experiments to investigate the effects of resource densities on species competition, then run these experiments multiple times. Summarize your results.