Dr. Janneke Hille Ris Lambers of University of Washington has found that when tree seeds are dispersed at high density, few germinate. One explanation for this pattern is that predation and disease increase when seed density is high.
a. Explain Dr. Lambers’ hypothesis in your own words. (ie, what does ―dispersed at high density mean?) Also explain WHY she thinks that predation and disease increase when predation is high.
Dr. Lambers conducted a study to test her hypothesis. She created 50 plots in a forest where seed density is high and 50 plots where seed density is low. In half of the plots of each type she excluded all predators and diseases, while she did not exclude anything from the other half of the plots.
b. How many independent variables are tested in Dr. Lambers’ experiment?
Of these, which one is the variable that she is testing to find out if her hypothesis is supported?
c. What is the control group?
d. Name two other conditions that might affect how many tree seeds germinate (besides the one she is testing).
e. Dr. Lambers believed she controlled for these other potential variables by locating her plots in random locations in the forest. Is this a valid approach? Why?