Week 3
ILab
Joy Major

Exercise 1: A biomass pyramid is a diagram that shows the flow of energy through each trophic level of a food chain by quantifying the amount of biomass present at each trophic level. As a general rule, 90% of the energy is lost as you move through each trophic level. The levels move as follows: primary producers to primary consumers/herbivores to secondary consumers (predators) to tertiary consumers (top of the food chain). For example, in an eastern deciduous forest, if the primary producers (i.e., deciduous trees, shrubs, and grasses) produce 10,000 kilocuries per square meter a year then the kilocalories available at the primary consumer level (i.e., bugs, deer, rabbits, small birds) will be 1,000 kilocalories; followed by 100 at the secondary consumer level (i.e., foxes, owls, skunks, large birds) and 10 at the tertiary consumer level (i.e., bears). An example of this flow of energy can be found below.

Exercise 2: Mount St. Helens has revealed some important factors that influence how an ecosystem can recover from such a cataclysmic eruption. One mudflow had cut through a forest, so it was surrounded by existing vegetation and recovered relatively quickly. The seasonal timing was a key factor because spring was late in coming to Mount St. Helens that year, and so there were still drifts of snow covering the understory of many sections of the forest, protecting the plant and animal species buried beneath them. The snowmelt also protected many of the trees and other plants that typically dominate the understory of the forest, particularly on the north side of the mountain. These saved species provided spots of green even right after the eruption when the snow melted and they emerged.
Exercise 3:
According to the rule of 70, if you start with 100 oxen and you have an increase rate of 23.33% then the population of oxen