1. A research group studied various abiotic factors and their effects on the overall productivity of a selected set of lake ecosystems. Productivity is the rate of biomass synthesis in a lake ecosystem. a. The researchers collected data from 12 lake ecosystems. They measured the total phosphorus content in each system as well as the fish productivity (rate of fish biomass synthesis) in each system. The data are plotted in the graph shown.

Identify the relationship between phosphorus content and fish productivity as shown in the graph above. Explain this relationship. (2 points)

b. The researchers also analyzed the amount of light irradiating each lake ecosystem. They plotted these values against fish productivity values to produce the graph shown below.

Identify the relationship between amount of light irradiance and lake productivity as shown in the graph above. Explain this relationship. (2 points)

c. Nutrients are a critical component of any ecosystem. Ecologists have worked under a model that assumed that nutrient availability is a limiting factor within an ecosystem, as its presence or absence can limit the productivity. Explain two factors that affect the validity of this model based upon the data from this study. Explain one possible refinement of the model that may need to be made. (3 points)

Fish productivity rate 600 400 200 20 10 Total phosphorus (g/L) 30 Fish productivity rate 600 400 200 500 1,000 1,500 2,000 Annual light irradiance (mol/m2/year)