The food web shown below utilizes an arrow pointing from a species feeds on another to indicate the trophic structure of a simplified estuarine ecosystem at the boundary between the ocean and the shore.

This figure shows four rows of blue dots represent organisms. Upward arrows connect organisms from the bottom level to the three upper levels. There are different letter points indicated, P and S are on the bottom level R is on the third, and T and Q are on the top most level.
Figure 37.24

A. Analyze the interactions among species and indicate primary producers by circling the node in the food web. Identify the primary producers by circling the nodes in the food web.

B. Predict quantitatively how free energy availability for a top species such as the one designated as T in the web changes if it feeds directly on S, assuming the abundance of species S is limited only by radiant energy input.

C. Consider the consequences of the dietary shift described in B if the abundance of species becomes depleted due to consumption by species T. Under those circumstances refine your analysis of the food web to describe the potential effect on species Q and R.

D. Based on the preceding analyses, construct a claim regarding the effect of the structure, in terms of biodiversity and number of interactions among species, on ecosystem stability.