Directions: Type your answer in the box. Use numerals, not words.
The yellow tang (Zebrasoma flavescens) is a tropical fish commonly found in the Pacific and Indian
oceans. Suppose a population of yellow tangs lives in a coral reef. The graph below shows the
distribution of body sizes within the population at the time the fish began to live in the reef.
1.200
Number of Individuals
08 208 408 608 80 g 100 & 1208 1408 160 1808
Body Size
The body sizes of the fish vary from about 20 grams to 180 grams, but most of the fish have a mass of
about 100 grams. The amount of calones each fish needs per day depends on its size, as shown
below.
Mass (grams) 20 40 60 80 100 120 140 160 180
Daily Caloric Needs 10
10 25 40 65 80 95 110 125 140
(calories)
Over time, selective pressures begin to act on the population. Food becomes scarce, limiting the
number of calories available to individual yellow tangs. Eventually, the average amount of calories that
are available to each yellow tang becomes 40 calories per day.
After several generations survive in the altered environment, what will the average body size of
yellow tangs in this population be?
grams