Use the following information to answer the question(s) below.
Martin Wikelski and L. Michael Romero (Body size, performance, and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]: 376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different-size classes for males and females.
-Currently, the only predators of Galápagos marine iguanas are Galápagos hawks. Iguana body size is not correlated with risk of hawk predation, although small iguanas can sprint faster than large iguanas. If predators (for example, cats) that preferentially catch and eat slower iguanas are introduced to the island, iguana body size is likely to ________ in the absence of other factors; the iguanas would then be under ________ selection.
A) increase; directional
B) increase; disruptive
C) decrease; directional
D) decrease; disruptive
E) stay the same; stabilizing

Question

Use the following information to answer the question(s) below.
Martin Wikelski and L. Michael Romero (Body size, performance, and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]: 376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different-size classes for males and females. 
-Currently, the only predators of Galápagos marine iguanas are Galápagos hawks. Iguana body size is not correlated with risk of hawk predation, although small iguanas can sprint faster than large iguanas. If predators (for example, cats) that preferentially catch and eat slower iguanas are introduced to the island, iguana body size is likely to ________ in the absence of other factors; the iguanas would then be under ________ selection.
A) increase; directional 
B) increase; disruptive 
C) decrease; directional 
D) decrease; disruptive 
E) stay the same; stabilizing

Quizplus · Accepted Answer

If predators preferentially catch and eat slower iguanas, then larger iguanas, which are slower, are more likely to be caught and eaten. This would lead to a decrease in iguana body size over time, as smaller, faster iguanas would be more likely to survive and reproduce. This is an example of directional selection, as the selection pressure is leading to a shift in the population towards smaller body sizes.

Use the Following Information to Answer the Question(s) Below