Use the following information to answer the question 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 preferably 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

Question

Use the following information to answer the question 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 preferably 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

Quizplus · Accepted Answer

If predators that preferably catch and eat slower iguanas are introduced, the small iguanas that can sprint faster would survive and reproduce more than larger iguanas. This would result in a decrease in iguana body size over time, indicating directional selection towards smaller body size.

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