Two Scientists Measured the Snout-To-Vent (Anus) Length of Galápagos Marine

Multiple Choice

Two scientists measured the snout-to-vent (anus) length of Galápagos marine iguanas (lizards) 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. (Data from M. Wikelski and L. Michael Romero. Body size, performance and fitness in Galapagos marine iguanas. Integrative and Comparative Biology 43:376-386 [2003].)
Currently, the only predators of Galápagos marine iguanas are Galápagos hawks. Although small iguanas can sprint faster than large iguanas, iguana body size is not correlated with risk of hawk predation. 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