The figure shоws а grаph with the hоrizоntаl axis labeled Number of Spines per Plant and the vertical axis labeled Relative Number of Cacti.There are evenly spaced tick marks on the horizontal axis labeled 70 through 130, in increments of 10. There are two lines on the graph. The solid line represents both herbivores present, and the dashed line represents neither herbivore present. From left to right, the lines are as follows. The solid line begins close to the horizontal axis above 80, moves steeply up to a high point above 90, moves steeply down to a much lower point above 100, and then ends close to the horizontal axis above 110. The dashed line begins slightly above 70 on the horizontal axis, moves gradually up to a point above 80 and above the solid line, moves more steeply to a high point above 90 but below the solid line, moves gradually down to a point above 100 and above the solid line, and continues gradually through points above 110 and 120 to end near the horizontal axis above 130. In a species of cactus, the number of spines on a plant is genetically determined. The graph above shows frequency distributions for populations of the cactus species growing in the presence or absence of two herbivores: peccaries (a New World pig) and wasp larvae. Which of the following best accounts for the different frequency distributions in the graph?