A biologist began studying a population of bullfrogs. In 1998, she found that most of the male frogs croaked, but some did not. A bat species known to
prey on male frogs migrated to the area in 2005. The biologist returned to the
area in 2008 and repeated population counts of male frogs. The table shows
her data
1998
2002
2004
2008
Number of
noncroaking males
244
368
208
1086
Number of croaking
males
742
1165
791
305
What factor most likely caused the noncroaking male population to increase
after 20042
A. Selective pressure in the form of a new predator
B. Learning to avoid the new predator
c. Extinction of the croakers because of the new predator
D. Adaptation of the croakers in the presence of a new predato