A biologist has determined that 16 distinct species of spiders on the Hawaiian Islands all descended from a common ancestor. The biologist also noted that there was a wide variety of different habitats on the various islands ranging from snow covered mountains to vocanic lava fields to tropical forests. Which of the following characteristics of this island chain increases the incidence of species change in the island habitat? a. current and past volcanic activity
b. isolation from the mainland
c. rapid expansion of human populations
d. a wide variety of environmental conditions