Tortoises with long necks were found to be abundant in regions that had vegetation on a higher level. a few years later, drought hit the region and the vegetation dried up. over time, grasses were observed in the region. shortly thereafter, an increase in short-necked tortoises was observed in the region. what does this change in the species of tortoises suggest? a. changes in the environment give rise to evolution of species. b. tortoises all around the world are now short necked. c. tortoises found only in this region are short necked. d. only changes in food availability affect the evolution of species.