Various theories have been suggested to explain the unique abundance and diversity of gliding animals in the rain forests of Southeast Asia. A. The fact that the abundance of gliding animals in different regions of the world corresponds to difference in tree height, canopy structure and amount of vines has been explained by ecologists. B. One theory suggests that so many gliding species evolved in Southeast Asia because the forests are exceptionally tall, but there is evidence that the theory is not enough. C. Jumping from tree to tree or descending to the ground and walking in forests that are dominated by tall trees may be a more energy-efficient way of traveling through the forest than gliding. D. The fact that gliding animals are most abundant in the short-structure forests of Southeast region indicates that gliding did not evolve as an adaptation to an environment of tall trees. E. Dipterocarp trees create an environment in which many species must travel widely to find food, and gliding may have evolved as a rapid and efficient way of moving between tree crowns. F. The hypothesis that gliding evolved to compensate for a scarcity of vines linking tree canopies overlooks problematic evidence from both Southeast Asian and Amazonian forests.