Terrestrial species 



34 per cent, ants 25 per cent, and all others 16 jjcr 

 cent. Planaria-like llatworins, a leech, and a land 

 crab are found, although in temperate climates they 

 are usually limited to aquatic habitats. Many dif- 

 ferent kinds of millipedes are a characteristic feature 

 of the fauna. Centipedes and snails are not abundant 

 (Williams 1941). 



Many animals of all sorts have developed an 

 arboreal-living habit although their close relatives 

 outside the tropics are ground-dwellers (Table 27-2 ). 

 These arboreal species tend to be limited in size and 

 possess opposable toes and prehensile tails. The 

 Xevv-\\'orld monkeys have prehensile tails but not 

 the 01d-\\'orld monkeys and apes. Porcupines, 

 climbing ant-eaters, the coatis, and the kinkajou 

 also possess prehensile tails (Haviland 1926). Some 

 sloths and lemurs hang upside down as they climb 

 around through the branches of the trees. Tree- 

 dwelling snakes and lizards are either long and whip- 

 like or heavy-bodied and with prehensile tails. Para- 

 chutes, similar in function to those of the flying 

 squirrels of temperate forests, have developed in 

 such diverse forms as marsupials, lizards, and frogs. 

 Some frogs are entirely arboreal and have sucking 

 discs on their toes to aid in climbing. Some species 

 of frogs lay their eggs in the trees in sacs made of 

 leaves, others glue their eggs to leaves, still others 

 carry them on their backs and the tadpole stage is 

 passed through before hatching. Snails climb to the 

 topmost branches of the trees. Some butterflies fly 

 continuously about the tree-tops and appear never to 

 alight on the ground. There is a group of tree-dwell- 

 ing tiger-beetles, Odontocheilae. Termite nests lo- 

 cated in trees are often connected to the ground by 

 covered passages. Leeches climb into bushes to get 

 onto the bodies of warm-blooded animals more easily. 

 During the wet season, the mosquito Anopheles 

 gamhiac spends most of its time below 7 meters in 

 the forest, but its close relative A. africanus is most 



abundant at heights of 13 to 25 m. Species of 

 Anopheles and Ciilex are mostly crepuscular or noc- 

 turnal in activity while the sabethine group and cer- 

 tain Actles are diurnal (Bates 1949). 



Many of the epiphytes, especially the bromeliads. 

 hold small quantities of water within the clump of 

 leathery leaves high up in the trees. These small 

 reservoirs usually contain protozoans, rotifers, flat- 

 worms, leeches, annelids, snails, isopods, copepods, 

 ostracods, onychophorans, centipedes, millipedes, 

 scorpions, spiders, a great variety of insects, and 

 small frogs which may spawn here (Haviland 1926). 



The true forest inhabitants keep well within the 

 forest shade and. like the monkeys, are quite sensitive 

 to direct exposure to the sun. Animal life is less 

 abundant, however, in the depths of the forest 

 interior than it is on the forest margin. It follows 

 that the fauna is richer both in species and in numbers 

 in the tropical savanna than in the tropical rain-forest 

 itself. 



HUMAN RELATIONS 



The tropics are the native home of the 

 black or negroid races of man. The death rate of 

 white man in some parts of the humid tropics is in- 

 creased ten times over what it is in temperate regions, 

 and he can seldom spend more than a few months at 

 a time there without impairment of health and vigor. 

 Relatively little effort is required by the native of the 

 tropics to secure food, and the need for clothing is 

 minimal. The biological environment, however, is 

 harsh and exacting. He must guard against malarial 

 Plasmodia, hookworms, and a variety of skin para- 

 sites (Dobzhansky 1950). 



African natives in tropical savanna are nomads 

 and have herds of cattle, goats, and other animals 

 which furnish them with milk, meat, and blood meals. 



Tropical biomes 349 



