frt- 3^ ^^^.. 





FIG. 27-4 Zebras in Tanganyika (courtesy S. Glidden Baldwin). 



BIOCIATIONS 



Brief attention has already been given to 

 desert and grassland (Table 25-1 ) animals in tropical 

 regions. We may recognize one or more tropica! 

 savanna biociations in Africa to include both the more 

 strictly grassland animals and those of the forest- 

 edge. On the basis of differences in bird distribution, 

 Moreau (1952) recognizes Sudanese arid, Somali 

 arid, southwest arid, northern savanna, and southern 

 savanna faunal areas. Among mammals, this com- 

 munity is especially characterized by extensive num- 

 bers of wildebeest, zebras, gazelles, antelopes, and 

 lions (Table 24-1) that occur in open country; and 

 the elephant, hippopotamus, rhinoceros, giraffe, wart- 

 hog, and African buffalo that spend considerable 

 time in thickets, swamps, and forests. The habits of 

 many of these animals have been described bv Selous 

 (1908), Chapman (1922), and Darhng '(I960). 

 Moreau (1935, 1937) has worked with the birds. 

 Termites are world-wide in distribution in tropical 

 regions and their large mound nests are conspicuous 

 in some parts of the savanna. Another noteworthy 

 insect of the savanna is the tsetse fly, the vector of a 

 parasite which is a scourge to both man and beast 

 (Buxton 1955). Perhaps another tropical savanna 

 biociation may be distinguished in Australia where a 

 variety of marsupials are characteristic, and there are 

 ecological equivalents for birds and other animals. 

 However, the savannas of South America lack these 

 herds of large mammals so conspicuous in Africa, 

 and this is doubtless due to the savannas of South 

 America being serai in nature and relatively recent 

 in origin. We do not at present recognize a climax 

 savanna biociation in South America. Forest and 

 forest-edge communities have been distinguished for 

 the tropical avifauna of Mexico (Edwards and 

 Tashian 1959). 



The animal inhabitants of the tropical forest biome 

 differ so greatly in taxonomic composition on the 



different continents that they are placed in three 

 different zoological regions. We may therefore desig- 

 nate the Indo-Malayan, Ajrican, and American trop- 

 ical forest biociations. It would be worthwhile at this 

 point to re-read the discussion of these three zoolog- 

 ical regions (Chap. 20) the better to become more 

 acquainted with the more conspicuous kinds of ani- 

 mals that occur in each. Noteworthy studies of the 

 animals of the American tropics are those of Bates 

 (1864), Belt (1873), Beebe et al. (1917, 1947), 

 Haviland (1926), Allee (1926), Strickland (1945), 

 Goodnight and Goodnight (1956). 



PALEO-ECOLOGY 



The tropical forest is of very great age and, 

 along with associated habitats, may represent the 

 center of origin for many modern groups of both 

 plants and animals (Darlington 1957). In past geo- 

 logical ages both on the Western and Eastern Hemi- 

 spheres, the tropical forest has expanded over great 

 areas when climates were warm and moist and con- 

 tracted when they became dry and cool. Perhaps, if 

 one were to work out a phylogenetic tree, all other 

 biomes could be traced back in origin to the tropical 

 biota of Mesozoic and Paleozoic times. Arctic com- 

 munities have been derived from temperate ones, and 

 temperate communities from tropical ones, as organ- 

 isms became adapted to occupy climatic and environ- 

 mental conditions that differed more and more from 

 the primitive optimum of tropical regions. This, 

 however, is conjecture. 



In the Andes of South America it is apparent 

 that the fauna of the lowland rain-forest (tropical 

 zone ) long antedates the elevations of the mountains. 

 After the mountains were formed, they were in- 

 vaded by those species of plants and animals adapted 

 to the lower temperatures and other differences in 

 habitat moving gradually upward. The animal life 



344 Geographic distribution of communities 



