36 
Psyche 
March 
ants, as well as of other kinds of animals, must be consider- 
able. It very possibly hastens the genetic divergence of local 
populations and plays an important role in the “exuberance’* 
and amplitude that characterizes evolution in the tropics. 
Probably as the fauna increases in size, in passing from 
temperate to tropical areas or from small islands to large 
ones, the diversifying effects of a kaleidoscopic population 
structure increase exponentially. 
There is abundant evidence that similar features of popu- 
lation structure occur in other groups of organisms in 
tropical forests. Aubrevi’le (1938), in his “mosaic” or 
“cyclical” theory of regeneration, has described a kaleido- 
scope pattern in forest trees of the Ivory Coast. Richards 
(1952) doubts whether the mosaic theory holds for all rain 
forest associations, but accepts its validity in special cases 
where certain conditions have been met. 
“The poor regeneration of the dominant species in 
African Forests seems in all probability to indicate that 
the composition of the community is changing. If the 
forest is in fact 'untouched and primitive’, as Aubreville 
c ] aims .... the changes must be cyclical as the Mosaic 
theory implies. On the other hand, if the community has 
undergone disturbance in the past, the present combina- 
tion of species [in a given sample plot] may be a serai 
stage and the changes part of a normal (not cyclical) 
process of development toward a stable climax”. 
Moreau (1948) finds patchiness a common feature in the 
distribution of rain forest birds in Tanganyika. Where a 
species is absent from a locality, it is usually replaced by a 
related species (from the same family), but not always, 
leaving some inexplicable gaps. The following example is 
typical : 
“Nearly all the montane forests of eastern Africa from 
Kenya southward are occupied by one or both of the little 
barbets, Pogoniulus hilineatus and Viridobucco leucomys- 
tax. On Hanang Mountain, where both these species are 
missing, Pogoniulus pusillus, normally a bird of deciduous 
trees at lower altitudes, appears in the mountain forests 
