THE BiULUCilCAL CONQUEST OF Till-: Would u) 



about through the underbrush. During the daytime tiie wonderful 

 morphous butterflies, brilhant spots of blue, add a touch of col.,!- to 

 the picture. 



The mid-jungle contains the most life. Here iimumeraljlc birds, 

 curassows, guans, pigeons, barbets, jacamars, trogons, and smaller 

 feathered species abound, in company witli ant-eaters, sloths, squir- 

 rels, bats, coatis, and small monkeys such as marmosets. 



The upper jungle of the tree-tops is the mo.st difficult region to 

 know. Red howlers and be.som monkeys move about in the tree- 

 tops, and occasional glimpses may be had of toucans, macaws, and 

 great flocks of parakeets and parrots that live ther(\ Fierce ants 

 prevent tree-climbing, and the relatively great height and mass of 

 foliage make living things not easily acce.ssible to observers in this 

 upper layer of the tropical rain forest. 



These two forests, the northern maple-birch and the jungle, by their 

 entirely dissimilar populations illustrate contrasts that might be 

 found in many parts of the world. Sometimes conditions in widely 

 separated areas may be almost similar, with diverse populations 

 inhabiting them, and again, localities close at hand may show remark- 

 able diversities in their living inhabitants. When regions far apart 

 have similar populations, which does not commonly happen, the 

 biologist is faced by a puzzling problem. 



The Why of Distribution 



Jordan and Kellogg ^ give three laws to account for the distril)u- 

 tion of organisms which they state as follows : E\ery species is found 

 everywhere that conditions are suitable for it unless (I) it was unable 

 to reach there in the first place, or (2) having reached there it was 

 unable to stay because it could not adapt itself to the new condi- 

 tions, or (3) having entered the new^ environment it became modified 

 into another species. It is not only the normal habitat that deter- 

 mines the presence of a given plant or animal, but its accessibility 

 from the place of origin. 



Although every species originated historicaUy from some i)receding 

 species at some definite place, its present distribution results from 

 the working of two opposing factors, expansion and repression. The 

 factors of expansion will be mentioned later, lliose of n^pression 

 are, first, inadequate means of dispersal because slow-moving animals 



1. Jordan, D. S.. and KellofiK. V. L., Animal Life. Appletou, 190(). 



