Amphibians and Reptiles oe Santa Marta 45 



one factor will account for the distribution of a fauna, and that zonal dis- 

 tribution of faunas based on temperature differences probably does not 

 occur on mountains. It should be understood that this is not equivalent to 

 saying- that there can be no such thing as zonal distribution on mountains. 

 Indeed, it may be accepted as a corollary of the proposition that the environ- 

 ment as a whole controls the distribution of each species, that when a large 

 number of conditions are changed at about the same place a considerable 

 part of the fauna may be affected. It has been shown that the dominant 

 habitats change at 2,200 feet, and this means a change in many conditions 

 of life. It is clear that zonal distribution occurs on San Lorenzo, and the 

 data indicate that temperature is probably not the principal factor. 



As stated, nine dry forest forms have not been found on the desert 

 at Santa Marta. Of these, eight have been found in dry forests elsewhere 

 on the plain. If there is a difference between the fauna of the desert and 

 dry forest, the factors are not evident. 



Of the lowland forms which do not get above 2,200 feet, five (lizards) 

 go a little higher and three range from 100 to 2,300 feet higher in artificial 

 clearings. This suggests that some other factors than temperature are, 

 under natural conditions, effective at this point in limiting the upward 

 range on San Lorenzo of the species of this group. 



Of the cloud forest species in all groups (18), twelve are known to 

 occur here or elsewhere in northern Colombia on the lowlands, which again 

 suggests that on San Lorenzo the temperature of this area is not the only 

 condition which limits the lower range of the species-. It is to be noted 

 that of the fourteen species known from the cloud forest and not lower 

 than 2,200 feet, ten are amphibians which quite certainly do not lay the 

 eggs in water, one being viviparous and nine more or less certainly known 

 to lay eggs which produce young in the adult form, while three, possibly 

 four, are associated with bromelias which do not descend lower. Further- 

 more, at least one lowland amphibian seems to be limited in its upward 

 distribution by the absence of standing water above 2,200 feet, since it 

 occurs well above that altitude apparently without breeding. In the cloud 

 forest, the nature of the forest, the absence of standing water and the 

 humidity are evidently factors with which to reckon. 



The wet forest comes down to the coast on the north side of the 

 mountains. Carriker (see p. 20) concludes from a study of the birds thar 

 the forest fauna on that side also comes down to sea-level, a conclusion 

 that is substantiated by the occurrence at Don Diego of Phrynonax poccilo- 

 jwtus and Phyllobates subpunctatus, species not found below 2,200 feet on 

 San Lorenzo. This lowering of the wet forest habitat is probably due in 

 large part to a greater rainfall, and while the temperatures are also lower 

 it is not possible that thev are as low as in the cloud forest. The greater 

 humidity and the forest are quite as likely to be critical conditons as is the 

 temperature. 



There is no reason to believe that the distribution of snakes is less 

 effected by differences in temperature than that of lizards, and yet the data, 

 while fragmentary, show less response on the part of the snakes to the 



