44 Alexander G. Ruthven 



tically the same, the ranges of but few of the species being affected at the 

 common boundary of the more open plains and scrub forest. 



There is a decided difference in the fauna roughly below and above 

 2,200 feet. Of a total fauna of twenty-three species in the dry forest, 

 thirteen species do not occur above 2,200 feet, five others occur higher only 

 in clearings, and still another is not known to breed above that altitude, 

 so that nineteen out of the twenty-three species are naturally limited in 

 upward range between 2,000 and 2,500 feet. The four species which range 

 higher are snakes. It will be noted that seven of the lizards out of sixteen 

 dry forest forms have not been found above 600 to 800 feet. These seven 

 undoubtedly range higher and were not found between 800 and 2,200 feet 

 because careful collecting could not be done in that region. The upper 

 limit may be placed tentatively at 2,000 feet, because they have not been 

 found at 2,200 feet, although some doubtless drop out well below this 

 altitude. In brief, then, none of the amphibians of the desert and dr\^ 

 forest (six species) apparently breed above 2,200 feet; the only lizards of 

 these habitats (16 species) ranging above this altitude are five which are 

 found in artificial clearings, and it is the distribution of the snakes which 

 seems to be little affected, four species out of six ranging higher. 



None of the eight forms found in the moderately wet forest, between 

 2,200 and 4,500 feet, are peculiar to this area. A number of forms have 

 not been found below it in this region, but these all range above it into the 

 cloud forest. The cloud forest fauna consists of eighteen species, of which 

 twelve have not been found below 4,000 to 4,500 feet. These are nine 

 amphibians, one lizard, and two snakes. Moreover, of the eight forms 

 which enter the moderately wet forest three forms (one amphibian and two 

 snakes) do not range entirely through the area, one (an amphibian) reaches 

 2,200 feet, and four (snakes) are found in the dry forest. In other words, 

 out of eleven forms of lizards and amphibians found in the cloud forest 

 not one occurs below 2,200 feet, and the cloud forest and dry forest faunas 

 are thus entirely different in respect to the lizards and amphibians and 

 overlap only when the snakes are added. 



As has been said, the moderately dry forest has no peculiar forms, 

 but is composed of species which range below or above it, or in both direc- 

 tions. It is thus to be considered as an intermediate zone in the distri- 

 bution of the reptiles and amphibians, and the fauna of the slopes falls into 

 three groups, distinct as to species — a desert and dry forest group, twenty- 

 four species ; a cloud forest group, fourteen species ; and a group of forms 

 of general distribution, four species (of snakes). This vertical distribution 

 corresponds to the vertical distribution of dominant terrestrial habitats. 



Bnvironmental Factors in the Vertical Distribution: It should be 

 clearly understood by geographers that geographic data yield only indirect 

 evidence of the environmental factors in distribution. It would be easy 

 to attribute the apparent zonal distribution above described to temperature, 

 to moisture, to the nature of the ground cover, or other factors, but this 

 would be pure assumption. The writer has expressed the opinion^ that no 



•'■ Tlic Geographical Rcficiv, X, pp. 241-248. 



