ECOLOGICAL CHARACTERISTICS OF MARIANA ISLANDS. 17 
in the southern part of Guam as well. On Orote Peninsula, on Cabras Island, and 
in the Talofofo region, as mentioned by Safford, “the growth of Cycas trees, with 
their cylindrical scarred trunks and luxuriant fronds, strongly recall ideal pictures 
of the vegetation of the Carboniferous age, in which the Cycadacee formed so 
important a part”’ (loc. cit., p. 253). 
The foregoing detailed description of the forests clearly indicates the type of 
plant association in which Partule are found most abundantly. Additional 
features impress the observer, but they are secondary in value. For example, there 
are four general levels or “‘stories”’ in the thickest bush, namely, (1) the high trees, 
(2) the shrubs and Pandanus, (3) the cycads and taller ferns, and (4) the succulent 
herbs such as Canna, turmeric, and the like. Owing to extensive wood-cutting, the 
first named may be sparse or absent. The distinctions in question are involved in 
Partula ecology only to the extent that the highest story is not invaded by the 
animals, which prefer the levels nearer to the ground; by way of contrast, in the 
Society Islands Partula attenuata is confined to the highest branches and leaves of the 
lofty trees, while another species of Tahiti, P. producta, lives always on the ground. 
The types of Guam agree closely with the more typical Polynesian forms. 
There is considerable variation in different places as regards the proportionate 
numbers of the component plants. In some instances, Pandanus will be dominant; 
in others, such as the Orote plateau, Cycas is the more abundant; while on Cabras 
Island, the ficoids constitute a far larger percentage than elsewhere. But the 
abundance of a particular kind of plant in no way determines the prevalence of a 
given species of Partula, or indeed the occurrence of any Partule whatsoever—a point 
that has been sufficiently discussed in the volume on the Tahitian species. Given the 
requisite amount of shade, of moisture, and of the humus for feeding, the animals will 
be found; specific botanical characteristics enter into the situation to the extent that 
a sufficiently thick growth can be constituted only by plants of suitable habits. 
As regards the density of vegetation, one may distinguish about eight degrees 
of compactness, from the thick forest at one extreme to the thicket, the scattered 
clush of the plantation borders, the sparser growth of village environs and coastal 
bearings, finally to the treeless open ground of the “mesetas”’ or savannas. In the 
Mariana Islands, Partule have been found in regions of at least three degrees of 
density, namely, forest, thicket, and scattered bush, whereas the Polynesian species, 
in the author’s experience, exist mainly in vegetation of the first or most dense 
degree, rarely exhibiting any tolerance of the thicket conditions, excepting in 
P. hyalina of Tahiti and the Cook Islands. A notable instance in the present group 
is that of the Chalankiya locality in Saipan, where as many as 30 partule were 
found on the under side of a single leaf of a caladium, growing in an area of the third 
degree of density (plate 9, a and B). In brief, then, the Mariana species are not so 
closely restricted to the forests remote from the sea as they generally are elsewhere; 
many times in Guam and Saipan, unusual numbers were collected from the thickets 
only a score of yards within the actual strand, or virtually at the water’s edge itself 
(plate 5 B). Obviously the Mariana species differ constitutionally from the majority, 
as manifested by their existence in drier and more open situations. 
