Ecology of Marcus Island— Sakagamx 
87 
Fig. 9 
along two paths penetrating the E. triangle 
(Figs. 1, 8). The coconut palm, which formerly 
had been the leading member of the arboreal 
stratum, was represented by only three under- 
nourished saplings, as is indicated by the crosses 
in Figure 1. 
The simplicity of the herbaceous layer was 
much more surprising. It was practically no 
more than an overwhelming dominance of 
Ipomoea pes-caprae. The density was also highest 
in the E. triangle, except its NW. section, but 
the stout runner extended its domain through- 
out the island except on the outermost margins 
of the sandy beaches. In the center of the E. 
triangle, this creeper constituted a pure com- 
munity of about 1 sq. km., excluding all other 
herbs; there one could walk hundreds of meters 
on a thick bed of intermingled vines, both 
Fig. 10 
living and withered, without touching the soil 
surface (Fig. 4). 
Consequently, other herbs and grasses, al- 
though most of them were very vigorous weeds, 
grew only in limited areas, apparently where 
the pressure of Ipomoea was not conspicuous, 
namely, in wooded edges, roadsides, and the 
MW. section of the E. triangle. In such zones, 
Portulaca and Cencbms were dominant mem- 
bers of the lower stratum, and Pennisetum, Ni- 
cotiana, Eleusine , and S one bus of the higher 
one. The area richest in species was the con- 
fluent point of the runway and the other broad 
road, where most species of herbs and grasses 
were collected. On the other hand, no plants 
other than Ipomoea were discovered on the 
beaches ( Fig. 9 ) . From this description, it may 
be recognized that the island is extremely simple 
in both floristic and vegetational aspects. 
FAUNA 
The birds and mammals collected or observed 
in our survey were described by Kuroda ( 1954) . 
