Abundance and Species Diversity of Ants in Forests of Yanbaru, the Northern Part of Okinawa Honto with Special Reference to Effects of Undergrowth Removal

To evaluate diversity of ant fauna in natural forests of Yanbaru, the northern part of Okinawa Honto, 30-minute samplings of individuals or nests were carried out. Through four series of collectings, 40 ant species were found, of which 32 were stenochoric (east Asian) species, including 14 species possibly endemic to the Ryukyus. Although there was no statistically significant difference in the ratios of stenochoric species and endemic species between with- and without-undergrowth plots, ratio of stenochoric species tended to be higher in without-undergrowth plots than in with-undergrowth plots (8/12). Simpson diversity (1 - D) and equitability index (J theta ), calculated using frequency of encounters with ants in 30 minutes, were 0.87 plus or minus 0.06 and 0.93 plus or minus 0.04 in with-undergrowth forests and 0.84 plus or minus 0.09 and 0.87 plus or minus 0.10 in without- undergrowth forests. Although values for with-undergrowth forests were significantly larger than those for without-undergrowth forests in the second series of collectings, there was no significant difference in other two series and combined data for three series. But J theta for combined data from with-undergrowth forests was larger than that from without-undergrowth forests at a nearly significant level (Mann-Whitney U-test; P=0.068). Both of 1-D and J theta based on the number of nests found in 30-minute samplings in intact natural forests inside U. S. Marine Corps Northern Training Area were 0.90, far higher than values for deciduous forests in Hokkaido and somewhat higher than natural evergreen forests in Iriomote Island, Okinawa.