The geographic pattern of nest height in a neotropical arboreal termite

摘要

Nasutitermes corniger tends to construct its distinctive, conspicuous nests at the bases of trees in the northern West Indies versus well above ground on trunks or branches in Trinidad & Tobago and further south. By means of data from 32 localities from the Equator to 17 degrees north latitude, we describe the geographic pattern of nest-height variation. The localities are from both continental areas (mainland and continental islands) and oceanic islands. The latter are all to the north of the former. If nest-height variation is mainly or solely due to abiotic (climatic) factors, a more or less monotonic south-north decline is predicted. If it is mainly due to biotic factors, a change in the trend is expected at a distinct latitudinal transition. The data show an overall tendency for nest height to decrease further from the Equator. However, there is a distinct change in the slope, consistent with the biotic hypothesis. Against expectation, this does not occur between Tobago (continental island) and Grenada (oceanic island) but between Venezuela (continental mainland) and Trinidad (continental island). The biotic factors affecting nest-site in this species are not known. However, the data are consistent with the hypothesis that the species involved are affected by biotic relaxation during the several millennia since Trinidad and Tobago isolated from the mainland.