Influence of rainfall levels and the Petit Saut reservoir in French Guiana on the distribution of Sphingidae (Lepidoptera)

The family Sphingidae has an important potential as bio-indicators given the 118 species so far enumerated in French Guiana. For instance, more than 25,000 individuals from 104 species have been captured during 90 monthly censuses between January 1990 and October 1997 in the region of Petit Saut, a low-altitude primary forest. Among these species, seven are considered as uncommon on the site of Petit Saut. Therefore, ca 50 % of the species with a sufficient number of individuals for the analysis (n = 30) display particular characteristics: the probability of occurrence differs significantly between months for 14.5 % of them, and for the majority of the species of this family seasonal variations in populations abundances are not linked to rainfall, which is usually the most important ecological factor in this environment, temperature being constant in Guianan forest. These fluctuations are therefore due to other factors. The filling of the dam reservoir affected about a third of the species. Adaptations to variations in environmental conditions are not identical across all species. Certain species were not affected by environmental modifications while others grew up taking advantage of these changes and colonized new biotopes, and others decreased.