Evolution temporelle des populations de Rhopalocères de deux collines boisées des environs de Yaoundé (Cameroun)

Résumé En Fr

During 7 consecutive years, the author has monitored the numbers and species composition of the butterfly community of two forested hills, Mount Fébé and Mount Messa, near Yaoundé (southern Cameroon). Butterflies were counted and identified by sight, their identity being checked by temporary capture when necessary. Observations were carried out along trails, between 9.30 am and 3.0 pm, seven times per month on the average. Out of a total of 774 species recorded at the two study sites (ca 560 of which being found at both places), only the more conspicuous and easily identified species and those observed at least once a month were taken into consideration for the present study (228 species). The results are displayed in the form of seven monthly histograms per year and per species, and of yearly averages for the seven years of the study. Those of 21 selected species are presented on figures 1-3 and 5-7. 176 (ca 77 %) of these more abundant butterfly species do not display statistically significant changes in numbers between months, contrary to a widespread assumption and Owen’s (1971) opinion. These species can therefore be regarded as «aseasonal» and considered as «aperiodic». Only 52 species (ca 23 %) display significant changes in numbers throughout the year and can be regarded as «seasonal» («periodic»). Only a few among the latter can completely disappear for months and be termed «cyclic». Species richness was always greater on Mt Messa than on Mt Febe. Throughout the year there was a slight, but significant, variation in butterfly species richness at the two sites, probably due to seasonal changes in the availability of caterpillar’s host plants.

Les résultats relatifs à l’observation de plus de 200 espèces de Rhopalocères pendant sept années consécutives montrent que, pour environ 80 % d’entre elles, l’activité ne varie pas de façon saisonnière ; celle des 20 % restants varie assez régulièrement au cours de l’année, mais seulement 8 % de ces espèces peuvent être qualifiées de «cycliques» ; la richesse spécifique ne varie que légèrement en fonction des saisons.