Seasonality of litter insects and relationship with rainfall in a wet evergreen forest in South Western Ghats

Abstract

The seasonality of litter insect abundance and its relationship with rainfall was analyzed in a wet evergreen forest on the windward side of south Western Ghats. Monthly litter samples were collected using Berlese funnels during 4 seasons of a year: southwest monsoon season June-August), northeast monsoon season (September-November), summer (March -May) and pre-summer season (December-February). Insect fauna as a whole showed no seasonal variation in abundance, however, some individual insect orders showed significant seasonal variation. Overall insect fauna and individual orders were distributed independently relative to rainfall. All insect orders with the exception of Psocoptera were present during all four seasons. Coleoptera (42%) was the dominant group in all seasons followed by Formicidae (12.3%), insect larvae (10.1%), Collembola (9.2%) and Thysanoptera (8.9%). Exceptionally high abundance of Ptiliidae contributed to the unprecedented abundance of litter Coleoptera. The aseasonality of litter insect fauna as a whole is attributed to year-round availability of rainfall and the absence of severe summer conditions.

Figure 1.

(A) Map of south Western India showing the location of the Western Ghats and (B) study site in the Wayanad region of the Western Ghats

Figure 2.

Rainfall received and litter insect abundance in the evergreen habitat during the study period 2002–03.

Figure 3.

Dendrogram based on hierarchical agglomerative clustering (group-linking) of litter insect faunal assemblage at Periya during 4 different seasons of the study period 2002–03.