Stratification and diel activity of arthropods in a lowland rainforest in Gabon

Abstract

The abundance, activity and species richness of arthropods, particularly of insect herbivores, were investigated in the upper canopy and understorey of a lowland rainforest at La Makande, Gabon. In total 14 161 arthropods were collected with beating, flight interception and sticky traps, from six canopy sites, during the day and at night, from midJanuary to mid-March 1999. The effects of stratum were most important, representing between 40 and 70% of the explained variance in arthropod distribution. Site effects represented between 20 and 40% of the variance and emphasized the need for replication of sampling among canopy sites. Time effects (diel activity) explained a much lower percentage of variance (6-9%). The density and abundance of many arthropod taxa and species were significantly higher in the upper canopy than in the understorey. Arthropod activity was also higher during the day than at night. In particular, insect herbivores were 2.5 times more abundant and twice as speciose in the upper canopy than in the understorey, a probable response to the greater and more diverse food resources in the former stratum. Faunal overlap between the upper canopy and understorey was low. The most dissimilar herbivore communities foraged in the understorey at night and the upper canopy during the day. Further, a taxonomic study of a species-rich genus of herbivore collected there (Agdus, Coleoptera Buprestidae) confirmed that the fauna of the upper canopy was different, diverse and very poorly known in comparison to that of the understorey. Herbivore turnover between day and night was rather high in the upper canopy and no strong influx of insect herbivores from lower foliage to the upper canopy was detected at night. This suggests that insect herbivores of the upper canopy may be resident and well adapted to environmental conditions there.

Optimisation of photosynthetic carbon gain and within-canopy gradients of associated foliar traits for Amazon forest trees

“…Studying upper-canopy leaves from across the Amazon Basin, Fyllas et al (2009) also observed significant variations in foliar carbon content, relating this to variations in M A and the extent of investment in constitutive defenses. Consistent with this and the observed positive vertical gradient in [C] DW both between and within trees is the tendency for leaves higher up rain forest canopies to have greater levels of carbon based defense compounds (Lowman and Box, 1983;Downum et al, 2001;Dominy et al, 2003), this perhaps being associated with higher abundances of herbivores such as insects and other arthropods also occurring there (Sutton, 1989;Kato et al, 1995;Koike et al, 1998;Basset et al, 2001).…”

Forest Structure and Composition Affect Bats in a Tropical Evergreen Broadleaf Forest

“…Certainly, a high insect abundance (i.e., bat food) has been associated with the canopy of Neotropical rainforests [72][73][74], as food resources for phytophagous insects (e.g., foliage, flowers, fruits) are more abundant in the canopy [75], and there is a greater diversity of niches than in the midstory or understory [76].…”

Body size, energy consumption and allometric scaling: a new dimension in the diversity?stability debate

“…Note also that the real value of areas scanned are likely to be smaller than ulτ 1 , as far as arthropods are only active during some parts of the day (Basset et al, 2001). We thus conclude that arthropod runners, crawlers and walkers with linear body size not exceeding several millimetres can yet be residents.…”