Arthropod Abundance, Canopy Structure, and Microclimate in a Bornean Lowland Tropical Rain Forest¹

Abstract

This study applies a novel, vertically stratified fogging protocol to document arthropod abundance, density, and biomass across a vertical gradient in a primary, lowland dipterocarp forest canopy in Borneo. We fogged arthropods at 5 m vertical intervals and 20 m horizontal intervals along six full‐canopy transects and measured leaf surface areas along the same transects. The results show that arthropod biomass in the aboveground regions was 23.6 kg/ha, the abundance was 23.9 million individuals/ha, and the density on leaf surfaces was 280 individuals/m2 leaf area. All three numbers are five to ten times higher than estimated by previous surveys of tropical lowland rain forest canopies using mass‐collection techniques. Arthropod abundance and biomass were analyzed in relation to canopy structure, composition, vapor pressure deficit (VPD), photosynthetic photon flux density (PPFD), and height. Using stepwise regression we found that 13 of 14 arthropod groups had significant positive relationships with one‐sided leaf area, 11 had significant negative relationships with VPD, 3 had significant relationships with height, and none showed positive relationships with light. Classifying the 14 taxa based on their responses to leaf area and VPD created three groups that corresponded roughly to the biology of these taxa. This study suggests that the biomass and abundance, and perhaps therefore—by extrapolation—the biodiversity, of tropical canopy arthropods may be very much higher than previously estimated.

On the vapour trail of an atmospheric imprint in insects

“…The integration of daily mean humidity is then transferred isotopically into the chitin (C 8 H 13 O 5 N), together with a systematic (and constant) enrichment factor when the insect moults [12], as we have shown for individual cockroaches from natural habitats, including those specifically associated with epiphytic bird's nest ferns in a rainforest canopy in Borneo (figure 2). Arthropods of this particular forest show a strong response to temperature and moisture gradients [5], which are a common feature of tropical forest canopies, often being associated with vertical stratification [2]. However, bird's nest ferns buffer microclimatic fluctuations [13], and provide discrete habitats for their invertebrate inhabitants [9].…”

“…Insects and other tracheated arthropods, which make up three-quarters of all animal species [4], show a strong response to moisture gradients in tropical forests [5]. These animals respire through a series of spiracles, the tracheal openings which allow air to diffuse into the animal while optimizing gas exchange and controlling respiratory water loss [6].…”

Biodiversity hanging by a thread: the importance of fungal litter-trapping systems in tropical rainforests

“…This represents a considerable proportion of arthropods found in the forest canopy as a whole. Based on previous work [19] in the same forest, which showed that 60.7 + 5.1% (n ¼ 6) of arthropods were found in the lower 16 m of the canopy, approximately 43 per cent of canopy arthropods could therefore be dependent on these networks.…”

Estimating biodiversity impacts without field surveys: A case study in northern Borneo

“…For the bottom-up methods used in this analysis, an arthropod census must be taxonomically broad, use indiscriminate sampling methods designed to sample arthropods with different habitat preferences, and be drawn from a complete and clearly defined contiguous area. Of the arthropod censuses conducted in Borneo (Kitching et al 2001;Basset et al 2003;Beck et al 2006;Dial et al 2006;Beck and Rüdlinger 2014;Stork 2015, and references therein), we are not aware of any that meet these three criteria. The most comprehensive census of which we are aware that meets these criteria is a survey of lowland tropical forest in the San Lorenzo forest, Panama (Basset et al 2012).…”