Canopy Ferns in Lowland Dipterocarp Forest Support a Prolific Abundance of Ants, Termites, and Other Invertebrates1

Abstract

The epiphytic Bird’s Nest Fern (Asplenium nidus complex) has a large basket-shaped rosette that accumulates leaf litter. We investigated the role of these ferns in supporting invertebrate populations in the primary lowland dipterocarp forest of Danum Valley, Sabah, Malaysia. Ferns were divided into three size classes: large (rosette diameter >60 cm), intermediate (30–60 cm), and small (<30 cm). Seven hectares of forest were surveyed: the canopy had a mean density of 30 large ferns/ha and 20 intermediate ferns/ha. Six large and five intermediate ferns were removed from the crowns of Parashorea tomentella (Dipterocarpaceae) at heights between 39 and 52 m. The largest ferns had fresh weights of ca 200 kg. The mean animal abundance in large and intermediate ferns was 41,000 and 8000, respectively. Termites and ants represented at least 90 percent of the abundance in these ferns. Of the 11 ferns, 4 contained a nest of Hospitalitermes rufus (Nasutitermitinae), while another contained a nest of an undescribed species of Hospitalitermes. An additional 56 small ferns were removed from the low canopy (2–6 m above the forest floor), of which only 1 contained a termite nest (Nasutitermes neoparvus). These results suggest that Bird’s Nest Ferns contain ca 0.5 million termites/ha and contribute almost one ton (dry mass) of suspended soil and plant material/ha. Five of the trees containing large ferns were fogged immediately before the removal of the ferns. From these samples we were able to estimate the total number of animals in each tree crown. When each estimate was added to the abundance in each fern, the results suggested that a single large fern may contain from 7 to 93 percent of the total number of invertebrates in the crown. Although these results must be treated with caution because of the small sample size, they have important implications for studies of canopy invertebrates.