Ant Fauna of the Lower Vegetation Stratum in Pasoh Forest Reserve with Special Reference to the Diversity of Plants with Extrafloral Nectaries and Associated Ants

Abstract

Associations of ants with plants can be regarded as one reason for the high abundance and diversity of ants in the tropics. A full spectrum of ant-plant partnerships is realised in the tropical forests, ranging from loose, opportunistically changing associations to obligate symbioses. In the simplest case the plant offers nutrient-rich nectar from special glands (extrafloral nectaries) which attracts ants. These associations are characterised by very different intensities of use of the plants resources and, therefore, also varying mutual dependence of the partners. From Southeast Asia almost no information on plants with extrafloral nectaries (EFN) and visiting ants existed, this is especially true for primary forests. Therefore the species richness and frequency of woody angiosperm plants with EFN were studied in the lowland dipterocarp forest of Pasoh Forest Reserve (Pasoh FR) which has a well-known tree-flora. EFN were present on 12.3% of the 741 species surveyed and comprised 19.7% of all tree individuals of the Pasoh Forest 50 ha plot. Ninetyone plant species belonging to 47 genera and 16 families were found to have EFN. Euphorbiaceae, Dipterocarpaceae, Rosaceae, Leguminosae and Ebenaceae were the families most frequently bearing EFN. Most common were flattened glands associated with the leaf blade. We found an increase in the number of species as well as in the percentage of individuals from the understorey to the canopy emergents. EFN were found more often among the abundant species (species with N > 500 trees). The interactions between ants and EFN-bearing plants appeared to be rather facultative and non-specific. In Pasoh FR 38 ant species from 18 genera of 5 subfamilies were collected at EFN. The majority of the EFN-associated ants belonged to the subfamily Formicinae while Ponerines were rare. Most species rich were members of the genera Polyrhachis, Camponotus and Crematogaster. The overlap in ant fauna composition between the different sites was low, suggesting a rather mosaic-like pattern of ant colonisation. In comparison to disturbed habitats less ants were found on EFN in primary forests. Data of diversity and abundance of EFN and associated ant fauna are also presented from 3 other forest areas in Malaysia. In addition, ant fauna on the lower vegetation in general was studied with transect surveys and baiting experiments. In general, ant species richness and activity was lower in the vegetation than on the ground. Baits were detected faster and to a higher percentage in more open areas in Ulu Gombak than in Pasoh. Details on ant diversity, abundance and species interactions at baits are reported. All ants found at EFN were also collected on honey as well as protein baits suggesting a rather generalised use of food resources. Long-term functional studies are needed to begin to reveal the role of non-specific ant-plant interactions in undisturbed compared with secondary habitats.