Distribution and abundance of plants with extrafloral nectaries in the woody flora of a lowland primary forest in Malaysia
The first data on the taxonomic distribution and abundance of woody plants with extrafloral nectaries (EFN) from SE Asia are reported. The species richness and frequency of woody angiosperm plants with extrafloral nectaries was studied in the Pasoh Forest Reserve, a primary lowland forest in Peninsular Malaysia. EFN were present on 12.3% of the 741 species surveyed. 91 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 whereas EFN were rare in the more primitive subclasses of the Magnoliopsida and common in the more advanced taxa (Dilleniidae, Rosidae, Asteridae). Most common were flattened glands associated with the leaf blade. A comparison with data from the Neotropics showed a great similarity in regard to the taxonomic distribution of plants with EFN. EFN-plants occupied 19.3% of the cover of the Pasoh Forest 50 ha plot.
Species with EFN were under-represented among shrubs and trees of the understorey. We found an increase in the number of species with EFN as well as in their cover from the understorey to the canopy emergents. EFN were found more often among the abundant species (species with n>500/50 ha). Percentage occurrence and cover of EFN-bearing plants in the 50 ha plot of primary forest was lower than recorded for secondary habitats in tropical areas. At present, in the core zone of the Pasoh Forest Reserve which has been investigated only few species known to indicate disturbance occur. Therefore most of the recorded EFN-species cannot be regarded as secondary forest plants.
The interactions between ants and EFN-bearing plants appear to be rather facultative and nonspecific. In Pasoh we found 28 ant species from seven genera visiting EFN. Most of the EFN-associated ants belonged to the subfamily Myrmicinae while Ponerines were rare, a pattern which was also reported for the Neotropics.