Habitat and successional status of plants in relation to the communities of their leaf-chewing herbivores in Papua New Guinea

1 The spatial distribution of 30 woody species (15 species each of Euphorbi aceae and Moraceae) and their associated leaf-chewing communities (Orthopte ra, Phasmatodea, Coleoptera and Lepidoptera) were studied in coastal, river ine and rain forest habitats. A successional series, from abandoned gardens to primary forest, was examined. Host plant records for more than 27 000 i nsects, all verified by feeding experiments, and spatial distribution of al most 9000 plant specimens were evaluated. 2 Phylogenetic (taxonomic) relatedness of host plants explained 56% of the variability in the composition of their herbivore communities, while the ec ological (distribution) similarity of plants explained only 4%. 3 The successional optimum of plant species was not an important determinan t of the composition of their herbivore communities. 4 Neither plant successional optimum nor plant palatability to a generalist herbivore were correlated with the number of species, abundance or host sp ecificity of its herbivores, nor was there a correlation between a plant's palatability to a generalist herbivore and its successional optimum. 5 Herbivore communities became dominated increasingly by a few abundant spe cies in later stages of succession. 6 On average, Ficus species had lower palatability and supported more speci es of herbivores than species of Euphorbiaceae. The abundance of herbivores and their dominance index were not significantly different between the two plant families. 7 These results contradict several previous studies of successional trends in temperate regions. Many tropical successions, however, start with pionee r trees, rather than with annual herbs, and may present a permanent and pre dictable habitat for insects even at the earliest stages, with no advantage for polyphagous species. Numerous pioneer trees in the tropics possess ant i-herbivore defences, resulting in their low palatability to generalists, i ncreased host specificity of herbivores, and often idiosyncratic compositio n of herbivore communities. Even plant traits such as species richness of t heir herbivores or palatability may have a phylogenetic component which sho uld not be ignored.