Recent advances in understanding insect communities in tropical forests have contributed little to our knowledge of large-scale patterns of insect diversity, because incomplete taxonomic knowledge of many tropical species hinders the mapping of their distribution records. This impedes an understanding of global biodiversity patterns and explains why tropical insects are under-represented in conservation biology. Our study of approximately 500 species from three herbivorous guilds feeding on foliage (caterpillars, Lepidoptera), wood (ambrosia beetles, Coleoptera) and fruit (fruitflies, Diptera) found a low rate of change in species composition (beta diversity) across 75,000 square kilometres of contiguous lowland rainforest in Papua New Guinea, as most species were widely distributed. For caterpillars feeding on large plant genera, most species fed on multiple host species, so that even locally restricted plant species did not support endemic herbivores. Large plant genera represented a continuously distributed resource easily colonized by moths and butterflies over hundreds of kilometres. Low beta diversity was also documented in groups with differing host specificity (fruitflies and ambrosia beetles), suggesting that dispersal limitation does not have a substantial role in shaping the distribution of insect species in New Guinea lowland rainforests. Similar patterns of low beta diversity can be expected in other tropical lowland rainforests, as they are typically situated in the extensive low basins of major tropical rivers similar to the Sepik-Ramu region of New Guinea studied here.
Bibliographical noteFunding Information:
Acknowledgements We thank D. Bito, W. Boen, A. Borney, L. Cizek, G. Damag, A. Krasa, J. Kua, R. Kutil, R. Lilip, M. Manaono, M. Rimandai, S. Sau, G. Sosanika, D. Stancik, V. Iwam and D. Wal for technical assistance, and V. O. Becker, J. Brown, A. Cognato, L. Craven, K. Damas, C. Drew, J. D. Holloway, M. Horak, K. Maes, J. Miller, E. G. Munroe, M. Shaffer, A. M. Solis, D. Stancik, W. Takeuchi and K. Tuck for taxonomic assistance. More than 150 insect collectors contributed to the study. P. Herbert provided DNA barcodes; J. Leps advised on statistical analysis; R. Condit, H. L. Davies, O. Diserud, J. Chave, M. Heads, J. Hrcek, D. H. Janzen, O. T. Lewis, F. Ødegaard, D. Storch and C. O. Webb commented on the manuscript. This work was supported by the National Science Foundation (USA), Grant Agencies of the Czech Republic, Czech Academy of Sciences and Czech Ministry of Education, Darwin Initiative for the Survival of Species (UK), David and Lucile Packard Fellowship in Science and Engineering, the National Geographic Society (USA), and The International Centre for the Management of Pest Fruit Flies (Griffith University). We thank Papua New Guinean customary landowners for allowing us to work in their forests. We dedicate this work to the late Richard Kutil.