Journal of Biogeography {J. Biogeogr.) (2005) 32, 1303-1314 ORIGINAL An altitudinal comparison of caterpillar ARTICLE (Lepidoptera) assemblages on Ficus trees in Papua New Guinea Vojtech Novotny^*, Scott E. Miller^, Yves Basset^, Lukas Cizek\ Karolyn ^ Darrow^, Borenke Kaupa*, Joseph Kua'' and George D. Weiblen^ 'institute of Entomology, Czech Academy of ABSTRACT Sciences and Biological Faculty, University of Aim This analysis of caterpillar (Lepidoptera) beta-diversity between tropical South Bohemia, Ceske Budejovice, Czech Republic, ^National Museum of Natural lowlands and highlands attempts to separate the effects of between-site ( 1 ) turnover History and National Zoological Park, of herbivore species on particular host plants, (2) changes in host use by herbivores, Smithsonian Institution, Washington, DC, and (3) turnover of plant species on changes in herbivore assemblages. USA, ^Smithsonian Tropical Research Location Two rain forest areas 130 km and 1700 altitudinal metres apart were Institute, Balboa, Ancon, Panama, ''New studied in Papua New Guinea: one in the lowlands (100 m a.s.l.) on the northern Guinea Binatang Research Center, Madang, coast of the island and one in the central New Guiñean cordillera at 1800 m a.s.l. Papua New Guinea and ^Department of Plant Biology, University of Minnesota, St Paul, MN, Methods The analysis is based on caterpillar feeding records obtained by USA quantitative sampling and rearing of caterpillars from four Ficus species studied in the mountains and 21 Ficus species and 62 plant species from other genera and families studied in the lowlands, including three Ficus species studied in both areas. Results Only 17% of species feeding on Ficus in the highlands also occurred in the lowlands. These species represented 1-46% of individuals in caterpillar assemblages on particular Ficus hosts. Widespread species included both Ficus specialists and generaUsts feeding on numerous plant famihes. Some of the Ficus speciahsts changed their preferred host species with altitude. High species turnover was not explained by changes in the species composition of host plants with altitude as lowland and montane assemblages feeding on the same Ficus species showed high turnover. Despite the rarity of widespread caterpillars, the lowland and montane Ficus assemblages were remarkably similar in their dominance structure, species richness, host specificity, generic composition and familial composition. Main conclusions PicMs-feeding Lepidoptera assemblages between tropical lowlands and highlands are characterized by substantial species turnover not explained by altitudinal changes in the composition of the vegetation. Further, species-rich plant genera can support caterpillar assemblages with relatively low beta-diversity compared with species-poor genera as caterpillars can switch their host preferences from one congeneric host species to another along an altitudinal gradient. Closely related plant species can thus represent a broad, continuously distributed resource along such gradients. "^Correspondence: Vojtech Novotny, Institute of Keywords Entomology, Branisovska 31, CZ 370 05 Ceske Budejovice, Czech Republic. Beta diversity, cryptic species, elevation gradient. Ficus, host specificity, E-mail: [email protected] Lepidoptera, Malesia, rain forest, species diversity, species turnover. geographical scales (Hebert, 1980; McCoy, 1990; Allison et al, INTRODUCTION 1993; Fernandes & Lara, 1993; Olson, 1994; Brehm & Fiedler, Gradients in environmental variation can cause substantial 2003). For instance, global maxima of plant diversity, measured species turnover with altitude and are thus among the most as the number of plant species per 10,000 km^, are associated pervasive factors explaining species diversity on larger with altitudinal gradients in the tropics (Barthlott et al, 1996). 2005 Blackwell Publishing Ltd www.blackwellpublishing.com/jbi doi:10.1111/j. 1365-2699.2004.01225.x 1303 V. Novotny ef al. We can only speculate that a similar pattern applies to spanning the northern coastal lowlands and the central New insects, as broad patterns of insect diversity and distribution Guiñean cordillera, dominated by the Mt Wilhelm massif are difficult to study in the tropics. The integration of local (4509 m a.s.l.). studies into regional databases is often impossible as many The lowland study area was located near Madang town, specimens are classified as unnamed morphospecies, which Madang Province. Fieldwork was concentrated in primary and cannot be cross-referenced geographically (Janzen, 1992; secondary lowland forests within a 10 x 20 km area, near Kitching, 1993). Even with voucher specimens available for Baitabag, Ohu and Mis villages (145°41-47' E, 5°08-14' S, comparisons between geographical areas, it is often difficult to c. 0-200 m a.s.l.). The montane study area was situated near differentiate sibling species due to poor taxonomic knowledge Kundiawa town, Chimbu Province. Fieldwork was concentra- and scarcity of collections. In New Guinea, for example, ted in primary and secondary forests and the partially limited data are available for only a few of the better known deforested landscape around Mu Village (145°02' E, 6°05' S, taxa (Miller, 1996), such as cicadas (de Boer & Duffels, 1996), 1800 m a.s.l.). butterflies (Parsons, 1999), and aquatic Heteroptera (Polhe- The Madang area has a lowland humid climate with mild mus & Polhemus, 1998). drought from luly to September, characterized by the rainfall Beta-diversity of herbivorous insects is a combination of seasonality index (the sum of mean monthly rainfalls for the between-site ( 1 ) turnover of herbivore species on particular host three consecutive wettest months divided by the sum for the plants, (2) changes in host use by herbivores, and (3) turnover of three consecutive driest months) of 2.6. The average annual plant species. The relative importance of these factors in the rainfall is 3558 mm and the annual average temperature is tropics is unknown as virtually all studies along altitudinal 26.5 °C (McAlpine et al, 1983). gradients analysed only overall patterns of insect beta-diversity The Kundiawa area has a lower montane humid climate on diverse vegetation, which also varied with altitude. The beta- with a mild dry season from June to August (rainfall diversity of plants can be separated from that of their insect seasonality index 2.6, average annual rainfall 2249 mm). herbivores by the analysis of herbivorous assemblages on a Long-term records on temperature are not available. The particular plant species at different altitudes. However, such temperature for the study area was therefore extrapolated, studies are surprisingly scarce (Allison et al, 1993). using regressions and data for nearby Mt Hagen (1630 m) and Steep altitudinal gradients in environmental parameters Wabag (1980 m) obtained from McAlpine et al (1983). The including temperature, rainfall and prédation (Givnish, 1999) annual average temperature was thus estimated at 17.5 °C. lead to the expectation of high species turnover in insect herbivores apart from changes in plant composition, but this Study plants hypothesis has not been tested. There seems to be no altitudinal change in herbivore species richness per host plant Ficus (Moraceae) is a large, pantropical genus with over species (c£ Basset, 1996; Novotny et al, 2002a). The data on 750 species, representing an important component of altitudinal trends in host specificity are not available as most tropical floras (Berg, 1989; Basset et al, 1997). New Guinea studies have focused on tropical lowlands (Novotny & Basset, is a major centre of diversity in the region, with 150 in press). Finally, there is no theoretical framework for described species (c. 20% of the world species count) from predicting dominance structure in herbivore communities all subgenera and a high degree of endemism (53% of (Novotny et al, 2002c). species; Corner, 1967). Ficus is an important component of Recent studies suggest that many herbivorous insects feed on rain forest vegetation, particularly in the lowlands. Our multiple closely related plant species in tropical forests (Novotny lowland and montane study areas hosted 51 and 19 sympatric et al, 2002a,b). This result raises a possibility that the turnover Ficus species, respectively (Appendix 1). of congeneric plant species with altitude may not necessarily lead Twenty-one locally common species of Ficus, including to turnover in the assemblages of insect herbivores. The present 19 forest and two seacoast species, were selected for the study study explores this possibility as it examines changes in species of their caterpillar assemblages in the lowland study area. Four composition of caterpillars (Lepidoptera) feeding on the large species were studied in the montane study area, including one plant genus Ficus (Moraceae) between montane (1800 m a.s.l.) species restricted to montane forest (-F. iodotricha) and three and lowland (100 m a.s.l.) sites in Papua New Guinea. This widespread species {Ficus copiosa, F. dammaropsis and altitudinal range thus encompasses a substantial floristic and F. wassa) also studied in the lowlands (Appendix 1). These structural change that occurs between 800 and 1200 m in three species have a wide altitudinal range from 0 to 2300- tropical forests (Ashton, 2003). 2600 m. Ficus wassa and F. copiosa are predominately lowland species as the median (1-3 quartile) altitude of specimens from New Guinea deposited at Lae Herbarium was 100 (25-1186) m METHODS for F.