Local and regional diversity of frog communities along an extensive rainforest elevation gradient in Papua New Guinea

Abstract

Rainforests on high tropical mountains are globally important species diversity hotspots. We studied amphibians along an extensive rainforest elevation gradient on Mt. Wilhelm (4509 m) in Papua New Guinea. We established eight sites at 500 m elevation increments between 200 and 3700 m a.s.l. and relate their community composition to the known species pool of New Guinea island. We recorded 3390 frogs from 55 species, which is three times more species than at any local community along the elevation gradient. Species diversity peaked at 1700 m a.s.l. for Mt. Wilhelm communities, and at 500–1100 m a.s.l. in the broader New Guinea fauna, probably reflecting increasing speciation and decreasing dispersal rates with increasing elevation. The beta diversity between frog communities was high and increased with increasing elevation. The change in frog community composition across 500 m elevation corresponded to the change over 200 km distance within lowland forests. A majority of frog species were distributed over narrow <500 m elevational ranges, at Mt Wilhelm and the New Guinea fauna more broadly. We did not detect Rapoport's pattern of wider elevation range for species at higher elevations than for lowland species, for Mt. Wilhelm communities or the New Guinea fauna. The high beta diversity patterns along elevation gradients generated by rapid species turnover with narrow elevation ranges make frog communities vulnerable to change in environment, including climate change.Abstract in Melanesian Pidgin is available with online material.

Figure 5 from: Richards SJ, Oliver PM (2024) Two new species of torrent-breeding treefrogs (Anura: Pelodryadidae: Litoria) from hill forests on the southern edge of New Guinea’s Central Cordillera. Vertebrate Zoology 74: 417-433. https://doi.org/10.3897/vz.74.e123251

“…Within the Kikori basin there appears to be high turnover of species across sites (beta diversity), a pattern that is particularly pronounced across different elevations . These broad patterns support the hypothesis that high beta diversity across islands, mountains or elevations is the key pattern underpinning the remarkably high species diversity of the Melanesian frog biota (Kraus 2021;Oliver et al 2022;Dahl et al 2023). If this pattern is confirmed in the lowlands of the Kikori River basin then it will demonstrate that the low beta diversity of amphibian assemblages across the lowlands of the Sepik River basin (Dahl et al 2009) may not be representative of the entire island of New Guinea.…”

“…However, extensive surveys of frog communities undertaken by the senior author across the Kikori River basin have to date failed to detect them in sympatry. Elevational segregation of closely related species is common in the mountain ranges of New Guinea (Oliver et al 2017;Slavenko et al 2021) and plays an important role in enabling the accumulation of high regional species diversity (Dahl et al 2023).…”

Figure 2 from: Richards SJ, Oliver PM (2024) Two new species of torrent-breeding treefrogs (Anura: Pelodryadidae: Litoria) from hill forests on the southern edge of New Guinea’s Central Cordillera. Vertebrate Zoology 74: 417-433. https://doi.org/10.3897/vz.74.e123251

“…Within the Kikori basin there appears to be high turnover of species across sites (beta diversity), a pattern that is particularly pronounced across different elevations . These broad patterns support the hypothesis that high beta diversity across islands, mountains or elevations is the key pattern underpinning the remarkably high species diversity of the Melanesian frog biota (Kraus 2021;Oliver et al 2022;Dahl et al 2023). If this pattern is confirmed in the lowlands of the Kikori River basin then it will demonstrate that the low beta diversity of amphibian assemblages across the lowlands of the Sepik River basin (Dahl et al 2009) may not be representative of the entire island of New Guinea.…”

“…However, extensive surveys of frog communities undertaken by the senior author across the Kikori River basin have to date failed to detect them in sympatry. Elevational segregation of closely related species is common in the mountain ranges of New Guinea (Oliver et al 2017;Slavenko et al 2021) and plays an important role in enabling the accumulation of high regional species diversity (Dahl et al 2023).…”