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Eastwood, Rodney Gordon

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Eastwood

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Rodney Gordon

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Eastwood, Rodney Gordon
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    Cross-continental comparisons of butterfly assemblages in tropical rainforests: implications for biological monitoring
    (Wiley-Blackwell, 2012) Basset, Yves; Eastwood, Rodney Gordon; Sam, Legi; Lohman, David; Novotny, Vojtech; Treuer, Tim; Miller, Scott E.; Weiblen, George D.; Pierce, Naomi; Bunyavejchewin, Sarayudh; Sakchoowong, Watana; Kongnoo, Pitoon; Osorio-Arenas, Miguel A.
    1. Standardised transect counts of butterflies in old-growth rainforests in different biogeographical regions are lacking. Such data are needed to mitigate the influence of methodological and environmental factors within and between sites and, ultimately, to discriminate between long-term trends and short-term stochastic changes in abundance and community composition. 2. We compared butterfly assemblages using standardised Pollard Walks in the understory of closed-canopy lowland tropical rainforests across three biogeographical regions: Barro Colorado Island (BCI), Panama; Khao Chong (KHC), Thailand; and Wanang (WAN), Papua New Guinea. 3. The length and duration of transects, their spatial autocorrelation, and number of surveys per year represented important methodological factors that strongly influenced estimates of butterfly abundance. Of these, the effect of spatial autocorrelation was most difficult to mitigate across study sites. 4. Butterfly abundance and faunal composition were best explained by air temperature, elevation, rainfall, wind velocity, and human disturbance at BCI and KHC. In the absence of weather data at WAN, duration of transects and number of forest gaps accounted for most of the explained variance, which was rather low in all cases (<33%). 5. Adequate monitoring of the abundance of common butterflies was achieved at the 50 ha BCI plot, with three observers walking each of 10 transects of 500 m for 30 min each, during each of four surveys per year. These datamay be standardised further after removing outliers of temperature and rainfall. Practical procedures are suggested to implement globalmonitoring of rainforest butterflies with Pollard Walks.
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    Comparison of rainforest butterfly assemblages across three biogeographical regions using standardized protocols
    (The Lepidoptera Research Foundation, 2011) Basset, Yves; Eastwood, Rodney Gordon; Sam, Legi; Lohman, David; Novotny, Vojtech; Treuer, Tim; Miller, Scott E.; Weiblen, George D.; Pierce, Naomi; Bunyavejchewin, Sarayudh; Sakchoowong, Watana; Kongnoo, Pitoon; Osorio-Arenas, Miguel A.
    Insects, like most other organisms, are more diverse in tropical than in temperate regions, but standardized comparisons of diversity among tropical regions are rare. Disentangling the effects of ecological, evolutionary, and biogeographic factors on community diversity requires standardized protocols and long-term studies. We compared the abundance and diversity of butterflies using standardised ‘Pollard walk’ transect counts in the understory of closed-canopy lowland rainforests in Panama (Barro Colorado Island, BCI), Thailand (Khao Chong, KHC) and Papua New Guinea (Wanang, WAN). We observed 1792, 1797 and 3331 butterflies representing 128, 131 and 134 species during 230, 231 and 120 transects at BCI, KHC and WAN, respectively. When corrected for length and duration of transects, butterfly abundance and species richness were highest at WAN and KHC, respectively. Although high butterfly abundance at WAN did not appear to result from methodological artefacts, the biological meaning of this observation remains obscure. The WAN site appeared as floristically diverse as KHC, but supported lower butterfly diversity. This emphasizes that factors other than plant diversity, such as biogeographic history, may be crucial for explaining butterfly diversity. The KHC butterfly fauna may be unusually species rich because the site is at a biogeographic crossroads between the Indochinese and Sundaland regions. In contrast, WAN is firmly within the Australian biogeographic region and relatively low species numbers may result from island biogeographic processes. The common species at each of the three sites shared several traits: fruit and nectar feeders were equally represented, more than half of common species fed on either epiphytes or lianas as larvae, and their range in wing sizes was similar. These observations suggest that Pollard walks in different tropical rainforests target similar assemblages of common species, and, hence, represent a useful tool for long-term monitoring of rainforest butterfly assemblages.