Effects of Oilpalm Plantations on Diversity of Tropical Anurans
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Contributed Paper Effects of Oil-Palm Plantations on Diversity of Tropical Anurans AISYAH FARUK,∗† †† DAICUS BELABUT,‡§ NORHAYATI AHMAD,§∗∗ ROBERT J. KNELL,∗ AND TRENTON W. J. GARNER† ∗School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, E1 4NS, London, United Kingdom †Institute of Zoology, Zoological Society of London, Regents Park, NW1 4RY London, United Kingdom ‡Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia §Institute for Environment and Development (LESTARI), Universiti Kebangsaan Malaysia, 43600 Bangi Selangor Darul Ehsan, Malaysia ∗∗Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi Selangor Darul Ehsan, Malaysia Abstract: Agriculturally altered vegetation, especially oil-palm plantations, is rapidly increasing in South- east Asia. Low species diversity is associated with this commodity, but data on anuran diversity in oil- palm plantations are lacking. We investigated how anuran biological diversity differs between forest and oil-palm plantation, and whether observed differences in biological diversity of these areas is linked to specific environmental factors. We hypothesized that biological diversity is lower in plantations and that plantations support a larger proportion of disturbance-tolerant species than forest. We compared species richness, abundance, and community composition between plantation and forest areas and between site types within plantation and forest (forest stream vs. plantation stream, forest riparian vs. plantation ri- parian, forest terrestrial vs. plantation terrestrial). Not all measures of biological diversity differed between oil-palm plantations and secondary forest sites. Anuran community composition, however, differed greatly between forest and plantation, and communities of anurans in plantations contained species that prosper in disturbed areas. Although plantations supported large numbers of breeding anurans, we concluded the community consisted of common species that were of little conservation concern (commonly found species include Fejervarya limnocharis, Microhyla heymonsi,andHylarana erythrea). We believe that with a number of management interventions, oil-palm plantations can provide habitat for species that dwell in secondary forests. Keywords: agriculture, Asia, indicators, inventory and monitoring, protected areas Efectos de las Plantaciones de Palma de Aceite sobre la Diversidad de Anuros Tropicales Faruk et al. Resumen: La vegetacion´ alterada por la agricultura, especialmente las plantaciones de palma de aceite, esta´ incrementando rapidamente´ en el sureste de Asia. Una baja diversidad de especies estaasociadacon´ este bien tangible, pero existen pocos datos sobre la diversidad de anuros en estas plantaciones. Investigamos como difiere la biodiversidad de anuros entre bosques y plantaciones de palma de aceites y si las diferen- cias observadas en la biodiversidad de estas areas´ estan´ relacionadas con factores ambientales espec´ıficos. Partimos de la hipotesis´ de que la biodiversidad es mas´ baja en las plantaciones y que ´estas soportan una mayor proporcion´ de especies tolerantes a los disturbios que los bosques. Comparamos riqueza de especies, abundancia y composicion´ de la comunidad entre areas´ de bosque y de plantaciones y entre sitios tipo dentro de plantaciones y bisques (franja de bosque contra franja de plantacion,´ riparia de bosque contra riparia de plantacion,´ terrestre de bosque contra terrestre de plantacion).´ No todas las medidas de biodiversidad difirieron entre las plantaciones de palma de aceite y sitios de bosque secundario. Sin embargo, la com- posicion´ de la comunidad de anuros vario´ de gran manera entre bosques y plantaciones; y las comunidades de anuros en las plantaciones tuvieron especies que prosperan en areas´ perturbadas. Aunque las plantaciones soportaron un gran numero´ de anuros reproductivos, concluimos que la comunidad consist´ıa de especies que son de poca preocupacion´ para la conservacion´ (especies comunmente´ encontradas que incluyen a ††Address for correspondence: Institute of Zoology, email [email protected] Paper submitted June 3, 2012; revised manuscript accepted October 9, 2012. 615 Conservation Biology,Volume27,No.3,615–624 C 2013 Society for Conservation Biology ⃝ DOI: 10.1111/cobi.12062 616 Effects of Oil-Palm Plantations on Anurans Fejervary limnocharis, Microhyla heymonsi y Hylarana erythrea). Creemos que con un numero´ de intervenciones de manejo las plantaciones de palma de aceite pueden brindar un habitat´ para las especies que radican en bosques secundarios. Palabras Clave: agricultura, ´areas protegidas, Asia, indicadores, inventarios y monitoreo Introduction Effects of habitat loss and alteration on anuran bio- logical diversity have been documented. However, re- Biological diversity loss is most commonly attributed to sults of studies of anuran responses to such changes are habitat loss and alteration (Stuart et al. 2004; Todd & inconsistent among studies (Hecnar & M’Closkey 1997; Rothermel 2006). The rise in global demand for agri- Gibbs 1998; Parris 2004). In some cases, land-use changes cultural commodities is a major driver of habitat mod- can make an area unsuitable for anuran reproduction ification, and the amount of land under cultivation is and survival. In Australia conversion of Eucalyptus forest predicted to expand substantially in the next 4 decades to pine monoculture reduced the number of detected (Wanger et al. 2009). A large component of this con- frog species 4-fold (Parris 2004). However, in other sit- version to cropland is for oil-palm plantations, much of uations disturbed or converted areas may still support which has occurred in Southeast Asia (Koh 2007). Oil- a substantial subset of the original anuran community palm plantations dominate the landscape of Malaysia and (Gibbs 1998). Anuran species that tolerate disturbed en- Indonesia and have steadily replaced other crops in these vironments often have high fecundity (Williams & Hero countries due to low maintenance requirements and high 1998), so the negative effects of conversion on abun- yield per unit area (Donald 2004; Koh & Wilcove 2008; dance, but not on species richness, may decrease over Danielsen et al. 2009). There has been a call to discourage time. the planting of oil palm on primary and secondary forests When an area is rendered unsuitable for the original and restrict it to cleared grasslands and other agricultural community, it may be colonized by previously rare or fields (Koh & Wilcove 2008). undetected species. A decline in species richness and Although large areas of old-growth forest and of forests abundance evident soon after conversion may eventu- with low levels of disturbance are protected in Malaysia ally be masked by species that can exploit the dis- and Indonesia from large-scale conversion to agriculture, turbed area. However, species diversity should exhibit smaller areas of secondary forest remain unprotected. strong correlations with habitat variables in disturbed Koh and Wilcove (2008) reported that from 1990 to 2005, and undisturbed landscapes. In North America the in- 55–59% of oil-palm expansion was at the expense of sec- troduction of non-native predatory fish has led, in some ondary forest. Secondary forests in Malaysia, although not cases, to the loss of small palatable amphibians na- as diverse as old-growth forests, retain substantial biologi- tive to the site and colonization by larger, unpalatable cal diversity and may contain unique assemblages relative amphibians (Hecnar & M’Closkey 1997). Changes to to monoculture plantations (Chazdon et al. 2009). the landscape may also result in a subset of the exist- Oil-palm plantations are associated with reductions in ing anuran community persisting in the disturbed area species richness, and species diversity and shifts in com- and new species colonizing the newly created niche munity composition (beetles: Chung et al. 2000; reptiles: space. Given time, little or no reduction in species Glor et al. 2001; birds: Koh & Wilcove 2008; ants: Bruhl¨ richness or abundance may be detectable, again due & Eltz 2010), but to date there has been only one study to colonization by disturbance-tolerant species. How- of anuran communities in oil-palm plantations (Gillespie ever, species correlations with habitat variables would be et al. 2012). The International Union for Conservation of inconsistent. Nature (IUCN) Red List reports 41% of 6300 described, We sought to describe abundance, species richness, extant amphibian species are at risk of extinction (IUCN and community composition of anurans in oil-palm plan- 2010); thus, Amphibia are the most threatened vertebrate tations and secondary forest on Peninsular Malaysia. By class assessed to date. Pollution, overharvesting, and in- using multiple methods, we avoided dependence on sin- fectious diseases have contributed to a global amphibian gle indexes, which cannot distinguish between the range decline, but habitat alteration consistently ranks as the of potential responses an anuran community may have to largest threat. Southeast Asia is an amphibian biological forest conversion. On the basis of the results of previ- diversity hotspot, yet amphibian studies in this region ous studies of the effects of agricultural landscapes on are rare (Sodhi et al. 2007, 2008). Eighty-two percent of anuran biological diversity (Gardner et al. 2007; Wanger global amphibian species are forest dependent,