ECOTROPICA 14: 129–136, 2008 © Society for Tropical Ecology DISTRIBUTION OF NATIVE AND NON-NATIVE RATS (RATTUS SPP.) ALONG AN ELEVATIONAL GRADIENT IN A TROPICAL RAINFOREST OF SOUTHERN LUZON, PHILIPPINES Cristina C. Salibay & Hazel Anne V. Luyon De La Salle University-Dasmariñas, Dasmariñas, Cavite, Philippines Abstract. Rats (Muridae) of the genus Rattus occur in the Philippines, both as native and as invasive species. While the invasive species are well known to use a large range of anthropogenic habitats, little is known about their potential to occur in forest areas. We studied the occurrence and relative abundance of different species of Rattus in forests along elevational gradients on three mountains within the Palay-palay / Mataas na Gulod National Park in Southern Luzon, Philippines. Four Rattus species were collected and their occurrence and relative abundance were found to differ significantly between species and along elevational gradients. Rattus norvegicus (40.3% of captures), R. tanezumi (21.5%), and R. argentiventer (5.6%) are invasive species and R. everetti (32.7%) a native forest-inhabiting species. While the three invasive species were most abundant at low elevations, R. everetti was most abundant at higher elevations. The number of invasive rats has been attributed to their survival and adaptation at lower elevations, where habitat conversion and degradation are most intense, while native species are more common at higher elevations where habitat is relatively un- disturbed. Key words: elevation, forest species, invasive species, Philippines, rainforest, Rattus species. INTRODUCTION and occur at high abundances in local mammal as- semblages (Heaney et al. 1998, Steppan et al. 2003). Rats (Muridae) use different habitats in tropical for- Most of the murid rodents occurring in higher ele- ests in variable abundance, and species may differ in vation habitats are endemic species. Many forest their ability to utilize different lowland, montane, or rodents are well adapted to pristine habitats, and mossy forests (Mallari & Jensen 1993, Heaney et al. forest destruction threatens the long-term survival of 1998, Tabaranza et al. 2002). Many lowland species these species (Heaney & Regalado 1998, Heaney et assemblages are known to include native as well as al. 1999, Tabaranza et al. 2002). It is assumed that invasive species (Rickart 1993). The Philippines are the invasion of exotic rat species in the Philippine known for their diverse mammal fauna, including at least 172 native and seven introduced non-native forest poses threats to the endemic species because terrestrial species. Philippine mammal assemblages invasive species affect their biological communities are characterized by an exceptionally high endemism through competition or predation, resulting in pos- of around 60% (Heaney et al. 1998). Newly discovered sible extinction of native species (Heaney 1995). In endemic species have been recorded recently either addition, the status of both endemic and invasive on relatively small islands or in the high mountain rodents is an excellent indicator of forest conditions, ranges of Luzon and Mindanao islands (Sinha & since endemic mammals can be among the most Heaney 2006). threatened species when conditions become unfavor- The murid rats, comprising 22 genera and 56 able (Goodman 1995), while the presence of large species native to the Philippines, are the most spe- populations of invasive species in the forest is indi- ciose and most diverse in terms of morphology and cative of an ecological imbalance within the habitat ecology. They comprise an important faunal element (Lehtonen et al. 2001). Mounts Palay-palay/Mataas na Gulod (MPMNG) lies in the provinces of Cavite and Batangas, Southern * e-mail: [email protected] Luzon, Philippines. It was established as a National [email protected] Park in October 1976 (DENR 1992). The park is 129 Umbruch Ecotropica 14_2.indd 129 23.01.2009 11:14:54 Uhr Salibay & Luyon FIG. 1. Map of Mts. Palay-palay / Mataas na Gulod National Park showing the three peaks: Palay-palay at 595 m a.s.l. ▲, Pico de Loro at 648 m ●, and Mataas na Gulod at 622 m ◆ (NAMRIA 1993). one of the few remaining low-elevation tropical rain- METHODS forests in the Philippines. The park is composed of approximately 62.5% forest and 37.5% non-forest Study Site. Mts. Palay-palay / Mataas na Gulod Na- vegetation and the main tree families include Verbe- tional Park is a 4000-ha mountain range at 14°12'– naceae (molave) and Dipterocarpaceae. 14°17'N, 120°38'–120°42'E, approximately 60 km We studied the rodent species of the forest in southeast of the capital Manila (DENR 1992). The order to contribute to the conservation efforts of range includes three main peaks: Palaypalay, with an MPMNG National Park. In this study, we surveyed elevation of 595 m above sea level, Mataas na Gulod the occurrence and distribution of Rattus species in at 622 m a.s.l., and Pico de Loro, the highest peak the wild in order to determine their diversity and to at 648 m a.s.l. (Fig. 1). Its topography ranges from establish the occurrence of native and invasive species rolling to moderately steep and steep terrain, and along an elevational gradient in relation to the type soils are composed of mountain sand with clay loam. of habitat. Further, our study focused on the abun- Average air humidity is 57% and temperature range dance and distribution of endemic and invasive ro- is 19–28°C. dents in the disturbed and undisturbed areas of the Our forest trapping sites at low and middle ele- forest. The availability of such data, particularly of vations were mostly dominated by endemic diptero- threatened, exploited, and exotic species, is essential carp trees with an average height of 10 to 12 m. The for developing successful wildlife management strate- forest floor is covered with aroids, grasses, and low gies. herbs with mixed dry and wet leaves as forest litter. 130 Umbruch Ecotropica 14_2.indd 130 23.01.2009 11:14:55 Uhr Distribution OF native AND NON-native Rattus species While a larger proportion of the park is still covered animal was trapped within the first day. The sites with trees, some areas up to 400 m a.s.l. have been with traps were marked with reflective tape to faci- converted to agricultural areas and croplands. Hu- litate relocation for retrieval or resetting. We noted man utilization is concentrated in the low and the sampling location for each trapped animal and middle elevations. Both the lower and middle eleva- marked it by tail-tagging prior to release. During tions are adjacent to trails and well-defined roads, handling of the captured rats, leather or fabric gloves that provide easy access to the National Park. were worn to minimize the chances of being bitten At higher altitudes there is abundant vegetation, or scratched. Captured rats were immobilized by dominated by canopy trees, which protect the under- an improvised metal stabilizer while morphological story. The average height of trees is 8 to 9 m. The measurements were taken. terrain becomes rocky as elevation increases and the Weight as well as head, hindfoot, and tail lengths vegetation is gradually replaced with high cogon were determined for identification of the species. grasses (Imperata cylindrica), shrubs, herbs, vines, and Rats were identified using Sanchez et al. (1985), fern. The forest floor is covered with grasses and leaf Sumangil (1990), Heaney et al. (1999), and Salibay litter. & Claveria (2005). Species identification was verified We studied three forest habitats, one on each at the Mammalogy Section, Zoology Division of the peak. Each habitat was divided into low elevation at National Museum, Manila. Voucher specimens are 0–207 m above sea level (m a.s.l.), middle elevation deposited in the Natural History Laboratory of De (208–414 m), and high elevation (415 m and above). La Salle University-Dasmariñas (DLSU-D). Animals A total of nine collection sites (three forest habitats were handled following the animal care guidelines x three collection areas covering the different ele- of the American Society of Mammalogists (ASM- vations) was determined using stratified random ACUC 2003) and PCARRD (1985). sampling with reference to the forest trail and the elevation was measured in m. Sampling points were RESULTS geo-referenced using a global positioning system In total, we captured 107 individuals of the four (GPS) receiver. species after nine collection periods over six months. The number of rats collected per collection period Capture and handling of rats. A 100-m transect line ranged from three to 19 individuals. Fewer rats were was used in the trapping procedure, slightly adapted caught during rainy days than on dry days. All of the et al et al from Soliman . (2001) and Heaney . (1999). four rat species caught belonged to the genus Rattus: Single-capture live cage-traps of 12 x 7 x 7 inches Rattus norvegicus Berkenhout (Norway rat), R. eve- (30.5 x 17.8 x 17.8 cm) were used for trapping. Each retti Gunther (common Philippine forest rat), R. transect line was located 15 m from the main forest tanezumi Temminck (Oriental / Asian house rat), and trail. The transect line was further subdivided into R. argentiventer Robinson and Kloss (ricefield rat). four subplots with an approximately 25-m vertical Among the rats collected, R. norvegicus was the most distance trapline. In each subplot, five spring-door abundant, followed by R. everetti; R. tanezumi and R. wire traps were deployed 5 m apart. We ran on each argentiventer were least abundant (Table 1). The total site 20 trap nights (= 20 traps deployed for one night) number of rats collected varied significantly across hence a total of 60 trap nights for each collection the species (χ2 = 29.03, p < 0.05).