Tiger Decline Caused by the Reduction of Large Ungulate Prey: Evidence from a Study of Leopard Diets in Southern India
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Biological Conservation 89 (1999) 113±120 Tiger decline caused by the reduction of large ungulate prey: evidence from a study of leopard diets in southern India Uma Ramakrishnan, Richard G. Coss *, Neil W. Pelkey Psychology Department and Graduate Group in Ecology, University of California, Davis, CA 95616, USA Received 13 August 1998; received in revised form 24 November 1998; accepted 4 December 1998 Abstract Populations of leopards and tigers in the Kalakad-Mundanthurai Tiger Reserve, India, appear to be declining. To identify the cause of this decline, we examined the diets and the relative densities of leopards and tigers, comparing scat from this park with that from the Mudumalai Wildlife Sanctuary, a park known to have high leopard and tiger densities. Results suggested that the leopard density in Mudumalai was approximately twice that in Mundanthurai. No evidence of tigers was found in Mundanthurai. Prey species found in leopard diets in the two parks was similar; albeit, mean prey weight and the proportion of large ungulates were markedly lower in the Mundanthurai leopard diet. These dietary dierences are consistent with the infrequent sightings of large ungulates in Mundanthurai. Analyses of satellite data revealed that large areas of grazing land in Mundanthurai have shifted to thicket, reducing available forage for large ungulates. Since large ungulates constitute important tiger prey, the low density of ungulates in Mundanthurai might explain the apparent absence of tigers. Our ®ndings suggest that the tiger population in the Kalakad-Mundanthurai Tiger Reserve could be enhanced via the application of habitat management for large ungulates. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Conservation; Habitat management; Scat analysis; Leopard; Tiger 1. Introduction (Karanth, 1987; Sunquist and Sunquist, 1989). Though facing the same threats, leopards (Panthera pardus) are The tiger (Panthera tigris) has been classi®ed as more successful than tigers, largely because of their endangered by the IUCN, with about 6000±8000 sur- ability to live in dierent environments and the ¯exiblity viving in the wild (Nowak, 1991). The major threat to in their diet (Bailey, 1993). The wide geographic dis- its survival is habitat loss and the poaching of tigers and tribution of leopards is also attributed to their ability to their prey (Nowell and Jackson, 1996). India supports coexist with other large carnivores (Bailey, 1993). Both the largest numbers of tigers in the wild, approximately tigers and leopards are solitary, stealth predators. Tigers two thirds of the world's tiger population (Sunquist and are usually restricted to the core areas of protected Shah, 1997). The most recent survey estimated the reserves and avoid areas of moderate to heavy human number of tigers throughout India at 3750 (Ghosh, disturbance. They are dependent on dense vegetative 1994). Their distribution in southern India is shown in cover and access to water (Nowell and Jackson, 1996). Fig. 1A. Tiger densities in the wild increased moderately in the 1980s because of intensive eorts to protect the 1.1. Recent habitat changes in the Kalakad- species with the establishment of reserves targeted for Mundanthurai Tiger Reserve tigers in India (Karanth, 1987; Panwar, 1987). This eort led to the rapid increase in prey populations with The Mundanthurai sanctuary was classi®ed as a tiger a corresponding increase in tiger populations (Sunquist, reserve in 1988 because of the occurrence of tiger sight- 1996). More speci®cally, tiger densities increased with ings and other tiger evidence. However, in the last 2 the availability of large ungulate prey in the region years, there have been very few sightings of tigers (For- est Department records). Some major changes in habitat management have occurred in Mundanthurai over the * Corresponding author. Tel.: +1-530-7521626; fax: +1-530- last decade; the frequency and intensity of forest ®res 7522087; e-mail: [email protected]. were controlled and cattle were excluded from most 0006-3207/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(98)00159-1 114 U. Ramakrishnan et al. / Biological Conservation 89 (1999) 113±120 Fig. 1. Distribution of tigers in southern India (A). Study sites for the collection of tiger and leopard scat on the Mundanthurai Plateau (B) within the Kalakad-Mundanthurai Tiger Reserve and within the Mudumalai Wildlife Sanctuary (C). areas of the park. These factors led to the decline of the diet of leopards and tigers in the Kalakad-Mun- grasslands available for herbivores. The reduction in danthurai Tiger Reserve with a region known for its forest ®res led to an increase in unpalatable exotic healthy carnivore population, the Mudumalai Wildlife thickets, such as lantana (Lantana camara) and eupa- Sanctuary. When the key item of a carnivores' diet is in torium (Eupatorium glandulosum). Although important short supply, the carnivore species will either alter its for forest management, the sudden removal of cattle diet or exhibit a drop in population size. A comparison from areas in the park coupled with ®re control aug- of carnivore densities and diets in these two wildlife mented the growth of these exotic weeds. At present, parks will shed light on which of these two eects have no systematic research has examined the eects of occurred. Previous studies on the diets of sympatric declining grazing lands on herbivore populations in this leopards and tigers have shown that their diets are very park. similar when prey are abundant (Schaller, 1967; John- A number of studies have been conducted on large singh, 1983; Karanth and Sunquist, 1995). However, carnivore species in southern India (Johnsingh, 1983; leopards tend to be more ¯exible in their diets than Karanth and Sunquist, 1995; Rice, 1986; Venkataraman tigers under deteriorating habitat conditions (John- et al., 1995). These studies were designed to obtain singh, 1983). It is reasonable to predict that a shift in the information on predator distribution and diet in a given diet of leopards toward smaller prey is an indication of park or reserve. The current study focused on comparing the low availability of larger prey favored by tigers. U. Ramakrishnan et al. / Biological Conservation 89 (1999) 113±120 115 2. Study sites and methods To create permanent slides for species identi®cation, ®ve hairs were selected randomly from each sample, Data collection was conducted from March to centered parallel on the slide, and mounted with cover September, 1997 at two study sites. The Kalakad- slip using DPX mount. Five slides were made per scat Mundanthurai Tiger Reserve is located between 8 250± sample (n 25 hairs/sample). Slides were examined at 8 530 N latitude and 77 100±77 350 E longitude, and 400X using an Olympus microscope. For identi®cation covers an area of 817 km2 (Fig. 1B). The habitat type of scat hairs, a set of reference slides was made from consists of moist evergreen rain forest, moist and dry captive prey species, museum specimens, and leopard deciduous forest, and scrub forest. Our sampling was kills. For statistical quanti®cation, each species found in restricted to the Mundanthurai Plateau and occurred one scat sample was assumed to characterize a single over multiple paths, totaling a 48.3-km distance. The predatory event. Dierence of proportions tests were habitat type of the plateau is classi®ed as mixed decid- conducted to compare diets between parks using NCSS uous (Ali, 1981). statistical software (Hintze, 1987). The Mudumalai Wildlife Sanctuary is located Apart from scat collection, the presence of tigers and between 11 320±11 430 N latitude and 76 220±76 450 E leopards during the entire study was recorded by direct longitude and covers an area of 321 km2 (Fig. 1C). This sightings, both by researchers and local residents, and park has a variety of vegetation types, consisting of the presence of tiger and leopard pug marks and tropical semi-evergreen forest, moist and dry deciduous scrapes. Sightings by local residents living in Mun- forest, and dry thorn forest (Sukumar et al., 1992). Our danthurai were recorded through an oral interview sampling was restricted to moist and dry deciduous using a formal questionnaire to quantify evidence of forest areas and occurred over multiple paths, totaling a predation on domesticated animals. The settlements 46.7-km distance. selected for study were ®ve separate tribal colonies, two These two forest sites are part of a complex classi®ed at the edge of the park and three in the forest interior. as ``high-priority'' tiger conservation sites, which aord One adult per household was interviewed (n 58). the highest probability of long-term persistence of tiger Although we did not attempt to estimate prey den- populations (Wikramanayake et al., 1998). Both study sities in the two parks, we recorded all sightings of chital sites have very similar mammalian species. The large deer while collecting scat throughout the parks. Because carnivores include the leopard, tiger, wild dog (Cuon the density of herbivore prey is aected by habitat pre- alpinus), and striped hyena (Hyaena hyaena). Prey spe- ferences (Eisenberg and Seidensticker, 1976), we also cies also appears to be similar in the two parks (Forest estimated changes in grass cover available for grazing in Department records). the two parks. Satellite data with a 1-km2 resolution The hair of prey is relatively undamaged in carnivore from the NOAA Advanced Very High Resolution scat and can thus be used to identify the prey species Radiometer was used to measure changes in grazing land eaten. We collected leopard and tiger scat from multiple between 1986 and 1996. This data set was produced by established forest paths. Each path was sampled once a the National Institute for Environmental Studies of the month for 5 months. This period covered two seasons, a Environment Agency of Japan. It consisted of cloud- dry and a wet season.