Responses of leopard Panthera pardus to the ... - Wiley Online Library

Journal of Applied Ecology 2011, 48, 806–814

doi: 10.1111/j.1365-2664.2011.01981.x

Responses of leopard Panthera pardus to the recovery of a tiger Panthera tigris population Abishek Harihar1,2*, Bivash Pandav1 and Surendra P. Goyal1 1

Wildlife Institute of India, Post Box 18, Chandrabani, Dehradun 248001, India; and 2Department of Anthropology, Durrell Institute of Conservation and Ecology, University of Kent, Marlowe Building, Canterbury, Kent CT2 7NR, UK

Summary 1. Several conservation initiatives are aiming to improve the status of the rapidly dwindling populations of tiger Panthera tigris. However, possible cascading effects of intra-guild competition on other sympatric carnivores are rarely considered while planning such recovery programmes. 2. In this study, we examine how, following the reduction of anthropogenic pressures by relocation of pastoralists, a recovering tiger population affects leopards Panthera pardus in the Chilla Range of Rajaji National Park (RNP), India. By combining data gathered over 4 years (2004–2005 to 2007– 2008) on prey availability, food habits and population density of the two predators, we investigate some of the mechanisms of niche partitioning. 3. Based on existing information, we predicted that there would be high dietary overlap between the two predators. Over time, optimal habitats would be dominated by tigers forcing leopards to the periphery of the protected area where they would subsist on small prey and domestic livestock. Consequently, leopards would occur at a lower density where sympatric with tigers. 4. Our results confirmed that annual dietary overlap (0Æ89, 0Æ82, 0Æ78, 0Æ77) between the two predators was high during the study. As expected, we observed a shift in the diet of leopards towards a significantly higher intake of domestic prey (6Æ8% to 31Æ8%) and small prey (9% to 36%). Mean leopard density declined from 9Æ76 animals per 100 km2 in 2004–2005 to 2Æ07 per 100 km2 in 2007–2008, while the mean density of tigers increased from 3Æ31 per 100 km2 to 5Æ81 per 100 km2 over the same period. 5. Synthesis and applications. Although based on small sample sizes, our study revealed that over the 4 years following the relocation of pastoralists out of RNP, the tiger population recovered but leopard densities declined sharply. The concurrent shift in leopard diet indicated heightened livestock depredation from the surrounding area. Therefore, it is important that conservation initiatives targeting the recovery of tigers should be preceded by careful examination of interspecific interactions with sympatric carnivores. Comprehensive human–carnivore conflict management measures like monitoring the extent of livestock depredation, improving livestock management and providing adequate compensation and ⁄ or insurance schemes are critical for successfully implementing such conservation efforts. Key-words: diet shift, food habits, intra-guild competition, spatial capture-recapture, sympatric large carnivores, Terai-Arc landscape, ungulate population

Introduction In many terrestrial ecosystems mammalian carnivores serve as flagship species in the conservation of biodiversity (Caro & O’Doherty 1999). While they are known to alter community structure through resource facilitation (Wilmers et al. 2003)

*Correspondence author. E-mail: [email protected]

and trophic cascades (Schmitz, Hamback & Beckerman 2000), there is also an increased recognition of the influence of competitive interactions between sympatric carnivores on their abundance and distribution (Linnell & Strand 2000). Evidence exists from studies across the globe that large carnivores adversely affect other guild members (Fedriani et al. 2000; Tannerfeldt, Elmhagen & Angerbjo¨rn 2002; Gehrt & Prange 2007), and can have negative impacts on conservation status (Hayward & Kerley 2008). It is in this context that scientific

2011 The Authors. Journal of Applied Ecology 2011 British Ecological Society

Response of leopard to recovery of tiger 807 data on intra-guild interactions among carnivores are vital while planning conservation interventions (Bangs & Fritts 1996). The geographic range of tigers Panthera tigris L. has declined by as much as 93% in the last 150 years owing to a continual loss of habitat (Dinerstein et al. 2007), thereby confining most existing populations to fragmented habitats interspersed within human-dominated landscapes. While considerable conservation investments are targeted towards recovering these dwindling populations (Walston et al. 2010), such efforts have rarely taken into account possible cascading effects on other sympatric carnivores which include leopards Panthera pardus L., dholes Cuon alpinus Pallas and wolves Canis lupus L. Tigers are socially dominant over all these species, with competitive interactions affecting the time of activity, habitat use and abundance of other sympatric carnivores (Seidensticker 1976; McDougal 1988; Seidensticker, Sunquist & McDougal 1990; Miquelle et al. 2005). Studies on tigers and sympatric carnivores have investigated behavioural factors and patterns of prey selection to infer the mechanisms facilitating their coexistence (Johnsingh 1992; Karanth & Sunquist 1995, 2000; Wang & Macdonald 2009; Wegge et al. 2009). In the prey-rich tropical forest habitats of southern India, studies suggest that the coexistence of tigers, leopards and dholes depends on differential prey selection in terms of species, body-size and age-sex classes (Karanth & Sunquist 1995; Andheria, Karanth & Kumar 2007). However, evidence from the Terai grassland habitats of Kaziranga (Karanth & Nichols 1998) and Bardia National Park (Odden, Wegge & Fredriksen 2010) is indicative of interference competition between tigers and leopards. These contrasting results imply that prey assemblages and density alone cannot allow for coexistence between the two species, and that regional ecological settings could play a major role in shaping carnivore assemblages. The recent recovery of a tiger population in the Chilla Range of Rajaji National Park (RNP) following the planned resettlement of pastoralist communities known as Gujjars presents a unique opportunity to investigate the responses of leopards to a re-establishing tiger population (Mishra, Badola & Bhardwaj 2007; Harihar, Pandav & Goyal 2009a). Previous surveys revealed that signs of leopard (35Æ8%) were encountered twice as frequently as tiger (16Æ3%) in the Chilla Range of RNP prior to the resettlement of Gujjars (Johnsingh et al. 2004). During the 3 years (2004–2005 to 2006–2007) following the reduction of anthropogenic pressures, Harihar, Pandav & Goyal (2009a) documented an increase in the density of tiger within the Chilla Range, which they attributed to increased breeding in addition to the possible immigration of dispersing adults from Corbett Tiger Reserve through the Rajaji-Corbett corridor. The study also revealed that the area supported high densities of prey (93 individuals km)2), with large prey (above 50 kg) contributing 20% of individual density and medium (20–50 kg) and small (below 20 kg) prey contributing 52% and 28% respectively. Our objective was to understand the factors influencing interactions between the two predators and to test predictions

regarding intra-guild competition. By assessing the dietary profiles of these two predators over a period of 4 years (2004– 2005 to 2007–2008), we predicted that dietary overlap between tigers and leopards would be high during the initial years of the recovery of tigers, thereby leading to intense competition. Secondly, as highlighted by McDougal (1988) and Seidensticker, Sunquist & McDougal (1990) in a similar ecological setting, the asymmetrical nature of competition between the two predators should lead to leopards shifting their diets to subsist on small-sized prey and domestic livestock as individuals are forced into hunting in peripheral habitats. Eventually, optimal habitats would be dominated by tigers, leading to a reduction in the density of leopards where the two species are sympatric.

Materials and methods STUDY AREA

Rajaji National Park, lying along the western limit of the Terai-Arc landscape, is bisected into eastern (220 km2) and western (600 km2) sectors owing to development activities along the river Ganga. This study focuses on the eastern part comprising of the Chilla forest range (148 km2), where the tiger population is recovering (Harihar, Pandav & Goyal 2009a; Harihar et al. 2009). This hilly tract is characterized by the northern Indian moist deciduous forest and northern tropical dry deciduous forest (Champion & Seth 1968), with valleys supporting extensive grasslands. Tigers and leopards are the principal large carnivores. Sambar Rusa unicolor Kerr, chital Axis axis Erxleben, nilgai Boselaphus tragocamelus Pallas, wild pig Sus scrofa L., barking deer Muntiacus muntjak Zimmermann, common langur Semnopithecus entellus Dufresne, hare Lepus nigricollis Cuvier and Indian peafowl Pavo cristatus L. are the more commonly encountered wild prey in the region. Domestic livestock (chiefly buffalo Bubalus bubalis L. and cattle Bos taurus Bojanus) ranging from the villages on the boundary of the forests also are potential prey. More details about the study area can be found in Harihar, Pandav & Goyal (2009a).

ASSESSING PREY-SPECIES AVAILABILITY

To assess the availability of principal wild-prey species, we estimated densities using line transects with conventional distance sampling (Anderson et al. 1979; Buckland et al. 2001) carried out each winter (December–February) from 2004 to 2008. In total, nine permanent line transects covering 102Æ8 km were walked every year. The transects varied in length from 0Æ91 to 2Æ49 km and were laid out following a stratified random design to ensure spatial coverage of the three distinct sub-basins of the River Ganga within the study area (Harihar, Pandav & Goyal 2009a). On every walk we recorded species, group size, sighting angle as measured using a hand-held compass and sighting distance measured by a laser range finder. We modelled detection functions to estimate the population density of principal prey using program distance 5 (Thomas et al. 2010). We first examined the data for each species per survey year for signs of evasive movement and peaking at great distance from the line transect. Following this, the data were either truncated at great distances or re-classed to ensure a reliable fit of key functions and adjustment terms. Akaike Information Criterion and goodness-of-fit (GOF-p) tests were used to judge the fit of the model. Using the selected model, estimates of group ^g), and individual density (D î) were derived for each survey density (D year.

2011 The Authors. Journal of Applied Ecology 2011 British Ecological Society, Journal of Applied Ecology, 48, 806–814

808 A. Harihar, B. Pandav & S. P. Goyal

Fig. 1. A section of the north-western limit of the Terai-Arc Landscape indicating the river Ganga and other streams, villages and forest settlements in the landscape and the two protected areas of Rajaji National Park and Corbett Tiger Reserve. Also indicated are the Chilla and Ghauri forest ranges of eastern Rajaji National Park, Shyampur Range of Hardwar Forest Division and Laldhang Range of Lansdowne Forest Division.

To assess the number of domestic livestock (chiefly buffalo and cattle) in the villages along the boundary of the Chilla Range, we focused on all villages and Gujjar settlements within a 5 km buffer. We randomly selected 20% of the households within the Shyampur Range of the Hardwar Forest Division to the south, Laldhang Range of Lansdowne Forest Division to the east and Ghauri Range of RNP to the north (Fig. 1). Household surveys were carried out to assess holdings in terms of the species and number of livestock kept.

ASSESSING DIETARY PROFILES AND OVERLAP

Predator diets were determined by identifying prey remains in scats. We collected scat samples opportunistically each winter of the four survey years. The distinction between tiger and leopard scats was made based on size and presence of secondary signs (Johnsingh 1992; Karanth & Sunquist 1995). Prey remains such as bones, hooves, teeth and hair were separated. Using microscopic features such as medullary and cuticular structures from the hair in the scats (Mukherjee, Goyal & Chellam 1994a,b), individual species were identified by comparisons with reference samples at the Wildlife Institute of India. The contribution of each prey species in the diet of the predators was computed as the frequency of occurrence, expressed as the percentage of scats in which a prey item was detected. As the frequency of occurrence is known to be misleading (Floyd, Mech & Jordan 1978; Ackerman, Lindzey & Hemker 1984), the correction factor (Y) for each individual prey species killed by tigers and leopards was estimated using the following regression model developed for pumas Puma concolor L. by Ackerman, Lindzey & Hemker (1984): Y ¼ 198 þ 0035ðXÞ where X = live weight of the prey species. Using the correction factor, the relative biomass and relative numbers of prey species consumed were estimated. We estimated the diversity of each predator’s diet using the Shannon diversity index (Magurran 2004), randomizing the original order of scat samples (100 iterations) using the software EstimateS (Colwell 2006). Following this, we assessed dietary diversity against sample size to determine whether the sample size was adequate to describe the diet of each predator. To compute the extent of year-wise dietary

overlaps, we used Pianka’s niche overlap index (Pianka 1973) given by: qffiffiffiffiffiffiffiffiffiffiffiffiffi Otl ¼ Rpit pil = Rp2it p2il where pi is proportion of prey species i in the diet of tiger t and leopard l. We then tested for significance of overall diet niche overlap by comparing observed values with values obtained by randomizing the original matrices (1000 iterations), using the default procedure (RA3) of ecosim 7 (Gotelli & Entsminger 2006). As we hypothesized that dietary competition from tigers was expected to increase the small prey and domestic livestock intake for leopards, we compared the diets of the two predators for evidence of diet shifts across years using Chi-square tests (Zar 1999) conducted separately for (i) prey size and (ii) prey type. Prey size was categorized into three classes: (i) large (above 50 kg; buffalo, sambar and cattle); (ii) medium (20–50 kg; chital, wild pig and barking deer); and (iii) small (below 20 kg; langur and hare) and prey type into two: (i) domestic (buffalo and cattle) and (ii) wild (sambar, chital, wild pig, barking deer, langur and hare). Based on this classification, we tested for differences in the absolute frequency of occurrence (AFO) of prey in terms of sizes and types. Scats were classified into m (prey categories) separate 4 · 2 contingency tables, where ‘4’ referred to the four sampling years and ‘2’ referred to the two possible outcomes (detection or non-detection of prey item). Under this method the proportional occurrence of prey items was represented as the AFO%, given by: AFOi ¼ si 100=n where si is the number of scat samples containing species i and n is the total number of scat samples.

ESTIMATING POPULATION DENSITY OF TIGER AND LEOPARD

In this study we estimated tiger and leopard densities for each year using a photographic capture–recapture method (Karanth & Nichols 1998). We deployed camera-traps following a reconnaissance. Thirty trapping stations maintained through the study period were selected based on the presence of secondary evidence that indicated the use of


Response of leopard to recovery of tiger 809 the area by tigers and ⁄ or leopards, thereby maximizing capture probabilities (Harihar, Pandav & Goyal 2009a,b). To systematically sample the area, we identified three sampling blocks (spatially separated), each consisting of 10 trap sites run for 15 consecutive days. In total we sampled for 45 days during the winters (December–February) of each survey year. The data were analysed using a recently developed Spatially Explicit Capture-Recapture (SECR) model (Royle et al. 2009) with a 10 km buffer around our trap array. We implemented this Bayesian analysis using programs r (R Development Core Team 2009) and WinBUGS (Gilks, Thomas & Spiegelhalter 1994). We employed data augmentation with 100 ‘all zero’ encounter histories and with 10000 iterations of the Markov Chain Monte Carlo algorithm. The posterior parameter estimates were generated from 8000 iterations after discarding the first 2000.

DIETARY PROFILE AND OVERLAP BETWEEN TIGER AND LEOPARD

Over the study, we collected 382 scat samples of which we assigned species identity to 361. The remaining 21 samples were unidentifiable. In total we detected the remains of eight prey species of which four were common to both tiger and leopard. Estimates of the Shannon diversity index for both predators in each survey year reached an asymptote with increasing sample size (Fig. 2), indicating that our sample sizes were adequate to describe the diet of both predators each year. Across the four sampling years, 125 scats were analysed to assess the dietary profile of leopards. Large prey contributed 63Æ5% of the overall biomass consumed, while medium and small body-sized prey contributed 29Æ25% and 7Æ25% respectively (Fig. 3a). In terms of the relative number of individuals consumed, small prey dominated the diet of leopards contributing 49Æ2%, while medium and large-sized prey contributed 34Æ3% and 16Æ5% respectively (Fig. 3b). Analysis of 236 tiger scats revealed that large prey contributed 69% to the overall biomass consumed, while medium-sized prey contributed 31% (Fig. 3c). In terms of the relative number of individuals consumed across all sampling years, large prey dominated the diet of tigers, contributing 70Æ15% while medium-sized prey contributed 29Æ85% (Fig. 3d). No remains of small prey were detected in the diet of tigers in any year. Pair-wise comparisons of the frequency of occurrence of prey items indicated extensive dietary overlap between tiger and leopard across all 4 years, ranging from 0Æ897 to 0Æ777, with a gradual decline in diet similarity over years (Table 2). Moreover, the overlap seemed to be non-random only in the first 2 years (2004–2005 and 2005–2006) with adequate sample size for analysis, based on our comparisons with simulated data. Subsequently, dietary overlap between the two predators was not different from random (P > 0Æ05). We observed significant inter-annual variation in the consumption pattern of large prey (v2 = 12Æ4, P = 0Æ006; Table 3) by leopards, owing mainly to an increase in the proportion of domestic prey (chiefly cattle), which is above 50 kg (v2 = 13Æ83, P = 0Æ006; Table 3). However, we observed no differences in the temporal

Results PREY-SPECIES AVAILABILITY

^g) and individual density (D î) The estimates of group density (D of six principal prey species (sambar, chital, nilgai, wild pig, peafowl and langur) were derived per survey year (Table 1). From the data, we estimated an average total prey-species density of about 90Æ9 individuals km)2 (Table 1), with 73% of individuals comprising wild ungulates (66 individuals km)2). Large prey contributed 19Æ6% to the overall individual densities (16Æ8 individuals km)2) and 38Æ5% to overall group densities (10Æ8 groups km)2), while the overall contribution of medium body-sized prey was 55% to the individual densities (49Æ5 individuals km)2) and 44% to group densities (12Æ6 groups km)2). Small-bodied animals contributed 25Æ4% to the overall individual densities (24Æ5 individuals km)2) and 17Æ5% to the overall group densities (5Æ06 groups km)2). No significant changes in prey densities were observed across the 4 years. Of the 2414 households in the study area, 546 households were questioned regarding their livestock holdings. Most respondents (97%) kept livestock, while the remaining kept poultry. In total, we recorded 6327 head of livestock, which comprised buffaloes (41%), cattle (39%), goats (14%) and sheep (6%). The mean number of livestock kept per household was 8Æ34 ± 5Æ6 (SD).

^g; number of groups km)2) and individual (D î; number of individuals km)2) densities of wild prey species in Chilla Table 1. Estimated group (D Range, Rajaji National Park, India, from 2004 to 2008. Total effort of 102Æ8 km per survey year 2004–2005

2005–2006

2006–2007

2007–2008

Species

^g (SE) D

î (SE) D

^g (SE) D

î (SE) D

^g (SE) D

î (SE) D

^g (SE) D

î (SE) D

Sambar Chital Nilgai Wild pig Ungulate Langur Peafowl Total

10Æ5 6Æ6 0Æ7 2Æ4 20Æ2 6Æ4 2Æ8 29Æ4

21Æ3 41Æ5 1Æ7 8Æ1 72Æ6 25Æ3 11Æ6 109Æ5

9Æ8 9Æ6 1Æ9 0Æ3 21Æ6 1Æ7 0Æ6 23Æ9

13Æ1 41Æ6 1Æ9 1Æ1 57Æ7 21Æ4 0Æ8 79Æ9

11Æ8 15Æ6 0Æ9 0Æ9 29Æ2 1Æ7 2Æ8 33Æ7

14Æ6 49Æ9 2Æ4 1Æ9 68Æ8 14Æ1 6Æ5 89Æ4

7Æ71 14Æ58 0Æ28 0Æ57 23Æ14 2Æ85 1Æ42 27Æ41

10Æ84 51Æ04 1Æ7 2Æ85 66Æ43 15Æ40 3Æ13 84Æ96

(1Æ8) (1Æ5) (0Æ3) (0Æ9) (8Æ4) (0Æ9)

(4Æ1) (10Æ7) (0Æ9) (3Æ9) (33Æ7) (4Æ6)

(1Æ8) (2Æ6) (0Æ9) (0Æ2) (0Æ7) (0Æ3)

(2Æ5) (13Æ6) (0Æ9) (0Æ9) (10Æ6) (0Æ5)

(2Æ8) (3Æ1) (0Æ9) (0Æ8) (0Æ6) (1Æ4)

(3Æ6) (13) (2Æ4) (1Æ3) (5Æ8) (3Æ7)

(1Æ7) (3Æ9) (0Æ09) (0Æ4) (1Æ1) (0Æ6)

SE = Standard error. 2011 The Authors. Journal of Applied Ecology 2011 British Ecological Society, Journal of Applied Ecology, 48, 806–814

(2Æ6) (7Æ8) (1Æ06) (1Æ5) (6Æ71) (1Æ8)

810 A. Harihar, B. Pandav & S. P. Goyal (a)

(b)

Fig. 2. Cumulative dietary diversity indexed by the Shannon diversity index, for (a) leopards and (b) tigers against an increasing number of scat samples for the years 2004–2008 from the Chilla Range of Rajaji National Park.

(a)

(c)

(d)

(b)

Fig. 3. Dietary composition represented by (a) the relative biomass consumed; (b) the relative number of individuals consumed for leopards; (c) the relative biomass consumed; and (d) the relative number of individuals consumed for tigers between 2004 and 2008 from the Chilla Range of Rajaji National Park. Presented in parentheses are the number of scat samples analysed.

pattern of prey consumption by tigers, either by prey size or by type (Table 4).

POPULATION DENSITY OF THE TIGER AND LEOPARD

We photographed 16 individual leopards and 14 tigers in 1800 trap nights across the four survey years. Using the SECR approach (Royle et al. 2009), we estimated the posterior mean (SD) density of predators per 100 km2. Over the four sampling years, leopard densities declined considerably from 9Æ76 (3Æ5) in 2004–2005 to 2Æ07 (1Æ63) in 2007–2008 (Table 5). During the same period the density of tigers increased from 3Æ31 (1Æ51) in 2004–2005 to 5Æ81 (2Æ26) in 2007–2008 (Table 5).

Discussion Our data clearly indicate that over the 4 years the tiger population recovered from a mean density of 3Æ31 tigers per 100 km2 in 2004–2005 to 5Æ81 tigers per 100 km2 in 2007–2008, while leopard densities declined sharply. Although densities of wild

prey species in our study area were high (90Æ9 individuals km)2) in comparison with many sites supporting tigers and other sympatric carnivores in India (Karanth et al. 2004), our results contrast with the general predictions of Karanth & Sunquist (1995). Unpublished data (A. Harihar, B. Pandav and S. P. Goyal) revealed that the study area experiences considerable inter-annual variation in ungulate densities. Since the Chilla Range of RNP is primarily a valley habitat consisting of three sub-basins of the River Ganga, water availability in the hilly regions reduces with the progression of the dry season and results in a congregation of ungulate species within the valley. The density of sambar within these valley habitats varied from 22Æ6 individuals km)2 in the dry season to 5Æ5 individuals km)2 in the wet, while the density of chital did not vary significantly (48 individuals km)2 in the dry season to 34 individuals km)2 in the wet). In Bardia National Park, Odden, Wegge & Fredriksen (2010) attributed the low availability of large prey, such as sambar, to decreased foraging efficiency of tigers, thereby leading to increased energetic stress and intense competition towards leopards. We feel that the reduced


Response of leopard to recovery of tiger 811 Table 2. Diets of leopard and tiger in the Chilla Range, Rajaji National Park, India, from 2004 to 2008. The numbers presented in parentheses below the predator names indicate sample sizes. Presented are the weights of prey species derived from published literature and relative frequencies of occurrence of each prey species in each survey year. Also shown are comparisons between observed values of Pianka’s niche overlap index of diet similarity between the two predators and randomly generated simulated indices (1000 iterations) 2004–2005 Leopard

2005–2006

2006–2007

2007–2008

Tiger

Leopard

Tiger

Leopard

Tiger

Leopard

Tiger

Species

X kg

(44)

(45)

(37)

(53)

(22)

(62)

(22)

(76)

Buffalo Sambar Cattle Chital Wild pig Barking deer Langur Hare Pianka’s overlap index Simulated index Mean Variance P (observed > expected)

250 185 175 50 35 25 10 4

1Æ9 37Æ7 3Æ8 45Æ3 – 3Æ8 3Æ8 3Æ8 0Æ897

5Æ5 41Æ8 20 27Æ3 5Æ5 – – –

2Æ2 23Æ9 2Æ2 41Æ3 – 10Æ9 8Æ7 10Æ9 0Æ827

6Æ8 47Æ5 10Æ2 30Æ5 5Æ1 – – –

– 31Æ4 5Æ7 17Æ1 – 22Æ9 11Æ4 11Æ4 0Æ778

5Æ1 50Æ6 16Æ5 22Æ8 5Æ1 – – –

5Æ4 27 16Æ2 13Æ5 – 21Æ6 13Æ5 2Æ7 0Æ777

7Æ4 46Æ8 16 22Æ3 7Æ4 – – –

0Æ388 0Æ055 0Æ035*

0Æ411 0Æ044 0Æ045*

0Æ467 0Æ036 0Æ065

0Æ523 0Æ029 0Æ073

*Significant (P < 0Æ05). Table 3. Chi-square tests of (a) prey size and (b) prey type by year comparisons from data estimated from absolute frequency of occurrence of prey items in leopard diet in the Chilla Range, Rajaji National Park, India, from 2004 to 2008

Years Detected 2004–2005 2005–2006 2006–2007 2007–2008 v2 (a) Prey size Large prey

P

Yes No

23 21

13 24

13 9

18 4

12Æ41 0Æ006*

Medium prey Yes No

26 18

24 13

12 10

13 9

0Æ66

Small prey

Yes No

4 40

10 27

8 14

6 16

7Æ708 0Æ052

Yes No

3 41

1 36

2 20

7 15

13Æ83 0Æ006*

Yes No

43 1

36 1

22 0

19 3

6Æ741 0Æ081

(b) Prey type Domestic Wild

0Æ882

*Significant (P < 0Æ05). Table 4. Chi-square tests of (a) prey size and (b) prey type by year comparisons from data estimated from absolute frequency of occurrence of prey items in tiger diet in the Chilla Range, Rajaji National Park, India, from 2004 to 2008

Years Detected 2004–2005 2005–2006 2006–2007 2007–2008 v2 (a) Prey size Large prey

P

Yes No

37 8

38 15

55 7

65 11

6Æ45 0Æ091

Medium prey Yes

18 27

21 32

22 40

28 48

0Æ34 0Æ952

Yes No

14 31

10 43

17 45

22 54

2Æ32 0Æ508

Yes No

41 4

49 4

62 0

72 4

5Æ34 0Æ148

(b) Prey type Domestic Wild


812 A. Harihar, B. Pandav & S. P. Goyal Table 5. Populations of (a) leopard and (b) tiger in the Chilla Range, Rajaji National Park, India, from 2004 to 2008. Presented here are the ^ and D. ^ N ^ is the number of activity centres in numbers of individuals photographed (Mt+1) and posterior summaries of the model parameters N ^ is the density per 100 km2 the population exposed to sampling and D Year

Mt+1

^ N

SD

2Æ50%

Median

97Æ50%

^ D

SD

2Æ50%

Median

97Æ50%

(a) Leopard 2004–2005 2005–2006 2006–2007 2007–2008

10 7 2 2

47Æ24 42Æ01 18Æ82 10Æ06

17Æ13 13Æ72 10Æ25 7Æ91

22Æ0 18Æ0 4Æ0 2Æ0

44Æ0 42Æ0 17Æ0 7Æ0

87Æ0 68Æ0 39Æ0 32Æ0

9Æ76 8Æ68 3Æ00 2Æ07

3Æ50 2Æ80 2Æ11 1Æ63

4Æ54 3Æ71 0Æ82 0Æ41

9Æ09 8Æ67 3Æ51 1Æ44

17Æ98 14Æ05 8Æ05 6Æ61

(b) Tiger 2004–2005 2005–2006 2006–2007 2007–2008

4 5 6 6

8Æ48 12Æ94 25Æ04 28Æ12

3Æ86 4Æ72 9Æ36 10Æ93

4Æ0 6Æ0 10Æ0 9Æ0

8Æ0 12Æ0 24Æ0 28Æ0

18Æ0 24Æ0 46Æ0 48Æ0

3Æ31 2Æ67 5Æ17 5Æ81

1Æ51 0Æ97 1Æ94 2Æ26

1Æ56 1Æ24 2Æ07 1Æ86

3Æ13 2Æ48 4Æ96 5Æ79

7Æ03 4Æ96 9Æ50 9Æ92

availability of large prey during the wet season in our study area could be forcing tigers to switch to medium-sized prey such as chital, thereby escalating the potential for increased competitive interactions between the two predators. This shift probably led to the observed decline in leopard density from within the study area, consistent with observations in similar Terai habitats (McDougal 1988; Odden, Wegge & Fredriksen 2010). In the absence of any direct evidence of intra-guild predation by tigers, we feel that indirect mechanisms such as restricted habitat use and avoidance by leopards could be important in controlling the distribution and abundance of the two predators. As predicted, dietary overlap over the study was high, and our data also revealed that the overlap was non-random in first 2 years of the tiger recovery (Table 2). This provides further support for our prediction that leopards were unable to cope with the re-establishing dominant competitor. An examination of the relative contribution of prey species to the diets of the predators revealed that the two numerically dominant wild prey species (sambar and chital) contributed 72% to the overall diet of tigers as opposed to a declining contribution of 83% to 40Æ5% to the relative frequency of occurrence of prey items in the diet of leopards across the 4 years. In addition, our prediction that leopards would increase their intake of small-sized prey was partially supported. Although across the 4 years the pattern was insignificant, our data revealed that the frequency of scats containing small prey increased from 9% to 36% in the first 3 years (Table 3). As expected, we observed a significant increase in the occurrence of domestic prey in the diet of leopards from 7% to 32% over the 4 year period (Table 3). Although our sample sizes were small and may not necessarily indicate the actual dietary habits of these carnivores, the gradual shift in relative intake of prey types and prey sizes is clearly evident among these carnivores over the study period. The increased intake of livestock in leopard diet indicates that leopards were being forced to range in peripheral habitats along the park boundary since livestock are available only in the villages located in the surrounding forested areas of Ghauri, Shyampur and Laldhang. Therefore, we suggest that the recovery of tigers may have resulted in the observed shifts in both leopard diet and distribution. Odden, Wegge & Fredriksen (2010) suggest that the avoidance of human-dominated areas

by tigers creates a competition refuge for leopards in areas with a high probability of conflict with surrounding human settlements. Given that our study area is surrounded by human settlements with livestock-holdings, conflict in terms of livestock depredation can be expected to rise (Bailey 1993; Edgaonkar & Chellam 2002; Athreya 2006). This may present considerable challenges to the park management and may potentially undermine the conservation success experienced with the rapid recovery of the tiger population observed within the park.

CONSERVATION IMPLICATIONS

While there has been much debate about conservation-induced displacement of people (Rangarajan & Shahabuddin 2006; Karanth 2007; Lasgorceix & Kothari 2009), our study clearly demonstrates that creation of inviolate space is a prime criterion for recovery of critically endangered large cats like tiger. Continued residence of previously nomadic Gujjars with unsustainable livestock holdings in RNP led to increased demand for fodder and firewood. Branches were lopped for fodder from many trees, drastically altering the forest canopy, affecting regeneration of trees and leading to a proliferation of weeds on the forest floor (Edgaonkar 1995). Immediately after the resettlement of Gujjars, reduced competition from livestock led to an increase in population performance among chital (Harihar, Pandav & Goyal 2009a). High prey density, enhanced protection and connectivity to the nearby source population (Corbett Tiger Reserve) created improved conditions for tigers to breed and increase in density. Our findings not only contribute to a greater understanding of the dominant role of tigers and their possible role in excluding leopards under intense competition, but have implications for conservation measures aimed at recovering tiger populations. Doubling wild tiger numbers by 2022 has become a global goal for conservation agencies worldwide [AMCTC (Asia Ministerial Conference on Tiger Conservation) 2010]. However, careful examination of interspecific interactions within the carnivore guild in recovery areas should precede management interventions (e.g. prey enhancement, translocation) targeted at increasing tiger numbers. In this context, understanding the nature of competitive interactions is a


Response of leopard to recovery of tiger 813 prerequisite for designing effective strategies to enhance the conservation of the entire predator guild within a region (Linnell & Strand 2000). For instance, in the Terai habitats where tigers exclude leopards, sympatry of these two species may not be possible throughout most protected areas and regional-scale zoning (May et al. 2008) might be required to ensure conservation of both threatened carnivores. As envisaged in our study, the recovery of top predators in an area may lead to increased depredation of livestock from human settlements around the edges, not necessarily due to the recovering top predator itself, but due to associated co-predators. In such cases, the conservation of tigers and leopards may be negatively impacted due to increased negative attitudes of local people leading to retaliatory killing of these predators in response to livestock depredation, and in certain cases, prompting authorities to resort to lethal control or removal from the wild. Therefore, conservation initiatives targeting increased tiger numbers must incorporate management efforts directed towards monitoring the extent of conflict with people and initiating preventive (e.g. improved livestock management) as well as mitigative measures (compensation and ⁄ or insurance schemes) to reduce conflict.

Acknowledgements We wish thank the Director and Dean of the Wildlife Institute of India (WII) and the Uttarakhand Forest Department for providing permissions. This study was possible thanks to grants from Save the Tiger Fund, WII and WWF-International. During the analytical and writing stages A.H. was supported by the Kaplan Graduate Award and Kathryn Fuller Doctoral Fellowship. We thank Andrew Royle and Beth Gardner for helping us at various stages in the analysis of the hierarchical model. We wish to thank Imam and Ameer for assistance in field and Mousumi Ghosh for help during the preparation of the manuscript. We also wish to thank Matthew Hayward and one anonymous reviewer for comments on the earlier versions of the manuscript.

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