Recent Evolutionary History of Tigers Highlights Contrasting Roles of Genetic Drift and Selection

Species conservation can be improved by knowledge of evolutionary and genetic history. Tigers are among the most charismatic of endangered species and garner significant conservation attention. However, their evolutionary history and genomic variation remain poorly known, especially for Indian tigers. With 70% of the world’s wild tigers living in India, such knowledge is critical. We re-sequenced 65 individual tiger genomes representing most extant subspecies with a specific focus on tigers from India. As suggested by earlier studies, we found strong genetic differentiation between the putative tiger subspecies. Despite high total genomic diversity in India, individual tigers host longer runs of homozygosity, potentially suggesting recent inbreeding or founding events, possibly due to small and fragmented protected areas. We suggest the impacts of ongoing connectivity loss on inbreeding and persistence of Indian tigers be closely monitored. Surprisingly, demographic models suggest recent divergence (within the last 20,000 years) between subspecies and strong population bottlenecks. Amur tiger genomes revealed the strongest signals of selection related to metabolic adaptation to cold, whereas Sumatran tigers show evidence of weak selection for genes involved in body size regulation. We recommend detailed investigation of local adaptation in Amur and Sumatran tigers prior to initiating genetic rescue.     

Responses of tiger (<Emphasis Type="Italic">Panthera tigris</Emphasis>) and their prey to removal of anthropogenic influences in Rajaji National Park,India

Presence of human settlements in most protected areas has forced tigers (Panthera tigris) to share space with humans. Creation of inviolate space for tigers in areas with high human densities is often daunting and requires hard political sacrifices. We conducted this study from 2004 to 2007 in the Chilla range of Rajaji National Park, along the northwestern portion of the Terai-Arc Landscape in the Indian subcontinent. Our objective was to document the recovery of prey and tiger populations following the resettlement of 193 gujjar (pastoralists with large buffalo holdings) families. We used distance sampling to estimate density of wild ungulate prey and camera traps to estimate tiger density. The study area supported ∼66 ungulates/km², with chital (Axis axis) and sambar (Cervus unicolor) contributing >91%. While prey densities did not vary across 3 years, an increase in proportion of chital fawns was observed following the near complete removal of livestock. We also documented an increase in the density of tigers (from three to five tigers per 100 km²), probably due to immigrating tigers from nearby Corbett Tiger Reserve. A high turnover of individual tigers was observed during the study. With photographic evidence of breeding tigers in Chilla range, we believe that this area could serve as a source population from where tigers can colonize adjoining forests across River Ganga. It is therefore concluded that securing the connectivity between forests on the east and west bank of Ganga through the tenuous Chilla-Motichur corridor assumes significance for long-term persistence of tigers within this landscape.     

Why the Indian Subcontinent Holds the Key to Global Tiger Recovery

With only ~3,000 wild individuals surviving restricted to just 7% of their historical range, tigers are now a globally threatened species. Therefore, conservation efforts must prioritize regions that harbor more tigers, as well try to capture most of the remaining genetic variation and habitat diversity. Only such prioritization based on demographic, genetic, and ecological considerations can ensure species recovery and retention of evolutionary flexibility in the face of ongoing global changes. Although scientific understanding of ecological and demographic aspects of extant wild tiger populations has improved recently, little is known about their genetic composition and variability. We sampled 73 individual tigers from 28 reserves spread across a diversity of habitats in the Indian subcontinent to obtain 1,263 bp of mitochondrial DNA and 10 microsatellite loci. Our analyses reveals that Indian tigers retain more than half of the extant genetic diversity in the species. Coalescent simulations attribute this high genetic diversity to a historically large population size of about 58,200 tigers for peninsular India south of the Gangetic plains. Furthermore, our analyses indicate a precipitous, possibly human-induced population crash ~200 years ago in India, which is in concordance with historical records. Our results suggest that only 1.7% (with an upper limit of 13% and a lower limit of 0.2%) of tiger numbers in historical times remain now. In the global conservation context our results suggest that, based on genetic, demographic, and ecological considerations, the Indian subcontinent holds the key to global survival and recovery of wild tigers.     

Spatial genetic analysis reveals high connectivity of tiger (Panthera tigris) populations in the Satpura–Maikal landscape of Central India

We investigated the spatial genetic structure of the tiger meta‐population in the Satpura–Maikal landscape of central India using population‐ and individual‐based genetic clustering methods on multilocus genotypic data from 273 individuals. The Satpura–Maikal landscape is classified as a global‐priority Tiger Conservation Landscape (TCL) due to its potential for providing sufficient habitat that will allow the long‐term persistence of tigers. We found that the tiger meta‐population in the Satpura–Maikal landscape has high genetic variation and very low genetic subdivision. Individual‐based Bayesian clustering algorithms reveal two highly admixed genetic populations. We attribute this to forest connectivity and high gene flow in this landscape. However, deforestation, road widening, and mining may sever this connectivity, impede gene exchange, and further exacerbate the genetic division of tigers in central India.     

中国野生东北虎数量监测方法有效性评估

虎数量监测是虎保护的核心内容之一。野生虎现存数量少、领域宽广,加之习性机警,很难对其数量和种群变化趋势做出准确的评估。合适的虎数量监测方法随着监测目标、监测尺度、虎密度、猎物密度、气候及其它环境因素的变化而不同。2002—2011年,用东北虎信息收集网络法,样线调查法,猎物生物量和捕食者关系法,对东北虎数量进行监测。(1)用老虎信息收集网络法研究2006年完达山东部地区东北虎的种群现状,结果显示东完达山地区2006年东北虎数量为6—9只,由1只成年雄虎,2—3只成年雌虎,2—4只亚成体虎和1只小于1岁的幼体虎组成;(2)用猎物生物量和捕食者关系法得到东完达山地区2002年东北虎的密度为0.356只/100 km2,能容纳22—27只东北虎;(3)用样线法在黑龙江的老爷岭南部和吉林省大龙岭北部面积1735.99 km2的区域内设置样线64条,总长609 km,没有发现东北虎足迹链。样线调查的结果表明,在2011年2—3月该调查区域东北虎的数量为0只。监测结果表明,用猎物生物量和捕食者关系得到东北虎数量远远超过现实数量,人们对有蹄类的盗猎和猎套对老虎的伤害可能是其主要原因;样线法调查得出的结果低于现实种群,主要原因是老虎数量极低和调查者对野生虎行为学了解甚少,较难在野外有效的发现虎信息;且样线法监测仅应用于当东北虎以一定的密度(即有定居虎)存在的情况下(多数监测样线能发现虎信息)。虽然和样线法一样存在着诸如专家估计密度和真实密度之间的关系,老虎足迹数量和老虎真实密度间关系不确定,保守估计等内在缺点,在目前中国东北地区野生东北虎种群密度极低,且多是穿越于中俄边境地区的游荡个体的现状下,信息收集网络法是一种高效,可行东北虎监测方法。因此,建议建立更广泛的监测信息收集网络,培训监测人员,严格执行信息收集程序,减少专家估计误差以完善此监测方法。此外,其他监测方法,如占有法、基于标志重捕远红外照相法、粪便DNA法、足迹数码信息法、警犬法等,应根据各种方法的理论前提、误差来源、适用范围和老虎是否定居及密度等具体情况有选择地加以应用,且有些方法可能成为未来中国野生东北虎种群的有效监测工具。     

Tigers of Sundarbans in India: Is the Population a Separate Conservation Unit?

The Sundarbans tiger inhabits a unique mangrove habitat and are morphologically distinct from the recognized tiger subspecies in terms of skull morphometrics and body size. Thus, there is an urgent need to assess their ecological and genetic distinctiveness and determine if Sundarbans tigers should be defined and managed as separate conservation unit. We utilized nine microsatellites and 3 kb from four mitochondrial DNA (mtDNA) genes to estimate genetic variability, population structure, demographic parameters and visualize historic and contemporary connectivity among tiger populations from Sundarbans and mainland India. We also evaluated the traits that determine exchangeability or adaptive differences among tiger populations. Data from both markers suggest that Sundarbans tiger is not a separate tiger subspecies and should be regarded as Bengal tiger (P. t. tigris) subspecies. Maximum likelihood phylogenetic analyses of the mtDNA data revealed reciprocal monophyly. Genetic differentiation was found stronger for mtDNA than nuclear DNA. Microsatellite markers indicated low genetic variation in Sundarbans tigers (He= 0.58) as compared to other mainland populations, such as northern and Peninsular (Hebetween 0.67- 0.70). Molecular data supports migration between mainland and Sundarbans populations until very recent times. We attribute this reduction in gene flow to accelerated fragmentation and habitat alteration in the landscape over the past few centuries. Demographic analyses suggest that Sundarbans tigers have diverged recently from peninsular tiger population within last 2000 years. Sundarbans tigers are the most divergent group of Bengal tigers, and ecologically non-exchangeable with other tiger populations, and thus should be managed as a separate “evolutionarily significant unit” (ESU) following the adaptive evolutionary conservation (AEC) concept.     

How much gene flow is needed to avoid inbreeding depression in wild tiger populations?

The number and size of tiger populations continue to decline owing to habitat loss, habitat fragmentation and poaching of tigers and their prey. As a result, tiger populations have become small and highly structured. Current populations have been isolated since the early 1970s or for approximately seven generations. The objective of this study is to explore how inbreeding may be affecting the persistence of remaining tiger populations and how dispersal, either natural or artificial, may reduce the potentially detrimental effect of inbreeding depression. We developed a tiger simulation model and used published levels of genetic load in mammals to simulate inbreeding depression. Following a 50 year period of population isolation, we introduced one to four dispersing male tigers per generation to explore how gene flow from nearby populations may reduce the negative impact of inbreeding depression. For the smallest populations, even four dispersing male tigers per generation did not increase population viability, and the likelihood of extinction is more than 90% within 30 years. Unless habitat connectivity is restored or animals are artificially introduced in the next 70 years, medium size wild populations are also likely to go extinct, with only four to five of the largest wild tiger populations likely to remain extant in this same period without intervention. To reduce the risk of local extinction, habitat connectivity must be pursued concurrently with efforts to increase population size (e.g. enhance habitat quality, increase habitat availability). It is critical that infrastructure development, dam construction and other similar projects are planned appropriately so that they do not erode the extent or quality of habitat for these populations so that they can truly serve as future source populations.     

Genetic evidence of tiger population structure and migration within an isolated and fragmented landscape in Northwest India

Background

Majority of the tiger habitat in Indian subcontinent lies within high human density landscapes and is highly sensitive to surrounding pressures. These forests are unable to sustain healthy tiger populations within a tiger-hostile matrix, despite considerable conservation efforts. Ranthambore Tiger Reserve (RTR) in Northwest India is one such isolated forest which is rapidly losing its links with other tiger territories in the Central Indian landscape. Non-invasive genetic sampling for individual identification is a potent technique to understand the relationships between threatened tiger populations in degraded habitats. This study is an attempt to establish tiger movement across a fragmented landscape between RTR and its neighboring forests, Kuno-Palpur Wildlife Sanctuary (KPWLS) and Madhav National Park (MNP) based on non-invasively obtained genetic data.

Methods

Data from twelve microsatellite loci was used to define population structure and also to identify first generation migrants and admixed individuals in the above forests.

Results

Population structure was consistent with the Central Indian landscape and we could determine significant gene flow between RTR and MNP. We could identify individuals of admixed ancestry in both these forests, as well as first generation migrants from RTR to KPWLS and MNP.

Conclusions

Our results indicate reproductive mixing between animals of RTR and MNP in the recent past and migration of animals even today, despite fragmentation and poaching risk, from RTR towards MNP. Substantial conservation efforts should be made to maintain connectivity between these two subpopulations and also higher protection status should be conferred on Madhav National Park.     

Estimating the Population Size and Genetic Diversity of Amur Tigers in Northeast China

Over the past century, the endangered Amur tiger (Panthera tigris altaica) has experienced a severe contraction in demography and geographic range because of habitat loss, poaching, and prey depletion. In its historical home in Northeast China, there appears to be a single tiger population that includes tigers in Southwest Primorye and Northeast China; however, the current demographic status of this population is uncertain. Information on the abundance, distribution and genetic diversity of this population for assessing the efficacy of conservation interventions are scarce. We used noninvasive genetic detection data from scats, capture-recapture models and an accumulation curve method to estimate the abundance of Amur tigers in Northeast China. We identified 11 individual tigers (6 females and 5 males) using 10 microsatellite loci in three nature reserves between April 2013 and May 2015. These tigers are confined primarily to a Hunchun Nature Reserve along the border with Russia, with an estimated population abundance of 9–11 tigers during the winter of 2014–2015. They showed a low level of genetic diversity. The mean number of alleles per locus was 2.60 and expected and observed heterozygosity were 0.42 and 0.49, respectively. We also documented long-distance dispersal (~270 km) of a male Amur tiger to Huangnihe Nature Reserve from the border, suggesting that the expansion of neighboring Russian populations may eventually help sustain Chinese populations. However, the small and isolated population recorded by this study demonstrate that there is an urgent need for more intensive regional management to create a tiger-permeable landscape and increased genetic connectivity with other populations.     

Prioritizing Tiger Conservation through Landscape Genetics and Habitat Linkages

Even with global support for tiger (Panthera tigris) conservation their survival is threatened by poaching, habitat loss and isolation. Currently about 3,000 wild tigers persist in small fragmented populations within seven percent of their historic range. Identifying and securing habitat linkages that connect source populations for maintaining landscape-level gene flow is an important long-term conservation strategy for endangered carnivores. However, habitat corridors that link regional tiger populations are often lost to development projects due to lack of objective evidence on their importance. Here, we use individual based genetic analysis in combination with landscape permeability models to identify and prioritize movement corridors across seven tiger populations within the Central Indian Landscape. By using a panel of 11 microsatellites we identified 169 individual tigers from 587 scat and 17 tissue samples. We detected four genetic clusters within Central India with limited gene flow among three of them. Bayesian and likelihood analyses identified 17 tigers as having recent immigrant ancestry. Spatially explicit tiger occupancy obtained from extensive landscape-scale surveys across 76,913 km² of forest habitat was found to be only 21,290 km². After accounting for detection bias, the covariates that best explained tiger occupancy were large, remote, dense forest patches; large ungulate abundance, and low human footprint. We used tiger occupancy probability to parameterize habitat permeability for modeling habitat linkages using least-cost and circuit theory pathway analyses. Pairwise genetic differences (F _ST) between populations were better explained by modeled linkage costs (r>0.5, p<0.05) compared to Euclidean distances, which was in consonance with observed habitat fragmentation. The results of our study highlight that many corridors may still be functional as there is evidence of contemporary migration. Conservation efforts should provide legal status to corridors, use smart green infrastructure to mitigate development impacts, and restore habitats where connectivity has been lost.     

Effects of human–carnivore conflict on tiger (Panthera tigris) and prey populations in Lao PDR

Unique to South-east Asia, Lao People's Democratic Republic contains extensive habitat for tigers and their prey within a multiple-use protected area system covering 13% of the country. Although human population density is the lowest in the region, the impact of human occurrence in protected areas on tiger Panthera tigris and prey populations was unknown. We examined the effects of human–carnivore conflict on tiger and prey abundance and distribution in the Nam Et-Phou Louey National Protected Area on the Lao–Vietnam border. We conducted intensive camera-trap sampling of large carnivores and prey at varying levels of human population and monitored carnivore depredation of livestock across the protected area. The relative abundance of large ungulates was low throughout whereas that of small prey was significantly higher where human density was lower. The estimated tiger density for the sample area ranged from 0.2 to 0.7 per 100 km². Tiger abundance was significantly lower where human population and disturbance were greater. Three factors, commercial poaching associated with livestock grazing followed by prey depletion and competition between large carnivores, are likely responsible for tiger abundance and distribution. Maintaining tigers in the country's protected areas will be dependent on the spatial separation of large carnivores and humans by modifying livestock husbandry practices and enforcing zoning.     

Genetic analysis shows low levels of hybridization between African wildcats (Felis silvestris lybica) and domestic cats (F. s. catus) in South Africa

Hybridization between domestic and wild animals is a major concern for biodiversity conservation, and as habitats become increasingly fragmented, conserving biodiversity at all levels, including genetic, becomes increasingly important. Except for tropical forests and true deserts, African wildcats occur across the African continent; however, almost no work has been carried out to assess its genetic status and extent of hybridization with domestic cats. For example, in South Africa it has been argued that the long‐term viability of maintaining pure wildcat populations lies in large protected areas only, isolated from human populations. Two of the largest protected areas in Africa, the Kgalagadi Transfrontier and Kruger National Parks, as well as the size of South Africa and range of landscape uses, provide a model situation to assess how habitat fragmentation and heterogeneity influences the genetic purity of African wildcats. Using population genetic and home range data, we examined the genetic purity of African wildcats and their suspected hybrids across South Africa, including areas within and outside of protected areas. Overall, we found African wildcat populations to be genetically relatively pure, but instances of hybridization and a significant relationship between the genetic distinctiveness (purity) of wildcats and human population pressure were evident. The genetically purest African wildcats were found in the Kgalagadi Transfrontier Park, while samples from around Kruger National Park showed cause for concern, especially combined with the substantial human population density along the park's boundary. While African wildcat populations in South Africa generally appear to be genetically pure, with low levels of hybridization, our genetic data do suggest that protected areas may play an important role in maintaining genetic purity by reducing the likelihood of contact with domestic cats. We suggest that approaches such as corridors between protected areas are unlikely to remain effective for wildcat conservation, as the proximity to human settlements around these areas is projected to increase the wild/domestic animal interface. Thus, large, isolated protected areas will become increasingly important for wildcat conservation and efforts need to be made to prevent introduction of domestic cats into these areas.     

Comparative evaluation of tiger reserves in India

Evidence is vital. Understanding what interventions are effective is critical for the conservation of wild tigers and conservation biology in general. We evaluated the effectiveness of tiger reserves within India, a country with more than half of the estimated wild tiger population, with comparative effectiveness research. Other complex environments, medicine and business use these techniques where cause and effects are often non-linear. These techniques also allowed us to evaluate data from the small sample size often seen in conservation interventions. The opinions of three tiger experts were used to generate a list of seven tiger reserves classified as successful and five reserves as failures. We also used expert opinion to identify any key individuals that garnered widespread support for tiger conservation at any of the identified reserves. Using data from the Indian Census, World Database on Protected Areas, and the Socioeconomic Data and Applications Center, we analyzed the human population around the tiger reserves. We found two surprising insights that have received scant attention in the peer-reviewed literature. First, one can achieve tiger conservation success even within a densely populated human landscape where a high percentage of the population is involved in agriculture. Second, the presence of “conservation champions” can dramatically affect the performance of individual reserves and have positive outcomes for tiger conservation.     

Genotyping faecal samples of Bengal tiger <Emphasis Type="Italic">Panthera tigris tigris</Emphasis> for population estimation: A pilot study

Background

Bengal tiger Panthera tigris tigris the National Animal of India, is an endangered species. Estimating populations for such species is the main objective for designing conservation measures and for evaluating those that are already in place. Due to the tiger's cryptic and secretive behaviour, it is not possible to enumerate and monitor its populations through direct observations; instead indirect methods have always been used for studying tigers in the wild. DNA methods based on non-invasive sampling have not been attempted so far for tiger population studies in India. We describe here a pilot study using DNA extracted from faecal samples of tigers for the purpose of population estimation.

Results

In this study, PCR primers were developed based on tiger-specific variations in the mitochondrial cytochrome b for reliably identifying tiger faecal samples from those of sympatric carnivores. Microsatellite markers were developed for the identification of individual tigers with a sibling Probability of Identity of 0.005 that can distinguish even closely related individuals with 99.9% certainty. The effectiveness of using field-collected tiger faecal samples for DNA analysis was evaluated by sampling, identification and subsequently genotyping samples from two protected areas in southern India.

Conclusion

Our results demonstrate the feasibility of using tiger faecal matter as a potential source of DNA for population estimation of tigers in protected areas in India in addition to the methods currently in use.

     

Genetic Variation,Structure, and Gene Flow in a Sloth Bear (Melursus ursinus) Meta-Population in the Satpura-Maikal Landscape of Central India

Sloth bears (Melursus ursinus) are endemic to the Indian subcontinent. As a result of continued habitat loss and degradation over the past century, sloth bear populations have been in steady decline and now exist only in isolated or fragmented habitat across the entire range. We investigated the genetic connectivity of the sloth bear meta-population in five tiger reserves in the Satpura-Maikal landscape of central India. We used noninvasively collected fecal and hair samples to obtain genotypic information using a panel of seven polymorphic loci. Out of 194 field collected samples, we identified 55 individuals in this meta-population. We found that this meta-population has moderate genetic variation, and is subdivided into two genetic clusters. Further, we identified five first-generation migrants and signatures of contemporary gene flow. We found evidence of sloth bears in the corridor between the Kanha and Pench Tiger Reserves, and our results suggest that habitat connectivity and corridors play an important role in maintaining gene flow in this meta-population. These corridors face several anthropogenic and infrastructure development threats that have the potential to sever ongoing gene flow, if policies to protect them are not put into action immediately.     

Nest Suitability,Fine-Scale Population Structure and Male-Mediated Dispersal of a Solitary Ground Nesting Bee in an Urban Landscape

Bees are the primary pollinators of flowering plants in almost all ecosystems. Worldwide declines in bee populations have raised awareness about the importance of their ecological role in maintaining ecosystem functioning. The naturally strong philopatric behavior that some bee species show can be detrimental to population viability through increased probability of inbreeding. Furthermore, bee populations found in human-altered landscapes, such as urban areas, can experience lower levels of gene flow and effective population sizes, increasing potential for inbreeding depression in wild bee populations. In this study, we investigated the fine-scale population structure of the solitary bee Colletes inaequalis in an urbanized landscape. First, we developed a predictive spatial model to detect suitable nesting habitat for this ground nesting bee and to inform our field search for nests. We genotyped 18 microsatellites in 548 female individuals collected from nest aggregations throughout the study area. Genetic relatedness estimates revealed that genetic similarity among individuals was slightly greater within nest aggregations than among randomly chosen individuals. However, genetic structure among nest aggregations was low (Nei’s G_ST = 0.011). Reconstruction of parental genotypes revealed greater genetic relatedness among females than among males within nest aggregations, suggesting male-mediated dispersal as a potentially important mechanism of population connectivity and inbreeding avoidance. Size of nesting patch was positively correlated with effective population size, but not with other estimators of genetic diversity. We detected a positive trend between geographic distance and genetic differentiation between nest aggregations. Our landscape genetic models suggest that increased urbanization is likely associated with higher levels of inbreeding. Overall, these findings emphasize the importance of density and distribution of suitable nesting patches for enhancing bee population abundance and connectivity in human dominated habitats and highlights the critical contribution of landscape genetic studies for enhanced conservation and management of native pollinators.     

Prey selection by the Indian tiger (Panthera tigris tigris) in Nagarjunasagar Srisailam Tiger Reserve, India

Very little is known about prey selection by the Indian tiger Panthera tigris tigris in tropical dry deciduous forests or in wild herbivore-depleted habitats with high livestock pressures. We undertook a short-term study in a large south Indian tiger reserve and examined two intensive study areas (SA's) from October 1998 – June 1999. In each area, herbivore sightings were recorded, scats were collected, and wild prey and livestock kills documented. Chital, wild boar and sambar were the most abundant among the wild herbivores in the study area. Scat analysis revealed wild boar (Sus scrofa) being the most common prey followed by chital (Axis axis) and sambar (Rusa unicolor). Livestock comprised less than 7% of diet intake. Here, the tigers consumed a lower mean prey mass (56.3 kg) than in other reserves. Our study suggests that in tropical dry deciduous forests with low natural prey density, smaller prey species, and high livestock biomass, tigers preferentially kill smaller prey and generally avoid livestock predation.     

Influence of connectivity, wild prey and disturbance on occupancy of tigers in the human-dominated western Terai Arc Landscape

Occupying only 7% of their historical range and confined to forested habitats interspersed in a matrix of human dominated landscapes, tigers (Panthera tigris) typify the problems faced by most large carnivores worldwide. With heads of governments of tiger range countries pledging to reverse the extinction process and setting a goal of doubling wild tiger numbers by 2022, achieving this target would require identifying existing breeding cores, potential breeding habitats and opportunities for dispersal. The Terai Arc Landscape (TAL) represents one region which has recently witnessed recovery of tiger populations following conservation efforts. In this study, we develop a spatially explicit tiger occupancy model with survey data from 2009–10 based on a priori knowledge of tiger biology and specific issues plaguing the western TAL (6,979 km²), which occurs in two disjunct units (Tiger Habitat Blocks; THBs). Although the overall occupancy of tigers was 0.588 (SE 0.071), our results clearly indicate that loss in functionality of a regional corridor has resulted in tigers now occupying 17.58% of the available habitat in THB I in comparison to 88.5% in THB II. The current patterns of occupancy were best explained by models incorporating the interactive effect of habitat blocks (AIC w = 0.883) on wild prey availability (AIC w = 0.742) and anthropogenic disturbances (AIC w = 0.143). Our analysis has helped identify areas of high tiger occupancy both within and outside existing protected areas, which highlights the need for a unified control of the landscape under a single conservation unit with the primary focus of managing tigers and associated wildlife. Finally, in the light of global conservation targets and recent legislations in India, our study assumes significance as we identify opportunities to secure (e.g. THB II) and increase (e.g. THB I) tiger populations in the landscape.     

Tiger and leopard co-occurrence: intraguild interactions in response to human and livestock disturbance

Intraguild interactions have important implications for carnivore demography and conservation. Differences in how predators respond to different forms of disturbance might alter their interaction patterns. We sought to understand how human and livestock disturbance impact co-occurrence of sympatric large carnivores such as tiger (Panthera tigris) and leopard (P. pardus) and thereby mediate the intraguild interaction pattern to enable coexistence of the species in a human-dominated landscape. We surveyed 361 locations in Chitwan National Park, Nepal, to examine how prey abundance and disturbance factors such as human and livestock presence might influence habitat use by tigers and leopards independently and when co-occurring. Single-species single-season models and two-species single-season models were developed to examine hypotheses on unconditional detection and occupancy and species interaction respectively. Pervasive human use of the park had negative impacts on tiger occupancy while the abundance of prey had a positive influence. Despite significant prey overlap between tigers and leopards, none of the native prey species predicted leopard habitat occupancy. However, habitats used extensively by livestock were also used by leopards. Further, we found strong evidence of intraguild competition. For instance tiger occupancy was higher in prey-rich areas and leopard occupancy was low in the sites where tigers were present. These findings, and a species interaction factor of < 1 clearly indicate that leopards avoid tigers, but their use of areas of disturbance enables them to persist in fringe habitats. We provide empirical evidence of how intraguild interaction may result in habitat segregation between competing carnivores, while also showing that human and livestock use of the landscape create disturbance patterns that facilitate co-occurrence of the predators. Thus, because large carnivores compete, some disturbance may mediate coexistence in small protected areas. Understanding such interactions can help address important conservation challenges associated with maintaining diverse carnivore communities in small or disturbed landscapes.     

亚洲虎种群恢复的机遇与挑战

虎(Panthera tigris)作为顶级捕食者, 对维持森林生态系统服务和结构完整性有着重要作用, 是研究和保护工作的旗舰物种。历史上, 虎曾广泛分布于亚洲大部分地区, 如今仅分布于南亚、东南亚和东北亚的破碎化栖息地, 各区域种群处于濒危或极度濒危状态。准确了解野生虎的种群状态和生态需求信息对于科学开展保护和恢复工作至关重要。本文通过综述近几十年的研究文献, 总结了野生虎种群现状和主要威胁因素, 评价了已有研究的重点与不足, 为未来亚洲虎种群的研究和保护提出了建议。目前与虎相关的研究主要集中在分布范围最广的孟加拉虎(P. t. tigris)和东北虎(P. t. altaica) 2个亚种, 而最急需关注的其他亚种仍研究不足。经过近十几年的努力和保护投入, 目前野生虎种群数量已从2010年的大约3,200只恢复到现在约4,500只, 但在越南、柬埔寨和老挝3个国家已经灭绝。虎面临的主要威胁包括持续的栖息地破坏和隔离、猎物缺乏、近交衰退、人虎冲突、贸易与盗猎和疾病威胁等。未来的研究和保护工作需要加强种群和栖息地连通性恢复、个体重引入、疾病管控以及加强跨境合作和反盗猎等。