- Journal Article2013Opportunistic exploitation: an overlooked pathway to extinctionTrends in Ecology and Evolution. 28(7): 409-413Download
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How can species be exploited economically to extinction? Past single-species hypotheses examining the economic plausibility of exploiting rare species have argued that the escalating value of rarity allows extinction to be profitable. We describe an alternative pathway toward extinction in multispecies exploitation systems, termed ‘opportunistic exploitation’. In this mode, highly valued species that are targeted first by fishing, hunting, and logging become rare, but their populations can decline further through opportunistic exploitation while more common but less desirable species are targeted. Effectively, expanding exploitation to more species subsidizes the eventual extinction of valuable species at low densities. Managers need to recognize conditions that permit opportunistic depletion and pass regulations to protect highly desirable species when exploitation can expand to other species.
- Journal Article2013Can wetlands maintained for human use also help conserve biodiversity? Landscape–scale patterns of bird use of wetlands in an agricultural landscape in north IndiaBiological Conservation 168: 49-56. http://dx.doi.org/10.1016/j.biocon.2013.09.016
Wetlands in tropical agricultural landscapes are maintained largely by local institutions explicitly for human use, which is assumed to deter biodiversity. Conservation efforts have been biased towards protecting large wetlands that are assumed to be adequate to conserve the majority of species of focal taxa, usually birds. These assumptions remain untested, and landscape-scale conservation planning for wetlands is largely absent, as is a generalised understanding of wetland use by focal taxa. We designed a landscape-scale survey to understand patterns and processes determining beta diversity of birds using agricultural wetlands in south-western Uttar Pradesh, India where wetlands have experienced prolonged and intensive human use for several centuries. Observed bird species richness (99 species in 28 wetlands) is the highest known for any agricultural landscape in south Asia signifying that even intensive human use of wetlands does not necessarily deter their ability to retain biodiversity. Birds exhibited strong scale
dependent wetland use underscoring the need to conserve wetlands of varying sizes and at varying densities on the landscape. Beta diversity was due largely to species turnover (0.877) with minimal effect due to nestedness (0.055) suggesting that conserving a few large wetlands will not adequately meet goals of conserving the majority of wetland bird species. Prevailing assumptions regarding biodiversity conservation in tropical agricultural wetlands require being revised, and a landscape-scale approach that incorporates ecological realities is needed. Incorporating local institutions alongside formal protectionist methods offer a potential win–win situation to maximise conservation of biodiversity in tropical agricultural wetlands.
- Journal Article2013Antelope mating strategies facilitate invasion of grasslands by a woody weed.Oikos. 122(10): 1441-1452.Download
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Intra and interspecific variation in frugivore behaviour can have important consequences for seed dispersal outcomes. However, most information comes from among-species comparisons, and within-species variation is relatively poorly understood. We examined how large intraspecific differences in the behaviour of a native disperser, blackbuck antelope Antilope cervicapra, influence dispersal of a woody invasive, Prosopis juliflora, in a grassland ecosystem. Blackbuck disperse P. juliflora seeds through their dung. In lekking blackbuck populations, males defend clustered or dispersed mating territories. Territorial male movement is restricted, and within their territories males defecate on dung-piles. In contrast, mixed-sex herds range over large areas and do not create dung-piles. We expected territorial males to shape seed dispersal patterns, and seed deposition and seedling recruitment to be spatially localized. Territorial males had a disproportionately large influence on seed dispersal. Adult males removed twice as much fruit as females, and seed arrival was disproportionately high on territories. Also, because lek-territories are clustered, seed arrival was spatially highly concentrated. Seedling recruitment was also substantially higher on territories compared with random sites, indicating that the local concentration of seeds created by territorial males continued into high local recruitment of seedlings. Territorial male behaviour may, thus, result in a distinct spatial pattern of invasion of grasslands by the woody P. juliflora. An ex situ experiment showed no beneficial effect of dung and a negative effect of light on seed germination. We conclude that large intraspecific behavioural differences within frugivore populations can result in significant variation in their effectiveness as seed dispersers. Mating strategies in a disperser could shape seed dispersal, seedling recruitment and potentially plant distribution patterns. These mating strategies may aid in the spread of invasives, such as P. juliflora, which could, in turn, negatively influence the behaviour and ecology of native dispersers.
- Journal Article2013People, predators and perceptions: patterns of livestock depredation by snow leopards and wolves.Journal of Applied Ecology 50 (3), 550-560
- Journal Article2013Understanding the patchy distribution of four-horned antelope Tetracerus quadricornis in a tropical dry deciduous forest in Central IndiaJournal of Tropical Ecology, 1-10. doi:10.1017/S0266467413000722
At the landscape level, the four-horned antelope is confined to tropical dry deciduous forests and within these, their distribution is patchy. Various factors have been proposed as determinants for their patchy distribution within landscapes, but none provided an adequate explanation. We hypothesized that availability of a constant supply of forage influenced the species distribution.We found that the four-horned antelope mainly fed on fruits and flowers, and that a total of 60% of the tree species in Panna Tiger Reserve bore fruits at different times of the year. High tree species richness in habitat patches was considered a surrogate for constant supply of forage for the four-horned antelope. Data from 547 sighting locations between 2002 and 2006 and six spatial layers were analysed using maximum entropy to produce a probability distribution model for the four-horned antelope in Panna Tiger Reserve. Our model predicted that habitat patches summing up to only 9.5% of the 543 km2 of Panna Tiger Reserve had high probability of distribution (>0.5) of four-horned antelope. Although all variables contributed to the distribution model of the four-horned antelope, explanatory power was highest for tree species richness within habitat patches. The distribution of four-horned antelope within tropical dry deciduous forests can be treated as an indicator of high tree diversity and hence habitat quality.
- Journal Article2013Design and Evaluation of a Robust Optical Beam-Interruption-Based Vehicle Classiﬁer SystemIEEE Transactions on Intelligent Transportation Systems 14(3): 1043-1052Download
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This paper presents the design and development of a novel optical vehicle classifier system, which is based on interruption of laser beams, that is suitable for use in places with poor transportation infrastructure. The system can estimate the speed, axle count, wheelbase, tire diameter, and the lane of motion of a vehicle. The design of the system eliminates the need for careful optical alignment, whereas the proposed estimation strategies render the estimates insensitive to angular mounting errors and to unevenness of the road. Strategies to estimate vehicular parameters are described along with the optimization of the geometry of the system to minimize estimation errors due to quantization. The system is subsequently fabricated, and the proposed features of the system are experimentally demonstrated. The relative errors in the estimation of velocity and tire diameter are shown to be within 0.5% and to change by less than 17% for angular mounting errors up to 30°. In the field, the classifier demonstrates accuracy better than 97.5% and 94%, respectively, in the estimation of the wheelbase and lane of motion and can classify vehicles with an average accuracy of over 89.5%.
- Journal Article2013Joint Indian initiative creates tiger corridorNature, 500, 29Download
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Short excerpt on the creation of 6,500 sq km of contiguous network of protected areas — the largest in the country.
- Journal Article2013Globalization of the Cashmere Market and the Decline of Large Mammals in Central AsiaConservation Biology 27, no. 4 (2013): 679-689
- Journal Article2013Influence of gaze and directness of approach on the escape responses of the Indian Rock Lizard, Psammophilus dorsalis (Gray, 1831).Journal of Biosciences. 38(5): 829–833.Download
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Animals often evaluate the degree of risk posed by a predator and respond accordingly. Since many predators orient their eyes towards prey while attacking, predator gaze and directness of approach could serve as conspicuous indicators of risk to prey. The ability to perceive these cues and discriminate between high and low predation risk should benefit prey species through both higher survival and decreased energy expenditure. We experimentally examined whether Indian rock lizards (Psammophilus dorsalis) can perceive these two indicators of predation risk by measuring the variation in their fleeing behaviour in response to type of gaze and approach by a human predator. Overall, we found that the gaze and approach of the predator influenced flight initiation distance, which also varied with attributes of the prey (i.e. size/sex and tail-raise behaviour). Flight initiation distance (FID) was 43% longer during direct approaches with direct gaze compared with tangential approaches with averted gaze. In further, exploratory, analyses, we found that FID was 23% shorter for adult male lizards than for female or young male (FYM) lizards. In addition, FYM lizards that showed a tail-raise display during approach had a 71% longer FID than those that did not. Our results suggest that multiple factors influence the decision to flee in animals. Further studies are needed to test the generality of these factors and to investigate the proximate mechanisms underlying flight decisions.
- Journal Article2013Role of Tibetan Buddhist Monasteries in Snow Leopard ConservationConservation Biology. DOI: 10.1111/cobi.12135
- Journal Article2013Globalization of the Cashmere Market and the Decline of Large Mammals in Central AsiaConservation Biology 27: 679-689
- Journal Article2013Large carnivores and low diversity of optimal prey: a comparison of the diets of snow leopards Panthera uncia and wolves Canis lupus in Sarychat-Ertash Reserve in KyrgyzstanOryx DOI:10.1017/S0030605313000306
- Journal Article2013Reversible immobilization of free-ranging snow leopards (Panthera uncia) using a combination of Medetomidine and Tiletamine-ZolazepamJournal of Wildlife Diseases DOI: 10.7589/2012-02-049
- Journal Article2012Structure and dynamics of South East Indian seagrass meadows across a sediment gradientAquatic Botany, 98 (1): 34-39Download
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In this study we examine the influence of non-monsoon sediment arrival on the high-diversity SE Indian seagrass meadows of the Palk Bay and the Gulf of Mannar. We used a gradient-based approach to examine the influence of increasing sediment loads on species composition and shoot density. In addition, for the ubiquitous seagrass (Cymodocea serrulata), we tested the influence of sediment on its biomass and productivity. We identified three sites in Palk Bay and four sites in Gulf of Mannar (SE India) along a gradient of sediment input. At each of the seven locations, sediment traps were deployed to measure sedimentation rates. Nine seagrass cores were taken systematically along 50 m transects at a constant sub-tidal depth to measure shoot density and biomass. A few shoots of C. serrulata were marked to estimate the above ground seagrass growth rate. Our results indicate that sedimentation rates that ranged from 8.6 to 62.4 mg DW cm−2 d−1 could not explain species composition of the meadow or shoot density of the observed species. C. serrulata was, by far, the most abundant species and present in all sediment condi- tions. Sedimentation rates did not alter shoot elongation rates in C. serrulata, ranging from 1.54 ± 0.29 SD to 0.25 ± 0.02 SD cm d−1 , but in contrast, increased vertical rhizome elongation rate. This increase was reflected in an increase in below ground biomass along the sediment gradient (R2 = 0.582, p = 0.01). C. serrulata appears to be able to adapt to the sediment dynamics in this area by allocating resources to rhizomes and roots to counteract burial and stabilizing sediments. Given that siltation is one of the most important threats to seagrass meadows, understanding the species-specific adaptive mechanisms of seagrass species in these high-sediment, high diversity South Asian meadows is an important first step in ensuring their long-term survival and functioning
- Journal Article2012Streamside amphibian communities in plantations and a rainforest fragment in the Anamalai hills, IndiaJournal of Threatened Taxa 4: 2849–2856.Download
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Stream amphibian communities, occupying a sensitive environment, are often useful indicators of effects of adjoining land uses. We compared abundance and community composition of anuran amphibians along streams in tea monoculture, shade coffee plantation, and a rainforest fragment in Old Valparai area of the Anamalai hills. Overall species density and rarefaction species richness was the highest in rainforest fragment and did not vary between the coffee and tea land uses. Densities of certain taxa, and consequently community composition, varied significantly among the land uses, being greater between rainforest fragment and tea monoculture with shade coffee being intermediate. Observed changes are probably related to streamside alteration due to land use, suggesting the need to retain shade tree cover and remnant riparian rainforest vegetation as buffers along streams.
- Journal Article2012Conservation needs of the Coconut Crab (Birgus latro) on the Nicobar Islands, IndiaOryx, 46: 175-178.Download
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We describe the distribution of the coconut crab Birgus latro, categorized as Data Deficient on the IUCN Red List, local perspectives towards the species, and its conservation needs on the Nicobar Islands in the eastern Indian Ocean. The species is threatened with extinction across most of its range and in India it is found only on a few islands in the Andaman and Nicobar archipelagoes. We carried out informal discussions with Nicobari commu- nities to examine issues regarding conservation of the species and conducted timed searches in areas where coconut crabs were likely to be found. The discussions revealed that there are social taboos against hunting the coconut crab on most of the Nicobar Islands. However, on some islands these taboos are not being followed and community members may hunt the crab for consumption. Athough the coconut crab is legally protected under the Indian Wildlife Protection Act none of the villagers were aware of this. Of the six islands surveyed we recorded the presence of 17 and 14 crabs on two islands, respectively. On four islands villagers reported the presence of the crab prior to the tsunami of 2004, and on two of these islands the species may now be locally extinct. A small population size and a fragmented distribution in areas of coconut planta- tions suggest that the species is threatened. We recommend monitoring and detailed research on the ecology and genetics of the coconut crab, along with community-based conservation initiatives to conserve the species and its habitat.
- Journal Article2012Distance-related thresholds and influence of the 2004 tsunami on damage and recovery patterns of coral reefs in the Nicobar IslandsCurrent Science 102:1199–1205
The earthquake and tsunami of 2004 resulted in the devastation of marine and coastal ecosystems across the Indian Ocean. However, without adequate baseline information it has been difficult to properly gauge its full impact. The reefs of the Nicobar Islands in the Bay of Bengal lie on a path that ranges from 190 to 500 km from Banda Aceh, the epicentre of the 2004 tsunami. In 2008, we recorded benthic damage as a result of the tsunami to reefs off 14 Nicobar Islands across a gradient of distance from the epicentre. A clear pattern was observed in the demographic structure of the most abundant coral genera, Acropora and Porites across the distance gradient. Significantly, for the largest coral individuals of both genera (> 50 cm diameter), there were distinct threshold effects – their abundance declining dramatically in reefs closer than 350 km from the epicentre. Corals between 20 and 50 cm diameter also increased with distance from the epicentre, but in a more linear fashion. Smaller size classes either showed no apparent trend (Acropora) or decreased linearly (Porites) with distance. These gen- era represent very different life-history strategies: Acropora is fast-growing and highly susceptible to a range of disturbances, while Porites typically grows slowly but is resistant to disturbance. The fact that both genera showed similar thresholds indicates that, close to the epicentre, the impact of the earthquake and tsunami was large enough to override any species- specific resistance. Also, algal cover was also much higher than at locations further north, linked to higher coral mortality at these locations. However, the fact that smaller size class coral individuals were rela- tively abundant and even increased close to the ep centre indicates possible paths of reef recovery after the catastrophe.
- Journal Article2012To eat and not be eaten: modelling resources and safety in multi-species animal groups.PLoS ONE. 7(7): e42071.Download
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Using mixed-species bird flocks as an example, we model the payoffs for two types of species from participating in multi-species animal groups. Salliers feed on mobile prey, are good sentinels and do not affect prey capture rates of gleaners; gleaners feed on prey on substrates and can enhance the prey capture rate of salliers by flushing prey, but are poor sentinels. These functional types are known from various animal taxa that form multi-species associations. We model costs and benefits of joining groups for a wide range of group compositions under varying abundances of two types of prey–prey on substrates and mobile prey. Our model predicts that gleaners and salliers show a conflict of interest in multi-species groups, because gleaners benefit from increasing numbers of salliers in the group, whereas salliers benefit from increasing gleaner numbers. The model also predicts that the limits to size and variability in composition of multi-species groups are driven by the relative abundance of different types of prey, independent of predation pressure. Our model emphasises resources as a primary driver of temporal and spatial group dynamics, rather than reproductive activity or predation per se, which have hitherto been thought to explain patterns of multi-species group formation and cohesion. The qualitative predictions of the model are supported by empirical patterns from both terrestrial and marine multi-species groups, suggesting that similar mechanisms might underlie group dynamics in a range of taxa. The model also makes novel predictions about group dynamics that can be tested using variation across space and time.
- Journal Article2012Methodological, temporal and spatial factors affecting modelled occupancy of resident birds in the perennially cultivated landscape of Uttar Pradesh, IndiaLandscape Ecology 27: 59-71. doi:10.1007/s10980-011-9666-3.
Biodiversity persistence in non-woody tropical farmlands is poorly explored, and multispecies assessments with robust landscape-scale designs are sparse. Modeled species occupancy in agricultural mosaics is affected by multiple factors including survey methods (convenience-based versus systematic), landscape-scale agriculture-related variables, and extent of remnant habitat. Changes in seasonal crops can additionally alter landscape and habitat conditions thereby influencing species occupancy. We investigated how these factors affect modeled occupancy of 56 resident bird species using a landscape-scale multi-season occupancy framework across 24 intensively cultivated and human-dominated districts in Uttar Pradesh state, north India. Convenience-based roadside observations provided considerable differences in occupancy estimates and associations with remnant habitat and intensity of cultivation relative to systematic transect counts, and appeared to bias results to roadside conditions. Modeled occupancy of only open-area species improved with increasing intensity of cultivation, while remnant habitat improved modeled occupancy of scrubland, wetland and woodland species. Strong seasonal differences in occupancy were apparent for most species across all habitat guilds. Further habitat loss will be most detrimental to resident scrubland, wetland and woodland species. Uttar Pradesh’s agricultural landscape has a high conservation value, but will require a landscape-level approach to maintain the observed high species richness. Obtaining ecological information from unexplored landscapes using robust landscape-scale surveys offers substantial advantages to understand factors affecting species occupancy, and is necessary for efficient conservation planning.
- Journal Article2012Trends in extinction and persistence of diurnal primates in Upper Brahmaputra ValleyOryx 46(2): 308-311Download
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The historical deforestation of the Upper Brahmaputra Valley in the Indian state of Assam has resulted in the transformation of its once-contiguous lowland rainforests into many isolated forest fragments that are still rich in species, including primates. We report the recent history and current status of six diurnal primates in one large (2,098 ha) and three small (, 500 ha) fragments of the Upper Brahmaputra Valley. We censused primates in the small fragments during 2002, 2005, 2009, in the large fragment in 2008, and used other published census data to derive population trends. We also used key informant surveys to obtain historical occurrence data for these populations. Our analyses reveal the recent extinction of some populations and the simultaneous long-term persist- ence of others in these fragments over 16 years. Most populations appeared to have declined in the small fragments but primate abundance has increased signific- antly in the largest fragment over the last decade. Addressing the biomass needs of the local human populations, which appears to drive habitat degradation, and better protection of these forests, will be crucial in ensuring the future survival of this diverse and unique primate assemblage in the last rainforest fragments of the human-dominated Upper Brahmaputra Valley.