Search

Climate plays a vital role in the carbon (C) uptake through vegetation productivity (Gross Primary Production; GPP) that is crucial to the persistence of the land as a carbon sink, thereby resulting in negative land-climate feedbacks. Large uncertainties persist in understanding the role of climate variability on this C flux, which influence future projections using Earth System Models (ESMs). One important source of uncertainty arises from the temporal variability in the carbon influx, and this includes effects of autocorrelation—i.e., similarity in observations with time-lag due to temporal structuring (“memory”) in the underlying dynamics. Evidence of the presence of memory in C uptake through GPP arises from field-based measurements through eddy covariance flux towers, but these lack widespread spatial distribution across environmental conditions and ecosystems. Therefore, estimating memory in the C cycle and its drivers on the global scale is important to our understanding of the global C cycle. For this, we used remotely sensed long-term GPP data from MODIS over the past two decades (2001-2021), to estimate long-term memory in C cycling through C-uptake by vegetation. Additionally, we also examined how the climate variables – temperature and precipitation- that are known to drive C influx, influenced the memory in C-uptake. We find that memory occurs in satellite-based estimates of GPP, corroborating field-based measurements. Interestingly, the memory in the C cycle was not limited to either short- or long-term but consisted of both these characteristics across different timescales. Climate variability through temperature and precipitation influenced memory and their effects are heterogeneous across ecosystems. With climate variability predicted to increase in the near future, our results suggest that these effects are likely to be consequential for the memory in C-uptake and, ultimately on the dynamics of the global C cycle. Therefore, estimating the memory in C cycle and its variation, is crucial for understanding as well as predicting the C-influx, under present and future climate change scenarios.

Grazing by mammalian herbivores can be a climate mitigation strategy as it influences the size and stability of a large soil carbon (soil-C) pool (more than 500 Pg C in the world’s grasslands, steppes, and savannas). With continuing declines in the numbers of large mammalian herbivores, the resultant loss in grazer functions can be consequential for this soil-C pool and ultimately for the global carbon cycle. While herbivore effects on the size of the soil-C pool and the conditions under which they lead to gain or loss in soil-C are becoming increasingly clear, their effect on the equally important aspect of stability of soil-C remains unknown. We used a replicated long-term field experiment in the Trans-Himalayan grazing ecosystem to evaluate the consequences of herbivore exclusion on interannual fluctuations in soil-C (2006 to 2021). Interannual fluctuations in soil-C and soil-N were 30 to 40% higher after herbivore exclusion than under grazing. Structural equation modeling suggested that grazing appears to mediate the stabilizing versus destabilizing influences of nitrogen (N) on soil-C. This may explain why N addition stimulates soil-C loss in the absence of herbivores around the world. Herbivore loss, and the consequent decline in grazer functions, can therefore undermine the stability of soil-C. Soil-C is not inert but a very dynamic pool. It can provide nature-based climate solutions by conserving and restoring a functional role of large mammalian herbivores that extends to the stoichiometric coupling between soil-C and soil-N.

SummaryDiversity-function relationships are well known for producers, and these are also known to be influenced by consumers at higher trophic levels. However, these are not well known for microbial decomposers and decomposition processes in soil. Further, it also remains unknown whether and how consumers such as large mammalian herbivores, who are a major feature across more than one-third of the world’s terrestrial realm, influence soil microbial decomposer diversity-function relationships.We used a14-year old long-term herbivore-exclusion experiment to answer two questions: (a) whether microbial functions vary with microbial diversity (both species richness and composition), and (b) whether herbivores alter the diversity-function relationships among microbial decomposers. We measured functional richness, and functional dispersion from the utilization profiles of 30 metabolic substrates. Alongside, we also measured species richness and species composition of soil microbes.We analysed soils from n=10 paired grazed-and-fenced plots, and sampled them three times during the growth season of 2019. Data were from 60 16S rDNA gene amplicon sequences with 7.6 million reads covering 1937 operational taxonomic units (OTU) across 47 phyla (of which 924 OTUs were identifiable to genus level), and 1800 catabolic profiles.Functional diversity in soil was positively related to microbial community composition, but not to species richness. This parallels the diversity-function relationships between producers and production; it also challenges the prevailing notion of functional redundancy in hyper-diverse soil microbial communities. Since certain combinations of species can outperform others, global change factors which can alter microbial communities may also impact decomposition processes and services. But this coupling between diversity and functions was unaffected by experimental herbivore-exclusion, indicating resilience and resistance among decomposers.Structural equation models suggested that the strength of this relationship is favoured by availability of soil moisture. These also showed microbial functions varied more strongly with temporal variables (e.g., seasonality) than with spatial variables (e.g., edaphic factors such as soil texture and pH). Although interpretations can be constrained by which and how many functions are investigated, the relationship between diversity and functions was generalizable and robust once 16 or more functions were quantified.While ecosystem functions and services derived from microbial decomposers have intrinsic resilience and resistance, they respond strongly to variability in water availability. Decomposition in grazing ecosystems may be particularly susceptible to how microbial community composition responds to rising precipitation variability under ongoing and projected climate change.HighlightsDiversity-function relationships for microbial decomposers remain uncertain.Microbial diversity is positively related to functionsThis relationship is robust to herbivore-exclusion.Microbial diversity-function relationship can be susceptible to altered precipitation

SummaryEutrophication impacts grassland diversity such as species richness, functional trait diversity and composition, but whether and how these changes affect ecosystem functional stability under increasing climate extremes is unknown. We quantify the direct and diversity-mediated effects of nutrient addition on functional stability of productivity as measured by resistance during and recovery after dry and wet growing seasons, and temporal invariability across 19 grasslands spanning four continents. We use leaf traits measured in the field to construct slow-fast leaf economic spectrum and calculate functional trait composition and diversity of the slow-fast trait. Nutrient addition increased resistance during dry growing seasons mainly through its direct effects. It also increased resistance during wet growing seasons directly, but these positive effects were weakened by indirect negative effects through reducing slow-fast functional diversity. Nutrient addition had weak effects on recovery after dry growing seasons, but it decreased recovery after wet growing seasons mainly through its direct effects. Nutrient addition increased temporal invariability through resistance, but decreased it through recovery and reducing species richness, leading to overall weak net effects. Thus, processes and influencing pathways independent of plant diversity should be carefully taken into account in understanding ecosystem stability in response to increasing global changes.

The effects of altered nutrient supplies and herbivore density on species diversity vary with spatial scale, because coexistence mechanisms are scale dependent. This scale dependence may alter the shape of the species–area relationship (SAR), which can be described by changes in species richness (S) as a power function of the sample area (A): S = cAz, where c and z are constants. We analysed the effects of experimental manipulations of nutrient supply and herbivore density on species richness across a range of scales (0.01–75 m²) at 30 grasslands in 10 countries. We found that nutrient addition reduced the number of species that could co-occur locally, indicated by the SAR intercepts (log c), but did not affect the SAR slopes (z). As a result, proportional species loss due to nutrient enrichment was largely unchanged across sampling scales, whereas total species loss increased over threefold across our range of sampling scales.

Aim Animal migrations influence ecosystem structure, dynamics and persistence of predator and prey populations. The theory of migratory coupling postulates that aggregations of migrant prey can induce large-scale synchronized movements in predators, and this coupling is consequential for the dynamics of ecological communities. The degree to which humans influence these interactions remains largely unknown. We tested whether creation of large resource pulses by humans such as seasonal herding of reindeer Rangifer tarandus and hunting of moose, Alces alces, can induce migratory coupling with Golden Eagles, Aquila chrysaetos, and whether these lead to demographic consequences for the eagles. Location Fennoscandia. Methods We used movement data from 32 tracked Golden Eagles spanning 125 annual migratory cycles over 8 years. We obtained reindeer distribution data through collaboration with reindeer herders based on satellite tracking of reindeer, and moose harvest data from the national hunting statistics for Sweden. We assessed demographic consequences for eagles from ingesting lead from ammunition fragments in moose carcasses through survival estimates and their links with lead concentrations in eagles' blood. Results In spring, eagles migrated hundreds of kilometres to be spatially and temporally coupled with calving reindeer, whereas in autumn, eagles matched their distribution with the location and timing of moose hunt. Juveniles were more likely to couple with reindeer calving, whereas adults were particularly drawn to areas of higher moose harvest. Due to this coupling, eagles ingested lead from spent ammunition in moose offal and carcasses and the resulting lead toxicity increased the risk of mortality by 3.4 times. Main conclusions We show how migratory coupling connects landscape processes and that human actions can influence migratory coupling over large spatial scales and increase demographic risks for predators. We provide vital knowledge towards resolving human-wildlife conflicts and the conservation of protected species over a large spatial and temporal scale.

Grazing is the dominant land use across the world, and large mammalian herbivores exert strong influence over biogeochemical cycles. Grazing ecosystems feature C-rich soils, even though herbivores consume a major fraction of plant production to reduce detrital input to soil. Yet, counter-intuitively, moderate grazing can promote net soil-C storage in many ecosystems compared to grazer-exclusion. We address this enigmatic influence of grazers on soil-C and test their indirect effect on proximate drivers of decomposition: microbial extracellular enzyme activity. We used a replicated long-term grazer-exclusion experiment to measure responses in above- and belowground plant biomass, soil-C stock, microbial biomass, labile/recalcitrant C pools and three enzymes relevant to the C-cycle: peroxidase—which initiates decomposition of recalcitrant matter, alongside beta-glucosidase and cellobiohydrolase—which act further downstream on more labile fractions. Consistent with other ecosystems, upto 12 years of herbivore exclusion did not increase soil-C in the fenced plots despite higher plant biomass and higher potential detrital C-inputs. Grazer-exclusion did not alter microbial biomass; peroxidase increased threefold and beta-glucosidase was doubled; cellobiohydrolase was unaffected. Grazer-exclusion also led to twofold increase in recalcitrant-C and in microbial respiration, but it did not influence labile-C. Structural equation models supported the hypothesis that grazing favours soil-C via its indirect effect on peroxidase, but they did not support that the effects can run in the opposite direction where soil-C affects enzymes. Grazer-mediated shifts in how microbes deploy enzymes emerge as a plausible mechanism that affects soil-C. These linkages may be important to maintain soil-C sequestration in drylands which support large mammalian herbivores.

Stability of the soil carbon (C) pool under decadal scale variability in temperature and precipitation is an important source of uncertainty in our understanding of land-atmosphere climate feedbacks. This depends on how two opposing C-fluxes-influx from net primary production (NPP) and efflux from heterotrophic soil respiration (Rh )-respond to covariation in temperature and precipitation. There is scant evidence to judge whether field experiments which manipulate both temperature and precipitation align with Earth System Models, or not. As a result, even though the world is generally greening, whether the resultant gains in NPP can offset climate change impacts on Rh , where, and by how much, remains uncertain. Here, we use decadal-scale global time-series datasets on NPP, Rh , temperature, and precipitation to estimate the two opposing C-fluxes and address whether one can outpace the other. We implement machine-learning tools on recent (2001-2019) and near-future climate scenarios (2020-2040) to assess the response of both C-fluxes to temperature and precipitation variation. We find that changes in C-influx may not compensate for C-efflux, particularly in wetter and warmer conditions. Soil-C loss can occur in both tropics and at high latitudes since C-influx from NPP can fall behind C-efflux from Rh . Precipitation emerges as the key determinant of soil-C vulnerability in a warmer world, implying that hotspots for soil-C loss/gain can shift rapidly and highlighting that soil-C is vulnerable to climate change despite widespread greening of the world. The direction of covariation between change in temperature and precipitation, rather than their magnitude, can help conceptualize highly variable patterns in C-fluxes to guide soil-C stewardship.

Grazing by mammalian herbivores can serve as a climate mitigation strategy as it influences the size and stability of a large soil-C pool (more than 200 Pg C in the world’s grasslands, steppes, and savannas). With the continuing decline in large mammalian herbivores, the resultant loss in grazer functions can be consequential for this soil-C pool, and ultimately for the global carbon cycle. While herbivore effects on the size of the soil-C pool and conditions under which they lead to gains/loss in soil-C are well known, their effects on the equally important aspect of stability of soil-C remain unknown. Also unknown is whether herbivore effects on soil-C and soil-N are related to each other. We use a replicated long-term grazer-exclusion experiment in the Trans-Himalayan ecosystem of northern India to evaluate the consequences of herbivore-loss on the stability of soil-C by quantifying interannual fluctuations (2006-2021). We test how grazers influence the stability of soil-C due to their impacts on both soil-C and soil-N. We find that experimental herbivore-exclusion raises inter-annual fluctuations in both soil-C and soil-N. Importantly, structural equations modelling show that herbivore-exclusion increases the soil-C and soil-N coupling, and weakens the stabilizing effect of soil-N on soil-C. Herbivore-loss, and consequent decline in grazer functions in soil, can therefore undermine the stability of soil-C. Conserving and restoring the functional role of large mammalian herbivores is critical for this valuable ecological service and towards climate mitigation.

Grazing by large mammalian herbivores impacts climate as it can favor the size and stability of a large carbon (C) pool in soil. As native herbivores in the world’s grasslands, steppes, and savannas are progressively being displaced by livestock, it is important to ask whether livestock can emulate the functional roles of their native counterparts. While livestock and native herbivores can have remarkable similarity in their traits, they can differ greatly in their impacts on vegetation composition which can affect soil-C. It is uncertain how their similarities and differences impact soil-C via their influence on microbial decomposers. We test competing alternative hypotheses with a replicated, long-term, landscape-level, grazing-exclusion experiment to ask whether livestock in the Trans-Himalayan ecosystem of northern India can match decadal-scale (2005-2016) soil-C stocks under native herbivores. We evaluate multiple lines of evidence from 17 variables that influence soil-C (quantity and quality of C-input from plants, microbial biomass and metabolism, microbial community composition, veterinary antibiotics in soil), and asses their inter-relationships. Livestock and native herbivores differed in their effects on several soil microbial processes. Microbial carbon use efficiency (CUE) was 19% lower in soils under livestock. Compared to native herbivores, areas used by livestock contained 1.5 kg C m−2less soil-C. Structural equation models showed that alongside effects arising from plants, livestock alter soil microbial communities which is detrimental for CUE, and ultimately also for soil-C. Supporting evidence pointed toward a link between veterinary antibiotics used on livestock, microbial communities, and soil-C. Overcoming the challenges of sequestrating antibiotics to minimize their potential impacts on climate, alongside microbial rewilding under livestock, may reconcile the conflicting demands from food-security and ecosystem services. Conservation of native herbivores and better management of livestock is crucial for soil-C stewardship to envision and achieve natural climate solutions.

Nutrients and herbivores have independent effects on the temporal stability of aboveground biomass in grasslands; however, their joint effects may not be additive and may also depend on spatial scales. In an experiment adding nutrients and excluding herbivores in 34 globally distributed grasslands, we found that nutrients and herbivores mainly had additive effects. Nutrient addition consistently reduced stability at the local and larger spatial scales (aggregated local communities), while herbivore exclusion weakly reduced stability at these scales. Moreover, nutrient addition reduced stability primarily by causing changes in local community composition over time and by reducing local species richness and evenness. In contrast, herbivore exclusion weakly reduced stability at the larger scale mainly by decreasing asynchronous dynamics among local communities, but also by weakly decreasing local species richness. Our findings indicate disentangling the influences of processes operating at different spatial scales may improve conservation and management in stabilizing grassland biomass.

Arbuscular mycorrhizal fungal (AMF) symbioses with plants can be influenced by top-down forces such as grazing, and also by bottom-up forces such as soil resource availability, both of which are being altered by anthropogenic and global change drivers. While the influence of each of these factors on AMF symbioses has been widely studied, explicit tests of the relative strengths of top-down versus bottom-up influences on these ubiquitous plant root symbioses are few. We studied AMF colonization responses of four species of graminoids (3 grasses Elymus longae-aristatus, Leymus secalinus and Stipa orientalis, and a sedge Carex melanantha) common to semiarid high-altitude rangelands of the Spiti region, Trans-Himalaya, to changes in a top-down driver, grazing intensity (through short-term clipping and long-term grazer exclusion experiments), and a bottom-up driver, water availability (using irrigation treatments, and by evaluating responses to annual precipitation levels across years). Over three years, AMF colonization in all four host species was influenced by precipitation, with the highest and lowest AMF colonization levels corresponding to years with the lowest and highest rainfall, respectively. However, responses to long-term grazer exclusion differed among host species, and across years: while some species showed decreases in AMF colonization levels under grazing, others showed increases from ungrazed control levels, and these responses changed, even reversed, across years. Responses to short-term clipping and irrigation treatments also differed among hosts, with some species responding to irrigation alone, some to clipping and irrigation combined, and others showing no changes in AMF colonization from control levels in any of the treatments. In our study, long-term changes in water availability influenced AMF colonization levels, while short-term responses were host specific. Responses to above-ground tissue loss, however, differed among host species both in the long- and short-term. Overall, this study demonstrates that while AMF colonization levels correspond to annual precipitation levels in this semiarid ecosystem, host species also play a role in influencing plant-AMF interactions in these rangelands, with colonization levels and responses to abiotic factors changing with host species.

Protanilla flamma sp. n. from Goa, India is described, which is the thirteenth species in the genus Protanilla and the second record of this genus from the country. The new species morphologically appears close to P. lini Terayama, 2009 in terms of mandibular teeth count and the structure of petiolar and post-petiolar nodes. However, it can be very easily differentiated based on the short antennal scape which does not exceed the posterior margin of the head.

Human–wildlife conflict arising from livestock-losses to large carnivores is an important challenge faced by conservation. Theory of prey–predator interactions suggests that revival of wild prey populations can reduce predator's dependence on livestock in multiple-use landscapes. We explore whether 10-years of conservation efforts to revive wild prey could reduce snow leopard's Panthera uncia consumption of livestock in the coupled human-and-natural Trans-Himalayan ecosystem of northern India. Starting in 2001, concerted conservation efforts at one site (intervention) attempted recovery of wild-prey populations by creating livestock-free reserves, accompanied with other incentives (e.g. insurance, vigilant herding). Another site, 50km away, was monitored as status quo without any interventions. Prey remains in snow leopard scats were examined periodically at five-year intervals between 2002 and 2012 to determine any temporal shift in diet at both sites to evaluate the effectiveness of conservation interventions. Consumption of livestock increased at the status quo site, while it decreased at the intervention-site. At the intervention-site, livestock-consumption reduced during 2002–2007 (by 17%, p=0.06); this effect was sustained during the next five-year interval, and it was accompanied by a persistent increase in wild prey populations. Here we also noted increased predator populations, likely due to immigration into the study area. Despite the increase in the predator population, there was no increase in livestock-consumption. In contrast, under status quo, dependence on livestock increased during both five-year intervals (by 7%, p=0.08, and by 16%, p=0.01, respectively). These contrasts between the trajectories of the two sites suggest that livestock-loss can potentially be reduced through the revival of wild prey. Further, accommodating counter-factual scenarios may be an important step to infer whether conservation efforts achieve their targets, or not.

Woody encroachment is of global concern in arid and semiarid regions around the world. Due to reduction in grass (forage), woody encroachment is viewed as ecosystem disservice and degradation, even though this may not reduce ecosystem functions. Often, management perceptions of degradation remain inadequately informed by knowledge of ecosystem processes. We compared 11 biotic variables related to soil and microbial functions under shrubs against paired-adjacent grassland:- carbon, nitrogen, C:N ratio, organic matter, plant-available N, N-mineralization rate, microbial biomass C and N, basal respiration, and metabolic-quotient. We summarized these as a multifunction-index. We also measured five soil physico-chemical covariates:- pH, conductivity, bulk density, texture and water holding capacity. These 11 biotic variables were 15–48% higher under shrubs than under grass; multifunction-index was also higher (by 366%). After accounting for spatial autocorrelation and background differences in physico-chemical covariates (redundancy analysis), altered ecosystem functions were attributable to shrubs. Overall, shrubs can enhance ecosystem functions, and maintain important ecological processes through concomitant changes in soil physico-chemical properties. While shrubs should not be equated to ecological degradation, they present a challenging triage of ecosystem service, disservice, and function for grasslands. Management strategies could benefit from targeting patterns of nutrient re-distribution under shrubs.

Understanding spatial-temporal patterns of terrestrial vegetation response to climate change (long-term greening/browning) is important for developing strategies to mitigate degradation. Semiarid rangelands are especially susceptible to degradation, which challenges wildlife conservation and human livelihoods that depend on livestock production. In the cold-arid Trans-Himalayan ecosystem (northern India), temperature is increasing, and it is also becoming progressively wetter. Yet, counter-intuitively, there are widespread concerns over degradation. We evaluated whether greening/browning patterns in long-term satellite-derived vegetation indices (normalized difference vegetation index NDVI]) are consistent across different spatial and temporal scales using 6 datasets: MODIS (250m, 500m, 1km, and 5.5km), SPOT 1km, and GIMMS 8km. Results indicate browning in the spring and greening in late summer. Location of hotspots of degradation (browning) was broadly consistent across spatial scales (10(-2)-10(2)km(2)) and were found in regions with warmer temperature and at higher elevations. Broadly, the spatial/temporal pattern of browning does not coincide strongly with location and timing of human land use via livestock grazing. This geographical and seasonal context indicates that vegetation response may be more strongly related to climate than to human land use (overgrazing). Importantly, the dynamic nature of greening/browning, across space and time, is not captured by composite annual metrics (sum-NDVI, max-NDVI, and mean-NDVI). This reiterates the importance of both intraannual and interannual assessments. Location of hotspots indicates that degradation occurs in a spatially contiguous manner, but these are not stationary and instead shift with seasons. Overall, the results show that evaluating the consistency of greening/browning trends across different spatial/temporal scales is critical for understanding and managing vegetation degradation.

Quantification of rates and patterns of community dynamics is central for understanding the organization and function of ecosystems. These insights may support a greater empirical understanding of ecological resilience, and the application of resilience concepts toward ecosystem management. Distinct types of dynamics in natural communities can be used to interpret and apply resilience concepts, but quantitative methods that can systematically distinguish among them are needed. We develop a quantitative method to analyze long-term records of plant community dynamics using principles of movement ecology. We analyzed dissimilarity of species composition through time with linear and nonlinear statistical models to assign community change to four classes of movement trajectories. Compositional change in each sampled plot through time was classified into four classes, stability, abrupt nonlinear change, transient reversible change, and gradual linear drift, each representing a different aspect of ecological resilience. These competing models were evaluated based on estimated coefficients, goodness of fit, and parsimony. We tested our method's accuracy and robustness through simulations, or the ability to distinguish among trajectories and classify them correctly. We simulated 16,000 trajectories of four types, of which 94-100% were correctly classified. Next, we analyzed 13 long-term vegetation records from North American grasslands (annual grasslands with warm-season and cool-season communities, shortgrass, mixedgrass, and tallgrass prairies, and sagebrush steppe), and a record of primary succession at Mt. St. Helens volcano. Collectively, we analyzed 14,647 observations from 775 plots, between 1915 and 2012. Dynamics could be reliably assigned for 705 plots (91%), and overall statistical fit was high (goodness of fit, 0.77 ± 0.15 SD). Among the perennial grasslands, stability was most common (44% of all plots), followed by gradual linear (22%), abrupt nonlinear (17%), and reversible (6%) change. Among annual grasslands, abrupt nonlinear shifts (33%) were more common in the warm-season community than in the cool-season (20%). As expected, abrupt nonlinear change was common during primary succession (51%) while reversible change was rare (3%). Generally, reversible dynamics often required 2-3 decades. Analysis of long-term community change, or trajectories, with principles of movement ecology provides a quantitative basis to compare and interpret ecological resilience within and among ecosystems.

Plant communities are structured by both competition and facilitation. The interplay between the two interactions can vary depending on environmental factors, nature of stress, and plant traits. However, whether positive or negative interactions dominate in regions of high biotic and abiotic stress remains unclear. We studied herbaceous plant communities associated with a dwarf shrub Caragana versicolor in semi-arid, high altitude Trans-Himalayan rangelands of Spiti, India. We surveyed 120 pairs of plots (within and outside shrub canopies) across four watersheds differing in altitude, aspect, and dominant herbivores. Herbaceous communities within shrub canopies had 25% higher species richness, but similar abundance when compared to communities outside the canopy, with the shrub edge having higher diversity than the centre of the canopy. Grasses and erect forbs showed positive associations with the shrub, while prostrate plants occurred at much lower abundance within the canopy. Rare species showed stronger positive associations with Caragana than abundant species. Experimental removal of herbaceous vegetation from within shrub canopies led to 42% increase in flowering in Caragana, indicating a cost to the host shrubs. Our study indicates a robust pattern of a dwarf shrub facilitating local community diversity across this alpine landscape, increasing diversity at the plot level, facilitating rare species, and yet incurring a cost to hosts from the presence of herbaceous plants. Given these large influences of this shrub on the vegetation of these high altitude rangelands, we suggest that the shrub microhabitat be explicitly considered in any analyses of ecosystem health in such rangelands.

Understanding factors that regulate carbon (C) pools is of high importance for offsetting greenhouse-gas emissions. Soils represent a vast C pool, whose size and stability are strongly influenced by land-use. Grazing, by native herbivores and livestock, is the predominant land-use across over 40% of the terrestrial surface and influences over 109 Mg of soil-C annually in the world’s dry regions. The interactions between plants, grazers, and soil microbes, is of critical importance for this soil-C pool. However, soil microbial responses to grazing, and associated feedbacks, remain poorly understood. Grazing management policies are unable to adequately accommodate key interactions that are important for effective ecosystem stewardship. After 10-yr of experimental herbivore-exclusion in the semiarid Trans-Himalayan ecosystem, we measured grazer effects on soil microbial abundance in n = 30 herbivore exclosures, each paired with an adjacent control plot using substrate-induced respiration, microbial-carbon, and microbial-nitrogen (SIR, MBC, MBN). We found that grazing reduced soil microbial biomass by 13–16%, over the course of the vegetation growing season. But, the strength and direction of grazer effects varied through time at different points in the growing season. Grazing also shifted fungal:bacterial ratio towards dominance by fungi which were more tolerant of periodic dry-down and seasonal fluctuations in soil moisture than bacteria. So, grazer influence on microbial abundance and community composition may collectively play crucial roles in net soil-C dynamics. But, this effect is constrained by environmental factors, such as moisture availability. The projected climatic trend in the Trans-Himalaya is towards progressively wetter conditions, and this may counter grazer effect on microbes, alter microbial communities, and ultimately impact potential soil-C storage. So, accounting for projected changes in precipitation, in addition to managing stocking density of herbivores, may also be crucial for these large soil-C pools.

Herbivores alter plant biodiversity (species richness) in many of the world’s ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet, empirical support for the importance of site productivity as a mediator of these herbivore impacts is equivocal. Here, we synthesize data from 252 large-herbivore exclusion studies, spanning a 20-fold range in site productivity, to test an alternative hypothesis—that herbivore-induced changes in the competitive environment determine the response of plant biodiversity to herbivory irrespective of productivity. Under this hypothesis, when herbivores reduce the abundance (biomass, cover) of dominant species (for example, because the dominant plant is palatable), additional resources become available to support new species, thereby increasing biodiversity. By contrast, if herbivores promote high dominance by increasing the abundance of herbivory-resistant, unpalatable species, then resource availability for other species decreases reducing biodiversity. We show that herbivore-induced change in dominance, independent of site productivity or precipitation (a proxy for productivity), is the best predictor of herbivore effects on biodiversity in grassland and savannah sites. Given that most herbaceous ecosystems are dominated by one or a few species, altering the competitive environment via herbivores or by other means may be an effective strategy for conserving biodiversity in grasslands and savannahs globally. Fil: Koerner, Sally E.. University of North Carolina at Greensboro. Department of Biology; Estados Unidos Fil: Smith, Melinda D.. State University of Colorado - Fort Collins; Estados Unidos Fil: Burkepile, Deron E.. University of California; Estados Unidos Fil: Hanan, Niall P.. New Mexico State University; Estados Unidos Fil: Avolio, Meghan L.. University Johns Hopkins; Estados Unidos Fil: Collins, Scott L.. University of New Mexico; Estados Unidos Fil: Knapp, Alan K.. State University of Colorado - Fort Collins; Estados Unidos Fil: Lemoine, Nathan P.. State University of Colorado - Fort Collins; Estados Unidos Fil: Forrestel, Elisabeth J.. University of California at Davis; Estados Unidos Fil: Eby, Stephanie. Northeastern University; Estados Unidos Fil: Thompson, Dave I.. University of the Witwatersrand; Sudáfrica. Kruger National Park. South African Environmental Observation Network. Ndlovu Node. Scientific Services; Sudáfrica Fil: Aguado-Santacruz, Gerardo A.. Tecnológico Nacional de México; México Fil: Anderson, John P.. New Mexico State University; Estados Unidos Fil: Anderson, T. Michael. University Wake Forest; Estados Unidos Fil: Angassa, Ayana. Botswana University of Agriculture and Natural Resources; Sudáfrica. Hawassa University; Etiopía Fil: Bagchi, Sumanta. Indian Institute of Science; India Fil: Bakker, Elisabeth S.. Netherlands Institute of Ecology; Países Bajos Fil: Bastin, Gary. Alice Springs; Australia Fil: Baur, Lauren E.. University of New Mexico; Estados Unidos Fil: Beard, Karen H.. State University of Utah; Estados Unidos Fil: Beever, Erik A.. United States Geological Survey; Estados Unidos. State University of Montana; Estados Unidos Fil: Bohlen, Patrick J.. University of Central Florida; Estados Unidos Fil: Boughton, Elizabeth H.. MacArthur Agroecology Research Center; Estados Unidos Fil: Canestro, Don. University of California; Estados Unidos Fil: Cesa, Ariela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina Fil: Chaneton, Enrique Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Cheng, Jimin. Northwest A&F University; China Fil: D?Antonio, Carla M.. University of California; Estados Unidos Fil: Deleglise, Claire. Université Grenoble Alpes; Francia Fil: Dembélé, Fadiala. Institut de Formation et de Recherche Appliquee; Sudáfrica Fil: Dorrough, Josh. Ecosystem Mangement Science; Austria Fil: Eldridge, David J.. University of New South Wales; Australia Fil: Fernandez Going, Barbara. University of Texas at Austin; Estados Unidos Fil: Fernández Lugo, Silvia. Universidad de La Laguna; España Fil: Fraser, Lauchlan H.. Thompson Rivers University; Canadá Fil: Freedman, Bill. Dalhousie University Halifax; Canadá Fil: García Salgado, Gonzalo. Dalhousie University Halifax; Canadá Fil: Goheen, Jacob R.. University of Wyoming; Estados Unidos Fil: Guo, Liang. Northwest A&F University; China Fil: Husheer, Sean. New Zealand Forest Surveys; Nueva Zelanda Fil: Karembé, Moussa. Université des Sciences; Malí Fil: Knops, Johannes M. H.. Universidad de Nebraska - Lincoln; Estados Unidos Fil: Kraaij, Tineke. Nelson Mandela University; Sudáfrica Fil: Kulmatiski, Andrew. State University of Utah; Estados Unidos Fil: Kytöviita, Minna Maarit. Universidad de Jyvaskyla; Finlandia Fil: Lezama, Felipe. Universidad de la República; Uruguay Fil: Loucougaray, Gregory. Université Grenoble Alpes; Francia Fil: Loydi, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina Fil: Milchunas, Dan G.. State University of Colorado - Fort Collins; Estados Unidos Fil: Milton, Suzanne J.. South African Environmental Observation Network; Sudáfrica Fil: Morgan, John W.. La Trobe University; Australia Fil: Moxham, Claire. Arthur Rylah Institute for Environmental Research; Australia Fil: Nehring, Kyle C.. State University of Utah; Estados Unidos Fil: Olff, Han. University of Groningen; Países Bajos Fil: Palmer, Todd M.. University of Florida; Estados Unidos Fil: Rebollo, Salvador. Universidad de Alcalá; España Fil: Riginos, Corinna. The Nature Conservancy; Estados Unidos Fil: Risch, Anita C.. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiza Fil: Rueda, Marta. Consejo Superior de Investigaciones Científicas. Estación Biológica de Doñana; España Fil: Sankaran, Mahesh. National Centre For Biological Sciences; India. University of Leeds; Reino Unido Fil: Sasaki, Takehiro. Yokohama National University; Japón Fil: Schoenecker, Kathryn A.. Fort Collins Science Center and Colorado State University; Estados Unidos Fil: Schultz, Nick L.. Federation University; Australia Fil: Schütz, Martin. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiza Fil: Schwabe, Angelika. Universitat Technische Darmstadt; Alemania Fil: Siebert, Frances. North West University; Sudáfrica Fil: Smit, Christian. University of Groningen; Países Bajos Fil: Stahlheber, Karen A.. University of Wisconsin Green Bay; Estados Unidos Fil: Storm, Christian. Universitat Technische Darmstadt; Alemania Fil: Strong, Dustin J.. United States Department of Agriculture. Agriculture Research Service; Estados Unidos Fil: Su, Jishuai. Northwest A&F University; China Fil: Tiruvaimozhi, Yadugiri V.. National Centre for Biological Sciences; India Fil: Tyler, Claudia. University of California; Estados Unidos Fil: Val, James. Office of Environment and Heritage; Australia Fil: Vandegehuchte, Martijn L.. University of Ghent; Bélgica. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiza Fil: Veblen, Kari E.. State University of Utah; Estados Unidos Fil: Vermeire, Lance T.. United States Department of Agriculture. Agriculture Research Service; Estados Unidos Fil: Ward, David. Kent State University; Estados Unidos Fil: Wu, Jianshuang. Lhasa National Ecological Research Station; China Fil: Young, Truman P.. University of California at Davis; Estados Unidos. Mpala Research Centre; Kenia Fil: Yu, Qiang. Chinese Academy Of Agricultural Sciences; China. Institute of Agricultural Resources and Regional Planning; China Fil: Zelikova, Tamara Jane. University Of Wyoming; . University of Wyoming; Estados Unidos

Theoretical models suggest that competitive coexistence of consumers over shared resources can occur only under very restrictive conditions. Yet, in apparent defiance of the competitive exclusion principle, large numbers of species form natural communities while sharing a small number of limiting resources. Consumers not only coexist, but also show positive facilitative interactions among themselves. Since body size and functional responses may play important roles in these interactions, we investigate their joint effects on two consumers over a single resource. We find that two consumers with unimodal Type IV functional response can facilitate each other by increasing each other's intake rates. But, this facilitation does not necessarily impact their co-existence. When the consumers differ in their body sizes, the larger consumer receives greater absolute benefits, and the smaller consumer gains more relative benefits. These results are consistent with empirical observations, and do not require any additional assumptions over the parameters governing dynamics of resources to explain net positive interactions between consumers.

Predator-prey interactions where livestock are killed by carnivores, are a serious global challenge. Conservation interventions to address this conflict are inadequately guided by ecological theory, and instead rely on pragmatic experiential decisions. I review four families of theoretical models that can accommodate essential features of this human-wildlife conflict, namely – prey-refuge, specialist/generalist predation, social-ecological, and metapopulation models. I evaluate their relevance for conservation and arrange each model's predictions along two conceptual dimensions: coexistence and stability. These models are described with examples of pastoralists and snow leopards in the Himalayas, but they can have broader relevance to other regions. All models suggest that livestock-loss can be better controlled in highly productive habitats, than under low productivity. But, they differ in the ease with which their predictions may be translated into real-world conservation interventions. These constraints can be circumvented through animal movement between patches which is represented only in metapopulation models. But, metapopulation models do not offer much clarity on the size of the predator population. Instead, they can prescribe rotational-grazing policies for livestock – another pragmatic management concern. This comparison of models identifies lacunae where ecological theory could be better integrated within conservation practice. One option is better integration with emerging knowledge of animal movement. Comparative analyses of models helps identify future directions where outcomes of alternative management interventions can be predicted and evaluated.

Summary 1. Resilience-based approaches are increasingly being called upon to inform ecosystem management, particularly in arid and semi-arid regions. This requires management frameworks that can assess ecosystem dynamics, both within and between alternative states, at relevant time scales. 2. We analysed long-term vegetation records from two representative sites in the North American sagebrush-steppe ecosystem, spanning nine decades, to determine if empirical patterns were consistent with resilience theory, and to determine if cheatgrass Bromus tectorum invasion led to thresholds as currently envisioned by expert-based state-and-transition models (STM). These data span the entire history of cheatgrass invasion at these sites and provide a unique opportunity to assess the impacts of biotic invasion on ecosystem resilience. 3. We used univariate and multivariate statistical tools to identify unique plant communities and document the magnitude, frequency and directionality of community transitions through time. Community transitions were characterized by 37–47% dissimilarity in species composition, they were not evenly distributed through time, their frequency was not correlated with precipitation, and they could not be readily attributed to fire or grazing. Instead, at both sites, the majority of community transitions occurred within an 8–10 year period of increasing cheatgrass density, became infrequent after cheatgrass density peaked, and thereafter transition frequency declined. 4. Greater cheatgrass density, replacement of native species and indication of asymmetry in community transitions suggest that thresholds may have been exceeded in response to cheatgrass invasion at one site (more arid), but not at the other site (less arid). Asymmetry in the direction of community transitions also identified communities that were ‘at-risk’ of cheatgrass invasion, as well as potential restoration pathways for recovery of pre-invasion states. 5. Synthesis and applications. These results illustrate the complexities associated with threshold identification, and indicate that criteria describing the frequency, magnitude, directionality and temporal scale of community transitions may provide greater insight into resilience theory and its application for ecosystem management. These criteria are likely to vary across biogeographic regions that are susceptible to cheatgrass invasion, and necessitate more in-depth assessments of thresholds and alternative states, than currently available.

Summary 1. India, a mega-diverse country in terms of both biodiversity and people, is battling environmental problems on many fronts: chronic dependence on natural resources, dwindling ecosystem services, declining environmental quality, effects of climate change and a biodiversity crisis. 2. We review the current focal areas and infrastructure for ecological research and education in India, along with the surrounding legal and policy aspects of related socio-economic issues. 3. Currently, ecological and applied research is predominantly focused on charismatic species within protected areas. This scope could be broadened beyond organismal biology towards functional landscapes and ecosystems; the education system also needs to promote ecology as a career choice for scientists. Expectedly, many environmental challenges are generic in nature, occur in other regions of the world, are primarily biophysical in origin but extend into human dimensions; some challenges are socio-political and have implications for biodiversity conservation. 4. Synthesis and applications. India’s environmental concerns include, but are not restricted to, the biodiversity crisis. The biodiversity crisis, in turn, includes, but is not restricted to, the most charismatic species. Greater integration and alignment among the mandates of government agencies, scientists, policymakers and educators are needed to meet contemporary environmental issues.

Plants allocate biomass to aboveground (shoot) and belowground (root) structures to capture light and nutrients, respectively. Plant allocation strategies are a key feature of ecosystem structure, and function, as they have broad influence over material and energy flow. Herbivores can exercise strong control over plant allocation, and thereby influence ecosystem structure and function. Theoretical models of plant allocation strategies predict that root:shoot ratio is related to leaf nitrogen (N) concentration; specifically root:shoot ratio declines monotonically over a broad range of N concentrations. Here, I assess whether grazing by large mammalian herbivores alters the inverse relationship between root:shoot ratio and leaf-N concentration. Data from an herbivore exclusion experiment in the arid Trans-Himalayan ecosystem were in general agreement with predictions of theoretical models. Herbivores did not affect the slope of the relationship, rather they lowered the intercept, and this change was independent of their influence over plant community composition. Reduction in root:shoot ratio with increasing leaf-N, and lowering biomass allocation to roots with grazing, are consistent with other studies on how herbivores influence plants.

A mechanistic understanding of the highly variable effects of herbivores on plant production in different ecosystems remains a major challenge. To explain these patterns, the compensatory continuum hypothesis (CCH) predicts plants to compensate for defoliation when resources are abundant, whereas the growth rate hypothesis (GRH) makes the opposite claim of high herbivory tolerance under resource-poor conditions. The limiting resource model (LRM) tries to reconcile this dichotomy by incorporating the indirect effects of herbivores on plant resources and predicts that the potential for plant compensation is dependent upon whether, and how, herbivory influences limiting resources. Although extensively evaluated in laboratory monocultures, it remains uncertain whether these models can also explain the response of heterogeneous and multi-species natural plant communities to defoliation. Here we investigate community-wide plant response to defoliation and report data from a field experiment in the arid and primarily water-limited Trans-Himalayan grazing ecosystem in northern India involving clipping, irrigation and nutrient-feedback with herbivore dung. Without nutrient-feedback, plants compensated for defoliation in absence of irrigation but failed to compensate under irrigation. Whereas, in the presence of nutrient-feedback plants compensated for defoliation when irrigated. This divergent pattern is not consistent with the CCH and GRH, and is only partially explained by the LRM. Instead, these pluralistic results are consistent with the hypothesis that herbivory may alter the relative strengths of water and nutrient limitation since irrigation increased root:shoot ratio in absence of fertilization in unclipped plots, but not in the corresponding clipped plots. So, herbivory appears to increase relative strength of nutrient-limitation for plants that otherwise seem to be primarily water-limited. Extending the LRM framework to include herbivore-mediated transitions between water and nutrient-limitation may clarify the underlying mechanisms that modulate herbivory-tolerance under different environmental conditions.

Species coexistence involving trophic interactions has been investigated under two theoretical frameworks—partitioning shared resources and accessing exclusive resources. The influence of body size on coexistence is well studied under the exclusive resources framework, but has received less attention under the shared-resources framework. We investigate body-size-dependent allometric extensions of a classical MacArthur-type model where two consumers compete for two shared resources. The equilibrium coexistence criteria are compared against the general predictions of the alternative framework over exclusive resources. From the asymmetry in body size allometry of resource encounter versus demand our model shows, counterintuitively, and contrary to the exclusive resource framework, that a smaller consumer should be competitively superior across a wide range of supplies of the two resource types. Experimental studies are reviewed to resolve this difference among the two frameworks that arise from their respective assumptions over resource distribution. Another prediction is that the smaller consumer may have relatively stronger control over equilibrium resource abundance, and the loss of smaller consumers from a community may induce relatively stronger trophic cascades. Finally, from satiating consumers’ functional response, our model predicts that greater difference among resource sizes can allow a broader range of consumer body sizes to coexist, and this is consistent with the predictions of the alternative framework over exclusive resources. Overall, this analysis provides an objective comparison of the two alternative approaches to understand species coexistence that have heretofore developed in relative isolation. It advances classical consumer–resource theory to show how body size can be an important factor in resource competition and coexistence.

Large mammalian herbivores may have positive, neutral, or negative effects on annual net aboveground plant production (NAP) in different ecosystems, depending on their indirect effects on availability of key nutrients such as soil N. In comparison, less is known about the corresponding influence of grazers, and nutrient dynamics, over annual net belowground plant production (NBP). In natural multi-species plant communities, it remains uncertain how grazing influences relative allocation in the above- and belowground compartments in relation to its effects on plant nutrients. We evaluated grazer impacts on NAP, NBP, and relative investment in the above- and belowground compartments, alongside their indirect effects on soil N availability in the multiple-use Trans-Himalayan grazing ecosystem with native grazers and livestock. Data show that a prevailing grazing intensity of 51% increases NAP (+61%), but reduces NBP (-35%). Grazing also reduced C:N ratio in shoots (-16%) and litter (-50%), but not in roots, and these changes coincided with increased plant-available inorganic soil N (+23%). Areas used by livestock and native grazers showed qualitatively similar responses since NAP was promoted, and NBP was reduced, in both cases. The preferential investment in the aboveground fraction, at the expense of the belowground fraction, was correlated positively with grazing intensity and with improvement in litter quality. These results are consistent with hypothesized herbivore-mediated positive feedbacks between soil nutrients and relative investment in above- and belowground compartments. Since potentially overlapping mechanisms, such as N mineralization rate, plant N uptake, compositional turnover, and soil microbial activity, may contribute towards these feedbacks, further studies may be able to discern their respective contributions.

Questions: Density dependence is thought to restrict exponential growth as well as give rise to size structure in populations. Size hierarchy in trees from tropical dry deciduous forests is studied to ask (1) whether nature of competition is symmetric or asymmetric and (2) what is the self thinning trajectory under a natural gradient of tree density. Location: Western India. Methods: Density was measured as the number of trees in 10-m radius circular plots (n = 96) and size was measured at DBH. Size variation was evaluated by the Gini coefficient (n = 1239 trees). Results: Size inequality between neighbours decreased with density but in a non-linear manner. In the backdrop of existing theory this indirectly suggests that competitive interactions may be symmetric over a ʻdepletiveʼ resource such as below-ground water (rather than a ʻpre-emptiveʼ resource such as light), which is very plausible in a semi-arid environment. The self thinning coefficient derived from the relationship between stem diameter and density (γ ≈ –1/4), is higher than expected from existing models of allometric plant growth (γ ≈ –1/3) which are based on above-ground interactions alone. Seen in conjunction, these results suggest that above-ground structures, such as stem size, do not adequately represent the outcome of competitive interactions when below-ground resources, such as water, may be more important under semi-arid conditions. Conclusions: The non-linear relationship between size inequality and density indicates that there exists a density threshold beyond which investment in above-ground biomass becomes sluggish in semi-arid, deciduous forests. Since current allometric models do not incorporate below-ground biomass for trees, these data suggest that a more comprehensive allometric growth model may have higher predictive power and wider applicability.

Livestock predation by large carnivores and their retaliatory persecution by pastoralists are worldwide conservation concerns. Poor understanding of the ecological and social underpinnings of this human¿wildlife conflict hampers effective conflict management programs. The endangered snow leopard Uncia uncia is involved in conflict with people across its mountainous range in South and Central Asia, where pastoralism is the predominant land use, and is widely persecuted in retaliation. We examined human-snow leopard conflict at two sites in the Spiti region of the Indian Trans-Himalaya, where livestock outnumber wild ungulates, and the conflict is acute. We quantified the snow leopard's dependence on livestock by assessing its diet in two sites that differed in the relative abundance of livestock and wild ungulates. We also surveyed the indigenous Buddhist community's attitudes towards the snow leopard in these two sites. Our results show a relatively high dependence of snow leopards on livestock. A higher proportion of the snow leopard's diet (58%) was livestock in the area with higher livestock (29.7 animals km¿2) and lower wild ungulate abundance (2.1¿3.1 bharal Pseudois nayaur km¿2), compared with 40% of diet in the area with relatively lower livestock (13.9 km¿2) and higher wild ungulate abundance (4.5¿7.8 ibex Capra ibex km¿2). We found that the community experiencing greater levels of livestock losses was comparatively more tolerant towards the snow leopard. This discrepancy is explained by the presence of a conservation-incentive program at the site, and by differences in economic roles of livestock between these two communities. The former is more dependent on cash crops as a source of income while the latter is more dependent on livestock, and thereby less tolerant of the snow leopard. These data have implications for conflict management strategies. They indicate that the relative densities of livestock and wild prey may be reasonable predictors of the extent of predation by the snow leopard. However, this by itself is not an adequate measure of the intensity of conflict even in apparently similar cultural settings.

Prey depletion is a major (but often neglected) factor driving the current decline of tigers (Panthera tigris L.) (Karanth & Stith 1999). Thus conservation planning for the tiger in a fragmented, human-dominated landscape requires reliable information on prey densities from various parts of its range. We report numerical and biomass density of six herbivores from the tropical dry-deciduous forests of Ranthambhore Tiger Reserve (RTR, 26°N and 76°E), Rajasthan, India, where these are important prey for tigers (Bagchi et al. 2003).

Niches of 2 cervids (chital, Axis axis and sambar, Cervus unicolor) and 2 bovids (nilgai, Boselaphus tragocamelus and chinkara, Gazella bennetti) from semiarid forests in western India were studied for habitat use and food habits. Habitat use was analyzed by discriminant analysis using 20 variables, and food habits investigated by analyzing undigested plant remains in pellets. Cervids and bovids differentiated primarily according to vegetation and terrain features, and the 2 deer species showed separation in diet. The 2 cervids selected forested areas, whereas the 2 bovids selected scrubland and were more tolerant of disturbances like livestock grazing and also showed a high similarity in food habits. Habitat use and food habits were analyzed with nonmetric multidimensional scaling to assess their combined effects. A greater degree of similarity in resource use between the 2 bovids suggests that they may be competitive, at least during periods of forage scarcity.

Food habits of tigers Panthera tigris in terms of prey abundance were studied in the semi-arid deciduous forests of Ranthambhore National Park, western India, between November 2000 and April 2001. Wild prey availability was assessed by line transects (n=8) and prey selection by the tigers was determined from analysis of scats (n=109). Compared to some other parts of the country, prey abundance was found to be high at 96.65 animals km−2. Chital Axis axis was the most abundant wild prey in the study area, followed by common langur Presbytis entellus, sambar Cervus unicolor, nilgai Boselaphus tragocamelus, wild pig Sus scrofa and chinkara Gazella bennetti. Chital (c. 31%) and sambar (c. 47%) constituted the bulk of the tigers' diet and were preferred prey. Nilgai and chinkara contributed minimally to the tigers' diet (c. 5–7% and

Grazing occurs over a third of the earth's land surface and may potentially influence the storage of 10(9) Mg year(-1) of greenhouse gases as soil C. Displacement of native herbivores by high densities of livestock has often led to overgrazing and soil C loss. However, it remains unknown whether matching livestock densities to those of native herbivores can yield equivalent soil C sequestration. In the Trans-Himalayas we found that, despite comparable grazing intensities, watersheds converted to pastoralism had 49% lower soil C than watersheds which retain native herbivores. Experimental grazer-exclusion within each watershed type, show that this difference appears to be driven by indirect effects of livestock diet selection, leading to vegetation shifts that lower plant production and reduce likely soil C inputs from vegetation by c. 25 gC m(-2) year(-1). Our results suggest that while accounting for direct impacts (stocking density) is a major step, managing indirect impacts on vegetation composition are equally important in influencing soil C sequestration in grazing ecosystems.

Grazing occurs over a third of the earths land surface and may potentially influence thestorage of 10 9 Mg year )1 of greenhouse gases as soil C. Displacement of nativeherbivores by high densities of livestock has often led to overgrazing and soil C loss.However, it remains unknown whether matching livestock densities to those of nativeherbivores can yield equivalent soil C sequestration. In the Trans-Himalayas we foundthat, despite comparable grazing intensities, watersheds converted to pastoralism had49% lower soil C than watersheds which retain native herbivores. Experimental grazer-exclusion within each watershed type, show that this difference appears to be driven byindirect effects of livestock diet selection, leading to vegetation shifts that lower plantproduction and reduce likely soil C inputs from vegetation by c. 25 gC m )2 year )1 . Ourresults suggest that while accounting for direct impacts (stocking density) is a major step,managing indirect impacts on vegetation composition are equally important ininfluencing soil C sequestration in grazing ecosystems.KeywordsBiodiversity, carbon dioxide, climate change, ecosystem function, ecosystem services,human natural ecosystems, land use change, livestock production, rangelands, wildlifeconservation.Ecology Letters (2010) 13: 959–968

The rain-shadow of the Himalayan Mountains in South and Central Asia constitutes the Trans-Himalayas, a vast rangelands system (2.6 million km2; Figure 11.1) comprising the Tibetan plateau and its marginal mountains. This high-altitude arid landscape north of the main Himalayan range is contiguous with the Eurasian steppes and has a history of pastoralism dating back at least 3 millennia (Handa 1994; Schaller 1998). Historically, nomadic pastoralism in the region presumably involved low-intensity grazing, much like the Central Asian steppes (Blench & Sommer 1999). The Trans-Himalayas is amongst the least productive of graminoid-dominated ecosystems on earth in terms of above-ground graminoid biomass (Mishra 2001). Yet, the Trans-Himalayan rangelands harbour a surprisingly rich assemblage of wild mountain ungulate

Grouping characteristics and population structure of chital (Axis axis Erxleben), sambar (Cervus unicolor Kerr), nilgai (Boselaphus tragocamelus Pallas) and chinkara (Gazella bennetti Sykes) were studied in dry tropical forests of Ranthambhore Tiger Reserve in semi-arid western India during November 2000 to April 2001. Mean and typical group sizes were highest for chital (winter: 4.7 and 9.2, respectively; summer: 4.5, 7.9), followed by sambar (winter: 3.4, 4.2; summer: 4.2, 6.8), nilgai (winter: 2.9, 4.5; summer: 2.5, 4.9) and chinkara (winter: 2.6, 3.3; summer: 2.5, 3.2). Population structure was biased towards females in chital (86.4 males: 100 females) and sambar (83.2:100), while it was biased towards males in nilgai (116.8:100) and chinkara (119.8:100). Ratio of young to adult females was highest for sambar (38.2 young: 100 females), followed by chinkara (35.2:100), chital (28.0:100) and nilgai (23.9:100). Variations in grouping patterns according to habitat and season have been investigated. The importance of constant monitoring of ungulate population structure is emphasised for this drought prone region.

The Tibetan gazelle Procapra picticaudata is on the verge of extinction in India with only c. 100 individuals remaining in the Hanle Valley of eastern Ladakh and Sikkim. Conservation planning and initiation of a recovery programme are hindered by lack of ecological information on the species and we therefore assessed the biotic and abiotic correlates of its occurrence in the Hanle Valley. Ecological attributes of areas selected by gazelles were compared with those of adjoining areas without gazelles. Resource selection functions revealed that gazelles use relatively flat areas (6-15°) disproportionately during both summer and winter, and preferred south-facing slopes and avoided north-facing slopes during winter. Measurements of plant production using exclosures showed that herbivores removed up to 47% of the forage biomass from areas without gazelles, whereas only 29% was removed from areas with gazelles. Although areas selected by gazelles were only marginally more productive than areas not selected, the proportional representation of forbs in plant biomass was significantly higher in the former. Spatial co-occurrence patterns examined using null models revealed a significant negative relationship between distribution of gazelles and goats and sheep, and a significant positive relationship between gazelles and wild kiang Equus kiang and domestic yak Bos grunniens. Future in situ recovery programmes for the Tibetan gazelle in Ladakh need to focus on securing livestock-free, forb-dominated areas, with participation from the local pastoral community.

(Jina, 1995), graze the rangelands of Changthang. TheChangpa are Buddhists and share cultural and linguisticaffinities with Tibet (Rizvi, 1996). They lost access toseveral traditional pastures on the Tibetan side when Indiaand China fought a war in the region in 1962 (Ahmed,1997). Around the same time, the Indian side saw a heavyinflux of Tibetan refugees (popularly known as TRs), who,like the Changpa, rear a variety of livestock includinghorse, yak, sheep and goat. These livestock types areadapted to the hostile and marginal pastures of the region,and provide a range of products and services. The domesticgoats of Changthang reportedly produce the finest cash-mere wool or Pashmina in the world (Misra et al., 1998;Ahmed, 2002). The Government of India has beenfacilitating Pashmina production by providing incentivesto the Changpas for several decades, in the form ofsupplementary cattle feed during severe winters andsubsidized food provisions etc.Recent studies of the people of Changthang suggestconsiderable social, economic and land tenure changes,particularly during the period after the war between Indiaand China (Saberwal, 1996; Jina, 1999; Chaudhuri, 2000;Ahmed, 2002; Hagalia, 2004; Goodall, 2004; Rawat andAdhikari, 2005; Rosing, 2006). These studies were con-ducted primarily in the Rupshu-Kharnak area that isrelatively close to the district headquarters, Leh, and is animportant tourist destination. However, there is virtually noinformation from other, parts of Changthang, especially theeastern Hanle Valley bordering China (c. 3,000 km

The high-altitude rangelands of the Trans-Himalaya represent a grazing ecosystem which has supported an indigenous pastoral community for millennia alongside a diverse assemblage of wild herbivores including burrowing mammals (pikas and voles). Pastoralists consider the small mammals to cause rangeland degradation and as competitors for their livestock, and actively eradicate them at many places. We present data on the ways in which small herbivores like pikas and voles mediate plant community dynamics. Vegetation cover and plant species richness were compared on and off both active and abandoned small mammal colonies. Plant species richness was higher inside colonies (about 4–5 species/plot) than outside (about 3 species/plot) whereas vegetation cover was only marginally lower (52% compared to 60%). Soil disturbance due to small mammals is seen to be associated with higher plant diversity without causing dramatic decline in overall vegetation cover. Such disturbance-mediated dynamics and vegetation mosaics produce a rich array of testable hypotheses that can highlight how small mammals influence assembly processes, succession, and dominance hierarchies in plant communities in this arid ecosystem. So, eradicating small mammals may lead to declining levels of diversity in this ecosystem, and compromise ecosystem-functioning. Changes in traditional pastoral practices and overstocking are more likely to be responsible for degradation. We emphasize that eradicating small mammals can lead to loss of diversity in this ecosystem and it is not a solution for the degradation problems.

Grazing can have implications for ecosystem management, biodiversity conservation, human livelihoods and global biogeochemical cycles. Grazers can either depress or promote plant production, with weak or strong effects on vegetation composition. Such variability is a major challenge for sustaining production while avoiding undesirable vegetation shifts. It is also uncertain how knowledge obtained from native herbivores can be used to manage domestic livestock and vice versa. In addition, grazer effects on production and vegetation composition tend to vary along prominent environmental gradients and are also negatively related to each other. Here, we evaluate these patterns for both livestock and native grazers under comparable grazing intensity and evaluate competing hypotheses that can account for the negative co-variation between these two types of grazer effects. A dataset from a four-year herbivore exclusion experiment in the Trans-Himalayan ecosystem in northern India shows the following: (a) grazer effects on plant production and on vegetation composition were indeed negatively correlated, but the relationship depends on the choice of data metrics; (b) incidental autocorrelation due to an underlying soil moisture gradient does not fully explain this pattern; instead, (c) their relationship is explained by variation in local plant species richness. Vegetation responses after excluding livestock and native grazers were qualitatively similar. But, despite comparable grazing intensity, livestock had quantitatively stronger effects on plant species composition. Production in species-rich communities was more grazing-tolerant and showed greater compositional stability. So, understanding the determinants of variation in species richness and how it is, in turn, influenced by grazing can offer a framework to interpret and manage highly variable impacts of herbivores on grazing ecosystems.