Evidence that the Tibetan fox is an obligate predator of the plateau pika: conservation implications

Food webs reveal coexistence mechanisms and community organization in carnivores

Globally, massive carnivore guild extirpations have led to trophic downgrading and compromised ecosystem services. However, the complexity of multi-carnivore food webs complicates accurate identification of species interactions and community organization. Here, we used fecal DNA metabarcoding to investigate three communities that together encompass eight large- and meso-carnivore species and their 44 prey taxa of the Qinghai-Tibet Plateau (QTP), one of the last places on Earth that still harbors intact carnivore assemblages. Quantitative food-web analyses revealed pronounced interspecific variations in the carnivores' prey compositions and dietary partitioning both between and within guilds. Additionally, body masses of the carnivores and their prey exhibited consistent hump-shaped correlations across communities. Overall, differences in prey diversity, size category, and proportional utilization among the carnivore species result in trophic niche segregation that likely promotes carnivore coexistence in the harsh QTP environment. Network structure analyses detected significant modularity in all food webs but nestedness in only one. Furthermore, network characterization identified pikas (Ochotona spp.), bharal (Pseudois nayaur), and domestic yak (Bos grunniens) as potential keystone prey across the areas. Our results paint a holistic and detailed picture of the QTP carnivore assemblages' trophic networks and demonstrate that the combined use of the molecular dietary approach and network analysis can generate structural insights into carnivore coexistence and can identify functionally important species in complex communities. Such knowledge can help safeguard carnivore guild integrity and enhance community resilience to environmental perturbations in the sensitive QTP ecosystems.

Effect of chronic traffic noise on behavior and physiology of plateau pikas (Ochotona curzoniae)

During the last two decades, numerous studies have shown the effects of traffic noise on animal vocal communication. However, studies on the influences of traffic noise on wildlife behavior and physiology are scarce. In the present study, we experimentally manipulated the traffic noise exposure of plateau pika, a native small mammal widely distributed in the alpine meadow of Qinghai-Tibet Plateau, to explore the effects of traffic noise exposure on its behavior and physiology. We showed that noise exposure increased the pika’s exploration and cortisol concentration (CORT) but decreased the resting metabolic rate (RMR). In addition, the relationships between RMR and exploration or CORT appeared under traffic noise treatment. This study suggests that traffic noise plays a large role in the behavior and physiology of plateau pikas and may have a long-term negative effect on the fitness of rodent populations. Generalizing these non-lethal effects to different taxa is crucial for the conservation and management of biodiversity in this increasingly noisy world.

Surviving winter on the Qinghai-Tibetan Plateau: Pikas suppress energy demands and exploit yak feces to survive winter

The Qinghai-Tibetan Plateau, with low precipitation, low oxygen partial pressure, and temperatures routinely dropping below -30 °C in winter, presents several physiological challenges to its fauna. Yet it is home to many endemic mammalian species, including the plateau pika (Ochotona curzoniae). How these small animals that are incapable of hibernation survive the winter is an enigma. Measurements of daily energy expenditure (DEE) using the doubly labeled water method show that pikas suppress their DEE during winter. At the same body weight, pikas in winter expend 29.7% less than in summer, despite ambient temperatures being approximately 25 °C lower. Combined with resting metabolic rates (RMRs), this gives them an exceptionally low metabolic scope in winter (DEE/RMRt = 1.60 ± 0.30; RMRt is resting metabolic rate at thermoneutrality). Using implanted body temperature loggers and filming in the wild, we show that this is achieved by reducing body temperature and physical activity. Thyroid hormone (T₃ and T₄) measurements indicate this metabolic suppression is probably mediated via the thyroid axis. Winter activity was lower at sites where domestic yak (Bos grunniens) densities were higher. Pikas supplement their food intake at these sites by eating yak feces, demonstrated by direct observation, identification of yak DNA in pika stomach contents, and greater convergence in the yak/pika microbiotas in winter. This interspecific coprophagy allows pikas to thrive where yak are abundant and partially explains why pika densities are higher where domestic yak, their supposed direct competitors for food, are more abundant.

Microhabitat use by plateau pikas: living on the edge

Mammals rely on habitat resources for survival and reproduction. We studied microhabitats used by plateau pikas (Ochotona curzoniae) of the Qinghai-Tibetan Plateau. Microhabitat features used by pikas include sedge meadows that provide forage, burrows that provide safety from predators and cover for nests, degraded open-dirt patches, and edges between sedge meadow and open dirt patches that often have a “lip” between those microhabitats. We investigated the extent to which these edges might serve as a preferred pika microhabitat. GIS techniques were used to overlay individual pika home ranges, determined by focal and scan sampling, on a digitized map containing microhabitat features. Regions that contained multiple coinciding individual home ranges, referred to as overlap polygons, were categorized numerically based on the number of individual home ranges that overlapped each polygon. These overlap polygons were used as relative measures of pika activity. We tested the spatial relationship between pika activity and the microhabitat features of edges, burrows, and proportional area of sedge. There was a significant relationship between the number of pikas in an overlap polygon and the number of pikas in an adjacent polygon. This pattern was controlled statistically to test whether activity was influenced by the presence of potentially favorable microhabitat features. Most of the variation in number of pikas that overlapped a habitat polygon was associated with the relative amount of “edge microhabitat” between sedge meadow and degraded open dirt patches (Cohen’s effect size, f2 = 0.91). Neither burrow openings nor sedge had a strong influence on the number of pika home ranges that overlapped. The importance of microhabitat edges appeared high for plateau pikas.

Functional-trait ecology of the plateau pika Ochotona curzoniae in the Qinghai-Tibetan Plateau ecosystem

Understanding a species' functional traits allows for a directed and productive perspective on the role a species plays in nature, and thus its relative importance to conservation planning. The functional-trait ecology of the plateau pika Ochotona curzoniae is examined to better understand the resilience and sustainability of the high alpine grasslands of the Qinghai-Tibetan Plateau (QTP). The key functional traits of plateau pikas are their abundance and behavior of digging extensive burrow systems. Plateau pikas have been poisoned over a significant part of their original geographic distribution across the QTP, allowing comparison of ecological communities with and without pikas. Nearly all mammalian and avian carnivores, most of which are obligate predators on pikas, have been lost in regions where pikas have been poisoned. Most endemic birds on the QTP nest in pika burrows; when pikas are poisoned, burrows collapse, and these birds are greatly reduced in number. Due to the biopedturbation resulting from their burrows, regional plant species richness is higher in areas with pikas than without. The presence of pika burrows allows higher rates of infiltration during heavy monsoon rains compared to poisoned areas, possibly mitigating runoff and the potential for serious downslope erosion and flooding. Thus, the functional traits of plateau pikas enhance native biodiversity and other important ecosystem functions; these traits are irreplaceable. As plateau pikas are not natural colonizers, active re-introduction programs are needed to restore pikas to areas from which they have been poisoned to restore the important functional ecological traits of pikas.

Evolution for extreme living: variation in mitochondrial cytochrome c oxidase genes correlated with elevation in pikas (genus Ochotona)

The genus Ochotona (pikas) is a clade of cold-tolerant lagomorphs that includes many high-elevation species. Pikas offer a unique opportunity to study adaptations and potential limitations of an ecologically important mammal to high-elevation hypoxia. We analyzed the evolution of 3 mitochondrial genes encoding the catalytic core of cytochrome c oxidase (COX) in 10 pika species occupying elevations from sea level to 5000 m. COX is an enzyme highly reliant on oxygen and essential for cell function. One amino acid property, the equilibrium constant (ionization of COOH), was found to be under selection in the overall protein complex. We observed a strong relationship between the net value change in this property and the elevation each species occupies, with higher-elevation species having potentially more efficient proteins. We also found evidence of selection in low-elevation species for potentially less efficient COX, perhaps trading efficiency for heat production in the absence of hypoxia. Our results suggest that different pika species may have evolved elevation-specific COX proteins, specialization that may indicate limitations in their ability to shift their elevational ranges in response to future climate change.

Debugging diversity - a pan-continental exploration of the potential of terrestrial blood-feeding leeches as a vertebrate monitoring tool

The use of environmental DNA (eDNA) has become an applicable noninvasive tool with which to obtain information about biodiversity. A subdiscipline of eDNA is iDNA (invertebrate-derived DNA), where genetic material ingested by invertebrates is used to characterize the biodiversity of the species that served as hosts. While promising, these techniques are still in their infancy, as they have only been explored on limited numbers of samples from only a single or a few different locations. In this study, we investigate the suitability of iDNA extracted from more than 3,000 haematophagous terrestrial leeches as a tool for detecting a wide range of terrestrial vertebrates across five different geographical regions on three different continents. These regions cover almost the full geographical range of haematophagous terrestrial leeches, thus representing all parts of the world where this method might apply. We identify host taxa through metabarcoding coupled with high-throughput sequencing on Illumina and IonTorrent sequencing platforms to decrease economic costs and workload and thereby make the approach attractive for practitioners in conservation management. We identified hosts in four different taxonomic vertebrate classes: mammals, birds, reptiles and amphibians, belonging to at least 42 different taxonomic families. We find that vertebrate blood ingested by haematophagous terrestrial leeches throughout their distribution is a viable source of DNA with which to examine a wide range of vertebrates. Thus, this study provides encouraging support for the potential of haematophagous terrestrial leeches as a tool for detecting and monitoring terrestrial vertebrate biodiversity.

Herbivory and Competition of Tibetan Steppe Vegetation in Winter Pasture: Effects of Livestock Exclosure and Plateau Pika Reduction

Rangeland degradation has been identified as a serious concern in alpine regions of western China on the Qinghai-Tibetan plateau (QTP). Numerous government-sponsored programs have been initiated, including many that feature long-term grazing prohibitions and some that call for eliminating pastoralism altogether. As well, government programs have long favored eliminating plateau pikas (Ochotona curzoniae), assumed to contribute to degraded conditions. However, vegetation on the QTP evolved in the presence of herbivory, suggesting that deleterious effects from grazing are, to some extent, compensated for by reduced plant-plant competition. We examined the dynamics of common steppe ecosystem species as well as physical indicators of rangeland stress by excluding livestock and reducing pika abundance on experimental plots, and following responses for 4 years. We established 12 fenced livestock exclosures within pastures grazed during winter by local pastoralists, and removed pikas on half of these. We established paired, permanent vegetation plots within and outside exclosures and measured indices of erosion and biomass of common plant species. We observed modest restoration of physical site conditions (reduced bare soil, erosion, greater vegetation cover) with both livestock exclusion and pika reduction. As expected in areas protected from grazing, we observed a reduction in annual productivity of plant species avoided by livestock and assumed to compete poorly when protected from grazing. Contrary to expectation, we observed similar reductions in annual productivity among palatable, perennial graminoids under livestock exclusion. The dominant grass, Stipa purpurea, displayed evidence of density-dependent growth, suggesting that intra-specific competition exerted a regulatory effect on annual production in the absence of grazing. Complete grazing bans on winter pastures in steppe habitats on the QTP may assist in the recovery of highly eroded pastures, but may not increase annual vegetative production.