达乌尔鼠兔扩散过程中的生境选择

通过调控牧压,研究了达乌尔鼠兔扩散过程中的生境选择。结果表明,放牧活动强了草原植被的斑块性,改变了植被为鼠兔提供的资源条件,导致鼠兔斑块间的扩散和扩散鼠兔对不同植被斑块的生境选择。     

高原鼠兔对垂穗披碱草及豆科植物生长特性的影响

高原鼠兔通过取食对高寒草甸产生广泛的影响,从而影响高寒草甸植物的个体生长特征。2012年在青海省果洛州矮嵩草草甸,以高原鼠兔喜食植物(豆科和垂穗披碱草)为研究对象,通过小区控制研究高原鼠兔取食（对照组、低密度处理组、中密度处理组、高密度处理组）对植物个体生长特征的影响。研究显示：在实验前期（5月和6月）,喜食植物个体特征基本上无明显规律;在实验后期（7月和8月）,随着高原鼠兔取食强度增大,高原鼠兔喜食植物的地上生物量、平均高度、分蘖枝数、分蘖枝长度、丛幅均呈下降趋势;叶片长度和叶片数均呈先上升后下降态势。2.高原鼠兔喜食植物个体特征的增长率对照组显著高于高密度处理组（P<0.05）。以上结果表明(1)高寒草甸豆类植物在其生长后期与高原鼠兔的取食强度呈一定的负相关关系;高原鼠兔取食强度在阈值（中、低密度）内有利于垂穗披碱草的生长,但超过其阈值的取食强度不利于其生长。(2)高原鼠兔高强度的取食对其喜食植物个体的生长率有明显的抑制作用。     

Effects of Acomastylis rossii tannins on a mammalian herbivore,the North American pika,Ochotona princeps

 I investigated the effects of tannin consumption, using plant tannins naturally occurring in the diet, on a herbivorous mammal, the North American pika, Ochotona princeps. The objectives were to determine if a high-tannin diet influenced protein and dry matter apparent digestibility, fiber digestibility and production of detoxification by-products. Additionally, I examined the possibility that pikas produce salivary tannin-binding proteins, a potential mechanism for avoiding detrimental effects of tannins. My results demonstrate that although pikas constitutively produce salivary tannin-binding proteins, animals consuming a high-tannin diet of Acomastylis rossii exhibited lower dry matter, protein and fiber digestion and excreted higher concentrations of detoxification by-products. Thus, A. rossii tannins are potential toxins as well as digestibility reducers. I propose a hypothesis coupling detoxification to reduced fiber digestion that is applicable to pikas as well as other mammalian herbivores consuming phenolic-rich diets. Received: 31 July 1995 / Accepted: 9 July 1996     

植被覆盖度和土地利用对高原鼠兔觅食与警戒行为的影响

野生动物的自然行为受当地家畜影响。作为与家畜共享一个栖息地、并具有挖掘行为的兔形目高原鼠兔,其行为也受当地高原家畜影响。本文采用了Poisson回归分析方法,确定牦牛、不同土地利用对高原鼠兔行为频次的影响。结果显示觅食、移动频次是高原鼠兔的主要行为频次。在冬季牦牛觅食地高原鼠兔觅食行为频次高于警戒行为频次。相反,在夏季,无论是在牦牛觅食地还是在其夜宿地,高原鼠兔警戒行为的频次高于觅食行为频次。高原鼠兔行为也受不同土地利用、植被覆盖度以及季节因素的影响。植被覆盖度与觅食频次成反比,植被覆盖度高的生境高原鼠兔觅食较少,相反,植被覆盖度较低生境觅食行为频繁。另外当前牧民的定居化趋势造成局域放牧过度,加速了土地荒漠化。因此本文也认为,季节性传统游牧模式对于草地可持续发展具有重要意义。     

Selection for nutrients by red deer hinds feeding on a mixed forest edge

We studied the nutritional behaviour of hinds foraging on a mixed-forest edge by direct observation of their choices at each season and by measuring nutrient concentration in the plants. We compared nutrient concentrations in the observed diets with those in the total available vegetation, and with those of 1,000 randomly simulated diets in which we included only those plants that were actually eaten by the animal. Whether the available or the consumed feeds were used as the basis for comparisons had important consequences due to the presence of conifers and ferns, which were high in soluble sugars but were never eaten by the animals (potentially due to their toxicity). The selected diets were lower in sugars than the total available vegetation in summer, but were actually higher in sugars than the random diets generated from consumed forage species only. Hind diets contained more soluble sugars but not more protein than simulated diets in all seasons. Contrary to our prediction, anti-nutritional compounds (ADL and tannins) were avoided only in winter. Compared to simulated diets, hinds consumed more tannins in spring and summer and more ADL in summer and autumn. We suggest that this was a consequence of selection for soluble sugars, because the preferred plant species, which had high soluble sugar concentrations, also contained a large proportion of the anti-nutritional compounds eaten. In winter, the grass-dominated diets contained more fibre (NDF) and less ADL than the simulated diets, indicating that hinds orient their feeding towards digestible fibres. The switch from a browser to a grazer diet was related to a change in the availability of the nutrients, mainly soluble sugars. In our study, grasses contained more soluble sugars and proteins than deciduous browse during winter. This calls into question the dichotomy usually assumed in the literature between grass and browse in terms of nutrient content. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A diet rich in C3 plants reveals the sensitivity of an alpine mammal to climate change

Plant–herbivore interactions provide critical insights into the mechanisms that govern the spatiotemporal distributions of organisms. These interactions are crucial to understanding the impacts of climate change, which are likely to have an effect on the population dynamics of alpine herbivores. The Royle's pika (Ochotona roylei, hereafter pika) is a lagomorph found in the western Himalaya and is dependent on alpine plants that are at risk from climate change. As the main prey of many carnivores in the region, the pika plays a crucial role in trophic interactions. We examined topographical features, plant genera presence and seasonal dynamics as drivers of the plant richness in the pika's diet across an elevational gradient (2,600–4,450 m). We identified 79 plant genera in the faecal pellets of pikas, of which 89% were forbs, >60% were endemic to the Himalaya, and 97.5% of the diet plant genera identified followed the C₃ photosynthetic pathway. We found that, during the premonsoon season, the number of genera in the pika's diet decreased with increasing elevation. We demonstrate that a large area of talus supports greater plant diversity and, not surprisingly, results in higher species richness in the pika's diet. However, in talus habitat with deep crevices, pikas consumed fewer plant genera suggesting they may be foraging suboptimally due to predation risk. The continued increase in global temperature is expected to have an effect on the distribution dynamics of C₃ plants and consequently influence pika diet and distribution, resulting in a significant negative cascading effect on the Himalayan ecosystem.     

Influence of food hoarding behavior on the over-winter survival of pikas in strongly seasonal environments

Food hoarding is a behavioral adaptation of some herbivores to manage food availability through time and space. In strongly seasonal environments, where summer growing seasons are short relative to winter, an earlier start to hoarding should increase the amount of vegetation stored for winter and improve subsequent survival. We examined hoarding behavior (‘haying’) and its impact on survival for a small alpine lagomorph, the collared pika (Ochotona collaris) in Yukon, Canada. We used a combination of video surveillance, haypile measurements, and survival data from marked individuals of known age and sex. Annual haypile initiation was strongly influenced by age and year. Adult pikas began haying an average of 16 days earlier in 2004 relative to 2005, whereas young of the year (juveniles) did not vary in the timing of haypile initiation. The mean haying rate per hour increased monthly from 3.7 ± 0.7 trips in June to 6.6 ± 0.8 trips in August. Simulation analysis estimated the median haypile mass (dry weight) by mid-September to be 5.5 kg. At least 75% of simulated haypiles had a minimum of 90 days (3 months) of food reserves, and 50% of simulated haypiles had a minimum of 177 days (5.9 months) of food reserves by mid-September, supporting the hypothesis that haypiles serve as the primary source of food during winter. Survival was greatest for pikas in 2005 when they began haying prior to 31 July, but the benefits of earlier accumulation of vegetation on survival also varied between years. The implications of earlier spring snowmelt are discussed with respect to pika foraging and overwinter survival.     

Wild reindeer foraging-niche organization

Part 1: Diet selection was studied on free-ranging reindeer fitted with an esophageal fistula (EF) and by analysis of rumen samples from reindeer shot in the field. Plant density was assessed from quadrats on field plots. Three measures of palatability were used, the nitrogen, fiber, and total non structural carbohydrate (TNC) contents of samples from clipped vegetation. As lichen density decreased the EK reindeer included progressively more vascular litter and pieces of winter dormant species in their diet. Diets with highest TNC and N/F and the lowest fiber, providing the most readily digestible diets, were selected. The combined density-quality criterion gave the best prediction of their diets. In summer, forbs, and to some extent grasses and dwarf shrubs, were selected. Plants of highest density and in an early growth phase gave the best prediction of summer diets. In winter the variety of vascular plants utilized increased with increasing herd size and decreasing density of lichens in the vegetation. The width of diets was a function of diversity of available plants. It is suggested that dietary selection by reindeer has been a three stage process: evolution of a gastro-intestinal system capable of digesting lichens containing secondary compounds, behavioural tracking of the plant production pulse, and diet width scaling according to density-quality of all potential foods. Part 2: Wild reindeer closely followed the wave of vascular plant production in spring and summer with a significant correlation being found between the daily foraging time per habitat type and the highest concentration of green phytomass. Snow-bed meadows were the most consistently selected vegetation type by the four herds studied, viz. Hardangervidda, Snøhetta, Prudhoe Bay, and Svalbard, during the summer. Habitat niche-breadths were narrow during the winter, largely due to the limitation of access to the food supply by the snow-cover, broadened as the landscape became clear of snow, narrowed again with the initiation of plant growth and broadened once more as the wave of plant production reached all habitat types. At high levels of food resources the alpine herd (Hardangervidda) narrowed the feeding niche breadth (or adopted a selective feeding strategy) as the habitat niche breadth increased. The high arctic herd (Svalbard) living in the least productive environment, at the same time of year adopted a generalist feeding strategy as their habitat niche breadth expanded. Part 3: In this part the temporal organization of a low-alpine herd of reindeer (Hardangervidda) is described, and subsequently compared with those of two arctic herds. Their foraging efficiencies under different degrees of food availability were analysed, in order to test the hypothesis that food intake changes in response to the prevailing state of the food resources. The number of daily feeding bouts increased from 2 to 6 as the diet changed from the winter to the summer pasturage. Strong winds in winter and insect harassment in summer severely depressed the daily time spent foraging. When these environmental factors were accounted for no significant inter-seasonal differences in daily foraging time of the low alpine herd were found; on average 50% of each day was spent grazing, of which 78% of the time was spent on actual ingestion (feeding rate). The feeding rate within the active periods varied with the snow-depth, due to the need to dig a food crater in the snow and due to the particular selective feeding strategy adopted. The data from the present and from other studies suggest that the foraging efficiency of wild reindeer, expressed as their daily food intake follows a Holling type II functional response as food availability changes. Part 4: Sheep is the only sympatric ruminant which grazes with the reindeer on alpine pastures in Norway. The inter-specific niche relationships ot the wild reindeer and the domestic sheep in summer were studied on part of the western Hardangervidda. to test the hypothesis of inter-specific competition. Three niche dimensions were meas-ured, diel, habitat utilization, and spatial distribution. The estimates of the degree of overlap obtained suggest that this is relatively high for diet and habitat utilization but low for spatial distribution, which leads to a low degree of foraging interference. Since the intensity of both interspeeific and intra-specific competition depends on the ratio of the herbivore densities to the food resource density, the degree ol overlap in utilization by the two species tell us nothing about the degree of competition. Present numbers of both species on Hardangervidda have a beneficial influence on the vegetation, by opening-up the shrub-layer canopy and thus facilitating the main-tenance of grasses and forbs in the field layer, which has a higher carrying capacity for ruminants. The balance between the beneficial effects and inter-generic competition (if any) deriving from the present-day stocking rales is so tar unknown. Only long-term monitoring of the performance of both populations will shed light on this competitive aspect.     

Does Supplemental Feed Increase Selective Foraging in a Browsing Ungulate?

ABSTRACT Provision of supplemental feed to large herbivores is a common management practice that may motivate selective foraging, thereby influencing plant community composition. Our objective was to assess the effect of a high-quality supplement on diet composition and nutritional quality for white-tailed deer (Odocoileus virginianus). We permanently released hand-reared deer into 4 81-ha enclosures; in 2 enclosures we provided a pelleted supplement. We conducted bite-count studies seasonally to assess diet composition and quality. Supplemented deer reduced mast (fruits and pods of woody plants and cacti) in their diets (P < 0.019) during spring and autumn compared to unsupplemented deer. Diets of deer in supplemented enclosures had 2 times greater proportion of browse during spring (P = 0.065) and 5 times greater proportion of forbs during autumn (P = 0.007). Quality of the forage portion of the diet did not vary by treatment during winter or summer. Metabolizable energy concentration was 13% greater (P = 0.054) in spring and digestible protein content was 3 times greater (P = 0.006) during autumn in diets of supplemented compared to unsupplemented deer. Our results support the selective foraging hypothesis during autumn but not during winter, spring, or summer. Furthermore, white-tailed deer did not reduce the proportion of their diet composed of browse, but did reduce consumption of mast. Supplemented deer continued to eat poor-quality, chemically defended forage, perhaps to alleviate ruminal acidosis induced by the supplement or because nutrients in the supplement increased the deer's ability to detoxify chemically defended browses. A decline in mast consumption by supplemented deer could influence plant communities, depending on the role of deer in seed dispersal and seed predation. Impacts of supplemental feed on selective foraging of white-tailed deer in shrub-dominated rangelands are more complex than suggested by previous research. Long-term studies of vegetation communities are needed before wildlife managers will be able to fully incorporate effects of supplemental feed into management decisions.     

植物次生代谢物含量的季节性变化及其对高原鼠兔食物选择的影响

2008 年6 ～9 月在中国科学院海北高寒草甸生态系统定位站通过自助餐式食物选择实验测定了高原鼠兔对20 种植物的取食量,采用紫外可见分光光度计法测定了不同季节20 种植物中黄酮、缩合单宁、简单酚和总酚4种植物次生代谢物的含量,分析了植物次生代谢物含量与高原鼠兔食物选择之间的相互关系。结果表明,在选定的20 种植物中高原鼠兔喜食的植物有7 种,可食的植物有7 种,厌食的植物有6 种。植物次生代谢物的含量在不同的植物间表现出一定的差异,且有生长季节早期含量低,随后逐渐增高的季节性变化趋势。高原鼠兔对植物的选择性与植物中黄酮含量有显著的负相关性,喜食植物的黄酮含量显著低于厌食植物,喜食植物的单宁含量显著小于可食植物,可食植物的单宁含量显著大于厌食植物。在喜食植物中,高原鼠兔取食量与简单酚和总酚含量呈显著负相关性。以上结果部分验证了植物次生代谢物作为植物的防御对策明显影响高原鼠兔对食物选择的假说。黄酮类次生代谢物明显抑制高原鼠兔的取食,缩合单宁对高原鼠兔食物选择也有一定的抑制作用,高原鼠兔有少量取食但避免大量取食简单酚和总酚含量高的植物的选择策略。     

高原鼠兔刈割行为与栖息地植物群落的关系

采用观察法和样条法对不同栖息地高原鼠兔刈割植物的行为、相对频次、生物量百分比以及刈割植物与鼠兔冬季食物组成之间的关系进行了分析,并阐述了高原鼠兔刈割植物的生物学意义。结果表明:高原鼠兔刈割植物始于每年的6 月下旬,早于其它草原小型哺乳动物贮草时间。不同栖息地鼠兔对植物的刈割频次和生物量比例并非完全一致。在矮嵩草草甸,鼠兔刈割频次较高的为垂穗披碱草、二柱头藨草、甘肃棘豆、短穗兔耳草、铺散亚菊和鹅绒萎陵菜;这些植物生物量所占比例亦较高,仅短穗兔耳草比例较低;在垂穗披碱草草甸,鼠兔刈割频次较高的为垂穗披碱草和早熟禾;垂穗披碱草生物量较高;而在杂类草草甸,鼠兔主要刈割植物为铺散亚菊、大籽蒿、黄帚橐吾、长茎藁本和圆齿狗娃花,生物量比例较高的主要为铺散亚菊。相似性分析结果表明,不同栖息地间鼠兔刈割植物频次和生物量比例差异较大,相似性系数最大分别为0. 7862 和0. 6100, 最小仅为0.1422 和0. 1035,而同一栖息地间鼠兔刈割植物频次和生物量差异相对较小,相似性系数最高达0. 9203 和0. 8490,最小亦达到0. 6662 和0. 4440,表明栖息地变化对鼠兔刈割植物频次和比例有明显的影响作用。鼠兔刈割主要植物频次和生物量比例与冬季主要食物组成的相关分析结果表明,生物量比例与主要食物组成呈显著的正相关(r =0.8412,df = 6, P <0. 05),而刈割植物频次与主要食物相关不显著。     

A Review of Environmental Factors Affecting Elk Winter Diets

Abstract: Decades of research have produced substantial data on elk (Cervus elaphus) diets in winter, when foraging conditions are most likely to affect population dynamics. Using data from 72 studies conducted in western North America between 1938 and 2002, we collated data on elk diets and environmental variables. We used these data to quantify diet selection by elk and to test whether variation in elk diets is associated with habitat type, winter severity, period of winter, human hunting, and study method. Graminoids (grasses and grass-like plants such as sedges) dominated elk diets and consistently occurred at a higher proportion in the diet than in elk foraging habitats, indicating preference. Forbs commonly made up ≤5% of the diet, with no evidence for preference; we conclude that forb use is largely incidental to grazing for graminoids. Browse was consumed in proportion to its availability, implying that the amount of browse in the diet was primarily determined by habitat use rather than selection. Comparing the diets of elk and sympatric ruminants, elk consistently selected graminoids more strongly than sympatric ruminants with the exception of bison (Bison bison), suggesting that elk are not environmentally forced to adopt the graminoid-biased diet that they normally select. The proportion of open meadows and grasslands on winter ranges was strongly and positively associated with graminoid consumption by elk. The proportion of graminoids in the diet was significantly lower in elk experiencing severe winter conditions or predation risk from human hunting. The period of winter (early, middle, and late) had only small effects on elk diets, as did the method by which the diet was determined. Overall, variation in elk diets is well-explained by a consistent tendency to select graminoids if available, modified by winter habitat type, predation risk, and winter severity, which can constrain habitat selection and access to grazing opportunities. To fully understand variation in foraging behavior, biologists should recognize these broad patterns when interpreting resource selection data. Managers should recognize that inconspicuous behavioral responses to environmental stimuli can alter the diet in ways that probably carry nutritional consequences.     

Human metabolic pathways of dietary flavonoids and cinnamates

Flavonoids and cinnamates are widespread phenolic secondary metabolites synthesized by plants for defensive purposes. Many foods and beverages contain high levels of phenolic compounds. Certain phenolics in the diet are particularly bioactive and have pronounced effects on mammalian cells. These effects, together with epidemiological studies and animal models, have led to the hypothesis that dietary phenolics contribute to the health benefits of a diet rich in fruit and vegetables. This paper examines the biochemistry of the uptake and metabolic route of two groups of plant phenolics, the flavonols and hydroxycinnamates.     

Talus fragmentation mitigates the effects of pikas, Ochotona princeps, on high alpine meadows

North American pikas (Ochotona princeps) are central-place foragers that are restricted to talus slopes in the mountains of western North America. They graze meadows surrounding talus producing a gradient of grazing pressure extending out from the talus edge. We asked: 1) how does the physical structure of the talus slope affect pika foraging behavior? and 2) how do differences in foraging behavior affect the relative abundance of different plant functional groups?
Pikas at three talus-meadow interfaces differed in the distances they traveled for forage, depending upon the structure of the talus slope. Pikas fed preferentially on vegetation within the talus, ventured into the surrounding meadow when intra-talus vegetation was rare, and ranged farther when haying than when grazing. They ventured into the surrounding meadow less when talus fields were more fragmented and intra-talus vegetation was more abundant.
We tested the effects of pikas on meadow vegetation by excluding pikas from small plots located at various distances from talus edges. When habitat structure forced pikas to venture out from the talus to forage, they decreased total vegetative biomass by as much as 80% and increased the relative importance of cushion plants and sedges. These effects were undetectable at distances beyond one meter. These patterns appear to result from a change in the relative performance of different plant functional groups caused by herbivory.     

Keystone status of plateau pikas (Ochotona curzoniae): effect of control on biodiversity of native birds

The plateau pika (Ochotona curzoniae) of the Qinghai–Xizang (Tibetan) plateau, People's Republic of China, has been considered a pest because it putatively competes with native livestock for forage and contributes to rangeland degradation. As a result the plateau pika has been poisoned across vast areas of the high alpine meadows of the plateau. The plateau pika has also been considered a keystone species for biodiversity on the plateau. As one test of the keystone species hypothesis, we investigated the effects of poisoning plateau pikas on avian species richness and abundance. We conducted standardized censuses of birds on a number of sites across the alpine grassland of Qinghai province on which pikas either had or had not been poisoned. Avian species richness and abundance were higher on non-poisoned sites, in particular for species that nest in pika burrows such as Hume's groundpecker (Pseudopodoces humilis) and six species of snowfinch (Montifringilla spp., Pyrgilauda spp.), and species that prey on pikas (upland buzzard, Buteo hemilasius; black-eared kite, Milvus lineatus). The plateau pika thus appears to be both an allogenic engineer and a keystone species. Poisoning pikas reduces biodiversity of native species on the Qinghai–Xizang plateau, therefore management decisions concerning plateau pikas should reflect caution and careful assessment.     

Diet breadth of mammalian herbivores: nutrient versus detoxification constraints

Two hypotheses, nutrient constraints and detoxification limitation, have been proposed to explain the lack of specialists among mammalian herbivores. The nutrient constraint hypothesis proposes that dietary specialization in mammalian herbivores is rare because no one plant can provide all requisite nutrients. The detoxification limitation hypothesis suggests that the mammalian detoxification system is incapable of detoxifying high doses of similar secondary compounds present in a diet of a single plant species. We experimentally tested these hypotheses by comparing the performance of specialist and generalist woodrats (Neotoma) on a variety of dietary challenges. Neotoma stephensi is a narrow dietary specialist with a single species, one-seeded juniper, Juniperus monosperma, comprising 85–95% of its diet. Compared with other plants available in the habitat, juniper is low in nitrogen and high in fiber, phenolics, and monoterpenes. The generalist woodrat, N. albigula, also consumes one-seeded juniper, but to a lesser degree. The nutrient constraint hypothesis was examined by feeding both species of woodrats a low-nitrogen, high-fiber diet similar to that found in juniper. We found no differences in body mass change, or apparent digestibility of dry matter or nitrogen between the two species of woodrats after 35 days on this diet. Moreover, both species were in positive nitrogen balance. We tested the detoxification limitation hypothesis by comparing the performance of the generalist and specialist on diets with and without juniper leaves, the preferred foliage of the specialist, as well as on diets with and without α-pinene, the predominant monoterpene in juniper. We found that on the juniper diet, compared with the specialist, the generalist consumed less juniper and lost more mass. Urine pH, a general indicator of overall detoxification processes, declined in both groups on the juniper diet. The generalist consumed half the toxin load of the specialist yet its urine pH was slightly lower. Moreover, the generalist consumed significantly less of the treatment with high concentrations of α-pinene compared to the control treatment, while the specialist consumed the same amount of food regardless of α-pinene concentration. For both groups, urine pH declined as levels of α-pinene in the diet increased. The generalist produced a significantly more acidic urine than the specialist on the treatment with the highest α-pinene concentration. Our results suggest that in this system, specialists detoxify plant secondary compounds differently than generalists and plant secondary compounds may be more important than low nutrient levels in maintaining dietary diversity in generalist herbivores. Received: 5 May 1999 / Accepted: 14 November 1999     

Diversity of diazotrophic gut inhabitants of pikas (Ochotonidae) revealed by PCR-DGGE analysis

Diazotrophic gut symbionts are considered to act as nitrogen providers for their hosts, as was shown for various termite species. Although the diet of lagomorphs, like pikas or rabbits, is very poor in nitrogen and energy, their fecal matter contains 30–40% of protein. Since our hypothesis was that pikas maintained a diazotrophic consortium in their gastrointestinal tract, we conducted the first investigation of microbial diversity in pika guts. We obtained gut samples from animals of several Ochotona species, O. hyperborea (Northern pika), O. mantchurica (Manchurian pika), and O. dauurica (Daurian pika), in order to retrieve and compare the nitrogen-fixing communities of different pika species. The age and gender of the animals were taken into consideration. We amplified 320-bp long fragments of the nifH gene using the DNA extracted directly from the colon and cecum samples of pika’s gut, resolved them by DGGE, and performed phylogenetic reconstruction of 51 sequences obtained from excised bands. No significant difference was detected between the nitrogen-fixing gut inhabitants of different pika species. NifH sequences fell into two clusters. The first cluster contained the sequences affiliated with NifH Cluster I (Zehr et al., 2003) with similarity to Sphingomonas sp., Bradyrhizobium sp., and various uncultured bacteria from soil and rhizosphere. Sequences from the second group were related to Treponema sp., Fibrobacter succinogenes, and uncultured clones from the guts of various termites and belonged to NifH Cluster III. We suggest that diazotrophic organisms from the second cluster are genuine endosymbionts of pikas and provide nitrogen for further synthesis processes thus allowing these animals not to be short of protein.     

Flexibility in the food selection by the European hare (<Emphasis Type="Italic">Lepus europaeus</Emphasis>) along the altitudinal gradient of the Southern Andean Precordillera (Argentina)

Predictions derived from the optimal foraging theory are interesting to test on wild herbivores living in mountain environments, considering the expected vegetation changes across altitudinal gradients. A lower food richness and a more generalist diet are expected as altitude increases, with higher diet diversity and a shift to browsing as food availability decreases seasonally. With broad diets and ecological adaptability, Lepus europaeus is a non-native herbivore inhabiting Andean altitudinal gradients. Diet and vegetation were analyzed using microhistological analysis and point-quadrat transects at six sampling sites, representative of altitudinal phytogeographic belts. The diet included 67 of the 109 species present in the vegetation. Lepus europaeus proved to be an intermediate feeder with a generalist and selective diet. Following the prediction for altitudinal gradients, dietary generalism increased as plant cover and diversity decreased with altitude. Differences in plant phenology and toxins justified changes in food preferences, from shrubs at the summit to grasses at lower altitudes. Seasonal changes in diet diversity were consistent with different hypotheses depending on altitude. The tundra climate at the summit determined a strong phenological decline and food scarcity during winter, when the less diverse diet was more focused on a preferred shrub, following the selective quality hypothesis. With a milder climate at lower altitudes, the winter increase in diet diversity, with inclusion of avoided shrubs, agrees with the food abundance hypothesis. Climate severity, food shortage, plant phenology, and secondary compounds are relevant for explaining the feeding strategy of European hares in these mountain environments.     

You are what you eat: describing the foraging ecology of southern elephant seals (Mirounga leonina) using blubber fatty acids

Understanding the trophodynamics of marine ecosystems requires data on the temporal and spatial variation in predator diet but, particularly for wide-ranging species, these data are often unavailable. The southern elephant seal (Mirounga leonina) consumes large quantities of fish and squid prey in the Southern Ocean relative to other marine mammals; however, how diet varies relative to seasonal and spatial foraging behaviour is unknown. We used fatty acid (FA) signature analysis of 63 blubber cores from adult female M. leonina over three seasons (winter 1999, summer 2000 and winter 2001) to determine diet structure. We detected significant differences between seasons and between the main foraging regions (Antarctic continental shelf versus pelagic). We used the FA profiles from 53 fish, squid and krill species to construct a discriminant function that would classify each seal, from its blubber sample as having a fish- or squid-FA profile. We determined that a higher proportion of M. leonina had fish-dominated diets during the winter and when foraging around the Antarctic continental shelf, and the majority had more squid-dominated diets during the summer when foraging pelagically. Thus, we were able to measure the coarse-scale diet structure of a major marine predator using FA profiles, and estimate its associated seasonal and temporal variation.     

The density of active burrows of plateau pika in relation to biomass allocation in the alpine meadow ecosystems of the Tibetan Plateau

Understanding the relationships between plateau pika population and plants biomass is essential for improving small herbivores management in alpine meadow ecosystems. Four degrees of active burrow densities were classified to evaluate pika populations and biomass allocation interactions. Our results showed that plant composition, overall vegetation height and cover, dominant species were significantly different among four sites. Additionally, plant functional groups, above ground, below ground and total biomass, root:shoot ratios and the living roots proportion were the greatest at the zero-density site, and those at the medium-density site were the lowest. We postulate that pika activities may not be the cause of the differences, but a symptom of grassland degradation. Further, pika population fluctuations should be monitored, and when the population exceeds the economic threshold of low-density (110 pikas or/and 512 active burrows ha⁻¹) or reaches high-density (200 pikas or/and 1360 active burrows ha⁻¹), integrated management strategies should be implemented to protect damage.