The benefits of being in a bad neighbourhood: plant community composition influences red deer foraging decisions

Diet selection by mammalian herbivores is often influenced by plant community composition, and numerous studies have focused on the relationships between herbivore foraging decisions and food/plant species abundance. However, few have examined the role of neighbour palatability in affecting foraging of a target plant by large mammalian herbivores. We used a large-scale field dataset on diet selection by red deer Cervus elaphus in Fiordland National Park, New Zealand to: (1) estimate the palatability of native forest plant species to introduced deer from observed patterns of browse damage; and (2) examine whether intraspecific variation in browsing of plants can be related to variation in the local abundance of alternative forage species. Overall, 21 of the 53 forest species in our dataset were never browsed by deer. At a community level, plants were more likely to be browsed if they were in a patch of vegetation of high forage quality, containing high abundances of highly palatable species and/or low abundances of less-palatable species. Our findings suggest that deer make foraging decisions at both a coarse-grain level, selecting vegetation patches within a landscape based on the overall patch quality, and at a fine-grain level by choosing among individual plants of different species.     

祁连山东段高原鼢鼠(Eospalax baileyi)土丘空间分布格局及其与环境因子的空间关联性

高原鼢鼠推土造丘行为对高寒草地生态系统的生产和生态功能有重要影响,研究高原鼢鼠土丘空间分布格局及其与环境因子的关系,可以揭示高原鼢鼠栖息地利用和选择规律,为合理控制鼠害及保护草地生物多样性提供科学依据。于2014年8月在祁连山东段选取面积为140m×100m的高原鼢鼠栖息地,消除景观尺度取样带来的气候、地形和土壤的异质性,利用地统计学方法,分析高原鼢鼠土丘的空间分布格局、并揭示其与环境因子中土壤容重、土壤水分、植物地上、地下生物量、根系营养物质含量(可溶性糖、粗蛋白、粗脂肪)以及各功能群丰富度(禾本科、莎草科、杂类草)的空间关系。半方差函数及普通克里格插值表明,高原鼢鼠土丘存在中等程度的空间变异且呈现聚集分布,各环境因子均存在不同程度的空间异质性。交方差函数分析表明,高原鼢鼠分布虽与各环境因子在多种尺度下表现出复杂的空间关联性(正的或负的),但mantel检验发现土壤容重、莎草科丰富度与高原鼢鼠土丘分布呈现显著的负空间关联性,杂类草丰富度和根系粗脂肪含量与高原鼢鼠土丘分布存在显著正空间关联性。综上所述,高原鼢鼠主要栖息利用在土壤疏松、莎草科丰富度较低、杂类草较多和根系粗脂肪含量较高的地方。     

Optimal foraging and community structure: The allometry of herbivore food selection and competition

I address the selection of plants with different characteristics by herbivores of different body sizes by incorporating allometric relationships for herbivore foraging into optimal foraging models developed for herbivores. Herbivores may use two criteria in maximizing their nutritional intake when confronted with a range of food resources: a minimum digestibility and a minimum cropping rate. Minimum digestibility should depend on plant chemical characteristics and minimum cropping rate should depend on the density of plant items and their size (mass). If herbivores do select for these plant characteristics, then herbivores of different body sizes should select different ranges of these characteristics due to allometric relationships in digestive physiology, cropping ability and nutritional demands. This selectivity follows a regular pattern such that a herbivore of each body size can exclusively utilize some plants, while it must share other plants with herbivores of other body sizes. I empirically test this hypothesis of herbivore diet selectivity and the pattern of resource use that it produces in the field and experimentally. The findings have important implications for competition among herbivores and their population and community ecology. Furthermore, the results may have general applicability to other types of foragers, with general implications for how biodiversity is influenced.     

Function‐related Drivers of Skull Morphometric Variation and Sexual Size Dimorphism in a Subterranean Rodent,Plateau Zokor (Eospalax baileyi)

Sexual dimorphism is prevalent in most living organisms. The difference in size between sexes of a given species is generally known as sexual size dimorphism (SSD). The magnitude of the SSD is determined by Rensch's rule where size dimorphism increases with increasing body size when the male is the larger sex and decreases with increasing average body size when the female is the larger sex. The unique underground environment that zokors (Eospalax baileyi) live under in the severe habitat of the Qinghai‐Tibetan Plateau (QTP) could create SSD selection pressures that may or may not be supported by Rensch's rule, making this scientific question worthy of investigation. In this study, we investigated the individual variation between sexes in body size and SSD of plateau zokors using measurements of 19 morphological traits. We also investigated the evolutionary mechanisms underlying SSD in plateau zokors. Moreover, we applied Rensch's rule to all extant zokor species. Our results showed male‐biased SSD in plateau zokors: The body‐ and head‐related measurements were greater in males than in females. Linear regression analysis between body length, body weight, and carcass weight showed significant relationships with some traits such as skull length, lower incisor length, and tympanic bulla width, which might support our prediction that males have faster growth rates than females. Further, the SSD pattern corroborated the assumption of Rensch's rule in plateau zokors but not in the other zokor species. Our findings suggest that the natural underground habitat and behavioral differences between sexes can generate selection pressures on male traits and contribute to the evolution of SSD in plateau zokors.     

植物化学防卫与植食性哺乳动物的适应对策

植物化学防卫与植食性哺乳动物的适应是动物—植物系统协同进化研究的重要内容。植物次生化合物可降低动物的食物摄入量及消化率、蛋白质可利用率。某些次生化合物还影响植食性哺乳动物的正常繁殖活动。单宁是动物的重要觅食阻遏剂之一。动物在学习食物选择的过程中,通过认知过程和感知过程处理食物信息,选择食物项目。幼体在胚胎期和哺乳期能从母体获得食物信息,或向有觅食经验的同胞伙伴学习处理食物的经验。动物亦可通过形成络和物,改变体内环境,通过微生物降解、氧化还原、基础代谢率等降低生理对策,以降低植物次生化和物的影响。     

高原鼢鼠对高寒草甸植被特征及生产力的影响

本研究结果表明,高原鼢鼠栖息10年的斑块,植物群落的物种数减少,植物物种多样性指数下降,地上、地下总生物量显降低,单子叶和可利用双子叶植物生物量极显减少,但不可利用双子叶植物生物量显增加。高原鼢鼠去除5年后,斑块内植物群落的单子叶植物物种数增加,而双子叶植物下降,植物群落物种多样性指数下降,地上、地下总生物量显增加,单子叶和可利用双子叶植物生物量增加极显,不可利用双子叶植物生物量显降低。高原鼢鼠栖息10年的斑块,净初级生产量较未栖息地区减少68.98%。高原鼢鼠去除5年后,净初级生产量增加,但仅达到未栖息地区的58.69%。     

青海门源地区大(狂鸟)和雕鸮的食性比较

1999～2002年的6～8月份,在青海门源地区收集了大(狂鸟)和雕鸮的吐弃块(pellets)和残留食物(food remains),带回实验室进行分检鉴定、研究分析.大(狂鸟)食物中共有736个猎物,其中高原鼢鼠28只、高原鼠兔139只、甘肃鼠兔142只、田鼠科动物422只、雀形目鸟类4只、香鼬1只;各猎物对大(狂鸟)食物的生物量贡献率分别为14.26%、40.79%、17.39%、26.99%、0.22%、0.35%.雕鸮食物中共有330个猎物,其中高原鼢鼠17只、高原鼠兔77只、甘肃鼠兔44只、田鼠科动物183只、雀形目鸟类2只、红脚鹬2只、高原兔5只;各猎物对雕鸮食物的生物量贡献率分别为11.83%、30.87%、7.36%、16.00%、0.15%、0.62%、33.17%.雕鸮的食物生态位宽度与大(狂鸟)的食物生态位宽度相近,食物生态位高度重叠,但是它们捕食同种猎物的比例显著不同.     

Roles of the volatile terpene, 1,8-cineole,in plant–herbivore interactions: a foraging odor cue as well as a toxin?

Olfaction is an important sense for many animals, yet its role in foraging by herbivores is poorly known. Many plants contain volatile compounds, such as terpenes, that are not only volatile but can be toxic if ingested. Volatile terpenes can be used by herbivores to assess leaf quality, but there is little evidence for whether they are also used as a searching cue. We applied the giving-up density (GUD) framework to examine fine-scale foraging by two free-ranging mammalian herbivores, the brush-tail possum (Trichosurus vulpecula) and the swamp wallaby (Wallabia bicolor), using patches with food and an inedible matrix that varied in content of a volatile terpene, 1,8-cineole. We tested the effect of (1) increasing dietary cineole concentration, and (2) masking the food odor by adding cineole to the inedible matrix, thus overriding the smell released by the diet. In both species GUD was affected by dietary cineole; a high cineole concentration raised GUD, consistent with its role as a toxin. There was a significant effect of masking on GUD for wallabies but not for possums, suggesting that odor was an important foraging cue at the feeding patch only for the former. Differences in ecological niche and diet may explain this pattern. We suggest that herbivores, such as the swamp wallaby, opportunistically eavesdrop on plant volatiles, i.e., take advantage of the signal proffered for a different function. The cost of this eavesdropping for plants, however, is presumably counteracted by other ecological benefits of these volatiles, including a reduction in leaf consumption as a function of toxicity.     

Olfactory and visual plant cues as drivers of selective herbivory

Food quality is an important consideration in the foraging strategy of all animals, including herbivores. Those that can detect and assess the nutritional value of plants from afar, using senses such as smell and sight, can forage more efficiently than those that must assess food quality by taste alone. Selective foraging not only affects herbivore fitness but can influence the structure and composition of plant communities, yet little is known about how olfactory and visual cues help herbivores to find preferred plants. We tested the ability of a free‐ranging, generalist mammalian browser, the swamp wallaby Wallabia bicolor, to use olfactory and visual plant cues to find and/or browse differentially on Eucalyptus pilularis seedlings grown under different nutrient conditions. Low‐nutrient seedlings differed from high‐nutrient seedlings, having lighter coloured leaves, red stems and lower biomass and nitrogen content. In the absence of visual cues, wallabies used odour to differentiate vials containing cut seedlings. They visited and investigated patches with high‐nutrient seedling odour most, followed by patches with low‐nutrient seedling odour, and patches with no added odour least. However, when visual and olfactory cues of seedlings were present, wallabies reversed their foraging response and were more likely to browse low‐ than high‐nutrient seedlings. This browsing difference, in turn, disappeared when long‐range visual cues were reduced by pinning seedlings horizontal to the ground. We suggest that visual cues overrode the effects of olfactory cues on browsing patterns of intact seedlings. Our study shows that herbivores can respond to odours of higher nutrient plants but in ecologically realistic scenarios they use a variety of visual and olfactory cues, with a context‐dependent outcome that is not always selection of high nutrient food. Our results demonstrate the importance of testing the sensory abilities of herbivores in realistic multi‐sensory settings to understand their function in selective foraging.     

Foraging Ecology of Fall-Migrating Shorebirds in the Illinois River Valley

Populations of many shorebird species appear to be declining in North America, and food resources at stopover habitats may limit migratory bird populations. We investigated body condition of, and foraging habitat and diet selection by 4 species of shorebirds in the central Illinois River valley during fall migrations 2007 and 2008 (Killdeer [Charadrius vociferus], Least Sandpiper [Calidris minutilla], Pectoral Sandpiper [Calidris melanotos], and Lesser Yellowlegs [Tringa flavipes]). All species except Killdeer were in good to excellent condition, based on size-corrected body mass and fat scores. Shorebird diets were dominated by invertebrate taxa from Orders Diptera and Coleoptera. Additionally, Isopoda, Hemiptera, Hirudinea, Nematoda, and Cyprinodontiformes contribution to diets varied by shorebird species and year. We evaluated diet and foraging habitat selection by comparing aggregate percent dry mass of food items in shorebird diets and core samples from foraging substrates. Invertebrate abundances at shorebird collection sites and random sites were generally similar, indicating that birds did not select foraging patches within wetlands based on invertebrate abundance. Conversely, we found considerable evidence for selection of some diet items within particular foraging sites, and consistent avoidance of Oligochaeta. We suspect the diet selectivity we observed was a function of overall invertebrate biomass (51.2±4.4 [SE] kg/ha; dry mass) at our study sites, which was greater than estimates reported in most other food selection studies. Diet selectivity in shorebirds may follow tenants of optimal foraging theory; that is, at low food abundances shorebirds forage opportunistically, with the likelihood of selectivity increasing as food availability increases. Nonetheless, relationships between the abundance, availability, and consumption of Oligochaetes for and by waterbirds should be the focus of future research, because estimates of foraging carrying capacity would need to be revised downward if Oligochaetes are truly avoided or unavailable for consumption.     

Diet of a rare herbivore based on DNA metabarcoding of feces: Selection,seasonality, and survival

In herbivores, survival and reproduction are influenced by quality and quantity of forage, and hence, diet and foraging behavior are the foundation of an herbivore's life history strategy. Given the importance of diet to most herbivores, it is imperative that we know the species of plants they prefer, especially for herbivorous species that are at risk for extinction. However, it is often difficult to identify the diet of small herbivores because: (a) They are difficult to observe, (b) collecting stomach contents requires sacrificing animals, and (c) microhistology requires accurately identifying taxa from partially digested plant fragments and likely overemphasizes less‐digestible taxa. The northern Idaho ground squirrel (Urocitellus brunneus) is federally threatened in the United States under the Endangered Species Act. We used DNA metabarcoding techniques to identify the diet of 188 squirrels at 11 study sites from fecal samples. We identified 42 families, 126 genera, and 120 species of plants in the squirrel's diet. Our use of three gene regions was beneficial because reliance on only one gene region (e.g., only trnL) would have caused us to miss >30% of the taxa in their diet. Northern Idaho ground squirrel diet differed between spring and summer, frequency of many plants in the diet differed from their frequency within their foraging areas (evidence of selective foraging), and several plant genera in their diet were associated with survival. Our results suggest that while these squirrels are generalists (they consume a wide variety of plant species), they are also selective and do not eat plants relative to availability. Consumption of particular genera such as Perideridia may be associated with higher overwinter survival.     

The dilemma of foraging herbivores: dealing with food and fear

For foraging herbivores, both food quality and predation risk vary across the landscape. Animals should avoid low-quality food patches in favour of high-quality ones, and seek safe patches while avoiding risky ones. Herbivores often face the foraging dilemma, however, of choosing between high-quality food in risky places or low-quality food in safe places. Here, we explore how and why the interaction between food quality and predation risk affects foraging decisions of mammalian herbivores, focusing on browsers confronting plant toxins in a landscape of fear. We draw together themes of plant–herbivore and predator–prey interactions, and the roles of animal ecophysiology, behaviour and personality. The response of herbivores to the dual costs of food and fear depends on the interplay of physiology and behaviour. We discuss detoxification physiology in dealing with plant toxins, and stress physiology associated with perceived predation risk. We argue that behaviour is the interface enabling herbivores to stay or quit food patches in response to their physiological tolerance to these risks. We hypothesise that generalist and specialist herbivores perceive the relative costs of plant defence and predation risk differently and intra-specifically, individuals with different personalities and physiologies should do so too, creating individualised landscapes of food and fear. We explore the ecological significance and emergent impacts of these individual-based foraging outcomes on populations and communities, and offer predictions that can be clearly tested. In doing so, we provide an integrated platform advancing herbivore foraging theory with food quality and predation risk at its core.     

Diet selection of African elephant over time shows changing optimization currency

Multiple factors determine diet selection of herbivores. However, in many diet studies selection of single nutrients is studied or optimization models are developed using only one currency. In this paper, we use linear programming to explain diet selection by African elephant based on plant availability and nutrient and deterrent content over time. Our results indicate that elephant at our study area maximized intake of phosphorus throughout the year, possibly in response to the deficiency of this nutrient in the region. After adjusting the model to incorporate the effects of this deficiency, elephant were found to maximize nitrogen intake during the wet season and energy during the dry season. We reason that the increased energy requirements during the dry season can be explained by seasonal changes in water availability and forage abundance. As forage abundance decrease into the dry season, elephant struggle to satisfy their large absolute food requirements. Adding to this restriction is the simultaneous decrease in plant and surface water availability, which force the elephant to seek out scarce surface water sources at high energy costs. During the wet season when food becomes more abundant and energy requirements are satisfied easier, elephant aim to maximize nitrogen intake for growth and reproduction. Our study contributes to the emerging theory on understanding foraging for multiple resources.     

Time allocation of bison in meadow patches driven by potential energy gains and group size dynamics

Understanding the behavioural mechanisms involved in broad‐scale spatial organisation of grazing herbivores requires uncovering the factors controlling foraging decisions, such as patch residency time. Foraging theory specifies that rate maximizers must simultaneously consider both the optimal residency time in a food patch and the optimal diet. Specifically, resource depletion or spatial variation in food type availability should not influence food choice, but only patch residency time. Few studies, however, have tested these principles together, and none on free‐ranging large herbivores. We evaluated the combined effects of forage characteristics, predation risk, and group size on residency time by free‐ranging bison Bison bison in summer. We hypothesized that residency time in meadows would increase with the availability of Carex atherodes, a highly profitable plant species maximizing energy intake rate, but decrease with sward complexity (i.e. plant species composition and structure) within foraging stations. We also anticipated that predation risk and group size would influence the relationship between vegetation characteristics and residency time. Residency times were measured in 44 sites using cameras located at meadow edges. We determined that residency time in meadows varied with meadow area, group size, biomass of C. atherodes available on the area, and proportion of C. atherodes within foraging stations. We found that the likelihood of departure decreased with an increase in the total biomass of C. atherodes available over the meadow, an effect attenuated by an increase in group size. Residency time in meadows was also influenced by plant species composition, with higher accessibility of C. atherodes within feeding stations increasing residency time. We found little evidence, however, that sward structure and predation risk influenced residency time. Overall, our study demonstrated that the search for rapid energy gains, together with the constraints imposed by group living, can explain time allocation in habitat patches by large gregarious herbivores.     

Differences between resource patches modify root herbivore effects on plants

While soil resource heterogeneity and root herbivory can have significant direct influences on plant growth, soil heterogeneity may also have indirect effects by influencing the foraging behavior of root herbivores. We used sand-filled greenhouse pots to assess root herbivore foraging behavior and potential interactions between patch quality, herbivore foraging, and plant biomass production (yield). Individual pots were divided into four quarters: one fertilized, and three unfertilized, two of which were planted with tree seedlings. Two treatments were used to create fertilized quarters: high-organic manure fertilizer, and slow-release mineral fertilizer. Seedlings of red maple (Acer rubrum L.) and Virginia pine (Pinus virginiana L.) were used to create two single-species and one mixed-species treatments. Root-feeding beetle larvae were added to the pots and allowed to forage freely for ∼8 weeks. At harvest, root herbivores in organic-fertilized pots were strongly attracted to fertilized quarters despite their relatively low-root biomass. Herbivore distribution was significantly different in mineral fertilized pots, where larvae were most abundant in planted quarters, which is also where most of the plant roots occurred. Whole pot plant yield was significantly reduced by larvae; this effect was stronger in the mineral fertilized pots than organic fertilized pots. While one of the plant species appeared more sensitive to herbivory, root herbivores had a greater influence on yield in mixed-species pots than in single-species pots. Overall, these results suggest that patch quality influences on herbivore foraging may indirectly alter yield and plant community composition. Responsible Editor: Angela Hodge.     

内蒙古天然草原不同放牧压力下亚洲小车蝗的食性及营养生态位（英文）

植物表皮蜡质中的饱和链烷作为内源指示剂广泛用于评价放牧家畜的食性和食量, 但用于天然草原蝗虫食性的评价研究较少。为了探讨天然草原蝗虫的食性及其生态位变化, 本研究以内蒙古天然草原为研究对象, 于2003年7-8月沿降水梯度选择3种典型植物群落（小针茅Stipa klemenzii、 羊草Leymus chinensis和大针茅Stipa grandis群落）, 在每个植物群落不同放牧压力下小区随机做20个植被样方, 样方内植物齐地面刈割, 测定其地上生物量和物种多样性, 取主要植物种测定其链烷模式, 同时采集放牧小区优势蝗虫种亚洲小车蝗Oedaleus asiaticus的粪便, 测定其链烷模式, 运用链烷技术评价蝗虫的食性及其营养生态位。结果表明： 不同植物群落中优势牧草种类及其比例不同, 其链烷模式存在种间差异, 链烷技术可以评价亚洲小车蝗的食性。亚洲小车蝗的食性在不同植物群落及不同放牧压力下存在显著的差异, 在羊草和大针茅群落中, 亚洲小车蝗是禾草采食者, 主要采食羊草和糙隐子草Cleistogenes squarrosa, 且与绵羊的营养生态位重叠指数较低, 分别为0.0619和0.0172; 在小针茅群落中亚洲小车蝗是杂类草采食者, 主要采食无芒隐子草Cleistogenes songorica、 猪毛菜Salsola collina和小针茅, 且与绵羊的营养生态位重叠指数较高, 达到0.1815。因此, 放牧不仅改变了群落的植物种类组成, 而且直接影响了亚洲小车蝗的食物组成, 二者对食物资源利用存在一定程度的竞争。     

Genetic variation in bitter taste receptor genes influences the foraging behavior of plateau zokor (Eospalax baileyi)

The ability to detect bitter tastes is important for animals; it can help them to avoid ingesting harmful substances. Bitter taste perception is mainly mediated by bitter taste receptor proteins, which are encoded by members of the Tas2r gene family and vary with the dietary preference of a specific species. Although individuals with different genotypes differ in bitterness recognition capability, little is known about the relationship between genetic variation and food selection tendencies at the intraspecific level. In this study, we examined the relationship between genotypes and diet in plateau zokor (Eospalax baileyi), a subterranean rodent endemic to the Qinghai‐Tibet Plateau that caches food for the winter. We assayed the composition and taste profile of each plant contained in temporary caches and vicinity quadrats, which were representative of selected and available food, respectively. Bitter plant selection indices (E_bitter) were estimated. We also sequenced 26 candidate Tas2r genes from zokors and determined their relationships with the E_bitter of their caches. We identified four key results: (1) zokors varied considerably in both bitter food preference and Tas2r sequences; (2) five genes (zTas2r115, zTas2r119, zTas2r126, zTas2r134, and zTas2r136) exhibited allelic variation that was significantly associated with E_bitter; (3) synonymous SNPs, nonsynonymous SNPs, and pseudogenization are involved in the genotype–phenotype relationship; (4) the minor genotypes of zTas2r115, zTas2r134, and zTas2r136 and the major genotypes of zTas2r119 and zTas2r126 cached more bitter plants. Our results link Tas2r variation with food selection behavior at the population level for the first time.     

Forage selection by Royle's pika (Ochotona roylei) in the western Himalaya,India

Forage selection decisions of herbivores are often complex and dynamic; they are modulated by multiple cues, such as quality, accessibility and abundance of forage plants. To advance the understanding of plant–herbivore interactions, we explored foraging behavior of the alpine lagomorph Royle's pika (Ochotona roylei) in Kedarnath Wildlife Sanctuary, India. Pika bite counts on food plants were recorded through focal sampling in three permanently marked plots. Food plant abundance was recorded by traditional quadrat procedures; forage selection was estimated with Jacob's selection index. Multiple food-choice experiments were conducted to determine whether forage selection criteria would change with variation in food plant composition. We also analyzed leaf morphology and nutrient content in both major food plants and abundantly available non-food plants. Linear regression models were used to test competing hypotheses in order to identify factors governing forage selection. Royle's pika fed primarily on 17 plant species and each forage selection decision was positively modulated by leaf area and negatively modulated by contents of avoided substances (neutral detergent fiber, acid detergent fiber, acid detergent lignin and tannin) in food plants. Furthermore, significance of the interaction term “leaf size × avoided substance” indicates that plants with large leaves were selected only when they had low avoided substance content. The forage selection criteria did not differ between field and laboratory experiments. The parameter estimates of best fit models indicate that the influence of leaf size or amount of avoided substance on pika forage selection was modulated by the magnitude of predation risk.     

The more the merrier? Multi-species grazing of small herbivores mediates plant community impacts

Small herbivores play keystone functional roles in grassland ecosystems. Recognising the combined effects where herbivores co-exist is important for guiding grassland restoration and biodiversity conservation. On the Tibetan Plateau, both plateau pikas and Himalayan marmots are regarded as pests by Tibetan people and local government, but little is known about their combined effects. We conducted a field study to determine the combined effects of pikas and marmots on plant biodiversity and vegetation structure. Plateau pikas alone consistently reduced the plant height and diversity and increased the vegetation cover of physically unpalatable plants. However, the co-existence of marmots with pikas decreased the vegetation cover of physically unpalatable plants, while increasing the cover of palatable plants and plant diversity, ultimately changing the impact of pikas alone and modulating aspects of the plant community. These results illustrate that increasing the abundance and richness of small herbivores in grassland ecosystems may promote plant diversity and benefit vegetation restoration rather than aggravate the degradation of grasslands.     

内蒙古草原布氏田鼠与绵羊的营养生态位研究

放牧活动对小型啮齿动物种群数量的影响是草原生态系统研究中的热点问题,确定绵羊和小型啮齿动物的营养生态位关系对于草原生态系统的管理具有重要的作用。运用粪便显微分析法分析了内蒙古草原动物生态研究站大型野外围栏内布氏田鼠和绵羊在6—9月份的食谱组成,确定两种草食动物食性选择和营养生态位的变化,从食物利用途径揭示放牧活动对布氏田鼠种群数量的影响方式及二者之间的竞争与共存关系。研究结果表明：围栏中共有23种植物,其中糙隐子草、克氏针茅、羊草和刺藜是围栏中的优势植物;布氏田鼠共取食10种植物,绵羊共取食8种植物,禾本植物为两种动物的主要采食植物。布氏田鼠和绵羊的喜食植物种类都存在季节性变化;除7月外,两种动物的食物多样性与围栏植物多样性有显著的正相关关系,表明动物的食性选择受植物资源变化的影响。布氏田鼠和绵羊具有很高的营养生态位重叠度,除8月(0.691)外,6、7、9月份的营养生态位重叠度均高于0.9,表明二者之间存在激烈的食物竞争;放牧活动极显著地降低了禾本科植物的地上生物量,导致布氏田鼠的食物数量减少;放牧处理下布氏田鼠的喜食植物的物种数和营养生态位宽度(除9月)增加,导致布氏田鼠的食物质量...