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。     

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...     

Identification of tannin–degrading microorganisms in the gut of plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus)

Gut microorganisms are thought to play a role in the degradation of plant secondary metabolites in herbivores. Here, we examined the presence of tannin–degrading microorganisms in the gut of two herbivores, plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus). Tannase activity in the feces of wild plateau pikas and root voles increased from June to August, corresponding to the increase in condensed and hydrolyzable tannin concentrations in plants during this period. Using intragastric tannic acid infusion, we found that tannase activities were significantly higher following administration of three concentrations of tannic acid than that in the control group for root voles. In contrast, for plateau pikas, animals administered tannic acid exhibited lower tannase activity in low–dose and high–dose groups than that in the control group. Tannase activities in root voles were higher than those in plateau pikas among different months and in different tannic acid infusion groups. Three tannin–degrading anaerobic strains were isolated from the cecum of plateau pikas (termed A1, A2, and A3) and root voles (termed M1, M2, and M3). 16 s rDNA sequencing assigned isolates A1 and M1 to the genus Enterobacter, A2 and M2 to the genus Shigella, and A3 and M3 to the genus Staphylococcus. These data provided the first evidence of microorganisms with tannin–degrading activity in the gut of plateau pikas and root voles. We speculated that both animals could degrade tannins in the gut, but that root voles would have a greater ability to process tannins than plateau pikas.     

Arctic Small Rodents Have Diverse Diets and Flexible Food Selection

The ecology of small rodent food selection is poorly understood, as mammalian herbivore food selection theory has mainly been developed by studying ungulates. Especially, the effect of food availability on food selection in natural habitats where a range of food items are available is unknown. We studied diets and selectivity of grey-sided voles (Myodes rufocanus) and tundra voles (Microtus oeconomus), key herbivores in European tundra ecosystems, using DNA metabarcoding, a novel method enabling taxonomically detailed diet studies. In order to cover the range of food availabilities present in the wild, we employed a large-scale study design for sampling data on food availability and vole diets. Both vole species had ingested a range of plant species and selected particularly forbs and grasses. Grey-sided voles also selected ericoid shrubs and tundra voles willows. Availability of a food item rarely affected its utilization directly, although seasonal changes of diets and selection suggest that these are positively correlated with availability. Moreover, diets and selectivity were affected by availability of alternative food items. These results show that the focal sub-arctic voles have diverse diets and flexible food preferences and rarely compensate low availability of a food item with increased searching effort. Diet diversity itself is likely to be an important trait and has previously been underrated owing to methodological constraints. We suggest that the roles of alternative food item availability and search time limitations for small rodent feeding ecology should be investigated.

Nomenclature

Annotated Checklist of the Panarctic Flora (PAF), Vascular plants. Available at: http://nhm2.uio.no/paf/, accessed 15.6.2012.     

放牧对布氏田鼠主要食物选择的影响

动物的食物选择受食物资源量、质量和喜好度决定。尽管放牧可减少鼠类的喜食植物的数量和质量,但其如何影响鼠类的食物选择尚不清楚。本研究于2014年5月至10月,在内蒙古锡林郭勒盟锡林浩特市毛登牧场的大型试验围栏内进行了布氏田鼠的食物选择实验。利用大型实验围栏内5年连续放牧处理所构建的植被变化条件,采用扣笼试验,调查了布氏田鼠对其三种主要植物的取食情况。研究发现：连续放牧后,糙隐子草的盖度增加,而羊草、克氏针茅盖度降低;糙隐子草的盖度显著高于羊草、克氏针茅,成为各季节的优势植物种类。放牧对布氏田鼠取食羊草、克氏针茅和糙隐子草的绝对取食频次均无显著影响。在季节上,布氏田鼠对克氏针茅和糙隐子草的取食在三个季节均无差异,但布氏田鼠对羊草取食的绝对频次夏季显著高于春季和秋季;布氏田鼠对三种植物的喜好程度依次为羊草>克氏针茅>糙隐子草,但季节和放牧因素对布氏田鼠对这三种植物的喜好度无显著影响。结果表明,布氏田鼠的食物选择及食物组成相对稳定,表现为其对放牧或季节因素造成的喜食植物资源量的变化具有很好的适应性,推测是其调整取食努力来实现食物组成的平衡。     

Induction and persistence of allelochemicals in the foliage of balsam fir seedlings following simulated browsing

The intensity, pattern, and timing of browsing disturbances influence the mobilization of chemical defenses (allelochemicals) and subsequent growth of conifers such as balsam fir, an important food source for various insect and mammalian herbivores. The objective of this study was to examine the induction and persistence of allelochemicals in foliage of balsam fir seedlings as affected by the pattern and timing of browsing disturbance. We conducted a simulated browsing study in a greenhouse environment using four browsing patterns and three persistence times. Total phenols were induced shortly after simulated browsing and persisted for at least 1 month, whereas condensed tannins exhibited a delayed induction but were more persistent, remaining above background levels 2 months after simulated browsing. The chemistry of non-browsed seedlings revealed that a seasonal pattern was evident for both total phenols and condensed tannins. As the experiment progressed through the growing season, background levels of total phenols decreased while those of condensed tannins increased with the two allelochemicals groups appearing to show a negative relationship. These trends suggest that total phenols, which are assumed to have a lower biosynthetic cost and are more quickly mobilized than condensed tannins, are a first line of herbivory defense followed by condensed tannins which take longer to mobilize but have a longer persistence time or that total phenols act as a primary defense against insect herbivores which disturb plants in the early growing season while condensed tannins are mobilized in the late season to defend against mammalian browsers of balsam fir in winter.     

Is space management of female meadow voles (Microtus pennsylvanicus) related to nutritive quality of plants?

Summary It is thought by many (see Ims 1987 for review; Desy and Batzli 1989) that high quality food regulate population processes, territoriality and mating systems among small herbivores like meadow voles (Microtus pennsylvanicus). We thought that comparisons of nutritive components from selected plants eaten by sexually active and inactive voles, as well as between territorial and non territorial sexually active females would bring some light into these theoretical considerations. Sexually active females did have a higher diet quality over inactive ones and over active and inactive males. Nutritive components of selected species from territorial reproductive females did not vary significantly from those of the non territorial females the year of higher crowding conditions but they varied significantly the following year when population density of voles was much lower. This decline in food quality coincided with a switch in food selection. Since there were only eight plant species involved in such processes, we think that crowding condition and availability of high quality food are two factors involved concurrently in space management and territoriality among voles.     

A mixed diet of toxic plants enables increased feeding and anti-predator defense by an insect herbivore

Some insect herbivores sequester plant secondary metabolites (PSMs) for their own defense, raising the interesting possibility that grazing herbivores are defended by combinations of PSMs from different plant species. In this study, we tested the hypothesis that the grazing caterpillar, Grammia incorrupta, deters the ant, Aphaenogaster cockerelli, by eating a mixture of plants containing iridoid glycosides (IGs) and those containing pyrrolizidine alkaloids (PAs), and that this deterrence is greater than that attained by eating either plant alone. This hypothesis was tested against the non-mutually exclusive hypothesis that mixing plants containing PAs with those containing IGs improves growth performance. Caterpillar survival and growth were measured on three experimental diets: a PA plant, an IG plant, and a mixture of the two. We measured the degree of deterrence associated with these, and an additional experimental diet devoid of PSMs at naturally occurring A. cockerelli nests. Caterpillars fed both plants gained more mass than those fed either plant alone, but took longer to develop. These differences were not caused by diet-based variation in growth efficiency, but by eating more food when offered the mixed-plant diet relative to single-plant diets. The mixed diet was shown to provide deterrence to ants, whereas caterpillars fed single-plant diets were not significantly more deterrent than caterpillars that had eaten the PSM-free diet. We hypothesize that enhanced defense results from increased food consumption in response to multiple plant species, perhaps leading to greater PSM sequestration. Through this mechanism, bottom-up and top-down effects may mutually reinforce the grazing dietary strategy.     

Chemical Variation in a Dominant Tree Species: Population Divergence,Selection and Genetic Stability across Environments

Understanding among and within population genetic variation of ecologically important plant traits provides insight into the potential evolutionary processes affecting those traits. The strength and consistency of selection driving variability in traits would be affected by plasticity in differences among genotypes across environments (G×E). We investigated population divergence, selection and environmental plasticity of foliar plant secondary metabolites (PSMs) in a dominant tree species, Eucalyptus globulus. Using two common garden trials we examined variation in PSMs at multiple genetic scales; among 12 populations covering the full geographic range of the species and among up to 60 families within populations. Significant genetic variation in the expression of many PSMs resides both among and within populations of E. globulus with moderate (e.g., sideroxylonal A h²op = 0.24) to high (e.g., macrocarpal G h²op = 0.48) narrow sense heritabilities and high coefficients of additive genetic variation estimated for some compounds. A comparison of Qst and Fst estimates suggest that variability in some of these traits may be due to selection. Importantly, there was no genetic by environment interaction in the expression of any of the quantitative chemical traits despite often significant site effects. These results provide evidence that natural selection has contributed to population divergence in PSMs in E. globulus, and identifies the formylated phloroglucinol compounds (particularly sideroxylonal) and a dominant oil, 1,8-cineole, as candidates for traits whose genetic architecture has been shaped by divergent selection. Additionally, as the genetic differences in these PSMs that influence community phenotypes is stable across environments, the role of plant genotype in structuring communities is strengthened and these genotypic differences may be relatively stable under global environmental changes.     

Consequences of plant–chemical diversity for domestic goat food preference in Mediterranean forests

The domestic goat, a major herbivore in the Mediterranean basin, has demonstrated a strong ability to adapt its feeding behaviour to the chemical characteristics of food, selecting plants according to their nutritive quality. In this study, we determine some chemical characteristics related to plant nutritional quality and its variability among and within five tree species, these being the main components of the mountain forests of SE Spain, with the aim of determining their influence on food selection by this generalist herbivore. We analyse nitrogen, total phenols, condensed tannins and fibre concentration as an indicator of the nutritive value of the different trees. To determine the preference by the domestic goat, we performed two types of feeding-choice assays, where goats had to select between different species or between branches of the same species but from trees of different nutritional quality. The analysis of the plant nutritional quality showed significant differences in the chemical characteristics between species, and a high variability within species. However, when faced with different tree species, the domestic goat selected some of them but showed striking individual differences between goats. When selecting between trees of the same species, the goats showed no differential selection. This limited effect of chemical plant characteristics, together with the variability in foraging behaviour, resulted in a widespread consumption of diverse plant species, which can potentially modulate the effect of the goat on vegetation composition, and open the way for the conservation of traditional livestock grazing on natural protected areas.     

High Energy or Protein Concentrations in Food as Possible Offsets for Cyanide Consumption by Specialized Bamboo Lemurs in Madagascar

Plants producing toxic plant secondary metabolites (PSMs) deter folivores from feeding on them. Animals that can cope with noxious PSMs have a niche with a competitive advantage over other species. However, the ability to cope with toxic PSMs incurs the costs of detoxification. To assess possible compensations for the ingestion of toxic PSMs, we compare the chemical quality of plants consumed by bamboo lemurs (genera Hapalemur and Prolemur; strepsirrhine primates of Madagascar) in areas with and without bamboo. Some bamboo lemurs consume bamboo containing concentrations of cyanogenic substances 10–50 times above the average lethal dosage for mammals, and we postulate that animals consuming cyanogenic substances need supplementary protein or readily available energy for detoxification. We compared the chemical composition of food consumed by three species of bamboo lemurs that feed mainly (>80% of their time) on bamboo in the evergreen rainforest of Ranomafana (Madagascar) with published data of the diets of bamboo lemurs at two sites without highly cyanogenic plants (reed beds of Lac Alaotra and the evergreen littoral forest of Mandena) and with food of sympatric folivorous lemur species that do not feed on bamboo. Lemurs feeding on bamboo consumed up to twice as much protein as bamboo lemurs in areas without bamboo and sympatric lemur species that feed on leaves of trees. Concentrations of nonstructural carbohydrates (a source of energy) showed the opposite trend. This result supports the hypothesis that feeding on cyanogenic plants is linked to high protein intake, either as a source of protein or for sulfur-containing amino acids that can be used for detoxification. Owing to the high protein concentrations in bamboo, however, we cannot distinguish between the hypothesis that lemurs that eat bamboo target additional food items with higher protein from the hypothesis that lemurs feeding on bamboo unavoidably obtain higher concentrations of protein than animals feeding on leaves of trees, without an added nutritional benefit.     

Recently duplicated sesterterpene (C25) gene clusters in Arabidopsis thaliana modulate root microbiota

Land plants co-speciate with a diversity of continually expanding plant specialized metabolites(PSMs) and root microbial communities(microbiota). Homeostatic interactions between plants and root microbiota are essential for plant survival in natural environments. A growing appreciation of microbiota for plant health is fuelling rapid advances in genetic mechanisms of controlling microbiota by host plants. PSMs have long been proposed to mediate plant and single microbe interactions. However,the effects of PSMs, especially those evolutionarily new PSMs, on root microbiota at community level remain to be elucidated.Here, we discovered sesterterpenes in Arabidopsis thaliana, produced by recently duplicated prenyltransferase-terpene synthase(PT-TPS) gene clusters, with neo-functionalization. A single-residue substitution played a critical role in the acquisition of sesterterpene synthase(sesterTPS) activity in Brassicaceae plants. Moreover, we found that the absence of two root-specific sesterterpenoids, with similar chemical structure, significantly affected root microbiota assembly in similar patterns. Our results not only demonstrate the sensitivity of plant microbiota to PSMs but also establish a complete framework of host plants to control root microbiota composition through evolutionarily dynamic PSMs.     

Fruit size, crop mass, and plant height explain differential fruit choice of primates and birds

Seed dispersal by animals is an important ecological process shaping plant regeneration. In general, seed dispersers are highly variable and often opportunistic in their fruit choice. Despite much research, the factors that can explain patterns of fruit consumption among different animal groups remain contentious. Here, we analysed the interactions between 81 animal species feeding on the fruits of 30 plant species in Kakamega Forest, Kenya, during 840 h of observations. Our aim was to determine whether plant characteristics, fruit morphology, fruit colours and/or fruit compounds such as water, sugar, phenols and tannins explained the relative importance of fruit consumption by the two most important consumer groups, primates and birds. We found significant differences in fruit choice between both groups. Primates fed on larger fruits and on higher trees that had larger fruit crops, whereas birds were observed feeding on smaller fruits and on smaller plants producing fewer fruits. Fruit colours did not differ between fruits consumed by primates and those consumed by birds. However, differences in the fruit choice among frugivorous birds were associated with differences in fruit colours. Smaller plants with smaller fruits produced red fruits which contrasted strongly with the background; these fruits were dispersed by a distinct set of bird species. The contents of water, sugar, phenols and tannins did not differ between fruits eaten by primates and those eaten by birds. Some phylogenetic patterns were apparent; primates fed preferentially on a phylogenetically restricted subsample of large plants with large fruits of the subclass Rosidae. We discuss why the observed primate dispersal syndrome is most likely explained by a process of ecological fitting.     

Contrasting effects of large herbivore grazing on smaller herbivores

Assemblages of large herbivores may compete for food or facilitate one another. However, small vertebrate herbivore species co-occurring with large herbivores may be affected by large herbivore grazing through changes in plant species composition, nutrient content and vegetation structure. These changes can be either positive or negative for the smaller herbivores, but this may depend on the species of small herbivores. We experimentally tested the impact of cattle grazing on habitat choice of European rabbits (Oryctolagus cuniculus) and common voles (Microtus arvalis). We excluded cattle for 7 years and measured changes in vegetation parameters, and the response of rabbits and voles. Rabbits were facilitated by cattle, whereas voles strongly preferred vegetation without cattle. The facilitation effect was stronger at low rabbit densities. Vegetation biomass and nitrogen concentration were not affected by cattle grazing, but vegetation height increased significantly where cattle were excluded. Plant species composition also changed following cattle exclusion; however, the main food plants of rabbits and voles remained abundant in each grazing treatment. We conclude that the response of both rabbits and voles predominantly reflect the differences in vegetation height in the presence and absence of cattle, but in a contrasting fashion. The difference in response between rabbits and voles may result from reduced perceived predation risk, which is lowest in high vegetation for voles, but in short vegetation for rabbits, which depend on their burrows for safety. The use of large herbivores in grassland conservation management can thus have a contrasting effect on different species of small herbivores.     

油松不同部位多酚与单宁的含量比较研究

油松为我国特有树种,药用历史悠久且分布广泛,其药用部位含有多酚和单宁等生物活性物质。本文采用Folin-Cicalten法和柠檬酸铁铵法对油松不同部位多酚与单宁含量进行了测定。实验结果表明,油松根、茎和叶多酚含量依次为89.24±12.06、68.18±11.20、104.30±12.51 mg·g^-1;单宁含量依次为25.38±5.85、20.92±3.55、39.02±5.68 mg·g^-1。油松多酚与单宁在油松各部位有相同的分布趋势,均为叶中最高,根次之,茎中最低。与其他中草药植物多酚含量相比,油松多酚含量较高,具有较大的开发前景和应用价值。     

野生地木耳中次生代谢产物含量测定与分析

测定了野生地木耳（Nostoc commune Vauch.）中次生代谢产物含量,并与4种常见食用菌藻黑木耳（Auricularia auricular-judae）、银耳（Tremella fuciformis）、紫菜（Porphyra）、海带（Laminaria japonica）进行比较分析,总酚、总黄酮和缩合单宁含量测定采用分光光度法,总生物碱含量测定采用高效液相色谱法（HPLC）。结果显示,野生地木耳中总酚含量为24.255 mg/g±1.631 mg/g,总黄酮含量为5.741 mg/g±0.239 mg/g,总生物碱含量为0.768 mg/g±0.073 mg/g,缩合单宁含量为0.069 mg/g±0.009 mg/g。4种食用菌藻中次生代谢产物含量范围为：总酚（5.520～62.326 mg/g）、总黄酮（0.847～7.010 mg/g）、总生物碱（0.408～4.132 mg/g）、缩合单宁（0.063～0.233 mg/g）;比较分析结果显示,野生地木耳次生代谢产物中的总酚和总黄酮物质含量较高,且总酚是主要次生代谢产物,缩合单宁与总生物碱含量较低;总酚含量约为黑木耳和银耳的2倍、紫菜的6倍;总黄酮含量约为黑木耳的7倍,银耳的3倍。     

What physiological processes permit insects to eat Eucalyptus leaves?

Many species of insects eat Eucalyptus foliage despite its relatively low nutritional value and the many plant secondary metabolites (PSMs) present, for example, terpenes, phenols and formylated phloroglucinols (FPGs). Formylated phloroglucinols are a new class of PSMs that act as antifeedants for possums and koalas. What physiological processes are present that permit insects to eat eucalypt foliage and how do PSMs influence insect feeding or digestion? Some trees seem to be repeatedly infested with eucalypt‐feeding insects, possibly as a result of previous chemosensory cues remaining from parental selection of a plant. Avoidance or storage of PSMs permit jarrah leafminers (Perthida glyphopa) and sawflies (Perga sp.) to consume eucalypt foliage without dealing with the majority of these compounds. Some PSMs can be metabolized by polysubstrate membrane oxidases as found in caterpillars or sawflies that feed on eucalypts. High midgut pH may be advantageous for nutrient extraction and PSM metabolism, and midgut pH ranges between 8.5 and 8.9 for caterpillars of Hyalarcta huebneri. Plant secondary metabolites may not be absorbed as a result of the combined presence of the peritrophic matrix and endogenous surfactants. Excretion of PSMs can be as metabolites or intact compounds. Both putative metabolites and sideroxylonal‐A, an FPG, are present in the faeces of larvae of the case moth, H. huebneri. The presence of sideroxylonal‐A in the food had an effect on the presence of 5‐hydroxytryptamine (5HT) in the central nervous system of caterpillars, as larvae fed leaves with a high concentration of sideroxylonal‐A had relatively more 5HT in the brain and central nervous system ganglia than larvae fed leaves containing a low concentration. Further work is necessary to clarify how PSMs are handled by eucalypt‐feeding insects and what effect FPGs have on feeding and digestion.     

Inter-population differences in the tolerance of a marsupial folivore to plant secondary metabolites

Plant secondary metabolites (PSMs) strongly influence diet selection by mammalian herbivores. Concentrations of PSMs vary within and among plant species, and across landscapes. Therefore, local adaptations may cause different populations of herbivores to differ in their ability to tolerate PSMs. Here, we tested the food intake responses of three populations of a marsupial folivore, the common brushtail possum (Trichosurus vulpecula Kerr), from different latitudes and habitat types, to four types of PSMs. We found clear variation in the responses of northern and southern Australian possums to PSMs. Brushtail possums from southern Australia showed marked decreases in food intake in response to all four PSMs, while the two populations from northern Australia were not as sensitive and their responses did not differ from one another. These results were unexpected, based on our understanding of the experiences of these populations with PSMs in the wild. Our results suggest that geographically separated populations of possums may have evolved differing abilities to cope with PSMs, as a result of local adaptation to their natural environments. Our results provide the basis for future studies to investigate the mechanisms by which populations of mammalian species differ in their ability to tolerate PSMs.     

Is habitat selection by the Cabrera vole (Microtus cabrerae) related to food preferences?

The Cabrera vole (Microtus cabrerae) is an Iberian endemism considered threatened both in Portugal and Spain. This vole is often referred to as a tall perennial grassland community specialist. However, a recent study revealed that the Cabrera vole exploits a wide variety of grasslands in south Portugal. The major aim of the present study was to test the palatability of 21 plant species of this region occurring within or outside typical perennial grassland colonies in order to assess vole's food preferences. Results showed a major consumption of monocotyledons and annual plants (such as Festuca ampla, Agrostis castellana, Brachypodium distachyon, B. phoenicoides and Vulpia geniculata), but no relationship was found between diet selection and perennial grassland plant communities. The preference of voles for annual species, occurring more abundantly outside the colonies, raises the hypothesis that the establishment of a colony might be determined by plant species abundance and persistence over the year, rather than by their palatability. This seems to be particularly evident in this region, where summer meteorological conditions make vegetation unavailable outside the colonies.     

饥饿和食物单宁酸对东方田鼠(Microtus fortis)食物摄入量和觅食行为的影响

实验室条件下,测定饥饿和食物单宁酸对东方田鼠食物摄入量和觅食行为的影响。结果表明,饥饿使实验个体的食物总摄入量增加,食物摄入率及口量大小随饥饿强度的增大而增加,而觅食频次则无显著改变,实验个体每取食回合的觅食时间呈缓慢增加的趋势,与对照组比较,觅食时间差异不显著。东方田鼠优先选择0%单宁酸食物,次为3%单宁酸食物,而对6%单宁酸食物的摄入量最少。在饥饿条件下,东方田鼠食物摄入率的增加主要源于其口量大小,觅食频次和觅摄食时间对食物摄入量增加的贡献不显著。在饥饿条件下,植食性小哺乳动物并未通过延长觅食时间,降低用于防卫、繁殖活动时间来增加食物摄入量,而是通过增加口量大小,提高其食物摄入率来满足其营养需要。验证了饥饿与植物次生化合物共同作用引起田鼠类动物生理的改变,能影响其食物摄入量及觅食行为的假设。