Post‐dispersal seed depletion by rodents in marginal populations of yew (Taxus baccata): consequences at geographical and local scales

Post‐dispersal seed predation is a crucial phenomenon for plant recruitment, and its incidence can be hypothesized to increase in ecologically and geographically marginal populations of threatened species, such as yew (Taxus baccata). Here we examine the among‐ and within‐population patterns of seed consumption by rodents and evaluate to what extent they are linked to marginality in Mediterranean low‐density yew stands. Among populations we tested: (i) whether the rates of seed predation found in our marginal sites were consistently higher than in populations from core regions; (ii) within populations we evaluated whether rodents preferred microhabitats with greater seed availability (beneath female yew trees) or with lower predation risk (shrubs) in two seeding seasons (fall–winter 2005 and 2006). Predation rates were extremely high (92.5%) and they were well above values reported for core populations (65.4%), to the extent that rodents almost completely depleted the experimental seeds in all populations and years. Our expectation of lower predation rates with decreasing vegetation cover was also confirmed for all years and populations, suggesting that rodent foraging was risk‐sensitive. This microhabitat effect outweighed the effect of seed availability under female yew trees, implying also that rodents selectively consumed the most valuable seeds in terms of their recruitment prospects. Overall, our results suggest that the mechanisms underlying seed depletion and its demographic consequences are linked to the effects of reduced yew performance in ecologically marginal habitats.     

冷驯化条件下高山姬鼠能量对策的初步研究

为进一步了解横断山区小型哺乳动物的能量代谢对策,本文主要研究了横断山的外来物种——高山姬鼠(Apodemus chevrieri)持续冷暴露28d的能量变化。结果表明,随着冷驯化时间延长,体重和体温降低;摄入能、消化能和可代谢能增加,至21d后这3项指标又下降;BMR和NST增加,并且28d后它们分别是对照组的187.19%和155.97%;(NST-BMR)/BMR比值7d时增加到1.02,21d后下降至0.53,并保持稳定。因此,在持续冷暴露下,高山姬鼠采取适当降低体重和体温、增加能量摄入、增加BMR和NST产热等途径来维持能量代谢平衡,但是NST在产热中的作用逐渐降低。这种能量模式很可能代表了一种外来小型啮齿动物对于在横断山生存独特的能量适应策略。     

Echinostome Infections in the Striped-Field Mouse, Apodemus agrarius, and the Ussuri White-Toothed Shrew, Crocidura lasiura, Caught Near the Demilitarized Zone, Gyeonggi-do (Province), Republic of Korea

A total of 1,498 small mammals (rodents and insectivores), including Apodemus agrarius (n = 1,366), Crocidura lasiura (54), Mus musculus (32), Micronytus fortis (28), Eothenomys regulus (9), Micronys minutes (6), and Cricetulus triton (3), were live-trapped in Gyeonggi-do (Province) (Paju-si, Pocheon-gun, and Yeoncheon-gun) near the demilitarized zone (DMZ) from December 2004 to September 2005. A. agrarius was found to be infected with 3 species of echinostomes (Echinostoma hortense, Echinostoma cinetorchis, and Euparyphium murinum), while C. lasiura was infected with 1 species (Echinochasmus japonicas) of echinostome. Other mammals were free from echinostome infections. Total 16 E. hortense were detected in 7 (0.5%) mice, 9 E. cinetorchis from 5 (0.4%), and 3 E. murinum from 2 (0.1%) out of 1.366 A. agrarius examined. E. japonicus was found only in 1 (1.9%; total 3 specimens) C. lasiura. These results demonstrate that A. agrarius and C. lasiura, inhabiting near the DMZ of Gyeonggi-do serve as the natural definitive hosts for several species of echinostomes, although their infection rates are low. This is the first record of natural infections of A. agrarius with E. cinetorchis and C. lasiura with E. japonicus in the Republic of Korea.     

Comparative study of the phylogenetic structure in six Apodemus species (Mammalia,Rodentia) inferred from ISSR-PCR data

The utility of the Inter Simple Sequence Repeat-Polymerase Chain Reaction (ISSR-PCR) was explored in order to determine genetic variation in six species of the genus Apodemus (A. flavicollis, A. sylvaticus, A. uralensis, A. agrarius, A. mystacinus and A. epimelas) at the individual level, population level, in separate geographic samples and in the species as a whole. Six optimized primers produced highly reproducible and polymorphic DNA markers with 98.3% polymorphic bands on a total sample of 91 individuals from 32 localities in Europe and Asia. Moreover, each primer allowed for an exact diagnosis of each of the six Apodemus species and thus provides a simple and reliable tool for the hitherto problematic discrimination of species from the subgenus Sylvaemus. Genetic distances between species ranged from 0.079, among the closely related A. flavicollis and A. sylvaticus, to 0.203 between A. mystacinus and A. agrarius. A. flavicollis, A. uralensis and A. sylvaticus display a strong population substructure. The range of genetic distances among geographic samples within last two species reaches the values obtained for closely related species. ISSR markers proved to be a simple and reliable tool for species diagnosis, as well as for estimating genetic diversity below the species level and for closely related species, but they showed questionable reliability for larger genetic distances.     

光周期和高脂食物对雌性高山姬鼠能量代谢和产热的影响

为了研究光周期和高脂食物对小型哺乳动物能量代谢和产热的影响,将成年雌性高山姬鼠分别驯化于长光照低脂、高脂食物和短光照低脂、高脂食物条件下,7周后测定动物的体重、能量摄入、产热、身体组成、血清瘦素浓度以及体脂含量等参数。结果发现:1)短光照抑制体重增长,降低血清瘦素浓度,增加非颤抖性产热;2)高脂食物使摄入能减少,消化率和体脂含量提高,但未显著影响体重、基础代谢率、非颤抖性产热和血清瘦素浓度;3)血清瘦素浓度与摄入能不相关,但与体脂重量正相关。结果暗示:短光照下瘦素作用敏感性增加和产热能力增强,可能介导了抵抗高脂食物诱导的肥胖。在野外条件下,高山姬鼠能通过能量代谢和产热的适应性调节避免体重的过度增长,有利于降低捕食风险,增强生存能力。     

三种啮齿动物的消化道形态特征

对棕背(Clethrionomys rufocanus)、林姬鼠(Apodemus speciosus)和黑线姬鼠(A.agrarius)夏季的消化道形态进行了比较。3种啮齿动物总消化道的长度及重量(含内容物重和总干组织重),各器官的长度,胃、小肠和盲肠等长度,小肠和盲肠含内容物重,盲肠和大肠去内容物重,小肠、盲肠和大肠总干组织重等均存在明显的种间差异。以植物为食的棕背的总消化道、小肠、盲肠和大肠的长度或重量明显长于或重于其他两种鼠类。后肠可作为衡量草食性动物食物质量的指标。3种啮齿动物可通过消化道形态改变以适应不同的食性。     

Two‐module organization of the mandible in the yellow‐necked mouse: a comparison between two different morphometric approaches

Mandibles of yellow‐necked mouse (Apodemus flavicollis) were used to explore modularity. We tested a biological hypothesis that two separate modules (alveolar region and ascending ramus) can be recognized within the mandible. As a second research goal, we compared two different morphometric procedures under the assumption that methodological approaches that use either geometric or traditional morphometric techniques should give similar results. Besides confirmation of the predicted hypothesis of modularity, the application of both approaches revealed that: (i) modularity was somewhat more evident when it was analysed on the asymmetric (fluctuating asymmetry, FA) than on the symmetric (individual variation) component of variation; (ii) there is correspondence in the patterns of individual variation and FA, which indicates that integration of mandibular traits among individuals is primarily due to direct developmental interactions; and (iii) allometry does not obscure the hypothesized modularity for individual variation or for FA. In addition, traditional morphometric method allowed us to check whether allometry influenced each module to the same extent and to conclude that the ascending ramus is more heavily influenced by general size than the alveolar region. In studies of modularity, differences in methods can lead to discrepancies in the results, and therefore, some caution is required when comparing findings from different investigations. The substantial agreement between our results provides evidence that, when considering two‐module organization of the mouse mandible, direct comparison among studies that use the methods applied herein is, in great part, reliable.     

The effect of cold-acclimation on energy strategies of Apodemus draco in Hengduan Mountain region

Environmental factors play an important role in the seasonal adaptation of body mass and thermogenesis in small mammals. The purpose of the present study was to test the hypothesis that ambient temperature triggers adjustments in body mass, body temperature, energy intake, digestible energy intake, metabolic energy intake, and the length and weight of the digestive tract, in Apodemus draco during 42 days of cold exposure. Body mass and body temperature of the cold-acclimated group decreased during the first 28 days and then stabilized at the lower levels. After 14 days of cold acclimation, the body mass of the cold-exposed group was significantly lower and the energy intake, digestible energy intake, and metabolic energy intake were significantly elevated relative to control animals. The differences were maximal after 21 days. The length and weight of the digestive tract (both wet and dry mass of the stomach, small intestine, large intestine, and cecum) changed significantly in response to decreasing temperature. During cold exposure, A. draco was able to maintain physiological functions and reduce its absolute energy demands by reducing the body mass, increasing energy intake, and adjusting the length of the digestive tract.     

Modelling habitat-suitability using museum collections: an example with three sympatric Apodemus species from the Alps

Aim, Location Although the alpine mouse Apodemus alpicola has been given species status since 1989, no distribution map has ever been constructed for this endemic alpine rodent in Switzerland. Based on redetermined museum material and using the Ecological-Niche Factor Analysis (ENFA), habitat-suitability maps were computed for A. alpicola , and also for the co-occurring A. flavicollis and A. sylvaticus .
Methods In the particular case of habitat suitability models, classical approaches (GLMs, GAMs, discriminant analysis, etc.) generally require presence and absence data. The presence records provided by museums can clearly give useful information about species distribution and ecology and have already been used for knowledge-based mapping. In this paper, we apply the ENFA which requires only presence data, to build a habitat-suitability map of three species of Apodemus on the basis of museum skull collections.
Results Interspecific niche comparisons showed that A. alpicola is very specialized concerning habitat selection, meaning that its habitat differs unequivocally from the average conditions in Switzerland, while both A. flavicollis and A. sylvaticus could be considered as 'generalists' in the study area.
Main conclusions Although an adequate sampling design is the best way to collect ecological data for predictive modelling, this is a time and money consuming process and there are cases where time is simply not available, as for instance with endangered species conservation. On the other hand, museums, herbariums and other similar institutions are treasuring huge presence data sets. By applying the ENFA to such data it is possible to rapidly construct a habitat suitability model. The ENFA method not only provides two key measurements regarding the niche of a species (i.e. marginality and specialization), but also has ecological meaning, and allows the scientist to compare directly the niches of different species.