鼠类种群动态:食物资源影响力的实验评估

本研究在美国伊利诺斯州中东部测定了中等食物质量(莓系属的牧草)和低食物质量(高杆草牧场)栖息地内橙腹田鼠(Microtusochrogaster)和草原田鼠(M.pennsylvanicus)种群对附加食物的响应。在中等食物质量栖息地内投放附加食物,橙腹田鼠种群的波动幅度高于对照样地,但同类型食物质量栖息地内,种群平均密度和波动模式无显著的差异。仅在低等食物质量的高杆草栖息地内,投放附加食物可导致草原田鼠的种群密度高于对照样地。附加食物不直接影响两种栖息地内橙腹田鼠的成活率或成熟率,在中等食物质量栖息地中投放附加食物,繁殖活跃的成熟雌性个体比例及雄性成体的体重高于对照。附加食物不影响莓系属牧草内草原田鼠,也不能影响该动物在高杆草环境中的存活率。然而,投放附加食物,可缩短低等食物质量栖息地内草原田鼠的成熟期,提高繁殖活跃雌性的比例和迁入个体比例,增加并引起雄性个体体重增加。据此,本研究证明食物资源在橙腹田鼠和草原田鼠种群动态中只起极小的作用。     

布氏田鼠对主要贮草种类的选储嗜好

布氏田鼠 (Ｍｉｃｒｏｔｕｓｂｒａｎｄｔｉ)为内蒙古典型草原区的主要害鼠 ,其危害主要表现在与牲畜争夺牧草资源[1,3 ,5,6,9] 。该鼠属不冬眠种类 ,冬季主要以洞群贮草仓库中的贮草为食 ,因此 ,研究其秋季集群的贮草习性 ,对于分析和了解该鼠的越冬生态特征具有一定的意义。有关布氏田鼠的贮草习性 ,已有一些报道[4 ,7] 。研究表明 ,在羊草 冷蒿 隐子草草场 ,布氏田鼠的越冬贮草以蒿属 (Ａｒｔｅｍｉｓｉａ)植物为主 ,其中冷蒿 (Ａ .ｆｒｉｇｉｄａ)与黄蒿 (Ａ .ｓｃｏｐａｒｉａ)占贮草比例超过 90 % [2 ] ,但上述研究均未涉及布氏田鼠…     

大型野外围栏实验揭示增食对布氏田鼠种群动态的复杂效应

尽管大多数实验都证明增加食物能提高动物的种群密度,但有关增食对动物的繁殖、存活和迁移的影响机制仍然存在争议.建立有效排除种群扩散和天敌捕食引起的复杂效应的野外大型围栏实验是目前解决这一争议必不可少的前提条件.2010~2014年,本课题组调查了增食处理对8个大型野外围栏(每个0.48 ha)内布氏田鼠(Lasiopodomys brandtii)种群动态和植物群落的影响.结果表明,增食通过增加幼体补充数量对种群密度产生正效应.然而,增食对布氏田鼠的存活产生复杂的效应:即在非繁殖季节产生正效应,在繁殖季节产生负效应.另外,增食提高了布氏田鼠植物食物的质量(蛋白质含量增加),但降低了围栏内植物群落中不喜食植物的数量.因此,增食通过增加食物的供给直接对小型啮齿类动物产生正效应.同时,食物引起的种群密度增加又通过密度制约效应间接对动物种群产生负效应,并且通过改变植物群落的结构和数量分布对啮齿动物产生长期的影响.     

布氏田鼠标志种群的社群等级及其季节变化

在内蒙古锡林郭勒地区,通过标志重捕、染色标记和直接观测法对布氏田鼠社群等级的季节变化进行了研究。结果表明:在繁殖季节,布氏田鼠洞群内存在明显的社群等级。越冬雄鼠在社群内社群序位最高,其次是越冬雌鼠、当年成体雌鼠、当年成体雄鼠,亚成体鼠和幼鼠的社群地位最低。在繁殖末期,越冬雄鼠的地位明显下降,而当年成体雄鼠的等级序位逐渐上升。在繁殖季节,当年雄鼠在洞群中的等级序位依然很低,很少能有机会进行有效的交配,有效交配主要由越冬雄鼠来完成,因而越冬雄鼠对种群繁殖的贡献较大。本实验倾向于支持该鼠的婚配制度为一雄多雌制的观点。     

局部环境增温对根田鼠冬季种群的影响

通过建立开顶式增温小室模拟全球变暖的实验, 对海北高寒草甸地区实验增温样地及其对照样地内根田鼠的冬季种群进行调查, 旨在研究局部增温对根田鼠冬季种群的可能影响。结果表明, 在冬季, 实验增温草甸样地和灌丛样地内根田鼠的种群密度均显著高于其对照( P < 0.05) ; 实验增温灌丛样地与对照间性比的差异不显著( P > 0.05) ; 增温样地和对照之间、不同植被类型的增温样地之间、对照样地之间, 根田鼠留存率、平均体重及年龄结构的差异均不显著( P > 0.05) ; 有从对照样地向增温样地单方向迁移的记录。总之, 局部环境增温导致实验样地内根田鼠的冬季种群密度明显上升, 而其性比、存活率、种群平均体重以及年龄结构无明显变化; 在冬季, 根田鼠有从对照样地向增温样地扩散或迁移的趋势。     

食物多样性对布氏田鼠幼体存活率和生长率的影响

为探明食物多样性对植食性小型哺乳动物种群的影响,以羊草、克氏针茅、紫花苜蓿、沙葱和阿氏旋花5种实验地常见的草本植物,组成不同食物多样性的食谱,饲喂布氏田鼠幼体,探究布氏田鼠幼体的存活率和生长率对不同食物多样性的响应。结果表明：（1）随着食物多样性种类的增加,布氏田鼠幼体存活率显著提高（P<0.05）。与单一食物组相比,2~4种食物组饲喂的布氏田鼠幼体存活率分别增加15.6%、18.0%和12.2%;不同食物占食谱的比例对布氏田鼠幼体存活率变化具极显著作用（P<0.01）;随着克氏针茅、阿氏旋花在食谱中比例的增加,布氏田鼠幼体存活率显著下降（P<0.05）。（2）随着食物多样性的增加,布氏田鼠幼体生长率在第5周时极显著降低（P<0.01）;不同食物在食谱中的比例对布氏田鼠幼体生长率变化具有显著影响（P<0.01）。随着羊草在食谱中比例的增加,在第5周时布氏田鼠幼体生长率极显著提高（P<0.01）,随着克氏针茅在食谱中比例的增加,至第3周和5周时布氏田鼠幼体的生长率均显著下降（P<0.05）,随着阿氏旋花在食谱中比例的增加,至第3周时布氏田鼠幼体生长率极显著下降（P<0.01）。结果表明,布氏田鼠幼体随着克氏针茅和阿氏旋花在其食物中所占比例增加,布氏田鼠幼体存活率和生长率相应下降,随着羊草在布氏田鼠幼体食谱中比例增加其生长率显著提高。因此,食物多样性在一定程度影响布氏田鼠幼体存活、生长和种群密度。     

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。     

达乌尔鼠兔和布氏田鼠食物资源竞争关系的研究

布氏田鼠和达乌尔鼠兔是内蒙古典型草原的两种主要害鼠。本文研究了重叠分布于内蒙古克什克腾旗阿其乌拉境内克氏针茅+冷蒿+羊草草场上的布氏田鼠和达乌尔鼠兔的食物资源竞争关系。胃内容物显微组织学分析结果表明,夏季布氏田鼠取食羊草、杂花苜蓿、阿尔泰狗娃花等20种植物,而达乌尔鼠兔则选择羊草、菊叶委陵菜和杂花苜蓿等15种植物为食     

布氏田鼠肝毛细线虫感染率与其体重的关系

2005年5月和8月,在内蒙古锡林郭勒北部典型草原调查了肝毛细线虫对布氏田鼠种群的感染特征,分析肝毛细线虫对布氏田鼠的感染率与其性别、年龄、体重及种群密度的关系。结果表明:肝毛细线虫对布氏田鼠感染率没有性别差异,雄鼠与雌鼠的感染率相当;但是与布氏田鼠体重/年龄密切相关:幼鼠的感染率较低,成鼠感染率较高,感染率和平均感染度均随着个体年龄的增长而增高。布氏田鼠达到一定的年龄(或体重)后才可感染肝毛细线虫病,其最低感染体重为24.3 g。布氏田鼠的种群密度对肝毛细线虫的感染率和平均感染度没有明显的影响,但同一样地不同季节感染率不同,本次调查显示,2005年5月份感染率高于8月份群体感染率,同一样地的春季感染率与秋季感染率之间呈现出显著的正相关。     

不育雄性对布氏田鼠气味选择和个体选择的影响

在Y型迷宫中进行了动情雌性布氏田鼠对结扎不育雄鼠及正常雄鼠气味和个体的选择实验。气味选择实验以动物的巢垫物为气味源,个体选择直接采用结扎雄性和正常雄性作为被选择个体。记录雌性布氏田鼠对选择源的选择频次以及停留时间。结果表明,无论在气味选择或是个体选择中,动情雌性布氏田鼠在选择频次和停留时间上都具有显的正相关性,而且都没有明显表现出对某—气味或个体选择上的偏好。激素测定结扎不育后雄鼠血清中的睾酮和皮质醇含量有听升高．但这种变化没有对雌性布氏田鼠的选择产生影响。     

Social overwintering and food distribution in the bank vole Clethrionomys glareolus

We studied overwintering in the bank vole Clethrionomys glareolus in four 0.5 ha enclosures in an abandoned field in central Finland in the winter 1987/88. In two of the enclosures food was offered evenly distributed over the whole enclosed area (Even Enclosures = EE), in the two others food was offered in one feeding patch with four feeding chambers 2 m apart (Patchy Enclosures = PE). Food was provided in about the same amount in both enclosures. The experiment commenced in early October, with 13 females and 11 males in EEs and 12 + 13 voles in PEs. After two months the voles in the PEs were concentrated around the feeding patches. Territoriality was not observed in EEs, instead the voles formed small exclusive overwintering groups consisting of 2-3 females and at least one male. The size of the home range of the females and males was identical during mid-winter as the voles were non-breeding. By the onset of breeding, range size increased in both sexes, but significantly more in males, however. The survival was about the same in all populations. Every population showed a mid-winter decline suggesting the effect of the mustelid predators observed in and around the enclosures. In the PEs the overwintering aggregations lasted until the maturation of the first litters. Food distribution affected the spatial distribution of the populations. We conclude that the patchiness of the habitat and especially the availability of food are the most important factors determining the social structure of overwintering populations.     

Do scent marks increase predation risk of microtine rodents?

Reproductive activities, including signalling with scents, may increase the risk of predation. Mammalian predators, like small mustelids, find voles by using odour cues of scent marks. Scent marks are also visible in ultraviolet light, and at least some diurnal raptors are attracted to these markings in the field. We performed a field experiment to find out whether manipulation of scent markings affects the density, survival and mobility of free-living voles, and the activity of mammalian and avian predators. A total of 20 plots (each 1 ha) were randomly divided into two treatments: scent manipulation and control plots. Scent manipulation plots were treated with vole scent-liquid and control plots with water. From each plot 1–2 voles were radio-collared and tracked for three weeks. Predators hunted more often on scent manipulation plots than on control plots leading to lower survival time of voles. Although scent manipulation attracted more avian predators, small mustelids were the main predators of voles. The density or the mobility of voles did not differ significantly between manipulation and control plots. Our results suggest that odour of scent marks may be a larger risk to voles than UV visibility of scent marks.     

Regulation of root vole population dynamics by food supply and predation: a two-factor experiment

This paper reports the effects of food supply, predation and the interaction between them on the population dynamics of root voles, Microtus oeconomus , by adopting factorial experiments in field enclosures. This two-factor experiment proved the general hypothesis that food supply and predation had independent and additive effects on population dynamics of root voles. The experimental results proved the following predictions: (1) predation reduced population density and recruitment significantly; (2) food supply increased population density; (3) predation and food supply influenced spacing behavior of root voles separately and additively: Exposure to predation reduced long movements of root voles between trapping sessions; additional food supply reduced aggression level and home range size of root voles. Less movement of individuals that exposed to predators possibly reduced their opportunity of obtaining food and lessened population survival rate, which led population density to decrease. Smaller home range and lower aggression level could make higher population density tolerable. The interactive effect of predation and food on home range size was highly significant (P=0.0082<0.01). The interactive effect of food and predation on dispersal rate was significant (P<0.01). From the experimental results, we conclude that the external factors (predation, food supply) were more effective than internal factors (spacing behavior) in determining population density of root voles – under the most favorable external conditions (−P, +F treatment), the mean density and mean recruitment of root vole population was the highest; under the most unfavorable external conditions (+P, −F treatment), the mean density and mean recruitment of root vole population was the lowest.     

布氏田鼠种群生态研究

1985年5-l0月用标志重捕法对布氏田鼠(Microtus brandti)的种群年龄组成、幼鼠生长率和季节迁移等进行研究,共标志2786只,重捕576只,822只次。发现布氏田鼠种群的年龄组成有较明显的季节变化。其幼鼠体重的日平均生长率随年龄增加而减慢。布氏田鼠还有季节迁移现象。     

Contrasting phenotypic correlations in food provision of male Tengmalm's owls (Aegolius funereus) in a temporally heterogenous environment

Summary We examined the food provision rate of male Tengmalm's owls,Aegolius funereus, during one 3 year vole cycle consisting of consecutive low, increase and peake vole years. The data were collected in the midnestling period when males provisioned the whole family. In the low vole year, males with a low loading index (g/cm²) of flying area fed their offspring more often than did males with a high loading index, whereas in the peak vole year the opposite trend was evident. Similar relationships were found in the food mass provisioned to the nest. In the increase vole year, male body size had no effect on feeding efficiency. In the peak vole year, when large voles are abundant, heavy males preyed on larger voles than were generally available in their territories, indicating that largeness may increase strike power in hunting attempts. In the low vole year, when breeding is costly due to food scarcity and extensive hunting area, small males are more economical fliers and efficient hunters than large males. The contrasting trends in correlations between male size and feeding efficiency in years of vole abundance versus scarcity suggest that no fixed phenotype may most efficiently cope with variable food supply.     

Population limitation of the northern red-backed vole in the boreal forests of northern Canada

1. Across the vast boreal forests of North America, no population cycles in Clethrionomys species occur. In Eurasia, by contrast, some Clethrionomys populations of the same species undergo regular 3-5-year cycles. We examined the effects of nutrients, food, competitors, predators and climate on population limitation in the northern red-backed vole (Clethrionomys rutilus Pallas) in the south-western Yukon to determine why this difference occurs. 2. From 1986 to 1996 we added food, reduced large mammal predators and excluded snowshoe hares (Lepus americanus Erxleben) from large plots and found that none of these manipulations affected red-backed vole abundance. Adding nutrients as nitrogen, phosphorus and potassium (NPK) fertilizer had a slight negative effect, probably acting through a reduction in dwarf shrub productivity caused by competition from grasses. 3. We monitored weasel populations directly through trapping and indirectly through snow tracking. Predation by these vole specialists was irrelevant as a limiting factor most of the time because voles in this area do not reach the densities needed to sustain weasel populations. Other boreal forest mammal and bird predators did not focus on red-backed voles. However, when red-backed vole populations increased in the forest and Microtus voles also increased in the meadows, weasel populations increased and may have temporarily depressed red-backed voles in winter. 4. We monitored one major potential food, white spruce seeds, but seed fall was not related to population changes in red-backed voles, even after mast years. 5. We assessed the impact of weather variables, and the average depth of the snow pack during winter (October-March) was correlated directly with vole demography, having both direct effects in that year and delayed effects in the following year. 6. Our long-term trapping data (1973-96) indicate that Clethrionomys populations fluctuated, with peaks following hare peaks by 2-3 years. 7. We propose that the key variable limiting these vole populations is overwinter survival, and this is a function of overwinter food from berries produced during the previous summer by dwarf shrubs. These shrubs may be stimulated by abundant moisture from winter snows or by periodic fertilization from large quantities of pellets produced at snowshoe hare peaks.     

Reproductive investment under fluctuating predation risk: Microtine rodents and small mustelids

Summary We studied the reproductive investment of microtine rodents (bank vole (Clethrionomys glareolus),Microtus epiroticus andMicrotus agrestis) in western Finland under predation risk from small mustelids. During 1984–1992, the yearly mean litter size of overwintered bank voles was smaller at high least weasel and stoat densities than at low densities (close to 3 versus 4–5). In addition, the annual mean litter size of young bank voles was negatively correlated to the least weasel density. In youngM. agrestis voles, the yearly late summer litter size was negatively associated with the autumn density of small mustelids. In the crash phase of the vole cycle (1989 and 1992), we removed small mustelids (mainly least weasels) from four unfenced areas in late April to late May and studied the reproduction of voles in four removal and comparable control areas (each 2–4 km²). Reduction of small mustelids significantly increased the proportion of pregnant bank vole females, but not that of pregnantMicrotus vole females. We conclude that predation risk apparently reduced reproductive investment of free-living bank vole females; these voles appear to trade their current parental investment against future survival and reproductive prospects. Accordingly, the presence of small mustelids (or their scent) may slow down the reproductive rate of voles. As antipredatory behaviours occurred on a large scale, our results add evidence to the hypothesis that crashes in multiannual vole cycles are driven by small mustelid predators.     

Phase dependence in winter physiological condition of cyclic voles

Lack of food resources has been suggested as a factor which limits the growth of cyclic vole populations. During peak phases of the cycle, vole population growth typically ceases during late autumn or early winter, and is followed by a decrease in density over the winter. To investigate whether this decrease is due to increased mortality induced by a depletion of food resources, we studied overwinter food consumption and physiological condition of field voles ( Microtus agrestis ) in western Finland in both an increase and a decrease phase of a three-year population cycle. The growth rate of vole populations was negatively related both to prevailing vole densities and to densities six months earlier. The condition index of voles, as well as their blood levels of haematocrit, proteins, free fatty acids and immunoglobulin G, were positively related to population growth rate when populations were declining. When populations were increasing, these parameters tended to be negatively related to population growth rate. The overall physiological condition of voles was lower in the winter of the decrease phase as compared to the increase phase. The return rate of voles, a proxy of survival, was also lower in the decrease than in the increase phase of the cycle and positively related to haematocrit levels. Almost 90% of all green vegetation shoots were consumed by voles during the winter of the decrease phase while only two thirds were eaten in the increase phase. Our results suggest that the winter decrease phase of cyclic vole populations is associated with both a deterioration in the physiological condition of voles and a significant depletion of winter food resources. This implies that malnutrition induces poor physiological condition in voles, which in turn may increase mortality either directly through starvation or indirectly through increased susceptibility to predators and pathogens.     

The effects of habitat manipulation on population distribution and foraging behavior in meadow voles

Individuals, free to choose between different habitat patches, should settle among them such that fitness is equalized. Alternatives to this ideal free distribution result into fitness differences among the patches. The concordance between fitnesses and foraging costs among inhabitants of different quality patches, demonstrated in recent studies, suggests that the mode of habitat selection and the resulting fitness patterns may have important implications to the resource use of a forager and to the survival of its prey. We studied how coarse scale selection between habitat patches of different quality and quitting harvest rate in these patches are related to each other and to fine scale patch use in meadow voles (Microtus pennsylvanicus). To demonstrate these relationships, we manipulated habitat patches within large field enclosures by mowing vegetative cover and adding supplemental food according to a 2×2 factorial design. We tracked vole population densities, collected giving‐up densities (GUDs, a measure of patch quitting harvest rate), and monitored the removal of seeds from lattice grids with 1.5 m intervals (an index of fine‐scale space use) in the manipulated habitat patches. Changes in habitat quality induced changes in habitat use at different spatial scales. In preferred habitats with intact cover, voles were despotic and GUDs were low, but increased with the addition of food. In contrast, voles in less‐preferred mowed habitats settled into an ideal free distribution, GUDs were high and uninfluenced by the addition of food. Seed removal was enhanced by the presence of cover but inhibited by supplemental food. Across all treatments, vole densities and GUDs were strongly correlated making it impossible to separate their effects on seed removal rates. However, this relationship broke down in unmowed habitats, where GUDs rather than vole density primarily influenced seed removal by voles. GUDs and seed removal correlated with predation on tree seedlings formerly planted into the enclosures, demonstrating the mechanisms between coarse‐scale habitat manipulations and community level consequences on a forager's prey.