小型啮齿动物种群系统调节复合因子理论的野外实验研究：食物可利用性和捕

本项研究在野外围栏条件下,采用析因实验设计,测定食物可利用性和捕食对根田鼠种群空间行为的作用模式。检验的特定假设为,高质量食物较大的可利用性能降低田鼠的攻击行为和活动,捕食能减少田鼠的活动。研究结果表明,食物可利用性能间接地和直接地影响根田鼠的空间行为,附加食物种群具有较高的密度和较小的巢区,且在诱捕期间具有较少的长距离活动和较低的攻击水平。捕食者的存在不直接影响攻击行为,但能影响诱捕期间的长距离     

小型啮齿动物种群系统调节复合因子理论的野外实验研究：食物可利用性和捕食对根田鼠种群动态作用的分析

本研究在野外围栏条件下采用析因实验设计,测定营养、捕食及空间行为对根田鼠（Ｍｉ－ｃｒｏｔｕｓｏｅｃｏｎｏｍｕｓ）种群统计特征的影响。本文旨在检验下述特定假设：高质量食物可利用性和捕食对限制小型啮齿动物种群密度具有独立的和累加的效应。３年期间,４种野外实验处理６个重复的研究结果表明,附加食物并预防捕食者处理的种群具有最高密度;未附加食物及不预防捕食者处理（对照）的种群密度最低;而单一处理的种群,其密度居中。不同处理条件下,新生个体在种群的补充模式以及种群瞬时增长率的变化均与种群密度的变动相应一致。双因素ＡＮＯＶＡ的结果证明,附加高质量食物能明显地提高根田鼠的种群密度,而对种群补充量的作用则较弱,仅接近显著水平;预防捕食者不仅能显著地作用于种群密度,更能强烈地影响种群补充量。高质量食物和捕食者的作用具有累加的性质,两者的交互作用对种群密度和补充量均无显著影响。     

东方田鼠种群扩散及活动对外部因子的反应格局

在野外围栏条件下,采用2×2×2析因实验,测定外部因子食物、捕食,以及同域分布物种黑线姬鼠的种间竞争对东方田鼠扩散和活动距离的独立作用及其交互作用的效应。研究结果表明,在所有的扩散个体中,幼体扩散的比例为71.0%。雄体扩散的比例为80.5%。东方田鼠扩散的趋势与其种群密度及补充量的变动一致。食物对扩散具有显著独立作用;捕食对扩散的作用接近显著;种间竞争对扩散的直接效应不显著;食物、捕食与种间竞争交互作用对扩散的效应亦不显著。在诱捕期内雄性的长距离活动比例及其诱捕期间长距离活动比例均显著大于诱捕期内雌性及其诱捕期间的长距离活动比例。不同处理种群间,仅雄体在诱捕期间的长距离活动比例具有显著差异;食物对雄体的长距离活动具有直接和间接(通过密度)的效应;而预防捕食者和竞争物种对不同处理种群雄体的长距离活动则无一致的效应。     

根田鼠攻击行为模式及其进化稳定对策分析

在捕食和附加食物交互作用条件下 ,测定根田鼠种群攻击水平与种群参数之间的关系 ,应用对策论分析攻击行为的模式。通过观测 1 6 5对实验个体的攻击行为 ,发现体重和繁殖特征决定根田鼠个体的攻击水平。体重较大个体及繁殖个体的攻击频次最高。攻击水平的性别差异显著。Kruskal- Wallis单侧秩方差检验结果表明 ,雄体攻击水平显著高于雌体。攻击水平与种群密度呈负相关关系 ,但不显著。与留居个体比较 ,扩散个体的攻击性弱。高质量的附加食物可降低根田鼠的攻击水平 ,捕食者的存在不直接影响攻击水平。根田鼠的攻击行为属仪式化非伤害行为。ESS的鹰 -鸽对策模型分析结果与实验结果一致 :不同处理种群 ESS集的鹰型对策者比例有显著差异 ,环境条件愈差 ,取胜的价值愈大 ,种群中鹰型对策者比例愈高。有捕食者、无附加食物( P,- F)种群的环境条件最差 ,鹰型对策者比例最高 ,为 0 .4 0 ;次为无捕食者、无附加食物 (- P,- F)种群 ,为 0 .33;有捕食者、有附加食物 ( P, F)种群 ,为 0 .1 8;无捕食者、有附加食物 (- P, F)种群的环境条件最优越 ,鹰型对策者比例最低 ,为0 .1 7。验证了捕食和食物交互效应能改变田鼠类动物攻击行为格局及对策模式的假设     

小型啮齿动物种群系统调节复合因子理论的野外实验研究：食物可利…

本研究在野外围栏条件下有用析因实验设计,测定营养、捕食及空间行为对根田鼠和群统计特征的影响。本文旨的检验下述特定假设;高质量食物可利用性和捕食对限制小型啮齿动物种群密度具有独立的和累加的效应。３年时间,４种野外实验处理６个重复和研究结果表明,附加食物并预防捕得处理的种群具有最高密度;未附加食物及预防捕食者处理（对照）的种群密度最低;而单一处理和种群,其密度居中。不同处理条件下,新生个体在种群的补充     

食物、捕食和种间竞争对东方田鼠种群动态的作用

采用2×2×2析因实验设计,在野外围栏条件下,测定食物、捕食和竞争物种黑线姬鼠(Apodemus agrarius)对东方田鼠(Microtus fortis)种群动态作用的格局.食物可利用性、捕食及种间竞争的独立作用对种群最小存活数均具有极显著的效应,除捕食与种间竞争的交互作用接近显著水平外,食物与种间竞争、食物与捕食者以及三者间的交互作用均不显著;三类外部因子对种群补充量的独立作用效应均达到极显著水平,且对种群补充量的作用具有累加效应;食物可利用性、捕食及种间竞争对种群繁殖成体的比例具有极显著的作用;三类外部因子对种群幼体与成体的比例具有极显著的作用.对种群年龄结构而言,与捕食者及种间竞争比较,食物可利用性是相对较弱的影响因子,在任何捕食与种间竞争交互作用条件下,食物的作用均不显著;三类外部因子均能显著地影响东方田鼠的体重增长率,但三者的交互作用对其影响不显著;MANOVA结果表明,捕食对成体存活率的作用最强烈,其次,为食物可利用性,种间竞争的作用最弱,但三者的交互作用效应不显著.对幼体的存活时间,除捕食的作用接近显著水平外,食物可利用性及种间竞争的作用均不显著.结果提供了食物可利用性、捕食和种间竞争对东方田鼠种群动态作用的充分证据,验证了食物、捕食和种间竞争对田鼠类种群动态具有独立或累加效应的总假设.     

捕食和食物交互作用条件下根田鼠季节性波动种群攻击水平及其行为多态性分析

在捕食和附加食物交互作用条件下,以恐吓、进攻、追逐、争斗及回避5类行为为变量,以恐吓、进攻、追逐计数之和的平均值作为攻击水平,测定根田鼠种群不同波动时期成体的攻击水平.发现根田鼠的攻击性与种群波动时期之间,存在明显的关联.统计分析结果表明,在种群3个波动时期,4种处理种群两性攻击型个体比例差异显著.除预防捕食者无附加食物（-P,-F）种群的雌体外,其它处理种群增长期和高峰期雌性和雄性攻击型个体的比例高于其衰减期.其中,预防捕食者附加食物（-P,＋F）种群、-P,-F种群及未预防捕食者附加食物（＋P,＋F）种群,雄性攻击型个体的比例均为增长期＞高峰期＞衰减期;在未预防捕食者无附加食物（＋P,-F）种群,雄性攻击型个体比例为高峰期＞增长期＞衰减期.各处理种群雌性攻击型个体比例的格局与雄体的不同.其中,-P,＋F种群及＋P,＋F种群为增长期＞高峰期＞衰减期,＋P,-F种群为高峰期＞增长期＞衰减期,而-P,-F种群攻击型个体比例为高峰期＞衰减期＞增长期.虽不同处理种群雌体及雄体的5类行为变量与种群密度的相关性不一致,而具有明显攻击性的恐吓、进攻及争斗3类行为则分别与种群密度呈显著或极显著的线性正相关关系,其结果与Chitty多态行为假设预测的一致;验证了所提出的特定假设：种群外部因子捕食和食物交互效应介导的攻击行为选择,是引起田鼠类种群季节性波动的主要内部因子.     

球虫感染与捕食对根田鼠繁殖性能的影响

在自然界,捕食者和寄生物是两种主要的种群外部调节因子,二者的交互作用会对猎物和宿主种群波动产生深远影响。较低的球虫感染强度与捕食对根田鼠（Alexandromys oeconomus）繁殖无显著的交互作用。自然界球虫感染存在季节性变化,秋季感染强度最高。为了探究较高感染强度下,球虫与捕食对根田鼠繁殖的主效应及交互作用,本研究采用2×2析因实验设计,在野外围栏中测定了根田鼠种群肠道内寄生物的感染率和感染强度、雄性睾丸指数、睾酮水平、精子密度、精子活力以及雌性卵巢指数。结果表明,较高的感染强度下,球虫能显著抑制根田鼠的繁殖性能,但球虫感染与捕食对根田鼠的繁殖无显著的交互作用,这可能与球虫感染和捕食效应在时间上的错配有关。本研究认为,球虫感染对繁殖期小哺乳动物种群的调节作用虽有限,但其可通过与捕食者的耦合来降低宿主越冬时的存活率,进而影响宿主种群波动。     

食物、捕食及种间竞争对东方田鼠(Microtus fortis)种群攻击行为的作用

在野外围栏条件下,采用重复的2×2×2析因实验设计,测定食物、捕食和竞争物种黑线姬鼠对东方田鼠攻击行为作用的格局。东方田鼠各处理种群攻击水平与其种群密度的相关甚为复杂,与Chitty多态行为假设的预测不一致。东方田鼠双冲突个体间的攻击水平与其体重的相关不显著,而与冲突个体的体重差异则呈显著的负相关,体重差异越大,冲突个体间的攻击水平越低。雄体攻击水平与其繁殖特征无显著的相关关系,而雌体间攻击水平则受繁殖状态的影响,动情雌体间的攻击水平显著地高于非动情雌体。体重差异和食物对雄体的攻击行为具有极显著的独立作用,捕食和种间竞争对雄体攻击行为的独立作用不显著,而捕食与种间竞争交互作用对雄体攻击行为的效应则达到显著水平。体重差异、食物、捕食和种间竞争对动情雌体的攻击水平均有极显著的独立作用,3类外部因子交互作用的效应达到极显著水平;而3类外部因子交互作用对非动情雌体攻击行为的效应则不显著。结果检验了外部因子食物、捕食、种间竞争对田鼠类动物种群攻击行为具有独立和累加的整合效应的假设。     

食物、捕食及种间竞争对东方田鼠(Microtus fortis)种群攻击行为的作用

在野外围栏条件下,采用重复的2×2×2析因实验设计,测定食物、捕食和竞争物种黑线姬鼠对东方田鼠攻击行为作用的格局。东方田鼠各处理种群攻击水平与其种群密度的相关甚为复杂,与Chitty多态行为假设的预测不一致。东方田鼠双冲突个体间的攻击水平与其体重的相关不显著,而与冲突个体的体重差异则呈显著的负相关,体重差异越大,冲突个体间的攻击水平越低。雄体攻击水平与其繁殖特征无显著的相关关系,而雌体间攻击水平则受繁殖状态的影响,动情雌体间的攻击水平显著地高于非动情雌体。体重差异和食物对雄体的攻击行为具有极显著的独立作用,捕食和种间竞争对雄体攻击行为的独立作用不显著,而捕食与种间竞争交互作用对雄体攻击行为的效应则达到显著水平。体重差异、食物、捕食和种间竞争对动情雌体的攻击水平均有极显著的独立作用,3类外部因子交互作用的效应达到极显著水平;而3类外部因子交互作用对非动情雌体攻击行为的效应则不显著。结果检验了外部因子食物、捕食、种间竞争对田鼠类动物种群攻击行为具有独立和累加的整合效应的假设。     

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.     

捕食风险对越冬根田鼠肠道寄生物易感性的影响

在自然生态系统中,不同营养级物种可通过特征介导间接效应对生态系统的稳定及种群产生深刻的影响。但目前有关特征介导间接效应的实验研究多见于无脊椎动物、鱼类和两爬类。本研究以根田鼠为对象,在野外围栏内建立预防捕食者和未预防捕食者两种实验处理种群,并通过采用麦克马斯特法测定两种处理种群实验个体肠道寄生物感染种类及感染率和感染强度,采用PHA（phytohemagglutinin）反应和白细胞分类计数测定不同处理种群实验个体免疫能力,以分析捕食风险对根田鼠肠道寄生物的感染效应。结果表明,未预防捕食者处理组根田鼠PHA反应、白细胞计数和淋巴细胞计数较预防捕食者处理组实验个体显著降低,而球虫 E. wenrichi 的感染率和感染强度则显著增加,但绦虫和线虫以及其他3种球虫的感染率和感染强度无显著差异。结果表明,捕食者可通过介导猎物免疫力特征而间接影响猎物肠道寄生物的感染,验证了本项提出的捕食风险可通过降低根田鼠的免疫能力而增加其肠道寄生物感染的假设。     

THE EFFECTS OF PREDATION ON THE AGE AND SIZE OF MATURITY OF PREY

The effects of nonselective predation on the optimal age and size of maturity of their prey are investigated using mathematical models of a simple life history with juvenile and adult stages. Fitness is measured by the product of survival to the adult stage and expected adult reproduction, which is usually an increasing function of size at maturity. Size is determined by both age at maturity and the value of costly traits that increase mean growth rate (growth effort). The analysis includes cases with fixed size but flexible time to maturity, fixed time but flexible size, and adaptively flexible values of both variables. In these analyses, growth effort is flexible. For comparison with previous theory, models with a fixed growth effort are analyzed. In each case, there may be indirect effects of predation on the prey's food supply. The effect of increased predation depends on (1) which variables are flexible; (2) whether increased growth effort requires increased exposure to predators; and (3) how increased predator density affects the abundance of food for juvenile prey. If there is no indirect effect of predators on prey food supply, size at maturity will generally decrease in response to increased predation. However, the indirect effect from increased food has the opposite effect, and the net result of predation is often increased size. Age at maturity may either increase or decrease, depending on functional forms and parameter values; this is true regardless of the presence of indirect effects. The results are compared with those of previous theoretical analyses. Observed shifts in life history in response to predation are reviewed, and the role of size-selective predation is reassessed.     

Multiple predators induce risk reduction in coexisting vole species

Large predators may affect the hunting efficiency of smaller ones directly by decreasing their numbers, or indirectly by altering their behaviour. Either way this may have positive effects on the density of shared prey. Using large outdoor enclosures, we experimentally studied whether the presence of the Tengmalm's owl Aegolius funereus affects the hunting efficiency of the smallest member of the vole-eating predator guild, the least weasel Mustela nivalis, as measured by population responses of coexisting prey species, the field vole Microtus agrestis and the sibling vole M. levis . We compared the density and survival probability of vole populations exposed to no predation, weasel predation or combined predation by a weasel and an owl. The combined predation of both owl and weasel did not result in obvious changes in the density of sibling and field vole populations compared to the control populations without predators, while predation by least weasel alone decreased the densities of sibling voles and induced a similar trend in field vole densities. Survival of field voles was not affected by predator treatment while sibling vole survival was lower in predator treated populations than in control populations. Our results suggest that weasels are intimidated by avian predators, but without changing the effects of predators on competitive situations between the two vole species. Non-lethal effects of intraguild predation therefore will not necessarily change competitive interactions between shared prey species.     

Does risk of predation by mammalian predators affect the spacing behaviour of rodents? Two large-scale experiments

Predator-prey interactions between small mammals and their avian and mammalian predators have attracted much attention. However, large-scale field experiments examining small-mammal antipredatory responses under the risk of predation by mammals are rare. As recently pointed out, the scale of experiments may cause misleading results in studies of decision-making under predation risk. We studied the effect of small mustelid predators on the spacing behaviour of the gray-tailed vole (Microtus canicaudus) and the bank vole (Clethrionomys glareolus) in two separate field enclosure experiments. The experiments were conducted during the breeding season in North America and northern Europe, where small mustelids have been suggested to be important mammalian predators of voles. As in most of the earlier laboratory studies, predation risk was simulated using fresh mustelid faeces and urine. This made it possible to compare the results from experiments at different spatial scales. We did not find any effect of increased predation risk on spacing behaviour (mean and/or maximum distance moved and home range size) or trappability in either vole species. Simulated predation risk did not affect the breeding of females in gray-tailed voles, as has previously been shown in bank voles. The results disagree with most of the studies conducted in laboratory conditions with small mammals. We discuss whether this discrepancy could be caused by differences in the scale of the experiments. Received: 12 April 1999 / Accepted: 7 October 1999     

Predator-induced changes in population structure and individual quality of Microtus voles: a large-scale field experiment

In small mammal populations with multiannual oscillations in density, observational data have revealed cyclic changes in population structure, reproduction, and individual quality, but mechanisms inducing these changes have remained an open question. We analysed data collected during a 3-year predator reduction experiment to find out the effects of predators on population structure, reproductive parameters, and individual quality of Microtus voles (the field vole M. agrestis and the sibling vole M. rossiaemeridionalis ) in western Finland. Voles were collected by snap trapping in April, June, August, and October during 1997–1999. The yearly reduction of predators from April to October had a clear positive effect on the abundance of sibling voles but did not significantly affect the densities of field voles. Predator reduction apparently also affected the age ratio and mean body size in late summer, as well as pancreatic weights of voles. However, all observed differences between predator reduction and control areas, except those in abundance, were small and may mainly reflect a generally higher survival leading to higher densities of voles in predator reduction areas. Our results also indicated a relative lack of high quality food at population peaks but not because of reduced foraging activity in the presence of predators. We conclude that the indirect effects of vole-eating predators on the population growth of main prey are small compared to the detrimental direct effects on prey survival. In the case of less preferred prey, indirect effects of predation through reduced interspecific competition may play a role at high densities.     

Voles on small islands: effects of food limitation and alien predation

Ecosystems of three trophic levels may be bottom-up (by food-plant availability) and/or top-down (by predators) limited. Top-down control might be of greater consequence when the predation impact comes from an alien predator. We conducted a replicated two-factor experiment with field voles (Microtus agrestis) during 2004-2005 on small islands of the outer archipelago of the Baltic Sea, south-west Finland, manipulating both predation impact by introduced American mink (Mustela vison) and winter food supply. In autumn 2004, we live-trapped voles on five islands from which mink had been consistently removed, and on four islands where mink were present, and provided half of these islands with 1.8 kg oats per vole. Body mass of female voles increased as a response to supplementary food, whereas both food supplementation and mink removal increased the body mass of male voles in subsequent spring. During winter, there was a positive effect of supplementary food, but in the subsequent summer, possible positive long-term impacts of food supplementation on field voles were not detected. Mink removal appeared not to affect density estimates of field voles during the winter and summer immediately after food addition. Trapping data from 2004 to 2005 and 2007 suggested, however, that in two out of three summers densities of voles were significantly higher in the absence than in the presence of mink. We conclude that vole populations on small islands in the archipelago of the Baltic Sea are mainly bottom-up limited during winter (outside the growing season of food plants), when food availability is low, and limited by mink predation during summer which slows population growth during the reproductive season of voles.     

Determinants of reproductive success in voles: space use in relation to food and litter size manipulation

Spacing behaviour of female mammals is suggested to depend on the distribution and abundance of food. In addition, food limitation has been found to constrain the reproductive success of females. However, whether females maximize their reproductive success by adjusting space use in relation to current food availability and reproductive effort (e.g. litter size) has not been experimentally studied. We examined these questions by manipulating simultaneously food resources (control vs. food supplementation) and litter sizes (control vs. plus two pups) of territorial female bank voles (Clethrionomys glareolus) in large outdoor enclosures. Females with supplementary food had smaller home ranges (foraging area) and home range overlaps than control females, whereas litter size manipulation had no effect on space use. In contrast, the size of territory (exclusive area) was not affected by food supplementation or litter size manipulation. As we have previously shown elsewhere, extra food increases the reproductive success of bank vole females in terms of size and proportion of weaned offspring. According to the present data, greater overlap of female home ranges had a negative effect on reproductive success of females, particularly on survival of offspring. We conclude that higher food availability increases the reproductive success of bank vole females, and this effect may be mediated through lower vulnerability of offspring to direct killing and/or detrimental effects from other females in the population. Moreover, it seems that when density of conspecifics is controlled for, home range sizes of females, but not territoriality, is related to food resources in Clethrionomys voles.     

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.