Space use,longevity, and reproductive success in meadow voles

Summary We addressed the question of how reproductive success (RS) was limited in the shortlived but highly fecund meadow vole, Microtus pennsylvanicus. In so doing, we asked how differential space use patterns could affect longevity and hence RS in each sex. The sample comprised all voles achieving sexual competency over the course of a 40-week breeding season in a live-trapped population in Manomet, MA USA. Matrilineal families were determined using a radionuclide labelling technique; paternity was estimated using a maximum likelihood model. Individual RS was defined as the number of offspring successfully recruited into the trappable population per adult. We found that the variance in RS among female meadow voles was greater than the variance among males. In an attempt to explain this pattern, reproductively successful individuals were compared to reproductively unsuccessful individuals with regard to survivorship, maximum body weight achieved, and spatial mobility. The only difference between fathers and reproductively unsuccessful males was that fathers were heavier. In contrast, mothers differed from unsuccessful females in every measurement. Females lived longer than males, and mothers lived longer than either fathers or reproductively unsuccessful females. The observed differences in longevity may have been largely the result of differences in levels of mobility, assuming more mobile voles were more susceptible to predation. Mothers were significantly more site tenacious than were either males or unsuccessful females. These patterns explain the distribution of RS in our population if predation differentially affects male and female meadow voles. The meadow vole is the only non-polyandrous vertebrate reported to date in which the variance in RS among females exceeds the variance in RS among males.     

Space use and social structure in meadow voles,Microtus pennsylvanicus

Summary Free-ranging, sexually mature meadow voles (Microtus pennsylvanicus) were tracked by using radiotelemetry from June through August in Front Royal, Virginia, U.S.A. Estimates of intraspecific spacing were derived from the concurrent movements of up to 16 voles. Positions were recorded hourly for 24 h, twice per week. A total of 16 male and 15 female voles were studied during sixteen 24-h sessions.The daily ranges of males (192.3±109.7 m²) were larger and more variable than those of females (68.6±39.4 m²). Males also changed locations more frequently (Fig. 2).Adult females usually maintained territories free of other females; males overlapped considerably among themselves (Fig. 2). Males temporarily moved into the areas occupied by estrous females, indicating intrasexual competition among males for access to receptive females (Fig. 3). M. pennsylvanicus appears to be promiscuous, is socially organized into territorial, maternal-young units during the breeding season, and fits the female territorial model of population regulation.     

Sex ratio shifts within litters of meadow voles (Microtus pennsylvanicus)

Summary Changes in the sex ratio of juvenile recruits into a population of meadow voles (Microtus pennsylvanicus) were correlated with shifts in the weight and mortality of pups within the population. The biased recruitment of female juveniles in the spring was reflected in differential allocation of energy within the litters, as measured by female pups being heavier than male pups (n=245). In the fall, the shift in recruitment to male juveniles was reflected within litters by male pups being heavier than female pups (n=139). Nestling mortality showed a similar gender bias. Skewed sex ratios were most evident within the litters of larger mothers, indicating the gender bias was not trigered by energy limitations. We postulate that gender differences in social spacing and behavior result in spring/fall fluctuations in the reproductive success of offspring, based on their gender.     

Grazing as a measure against grass encroachment in Dutch dry dune grassland: effects on vegetation and soil

A grazing experiment was started in 1984 and 1989 respectively, in two parts of a dune grassland in the nature reserve ‘Zwanenwater’, North Holland; a third part with similar geology and topography was used as a control area and not grazed. An evaluation of the effects of grazing on vegetation patterns, species composition, vegetation structure and humus form was made with the help of vegetation maps from 1986 and 1992 as well as field surveys. Dense tall-grass communities dominated byAmmophila arenaria increased over the period 1986–1992 in the grazed areas, and especially in the non-grazed area (increase in area to 20 %, 22 % and 50 %, respectively). Open communities decreased in the grazed areas, but are still prevalent, while in the ungrazed area they virtually disappeared, with the result that the present percentage areas are 53 %, 38 % and 17 %. Field survey data were classified by TWINSPAN producing four vegetation types. These occur more or less equally in grazed and ungrazed areas, albeit with different percentage areas: (1) open vegetation dominated byCorynephorus canescens; (2) open vegetation characterized byKoeleria macrantha; (3) heathland dominated byEmpetrum nigrum; and (4) tall-grass communities dominated byAmmophila arenaria. Within a vegetation type, species composition was only marginally affected by grazing regime. Within the open communities the number of species, vegetation height, vegetation cover and soil organic horizons were not affected by grazing. In the tall-grass communities the number of species was significantly larger and the height of the vegetation significantly lower in the area grazed since 1984. In the heathland community the number of species and cover of the moss layer were significantly higher in the 1984 area and ectorganic and endorganic horizons significantly thicker in the ungrazed area. It is suggested that these effects are the result of an increased availability of light, but possibly also of a decreased stock of organic matter and nutrients, due to a decreased input of litter and accelerated rates of decomposition. Nomenclature: Van der Meijden et al. (1992) for phanerogams; Corley et al. (1981) for mosses; Grolle (1983) for hepatics.     

Grazing as a measure against grass encroachment in Dutch dry dune grassland: effects on vegetation and soil

A grazing experiment was started in 1984 and 1989 respectively, in two parts of a dune grassland in the nature reserve ‘Zwanenwater’, North Holland; a third part with similar geology and topography was used as a control area and not grazed. An evaluation of the effects of grazing on vegetation patterns, species composition, vegetation structure and humus form was made with the help of vegetation maps from 1986 and 1992 as well as field surveys. Dense tall-grass communities dominated byAmmophila arenaria increased over the period 1986–1992 in the grazed areas, and especially in the non-grazed area (increase in area to 20%, 22% and 50%, respectively). Open communities decreased in the grazed areas, but are still prevalent, while in the ungrazed area they virtually disappeared, with the result that the present percentage areas are 53%, 38% and 17%. Field survey data were classified by TWINSPAN producing four vegetation types. These occur more or less equally in grazed and ungrazed areas, albeit with different percentage areas: (1) open vegetation dominated byCorynephorus canescens; (2) open vegetation characteized, byKoeleria macrantha; (3) heathland dominated byEmpetrum nigrum; and (4) tall-grass communities dominated byAmmophila arenaria. Within a vegetation type, species composition was only marginally affected by grazing regime. Within the open communities the number of species, vegetation height, vegetation cover and soil organic horizons were not affected by grazing. In the tall-grass communities the number of species was significantly larger and the height of the vegetation significantly lower in the area grazed since 1984. In the heathland community the number of species and cover of the moss layer were significantly higher in the 1984 area and ectorganic and endorganic horizons significantly thicker in the ungrazed area. It is suggested that these effects are the result of an increased availability of light, but possibly also of a decreased stock of organic matter and nutrients, due to a decreased input of litter and accelerated rates of decomposition.     

放牧管理对藏北高寒沼泽草甸群落结构的影响

采用样带法研究了冬季放牧、冬春季放牧和全年放牧3种放牧管理模式对西藏高寒沼泽草甸高度、盖度、地上生物量及群落结构的影响.研究表明,3种放牧管理模式下的高寒沼泽草甸植被群落物种数差异不显著（p〉0.05）,高度、盖度和地上生物量差异显著（p〈0.05）。冬季放牧、冬春季放牧和全年放牧沼泽草甸地上生物量依次降低。放牧管理对沼泽草甸群落多样性影响较大,不同放牧管理模式下的沼泽草甸Shannon-Wiener指数差异显著（p〈0.05）,冬春放牧沼泽草甸Shannon-Wiener指数较冬季放牧和全年放牧沼泽草甸低。冬季放牧和全年放牧沼泽草甸Margalef指数和Pielou指数差异不显著,显著（p〈0.05）高于冬春季放牧沼泽草甸。     

Multiple paternity in meadow voles (Microtus pennsylvanicus): investigating the role of the female

Multiple paternity in single litters conceived in the wild was recently demonstrated in meadow voles (Microtuspennsylvanicus). In this study, we used an experimental approach (males tethered and females allowed to mate freely with one or several males) to investigate the role of female meadow voles in multiple paternity. We found that among 29 (of 39) females that copulated during our experiment, 79.3% chose to mate with more than one male. Female behavior in meadow voles thus clearly promotes multiple paternity and their role is an active one. Some of the hypotheses explaining promiscuity in meadow voles should be reconsidered in light of this result. We do not know the primary determinant of female mate choice, but male body mass played a secondary role in driving female preferences. The partial dependence between male body mass and female choice, coupled with the active role played by females, indicates that intersexual selection has the potential for reinforcing the effects of intrasexual selection (male-male dominance relationships) in this species. Finally, we demonstrate that the time period over which tests are conducted is an important part of the design of experiments aimed at understanding the role of females in multiple paternity. Received: 14 April 1998 / Accepted after revision: 12 September 1998     

高寒草甸不同植被类型土壤全氮含量变化动态分析

采用凯氏定氮法对高寒草甸不同植被类型土壤全氮进行季节动态测定分析,结果表明:在整个生长季中0～20 cm层土壤全氮质量分数的顺序为:藏嵩草沼泽化草甸(Kobresia-swamp meadow)>露梅灌丛草甸(Dasiphoru fruticosa shrubs)>人工燕麦草地(Avena sativa artficial grassland)>矮嵩草草甸(Kobresia humilis meadow)>矮嵩草退化草地(Kobresia humilis-degraded grassland).原生植被草甸类型下单位面积土壤全氮含量远高于退化草地.藏嵩草沼泽化草甸土壤每平方米的全氮含量最高,达到0.712 kg,金露梅草甸次之,两者之间差异性不显著(p>0.05);其他三种草地类型单位面积土壤全氮含量差异性显著(p<0.05);原生草甸矮嵩草草甸每平方米全氮平均含量为0.406 kg,而退化的矮嵩草草地每平方米全氮平均含量为0.301 kg,可以推算,土地退化导致土壤全氮流失的量为0.105kg,即高寒草地退化导致25.86%氮流失.随着季节的变化,土壤全氮质量分数随生长季均有所增加,最高值都出现在8月份,但各月份之间土壤全氮质量分数变化差异性不显著(p>0.05).原生植被0～10 cm层土壤全氮含量高于10～2O cm层,人工草地与退化草地差异性不显著.     

Competition, resources, and vegetation during 10 years in native grassland

A 10-year experiment tested for variation in competition intensity over time in a natural grassland at the northern edge of the Great Plains. Growing-season precipitation varied fivefold during the study. All ecosystem-level variables varied significantly among years, and most covaried in expected ways. The covers of all common grasses possessing the C3 photosynthetic pathway varied significantly among years; in contrast, all common species with traits associated with drought tolerance (a C4 grass, a lichen, a spikemoss, and a subshrub) did not vary. Annual transplant experiments measured the competitive effects of neighbors on the growth of individuals of the native grass Bouteloua gracilis. A significant interaction between year and competition showed that competition intensity varied among years. The size of this effect, however, was small (eta2 = 0.074) relative to the size of the direct effect of competition (eta2 = 0.20) or the year in which the experiment was conducted (eta2 = 0.51). Further, competition intensity was not significantly related to any variable describing standing crop or resources, or species richness. Species richness was highest in years with high precipitation, standing crop, and individual growth, due to the recruitment of rare species that were absent from dry years. In summary, variation in competition intensity was statistically significant but had small effects relative to the direct effects of climate.     

Dynamics of social nesting in overwintering meadow voles (Microtus pennsylvanicus): possible consequences for population cycling

Summary A small population of meadow voles (Microtus pennsylvanicus) in a field enclosure was studied from August to February in Apalachin, New York, USA. Radiotelemetry provided direct measures of intraspecific spacing and social nesting through the fall-winter transition. Data on weather and predation were collected concurrently. A total of 32 voles were radiotracked during 6 tracking sessions, with an average of 17.3 voles (11 to 25 range) tracked per session (Figs. 1, 2a). Discrete social nesting constellations first occurred during October, primarily as a result of the formation of extended maternal families (Figs. 1, 2e). Recruitment of adult males and offspring into these early nesting groups was male biased. The average number of voles in these groupings varied from 3.2 (Jan; 3–4 range) to 7.0 (Oct; 4–10 range); but the average number of voles that slept together at any given time, the nesting cluster, remained steady at 2.4 (2–5 range) (Fig. 2e). During late December and early January under the protection of snow, many voles shifted their home areas and nesting affiliations with the result that non-lineage nesting constellations formed (Fig. 1, 3). The thermoregulatory benefits of huddling and the threat of predation appear to be important governors of movement, group formation and dispersion. The existence of an optimum group size produces and Allee Effect that may contribute importantly to population lows and multi-annual cycles.     

A field test of the effects of familiarity and relatedness on social associations and reproduction in prairie voles

Inbreeding depression is a well-documented phenomenon. In animals, one means of avoiding the costs of inbreeding is through the recognition and avoidance of kin as mates. Prairie voles (Microtus ochrogaster) are short-lived, socially monogamous rodents that demonstrate inbreeding depression in the laboratory. Field data indicate that pair formation in nature is opportunistic but pairing among close relatives seems uncommon. We examined the role of relatedness and familiarity on prairie vole social associations and reproduction by placing adult voles into 0.1-ha enclosures with familiar siblings, unfamiliar siblings, and unrelated, unfamiliar conspecifics. Live-trapping data indicated that indices of social pair bonding were random with respect to relatedness and familiarity. Among females whose litters were sired by a single male, litters were significantly more likely to be sired by unfamiliar than familiar males, but the number of litters sired by males that were unrelated to their partner was not different from the number of litters sired by males that were related to their partner. Additionally, females that produced offspring with familiar siblings were significantly more likely to have litters with multiple paternity than females not producing offspring with familiar siblings. However, multiple paternity was not influenced by relatedness of sires. Finally, older individuals were more likely to produce offspring with each other than with younger individuals. Our findings suggest that prior association is a more important mechanism of inbreeding avoidance than phenotype matching for prairie voles mating under ecologically relevant conditions.     

Long-term effects of short-term perturbation in a subalpine grassland

Theoretical advances and short-term experimental studies have furthered our understanding of how ecosystems respond to perturbation. However, there are few well-replicated experimental studies that allow an assessment of long-term responses. Results from a controlled, large-scale field experiment in a subalpine grassland near Interlaken, Switzerland, show that 2-4 years of liming (Ca: 40 g x m(-2) x yr(-1)) still significantly affected the composition of the vegetation and the soil microbial community nearly 70 years after the treatments were imposed, whereas NPK fertilization (8 g x m(-2) x yr(-1)) only marginally affected vegetation composition. The exchangeable content of Ca ions and soil pH were higher in limed plots but were unaffected in fertilized plots. Plant species and PLFAs (phospholipid fatty acids) indicating low pH values were found in higher abundance in the unlimed plots, suggesting that the long-lasting effects of liming on the above- and belowground communities were mediated through changes in soil pH. The results of this long-term study indicate that the resilience of mountain ecosystems may be particularly low in response to perturbations that substantially alter soil pH or other key determinants of belowground processes.     

The effects of littoral zone vegetation on turbulent mixing in lakes

Micro-scale thermal profile data were acquired in four lakes in northwest England and southeast Australia that ranged from a small, sheltered pond with a surface area of about 1 ha to more open lakes with surface areas of several square kilometres. These lakes provided a range of topographic and climatic contexts, basin morphologies and dominant macrophyte species. The data were acquired using two SCAMP profilers, one deployed in the open water and the other mounted on a field traverse deployed within the vegetated littoral zone. From these profile data, turbulence parameters were calculated. The results show the variation in the influence of vegetation on turbulence in the four lakes, which depends on the combination of wind stress, solar radiative forcing and macrophyte mechanical properties. In the sheltered pond, the vegetation alters the light climate within the water, thus reducing stratification and allowing weak, thermally-driven mixing. In the larger lakes, however, the primary action of the vegetation is to prevent surface-generated TKE from penetrating the water column, although this effect becomes less important as the plant separation increases. A simple mechanistic model, calibrated against the field data, suggests that the macrophyte mechanical properties are most important in determining the turbulent kinetic energy (TKE) profile. Increasing the number of turbulence-generating plants reduces the transport of surface-generated TKE into the deeper water, consistent with the field observations. The model suggests that solar forcing, as measured by the temperature gradient between the surface and bottom waters, is of less importance since the TKE profile is similar in runs with different gradients. Perhaps most surprisingly, the value of the surface-wind stress used in the model is not important, within the limitations of the model, as it does not change the TKE profile, except in a thin surface layer.     

Interactive effects of natural and human disturbances on vegetation dynamics across landscapes.

Accurate measures of human effects on landscape processes require consideration of both the direct impacts from human activities and the indirect consequences of the interactions between humans and the landscape. This is particularly evident in systems experiencing regular natural disturbances such as in the mountainous areas of southwestern China, where the remaining population of giant pandas (Ailuropoda melanoleuca) is supported. Here the spatiotemporal patterns of human impacts, forests, and bamboo episodic die-offs combine to determine the distribution of panda habitat. To study the complex interactions of humans and landscapes, we developed an integrated spatiotemporally explicit model of household activities, natural vegetation dynamics, and their impacts on panda habitat. Using this model we examined the direct consequences of local fuelwood collection and household creation on areas of critical giant panda habitat and the indirect impacts when coupled with vegetation dynamics. Through simulations, we found that over the next 30 years household impacts would result in the loss of up to 30% of the habitat relied on by pandas during past bamboo die-offs. The accumulation and spatial distribution of household impacts would also have a considerable indirect influence on the spatial distribution of understory bamboo. While human impacts influence both bamboo die-off and regeneration, over 19% of pre-existing low-elevation bamboo habitat may be lost following an episodic die-off depending on the severity of the impacts and timing of the die-offs. Our study showed not only the importance of the spatial distribution of direct household impacts on habitat, but also the far-reaching effects of the indirect interactions between humans and the landscapes they are modifying.     

Shear layer over floodplain vegetation with a view on bending and streamlining effects

Environmental Fluid Mechanics - Shrubby and woody vegetation growing on floodplains profoundly influences hydrodynamic and transport processes in riverine systems. Existing hydrodynamic research is...     

Ecological properties of soil water and effects on forest vegetation in the Loess Plateau

In the Loess Plateau of China, soil water has three ecological properties: high infiltration capacity, high storage capacity and availability to deep plant roots. Soil desiccation is the most serious problem for forest vegetation in the Loess Plateau. Arid soils are the result of intensified soil desiccation caused by disturbances in plant succession, which constitute the ecological foundation of soil water. The negative effects of the arid soil layer on surface water infiltration for recharging underground water are discussed in terms of ecological hydrology. The arid soil layer disrupts the link between surface water and underground water and prevents vertical precipitation infiltration from supplementing underground water. Forest vegetation has a significant runoff-retaining efficiency that reduces total runoff from forest areas leading to low surface and ground runoff which affect the water cycle on a watershed scale.     

丛枝菌根真菌对内蒙古草原大针茅群落的影响

使用真菌抑制剂在内蒙古草原开展原位试验,人为创造菌根受抑制和正常两种环境,通过分析菌根侵染率,测定大针茅群落的物种组成、丰富度和多样性等结构指标,分析丛枝菌根真菌对群落结构和净初级生产力的影响。试验结果表明,两种处理群落的菌根侵染率不同,苯菌灵有效地降低了植株的菌根侵染率。丛枝菌根真菌短期内未能对植物群落的物种丰富度、多样性产生影响,未能改变植物群落的结构和净初级生产力。但丛枝菌根真菌的存在,会对植物群落内不同植物种的地上部生物量实现再分配,降低了优势种垄断资源的能力,使群落内物种的生物量和营养元素含量趋于均匀,有利于保护关键种,有利于植被的恢复与重建。因此,研究结论为内蒙古退化草原生态系统的恢复和重建提供了重要的理论依据和参考价值。     

植被恢复的生态效应研究进展

植被在水土保持、水源涵养及生态系统的固碳过程中起着重要的作用。植被恢复是指运用生态学原理,通过保护现有植被、封山育林或营造人工林、灌、草植被,修复或重建被毁坏或被破坏的森林和其他自然生态系统,恢复其生物多样性及其生态系统功能。目前,植被的自然及人工恢复是改善脆弱生态系统及退化生态系统生态环境现状最有效的措施。植被在恢复过程中对地上植被生态系统,物种多样性的恢复有着重要影响,同时通过凋落物及根系的输入,可以有效改善地下生态系统,增加土壤的养分含量、改善土壤的物理结构、增加土壤生物的生物量及活性。文章以地上及地下生态系统为出发点,综述了植被恢复过程中自然及人工恢复过程中不同的植被类型、不同的恢复时间下植物物种组成和多样性、土壤理化性质及土壤微生物群落的变化。植被的自然及人工恢复在一定程度上均能增加植物物种的多样性,随着恢复年限的增加物种的组成发生改变且多样性呈增加趋势,但一些特殊环境下不当的人工恢复可造成植被演替向退化方向发展,降低生物多样性。不同的植被类型由于其生长方式的不同对土壤理化性质和土壤微生物的影响存在差异,随着恢复年限的增长,土壤理化指标及微生物学指标呈现先增加而后趋于平稳的状态。针对已有的研究进展,提出在未来的研究过程中,一方面应该增加更多的对比研究,对不同环境下,不同的恢复物种,不同的恢复方式进行更深入地探讨;另外一方面应增加不同尺度的研究,现有的研究多集中在样地尺度,未来应在更大尺度上进行分析;再者,地上及地下生态系统之间的相互关系及影响机理一直是土壤学科研究的热点,植被恢复过程中应增加更多该方面的机理研究。     

植物影响空气中持久性有机污染物的研究进展

持久性有机污染物(POPs)在植物与空气两相界面之间存在动态交换过程,一方面,植物叶片吸附、吸收空气中的POPs,净化了空气,并将其转移到食物链和土壤等其它环境介质中;另一方面,植物叶片通过挥发使其吸附的POPs重新回到空气中,最终对全球范围内POPs的循环和环境归趋产生重要影响.本文综述了植物与空气中POPs的动态交换过程,分析了影响植物吸附和挥发POPs的主要因素,包括POPs的理化性质、植物特征和环境条件.同时,就城市绿地对空气中POPs浓度水平的影响展开讨论,由于该过程受多种因素共同影响,植被清除的POPs是否足以改善空气质量仍有争议,其中影响机制有待深入研究.此外,本文总结了植物中POPs的检测技术,传统检测技术灵敏性和准确性高,而原位检测技术可以直接观察活体植物中POPs的吸收、迁移、存储等环境行为.最后,本文探讨了现有研究的不足和未来发展的方向,以期为今后研究植物-空气界面过程以及POPs多介质环境行为提供理论和技术参考.     

鄱阳湖双退区受损湿地植被恢复对水质的影响

退化湿地的植被恢复有助于提高湿地生物多样性和净化水体功能。通过监测鄱阳湖双退区（湿地）生态恢复过程中前后水质变化,分析了不同植被覆盖率和植物残体分解对水质的影响。结果表明,在植物生长期间,湿地水体TN质量浓度下降65.4%～71.3%,NO3--N也呈较大幅度下降,并能降低水体TP浓度水平;高植被覆盖增加水体叶绿素质量浓度水平,中低植被覆盖不影响水体叶绿素质量浓度,植被覆盖能有效保持水体较高透明度,但不能降低水体COD质量浓度。在枯水期,高植被覆盖因为植物残体分解使氮素回流水体,导致水体含TN,NH4＋-N,NO3-_N质量浓度显著升高,中低植被覆盖植物残体分解同样显著增加水体氮素,但增加程度小于高植被覆盖;植物残体分解不影响水体TP质量浓度水平;高植被覆盖植物残体分解增加水体叶绿素质量浓度,中低植被覆盖则无影响;高中低植被覆盖区植物残体分解都显著增加水体混浊度,也提高了水体的BOD,对水体COD没有影响。