Fox predation on cyclic field vole populations in Britain

The diet of the red fox Vulpes vulpes L. was studied during three winter periods in spruce pklantations in Britain, during which time the cyclic field vole Microtus agrestis L. populations varied in abundance. Field voles and roe deer Capreolus capreolus L. were the two main prey species in the diet of the red fox. The contribution of lagomorphs to fox diet never exceeded 35% and species of small mammal other than field voles were of minor importance. The contribution of field voles was dependent on vole density. The non-linear density dependent relationship with a rather abrupt increase of field voles in fox did when vole density exceeded ca 100 voles ha⁻¹ was consistent with a prey-switching response. The contribution of field voles to fox diet during the low phase of population cycles was lower in Kielder Forest than in other ecosystems with cyclic vole populations. The number of foxes killed annually by forestry rangers was consistent with the evidence from other studies that foxes preying on cyclic small rodents might show a delayed numerical response to changes in vole abundance. Estimates of the maximum predation rate of the fox alone (200–290 voles ha⁻¹ of vole habitat year⁻¹) was well above a previously predicted value for the whole generalist predator community in Kielder Forest. Our data on the functional response of red foxes and estimates of their predation rates suggest that foxes should have a strong stabilising impact on vole populations, yet voles show characteristic 3-4 yr cycles.     

Seasonal metabolism of a small, arboreal monitor lizard, Varanus scalaris, in tropical Australia

The field metabolic rates (FMR) and water fluxes of Varanus scalaris were measured during the wet and dry seasons by the doubly-labelled water technique. Seasonal measurements of standard (night-time) metabolism (SMR) and resting (daytime) metabolism (RMR) were made in the laboratory at 18, 24, 30 and 36°C, and maximal oxygen consumption was measured at 36°C on a motorized treadmill. This population was active throughout the year. In the wet season, the mean FMR was 7.8 kJ day⁻¹ (128.0 kJkg⁻¹ day⁻¹; mean mass = 66.4 g, n = 13), and during the dry season the mean was 5.0 kJ day⁻¹ (67.6 kJ kg⁻¹ day⁻¹; mean mass = 77.4 g, n = 17). The mean water flux rates for these animals were 3.6 and 1.2 ml day⁻¹, respectively (60.4 and 16.6 ml kg⁻¹ day⁻¹). The seasonal means of FMR and water flux were significantly different by ANCOVA ( P < 0.0001). Measurements of SMR and RMR were significantly higher in the wet season (ANCOVA: P < 0.0001), but we found no difference in the maximal oxygen consumption between seasons (ANCOVA: P = 0.6). The maximal oxygen consumption of the lizards on the treadmill (2.9 ml min⁻¹= 1.8 ml g⁻¹ h⁻¹), mean mass = 97.4 g, n = 16) was 20 times that of the SMR at the same temperature during the dry season, and 11 times that of the SMR during the wet season. The seasonal differences in FMR were attributable to: changes in SMR (12.2%) and RMR (16.4%); differences in night-time body temperatures (11.3) and daytime body temperatures (16.4%); and activity (broadly defined to include locomotion, digestion, and reproductive costs (43.7%).     

Mosquito control in Dar es Salaam.

Abstract. In preparation for a trial of polystyrene beads and pyriproxyfen for the control of Culex quinquefasciatus mosquitoes, surveys of their breeding were carried out in two contrasting areas of Dar es Salaam, Mikocheni and Ilala, during the dry season.
Sanitation structures (latrines, soakage pits, septic tanks and cess pits) were the most prolific breeding places, totalling 780 in Mikocheni and 1544 in Ilala. Those in Mikocheni were estimated to contain about 1.4 times more mosquito pupae, per site, than in such structures in Ilala. This was both because a higher proportion of sites contained visible water and because sites with water were more likely to contain pupae in Mikocheni. The relative importance of the different types of structure, in terms of productivity, was the same in both areas. Although septic tanks and cess pits made up only 10.5% of the on-site sanitation structures in Ilala, they contained 53% of the total number of pupae in enclosed sites; they were therefore particularly important targets for treatment with polystyrene beads. A survey during the rainy season of sites in Ilala revealed little change in the proportion that were wet, or in the frequency of breeding in those with visible water.
The number, type and area of open breeding sites varied greatly between the two study areas. In Mikocheni the area of open breeding sites was 100 times greater than in Ilala, with 97% of the 13 ,000 m² being flooded grassland. In Ilala all but four of the sixty-six open breeding sites were puddles of sullage water derived from bathrooms. Different strategies for control in open breeding sites are required in the two areas of Dar es Salaam.     

White rhinoceros range size in the south-western Kruger National Park

White rhinoceros range size was ascertained telemetrically in the south-western Kruger National Park. The mean annual range size of territorial males was 9.86 km² compared to 22.83 km² for adult females. White rhinoceros females' summer wet season range was larger (21.44 km²) than the winter dry season range (11.64 km²). It is argued that abundant field-water during the wet season enables animals to range further from permanent water supplies and to utilize larger foraging areas. White rhinoceros have core areas in their individual ranges that usually are situated along riverbanks in the preferred grazing regions. These core areas also include some favourite resting spots on high-lying areas. White rhinoceros range sizes in the south-western Kruger National Park were similar to those of other reserves with comparable white rhinoceros densities. In the Umfolozi Game Reserve, which has a higher white rhinoceros density than the Kruger National Park, the individual ranges are much smaller.     

粪便激素水平反映不同出生时期雄性布氏田鼠的繁殖策略

布氏田鼠是我国内蒙古草原的主要害鼠之一,具有明显的季节繁殖特征,不同季节出生个体可能具有不同的繁殖策略,但尚缺乏内分泌证据支持。本研究采用标志重捕法,连续监测大型自然围栏中不同年龄雄性布氏田鼠的繁殖状态和应激水平的季节变化,分析各年龄组雄鼠的繁殖发育策略。结果表明,越冬雄鼠可保持较高的睾丸下降率和睾酮水平至8月初;而部分5月生雄鼠的繁殖期睾酮水平较接近越冬鼠,但8月初已降至年内最低水平,而6月及以后出生雄鼠睾酮始终处于较低水平;这说明越冬鼠的繁殖状态可贯穿繁殖期始终,只有部分5月生雄鼠可能参与当年繁殖,而6月及以后出生雄鼠则不能在当年繁殖。越冬鼠皮质醇水平高于当年鼠,繁殖期高于非繁殖期,这可能是越冬鼠由于繁殖需要而保持较高应激状态,从而造成繁殖盛期后死亡率升高。这些结果说明,不同时期出生的雄性布氏田鼠具有不同的出生后性腺发育模式和繁殖策略,反映出生存与繁殖之间的权衡。     

Occurrence of phosphorus and its potential remohilization in the littoral sediments of a productive English lake

SUMMARY. 1. Vertical profiles of pH were measured at nine shallow water (<5m) locations in Esthwaite Water. These indicate strong gradients of pH near the sediment water interface suggesting a marked buffering capacity of the sediments.
2. Thirteen littoral sediment cores were horizontally sectioned and sequentially extracted (0.5 M NaHCO₃, 0.1 M NaOH, 1 M HCI) and analysed for soluble reactive phosphorus. The core sections were also analysed for total phosphorus and per cent organic content to determine the vertical and areal variability of phosphorus within the littoral sediments of Esthwaite Water.
3. The rate of release of phosphorus from intact sediment cores was measured in the laboratory as a function of the pH of overlying water, yielding the relationship log K=0.54 pH−3.94, K=mg Pm⁻²day⁻¹. The maximum release rate measured was 75 mg P m⁻² day⁻² at pH = 10.5.
4. Experiments on sediment slurries indicate that the release of phosphorus at pH 10 is rapid with approximately 50% of the total NaHCO₃+ NaOH extractable phosphorus being released within 3 h.
5. Phosphorus release from the littoral sediments may equal or exceed external sources plus hypolimnetic inputs during periods of high pH associated with times of maximum algal biomass.     

Experimental manipulation of the timing of reproduction in the California vole

Summary The potential role of food and water in determining 1) the timing of the normal breeding season in the California vole, and 2) two frequently occurring exceptions to this normal pattern, are explored by using experimentally manipulated enclosed populations. Hypotheses derived from field observations were tested in the enclosed populations by the manipulation of green food, dry food, water, and vole density. The results of three experiments involving five populations are reported. In all populations densities were maintained at near-normal levels (475 to 1750 per ha). In all three experiments, it was shown that breeding was possible in the summer if sufficient food and water were available, although perhaps with reduced litter sizes and rates of growth and reproductive maturation of young. In two cases, severe weight losses and high mortality were induced by insufficient water. When water was provided, survivors recovered weight and reproductive competency in between five weeks and eight months. In three populations, starvation induced weight losses and mortality. In these cases recovery of the voles took only one month or less. In two of these last, the inadequate food situation was produced during the normally wet season by outbreaks of a European slug. It is concluded that available moisture is the most important factor in triggering both the end and beginning of the normal breeding season. Of course, inadequately fed mice do not breed at any season. Summer (dry season) breeding can occur when food and water conditions are adequate due to locally favorable conditions or very low population densities. Prolonged delays in growth and reproduction following the return of favorable conditions are most likely the consequence of chronic and severe water deprivation.     

Comparative effects of downslope water and nutrient movement on plant nutrition, photosynthesis, and growth in Alaskan tundra

Changes in water and nutrient movement are common disturbances resulting from human activities in arctic regions. To assess the influence of water and nutrient movement on different plant growth forms, we added water and NPK fertilizer along 10 to 20 m linear transects across small natural drainages on an Alaskan tundra slope. Water was added by continuous-flow emitters from a drip irrigation system at a rate of 450 L m⁻¹ d⁻¹ during the 1986 growing season and 110 L m⁻¹ d⁻¹ in the 1987 growing season. NPK in the form of Osmocote, a slow release fertilizer, was applied at 0.5 kg per linear meter in early and mid-season of the 1985 growing season. Tissue N and P contents, light-saturated photosynthetic rates, and aboveground biomass production were measured at peak season for key species 2 m above and 2 and 6 m below the water and nutrient applications in 1986 and 1987.
Mean leaf N and P of the species tested increased slightly 2 m below the water addition sites and dramatically below the fertilizer addition sites. Increases in tissue N and P were also found 6 m below the fertilizer addition points. Leaf photosynthesis tended to increase 2 m below the water and nutrient additions for the species tested. Six meters below the treatment application points, photosynthesis was minimally affected in 1986 but increased in 1987. Increases in leaf area on the irrigation treatments were found only for the evergreen species, Ledum palustre and Vaccinium vitis-idaea , 2 m below the site of addition. In contrast, fertilizer addition caused large increases in leaf area production for all species tested at 2 m below the treatment, and for some species at 6 m below treatment. The overall effects of the two treatments were similar, but were greater for the fertilizer addition.     

Phenology, Lignotubers, and Water Relations of Cochlospermum vitifolium, a Pioneer Tropical Dry Forest Tree in Costa Rica

We examined structural and physiological traits relevant to the phenology of the tropical dry forest (TDF) pioneer tree Cochlospermum vitifolium . Despite marked seasonality in rainfall, meristem activity occurred throughout the year. Leaves were produced almost continuously during the rainy season, while leaf shedding started early during drought, before changes in soil water content were observed. Phenological activity under drought included flowering and fruiting of leafless trees; bud break and shoot extension took place before the end of the dry season. Low wood density of C. vitifolium stems (0.17 g/cm³) and lignotubers (0.14 g/cm³) provided water and starch storage needed to support phenological events such as branch extension, leaf flushing, and reproduction during the dry season, and probably also contributed to survival following mechanical damage and fire, typical of early TDF successional stages. Lignotuber water and starch contents showed substantial seasonal variation, declining from the beginning of the dry season to their lowest levels at the time of reproduction and dry-season flushing. Stems progressively replaced lignotubers as main storage organs as tree size increased. Evidence for a role of water stores in buffering daily water deficits was weak. Leaf water potentials remained above −1.2 MPa and stomatal conductance below 350 mmol/m²/s, suggesting that gas exchange during the rainy season was limited to prevent xylem cavitation. Leaf shedding occurred when early-morning and mid-day Ψ_L converged at the rainy–dry season transition, without changes in lignotuber or soil water content, suggesting that leaves of C. vitifolium are closely tuned to atmospheric drought.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp .     

A rodent plague on prairie diversity

Selective vole ( Microtus pennsylvanicus ) suppression of prairie grasses and forbs in experimental restorations suggests why many of the plants are likely to be uncommon in nature. Vole herbivory reduced densities of legumes and grasses and increased unpalatable forbs in replicated plantings in Illinois: six otherwise common species ( Dalea purpurea , Desmanthus illinoensis , Elymus canadensis , Panicum virgatum , Phalaris arundinacea , Sorghastrum nutans ) declined 27–89% in abundance, whereas two species ( Echinacea purpurea and Rudbeckia hirta ) increased by 61% and 1023%. Species number dropped by 19% and plant diversity (Simpson's D) by 37% in one treatment to which voles had access. Plots were planted with 18 prairie species of the region, but in even distributions of 35 or 350 seeds species⁻¹ m⁻², rather than skewed in favour of large C₄ grasses common in native remnants. Manipulation of plant composition and vole access revealed what are likely to be formative effects of rodent herbivory on vegetative composition. These experimental tallgrass communities appear to be assembling from plant species that voles prefer not to eat.     

The role of sulphur compounds for breeding success of Ips typographus L. (Col., Scolytidae) on Norway Spruce (Picea abies [L.] Karst.)

Bark beetles, especially Ips typographus L. represent a severe biotic threat for spruce ( Picea abies [L.] Karst.) at low altitudes in Europe. We compared sulphur (total S, SO₄²⁻, glutathione, cysteine, methionine), nitrogen (total N, NO₃⁻, total protein, free amino acids), carbon, total phosphorus and PO₄³⁻, tree vigour index (TVI) and water content of the phloem after felling, and their dependent changes (tdc) with the breeding success of I. typographus . Twenty trees were classified according to age (34/90 years) and crown density (high/intermediate/low). Water content was higher in young trees than in old trees, higher in the crown than at breast height, and decreased significantly within the 8-week study period. In old trees, breeding success, length of mother galleries and SO₄²⁻ were significantly higher, while total protein, NO₃⁻ and water content were significantly lower than in young trees. Trees with intermediate crown density provided the best breeding success for I. typographus and had significantly higher arginine content and C/N ratio as well as low amounts of phosphate and glutamine. During the period of bark beetle breeding, total sulphur, glutathione, protein, NO₃⁻, aspartate, glutamine, glutamate, arginine and γ-aminobutyrate decreased significantly. The results support previous investigations that I. typographus develops best in physiologically weakened trees.     

Fish production in Oued Sebaou, a seasonal river in North Algeria

Fish were sampled by electrofishing at three contiguous sites 26 km from the source of Oued Sebaou, a seasonal river in North Algeria. River discharge ranges from 300 m³s⁻¹ in the peak of the rainy season to 0.1 m³s⁻¹ at the end of the dry season. Extensive gravel extraction from the river bed takes place during the dry season.
Two species were recorded at each site: Barbus callensis , which is heavily fished locally, and Anguilla anguilla . The three sample maximum likelihood Zippin method was used to estimate mean density and standing crops, which were: barbel, 452 fish ha⁻¹, 5.33 kg ha⁻¹; eels, 149 fish ha⁻¹, 3.04 kg ha⁻¹. Estimated average biomass and production were: barbel, 2.31 kg ha⁻¹, 4.27 kg ha⁻¹ year⁻¹; eels, 1.51 kg ha⁻¹, 2.60 kg ha⁻¹ year⁻¹.     

Uptake of copper and lead by a metaltolerant isopod Asellus meridianus Rac.

SUMMARY. Asellus meridianus from sites on the rivers Hayle and Gannel accumulates both copper and lead from experimental solutions: tolerant animals also accumulate copper and lead from metal-enriched food. Copper-tolerant animals accumulated up to 6.8 μg mg⁻¹ copper after feeding on a copper-enriched diet for 12 days whereas non-tolerant animals showed no evidence of copper accumulation from food and no survivors remained after 8 days. Lead-tolerant animals accumulated up to 28 μg mg⁻¹ lead during a 14-day exposure to a lead diet: non-tolerant animals showed no accumulation of lead from food and no live animals remained after 10 days.
A marked difference in the storage forms of copper is observed in the hepatopancreas of copper-tolerant isopods, as compared with non-tolerant animals, when samples are taken from natural populations.     

Seasonal patterns in water, sodium and energy turnover in free-living echidnas, Tachyglossus aculeatus (Mammalia: Monotremata)

The energetics of an egg-laying mammal, the echidna ( Tachyglossus aculeatus ), were studied in the wild by means of isotope turnover techniques. Water and sodium influx rates were highest in summer (47.7±15.3 ml kg^-1 day^-1 and 1.20±0.52 mmol kg^-1 day^-1, respectively) and associated with high metabolic rates (0.509±0.048 ml CO₂ g^-1 h^-1). Water and sodium influxes and metabolic rates were lowest in May and June (7.8±6.4 ml H₂O kg^-1 day^-1, 0.21±0.12 mmol Na kg^-1 day^-1 and 0.205±0.129 ml CO₂ g^-1 h^-1, respectively). These low rates in late autumn/early winter are associated with reduced activity, the animals spending substantial periods of time in torpor. The comparatively low isotope turnover rates of echidnas are a consequence of their diet; ants and termites which have low mass-specific energy contents.     

Continuous drift samples of macroinvertebrates in a large river, the Danube in Austria

SUMMARY 1. A new method is described for sampling the drift in large rivers continuously and automatically, using equipment based on the marine, continuous plankton sampler of Hardy (1936).
2. Between April and November 1989, about 790 h were sampled continuously, equivalent to a water volume of 2937m³ and the total catch was 527 drifting macroinvertebrates, in forty-nine taxa. Twenty-five of these taxa are recorded in the drift for the first time and twenty-eight of the drifting taxa were present in benthos samples from the Danube.
3. Total drift density varied between 12 and 31 animals per 100m³ of water sampled throughout the year, with a maximum of 31 animals in May, The composition of major faunal groups showed a significant seasonal pattern, with Oligochaeta and Diptera predominant in spring, Crustacea and Insecta in summer and only Crustacea in autumn. The overall density of the macrozoobenthos from October 1986 to December 1987 was about 19360 animals m⁻² and the proportion of total benthos animals, drifting at any instant in time, ranged from 0.0026 to 0.0064%.
4. The relationship between drift density day⁻¹ and mean daily discharge was described by a power-function. Total mean drift rate of macroinvertebrates in the Danube was estimated to be 13 600 000 animals per 24 h and the mean drift distance was estimated to vary between about 4 and 31 m, dependent on the animal group and the water velocity.
5. No obvious consistent diel pattern could be established from the continuous samples, and no marked diel rhythm could be detected for Oligochaeta, Diptera larvae and Crustacea.     

Cold hardiness and water relations parameters in Rhododendron cv. Catawbiense Boursault subjected to drought episodes

We determined whether increase in cold hardiness of Rhododendron cv. Catawbiense Boursault induced by water stress was correlated with changes in tissue water relations. Water content of the growing medium was either maintained near field capacity for the duration of the study or plants were subjected to drought episodes at different times between 15 July and 19 February. Watering during a drought episode was delayed until soil water content decreased below 0.4 m³ m⁻³ then watering was resumed at a level to maintain soil water content between 0.3 and 0.4 m³ m⁻³. Cold hardiness was evaluated in the laboratory with freeze tolerance tests on detached leaves. Water relations parameters were determined using pressure-volume analysis. Exposure to drought episodes increased cold hardiness during the cold acclimation stage in late summer and fall but not during the winter. When water-stressed plants were re-watered to field capacity, the previous gain in cold hardiness gradually disappeared. Water relations parameters correlating with seasonal changes of cold hardiness included dry matter content (r =−0.67). apoplastic water content (r =−0.60), and water potential at the turgor loss point (r = 0.40). Changes of cold hardiness in water-stressed plants in reference to well-watered plants were correlated with changes of all water relations parameters, except for osmotic potential at full turgor (r = 0.13). It is proposed that water stress reduced the hydration of cell walls, thereby increasing their rigidity. Increased rigidity of cell walls could result in a development of greater negative turgor pressures at subfreezing temperatures and therefore increased resistance to freeze dehydration.     

Effects of competition and season on survival and maturation of young bank vole females

In territorial microtines intra-specific density dependent processes can limit the maturation of individuals during the summer of their birth. This may have demographic consequences by affecting the number and the age distribution of breeding individuals in the population. Little is known about this process on a community level, though populations of many northern microtine species fluctuate in synchrony and are known to interfere socially with each other. We experimentally studied the influence of the field vole Microtus agrestis on maturation, breeding, space use and survival of weanling bank voles, Clethrionomys glareolus. Two additive competition experiments on bank vole populations were conducted in large outdoor enclosures, half of them additionally housing a field vole population. In a mid-summer experiment low population density and absence of older breeding females minimised intra-specific competition. Survival was not affected by the presence of field voles. Season had a significant effect on both the probability of maturation and breeding of the weanlings. Competition with field voles significantly delayed breeding, and coupled with seasonal effects decreased the probability of breeding. In a late-summer experiment breeding and survival of bank vole weanlings were studied for three weeks as part of a high density breeding bank vole population. Weanlings did not mature at all nor were their space use and survival affected by the presence of field voles. Our results show that competition with other species can also have an impact on breeding of immatures. In an extreme seasonal environment, even a short delay of breeding may decrease survival chances of offspring. Seasonal and competition effects together may thus limit the contribution of year born females to reproductive output of the population. Other studies have shown that adult breeding bank voles suffer lower survival in the presence of field voles, but this study showed no survival effects on the weanlings. Thus it might be beneficial for weanlings to stay immature especially in the end of the breeding season and postpone reproduction to the next breeding season if densities of competing species are high.     

Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings I. Growth, whole-plant water use efficiency and water loss

Seeds of cherry ( Prunus avium ) were germinated and grown for two growing seasons in ambient (∼350 μmol mol⁻¹) or elevated (ambient+∼350 μmol mol⁻¹) CO₂ mole fractions in six open-top chambers. The seedlings were fertilized once a week, following Ingestad principles in order to supply mineral nutrients at free-access rates. In the first growing season gradual drought was imposed on rapidly growing cherry seedlings by withholding water for a 6-wk drying cycle. In the second growing season, the rapid onset of drought was imposed at the height of the growing season on the seedlings which had already experienced drought in the first growing season. Elevated [CO₂] significantly increased total dry-mass production in both water regimes, but did not ameliorate the growth response to drought of the cherry seedlings subjected to two sequential drying cycles. Water loss did not differ in either well watered or droughted seedlings between elevated and ambient [CO₂]; consequently whole-plant water- use efficiency (the ratio of total dry mass produced to total water consumption) was significantly increased. Similar patterns of carbon allocation between shoot and root were found in elevated and ambient [CO₂] when the seedlings were the same size. Thus, elevated [CO₂] did not improve drought tolerance, but it accelerated ontogenetic development irrespective of water status.     

The population dynamics of small mammals living in set-aside and surrounding semi-natural and crop land

Small mammals were found on set-aside and surrounding farmland. Wood mice showed a different pattern of demography at two sites, with higher densities, greater survival, heavier weights and longer breeding seasons at Aldroughty than at Newburgh. These differences were thought to be due to a difference in habitat productivity at the two sites. Field voles showed less of a difference in population dynamics between the two sites, and both species of vole maintained populations at low densities.     

Habitat selection by grayling—I. Spawning habitats

Grayling spawning sites were investigated in two French rivers, the Pollon (1 year) and the Suran (2 years) and described by current velocity, water depth, and substrate composition, completed by an assessment of bottom shear stress with FST-hemispheres. A comparison was made between used and available habitats, the latter being characterized by random sampling of 300 m long (Pollon) and 510 m long (Suran) river sections, both including three riffle/pool sequences. Mean velocities observed on spawning sites did not differ significantly between rivers or years (overall mean 48–9 cm s^-1 S.D. = 11.9, range 25.8–91.7 cm s^-1, n =150). Most water depths ranged from 10 to 40 cm in both rivers, but mean depths were significantly different ( P <0.05). Substratum of spawning grounds was dominated by gravel and pebbles (2–64 mm) in both rivers. Most spawning sites (99%) were characterized by a narrow range of hemispheres (nos 9–13), i.e. a range of shear stress of about 5–16 dyn m^-2. In the Pollon, spawners between spawning acts were found in a resting pool located immediately downstream from the spawning area and characterized by slow-flowing water (mainly <20 cm s^-1) and great depth (mainly >60 cm), with cover provided by overhanging branches and tree roots.