Terrain structure and selection of denning areas by arctic foxes on Svalbard

We examined the relationship between the distribution of arctic fox dens and the occurrence of rugged terrain on Svalbard, Norway, using indices of terrain ruggedness (TRI) based on contour characteristics from topographic maps in 240 grid cells, each 4 km². The distribution of rugged terrain co-varied with occurrence of arctic fox dens. Moderately rugged terrain (TRI=1.5–3.0) constituted only 21% of the total study area, but contained 77% of all natal dens recorded in the study area. Large clusters (8–36 km²) of moderately rugged terrain were generally preferred for location of den sites compared to smaller scattered clusters of rugged terrain. The importance of rugged terrain is discussed in relation to snow cover, exposure, soil conditions and distribution of prey species. This simple and non-invasive analysis of terrain ruggedness may be used to predict the distribution of potential arctic fox denning areas across landscapes. Accepted: 6 September 2000     

The marine side of a terrestrial carnivore: intra-population variation in use of allochthonous resources by arctic foxes

Inter-individual variation in diet within generalist animal populations is thought to be a widespread phenomenon but its potential causes are poorly known. Inter-individual variation can be amplified by the availability and use of allochthonous resources, i.e., resources coming from spatially distinct ecosystems. Using a wild population of arctic fox as a study model, we tested hypotheses that could explain variation in both population and individual isotopic niches, used here as proxy for the trophic niche. The arctic fox is an opportunistic forager, dwelling in terrestrial and marine environments characterized by strong spatial (arctic-nesting birds) and temporal (cyclic lemmings) fluctuations in resource abundance. First, we tested the hypothesis that generalist foraging habits, in association with temporal variation in prey accessibility, should induce temporal changes in isotopic niche width and diet. Second, we investigated whether within-population variation in the isotopic niche could be explained by individual characteristics (sex and breeding status) and environmental factors (spatiotemporal variation in prey availability). We addressed these questions using isotopic analysis and Bayesian mixing models in conjunction with linear mixed-effects models. We found that: i) arctic fox populations can simultaneously undergo short-term (i.e., within a few months) reduction in both isotopic niche width and inter-individual variability in isotopic ratios, ii) individual isotopic ratios were higher and more representative of a marine-based diet for non-breeding than breeding foxes early in spring, and iii) lemming population cycles did not appear to directly influence the diet of individual foxes after taking their breeding status into account. However, lemming abundance was correlated to proportion of breeding foxes, and could thus indirectly affect the diet at the population scale.     

Sika deer distribution and habitat selection: the influence of the availability and distribution of food, cover, and threats

Large populations of sika deer occur in lowland heath, woodland, and grassland mosaics in southern England. Previous studies have focused on understanding single factors potentially affecting distribution and habitat selection of sika deer rather than considering simultaneously effects of landscape configuration and human disturbance on their distribution and habitat selection. This study measured effects of habitat availability, landscape structure, and human disturbance on where sika deer placed their home ranges and habitat selection within those ranges. Two main hypotheses were tested: (1) habitat selection differs according to landscape structure and habitat availability at both landscape and home range scales and (2) distribution of sources of human disturbance within the home range of deer affects their distribution. Results from radiotracking 31 females provided support for the first hypothesis and partial support for the second. Habitat selection at the landscape and home range scales differed between landscapes with different habitat structure and availability and was driven by distribution and availability of food and cover and a perceived risk linked to disturbance. Furthermore, deer selected open areas close to cover and this selection was stronger with presence of human disturbance, although results differed between study areas with different habitat distribution and level of disturbance. The study highlights the importance for managing deer of a balance between grazing and cover resources and the distribution of human disturbance.     

The tradeoff between reproductive and food resources in the crayfish Orconectes virilis

The conflict between mating and foraging is one of the many tradeoffs associated with reproduction. The relative attraction to sex pheromone and food stimuli by male virile crayfish (Orconectes virilis) were tested using two experiments. In the first experiment, the responses by males to pheromone and food stimuli alone were assessed. In the second experiment, males were exposed to both pheromone and food stimuli in a choice maze. To determine the effects of feeding motivation, the males in the choice experiment were fed either one day or seven days prior to observation. Male crayfish exhibited similar responses to the pheromone and food stimuli individually. Males exhibited a preference for the pheromone stimulus over the food stimulus in the choice trials, and that preference that was not influenced by starvation.     

Prevalence and geographical distribution of the ear canker mite (Otodectes cynotis) among arctic foxes (Alopex lagopus) in Iceland

Three hundred forty five adult arctic foxes (Alopex lagopus) from all counties in Iceland were examined for excess cerumen and ear canker mites (Otodectes cynotis). Only 13 foxes (4%) from a single county in northwestern Iceland were infested, where the prevalence of otodectiasis was 38%. Whether or not this parasite is new to the arctic fox in Iceland is unknown. If it is recently introduced, possible sources of infestation are farmed silver foxes (Vulpes vulpes), domestic dogs, domestic or feral cats, and arctic foxes from Greenland. It appears that the rate of transmission between adult foxes is low; a more common route of transmission is probably from the mother to her offspring or between vixens breeding in the same dens in subsequent years by contamination of the dens. No correlation was found between the prevalence of mites in foxes and Samson character.     

Riding across the selection landscape: fitness consequences of annual variation in reproductive characteristics

Evolutionary models estimating phenotypic selection in character size usually assume that the character is invariant across reproductive bouts. We show that variation in the size of reproductive traits may be large over multiple events and can influence fitness in organisms where these traits are produced anew each season. With data from populations of two orchid species, Caladenia valida and Tolumnia variegata, we used Bayesian statistics to investigate the effect on the distribution in fitness of individuals when the fitness landscape is not flat and when characters vary across reproductive bouts. Inconsistency in character size across reproductive periods within an individual increases the uncertainty of mean fitness and, consequently, the uncertainty in individual fitness. The trajectory of selection is likely to be muddled as a consequence of variation in morphology of individuals across reproductive bouts. The frequency and amplitude of such changes will certainly affect the dynamics between selection and genetic drift.     

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。     

Density-dependent reproductive output in relation to a drastically varying food supply: getting the density measure right

When a limiting resource (e.g. food) varies drastically between years, and population density is measured in the conventional way as individuals per area, demographic processes such as productivity and survival may erroneously be considered density-independent. We tested the hypothesis that if the variation in a limiting resource is not taken into account in the density measure, this may lead to erroneous conclusions about the density-dependence of demographic variables. We studied the food-related variation in productivity of bramblings Fringilla montifringilla , an insectivorous passerine bird, using 19 years of standardised insect censusing, bird censusing and mist-netting of birds in subalpine birch forest in Swedish Lapland. The yearly variation in our measure of brambling per capita productivity (numbers of juveniles per adult trapped) was explained to 30–40% by the larvae abundance of the moth Epirrita autumnata . Taking larvae density into account, no other environmental variable (inferred predation pressure, breeding phenology, and summer temperature) was significantly related to variation in reproductive output. There was no effect of brambling population density on per capita productivity, that is, when density was measured the conventional way, productivity seemed density-independent. However, per capita productivity was significantly and negatively correlated to the food-related population density (population density divided by larval density), supporting the hypothesis that not including a limiting resource into the density measure may indeed lead to erroneous conclusions about the density-dependence of demographic variables.     

Behavioural budgeting by wild coyotes: The influence of food resources and social organization

Daytime behavioural budgets of coyotes (Canis latrans) living in the Grand Teton National Park, Jackson, Wyoming, were analysed in order to determine how activity patterns were influenced by food resources and social organization. In winter, coyotes rested more and hunted less than in other seasons. Pack-living coyotes rested more and travelled less than resident pairs or solitary residents or transients during winter months when the major food resource was ungulate (predominantly elk, Cervus canadensis) carrion. A mated female living in a pack rested significantly more and travelled significantly less than a mated female living only with her mate (as a resident pair) during winter. We predict that in times of food shortage, pack-living coyotes, and particularly reproductive females, might be at an advantage when compared to resident pairs and solitary individuals.     

Brent goose colonies near snowy owls: Internest distances in relation to abundance of lemmings and arctic foxes

Brent goose colonies around snowy owl nests have been studied near Medusa Bay (73°21′ N, 80°32′ E) and in the lower reaches of the Uboinaya River (73°37′N, 82°10′E), the northwestern Taimyr Peninsula, from 1999 to 2006. All brent nests within 680 m from an owl nest have been regarded as an individual colony. The results show that the area of the colony is always larger than the protected area around the owl nest. In years of low abundance of lemmings, brent geese nest generally closer to the owl nest than in years of high abundance. When arctic foxes are abundant, however, brent geese nest significantly closer to owls than when the foxes are scarce, irrespective of lemming abundance. The mechanism of brent colony formation around owl nests is based on a number of stimuli.     

Exploitation of home range and spatial distribution of resources in German cockroaches (Dictyoptera: Blattellidae)

We analyzed the expression of edge following behavior in German cockroaches, Blattella germanica (L.). Structure of the environment and spatial distribution of resources modified both expression of locomotory behavior of cockroaches and its distribution between the edge and the central area of an experimental arena. When they are in a familiar environment, German cockroaches are definitely not edge followers and they exploit similarly the different parts of the accessible surface of their home range. Cockroaches placed in a new environment tended to follow edges more than undisturbed insects. This modification could be assimilated to a response to stressful conditions.     

Winter habitat use does not influence spring arrival dates or the reproductive success of Yellow Warblers breeding in the arctic

Winter habitat use can influence the breeding success of migratory songbirds in temperate regions due to its impact on bird condition and breeding phenology. How such carry-over effects vary with latitude is unknown. To address this question, we examined how winter habitat use, inferred from δ¹³C and δ¹⁵N signatures in winter-grown feathers, influenced the breeding phenology and productivity of Yellow Warblers (Setophaga petechia) at the extreme north of their range in the Canadian arctic (68°N) and compared this population with midlatitude Yellow Warbler (51°N) and American Redstart (Setophaga ruticilla; 44°N) populations reported in previous studies. In the arctic, we examined male arrival dates, female clutch initiation dates and the relationship between these timing variables and the number and quality of offspring produced within the season. In contrast to warblers breeding at midlatitudes, we find no support for an impact of winter habitat use on breeding phenology or productivity. Male arrival dates and female clutch initiation dates in both young and older individuals were not correlated with isotopic signatures acquired on the wintering grounds. Males with enriched δ¹⁵N signatures paired more rapidly after arrival, indicating a possible relationship between winter habitat use and condition. This relationship did not enhance annual productivity for these individuals, however, as the negative relationship between breeding phenology and reproductive success in our arctic population was significantly weaker than among Yellow Warblers breeding further south. This reduction or absence of timing effects on productivity in the north effectively removes one pathway through which carry-over effects can act.     

Juvenile fishes in macrophyte beds: influence of food resources, habitat structure and body size

Mean juvenile fish abundance and fish frequency in a large lowland river during low discharge largely differed among the unvegetated and three morphologically contrasted macrophyte habitats. Single separate models revealed that juvenile fish distribution was largely influenced by trophic variables. With the exception of Leuciscus cephalus , which responded mainly to physical variables (depth and substratum), multiple regression models emphasized the importance of trophic variables for fish distribution. For Blicca bjoerkna , L. cephalus and Lepomis gibbosus , habitat shifts with respect to prey size were apparent; small juvenile fishes mainly responded to small zooplankton abundance, whereas large individuals were more influenced by the abundance of large zooplankton. Whatever the species, predictions from multiple regression models were always better for large individuals. Small juvenile fishes appeared to be less affected by the habitat variables measured, and exhibited more uniform spatial distribution. The relative importance of trophic resources and habitat physical structure among macrophyte types for fish-habitat relationships is discussed, and the necessity of quantifying habitat structural complexity is emphasized.     

The distribution of Ephemerella ignita (Ephemeroptera) in streams: the role of pH and food resources

SUMMARY. 1. The mayfly Ephemerella ignita does not occur in upland streams of the River Duddon catchment which have waters with low pH values of 4.8-5.2, negative alkalinities and low ionic contents. However, it does occur in lowland streams of the catchment which have waters with higher pH values of 6.6 and above, large positive alkalinities and high ionic contents. This study addresses the question of whether the absence of the animal in the acid water streams is due directly to the water chemistry or to the absence of suitable food.
2. In comparative experiments using unfed animals of several species it was shown that E. ignita has a considerable tolerance of low pH, low ion water. In this it is similar to Amphinemura sulcicollis (Plecoptera), a stonefly which occurs in the acid water streams of the River Duddon catchment.
3. Growth rates in laboratory experiments with E. ignita were equally good whether the food supplied was that available in the low pH water streams (bryophyte Nardia compressa plus filamentous alga Hormidium subtile) or typical of that available in high pH water streams (moss Rhynchostegium riparioides with the epiphytic diatom Cocconeis placentula). However, a consideration of the natural habits of the animal suggests that it is the inaccessibility of the H. subtile algal food, rather than its unsuitability, which is relevant to the exclusion of E. ignita from the low pH streams. In addition, the very limited diversity of other algae in the low pH water streams, in the summer season, may well be influential in inhibiting the establishment of E. ignita.
4. The comparative experiments using unfed animals suggested that, contrary to the findings for E. ignita , the mayflies Baetis muticus and Beatis rhodani are probably excluded from the acid water streams of the Upper Duddon because of water chemistry.     

Seasonal trends in body mass, food intake and resting metabolic rate, and induction of metabolic depression in arctic foxes (Alopex lagopus) at Svalbard

 Post-absorptive resting metabolic rates (RMRs), body mass and ad libitum food intake were recorded on an annual cycle in captive arctic foxes (Alopex lagopus) at Svalbard. During the light season in May and in the dark period in November, RMR during starvation and subsequent re-feeding were also measured. In contrast to earlier findings, the present study indicated a seasonal trend in post-absorptive RMR (in W · kg⁻¹ and W · kg^−0.75). The values in the light summer were 15% and 11% higher than the values in the dark winter, suggesting a physiological adaptation aiding energy conservation during winter in arctic foxes. Body mass and ad libitum food intake varied inversely through the year. A significant reduction in RMR (in W and W · kg^−0.75) with starvation (metabolic depression) was recorded both in May and November, indicating an adaptation to starvation in arctic foxes. The lack of metabolic depression during a period of starvation that was concomitant with extremely cold ambient temperatures in November 1994 indicates that metabolic responses to starvation may be masked by thermoregulatory needs. At very low ambient temperatures, arctic foxes may require increased heat production which cannot be achieved via below-average rates of metabolism. Accepted: 7 June 1999     

Life history strategies in a fluctuating environment: establishment and reproductive success in the arctic fox

Natal dispersal, territoriality and reproductive success can have a major impact on the range, genetics and risk of extinction of a population. The proportions of animals that disperse have often been investigated, but not their fate. We have studied the lifetime reproductive success of arctic foxes that successfully emigrated, travelled and settled. Of these, some settled in the vicinity of their natal site as residents and some immigrated from other areas, i.e. short- and long-range dispersers respectively. We found no sex bias in migration patterns. In presaturation years, more immigrants than residents settled. Immigrant females had higher reproductive success than resident females. There was strong support for the ultimate hypothesis of Competition For Resources (CFR), but not for the hypotheses of Competition For Mates (CFM), Resident Fitness (RFH) and Inbreeding Avoidance (IA). Our data on arctic foxes could not be fully explained by any of four proximate hypotheses. We suggest that the reason is that dispersal and establishment should be considered as state dependent life history characteristics of individuals rather than population averages.     

滇龙胆草野生资源的地理分布与生物气候特征

利用国家标本资源共享平台提供的物种分布数据,结合野外实地调查和MaxEnt模型对滇龙胆草适宜分布区进行模拟和验证,分析滇龙胆草地理分布与气候因子间的关系.结果表明:模型训练集和验证集曲线下面积(area under curve,AUC)值均>0.90,表明模型预测精度高,预测结果较准确.滇龙胆草分布区地理坐标范围:22.2°-28.75°N,98.48°-110.59°E.适宜的海拔范围为1830^1959 m.适生区总面积约63.92×10^4 km^2;其中,高度适生区4.33×10^4 km^2,中度适生区21.42×10^4 km^2.云南、四川、贵州3省适生区面积合计约59.10×10^4 km^2,占全国适生区面积的92.46%.影响滇龙胆草地理分布的主要气候因子有3、6和8月太阳辐射,温度年较差,最暖季均温,10月和11月平均降水量及最干季降水量.偏最小二乘回归(partial least squares regression,PLSR)分析表明,分布区以北和以东的太阳辐射(3月、6月和8月)、温度年较差、10-11月平均降水量、最干季降水量是主要的限制因子;分布区以南主要限制因子是6月太阳辐射、最暖季均温、10月和11月平均降水量.限制滇龙胆草向四川盆地、广西盆地分布的主要气候因子是太阳辐射、温度年较差、最暖季均温、年生物温度和年可能蒸散量.综合分析认为,滇龙胆草的适生区主要位于云贵高原,上述地区的亚热带湿润气候最适宜滇龙胆草生长.     

Genetics and phenogenetics of the hormonal characteristics of animals. II. Changes in the reactivity of the pituitary-adrenal system and influence of the sex glands in selection of silver-black foxes by behavior]

Seasonal changes in the reactivity of adrenal cortex to ACTH and of the pituitary-adrenal system to psychic stress in intact and castrated domesticated (tame) and non-domesticated (non-tame) silver foxes of both sexes were studied. It is demonstrated that in tame foxes there are differences among the intact and castrated animal in their reaction to ACTH and psychic stress. These differences are maifested especially in autumn (September, October) which is the period of extra-seasonal sexual activity for domesticated animals. This points to the fact that the sex glands exert a great influence on the condition of central regulating mechanisms of the pituitary-adrenal complex and that the selection of silver foxes for tame behaviour changes the functional state of these mechanisms through the change of the functional state of the sex glands.