Comparative aerial and underwater visual acuity of the mink, Mustela vison schreber, as a function of discrimination distance and stimulus luminance

The aerial threshold visual angle of mink rose from 15.4 min at 10 cm stimulus distance to 19.1 min at 90 cm and the underwater angle varied from 32.7 min at 10 cm to 46.6 min at 90 cm, all at 34 mL luminance. At constant 30 cm stimulus distance, the aerial angle rose from 15 min at 34 mL to 51.7 min at 0.012 mL, the underwater angle from 31.4 min at 34 mL to 95 min at 0.012 mL, the aerial and underwater data forming similar curves. If mink hunt in water at somewhat higher light levels than in air they can obtain equal acuities in the two media.     

Comparative aerial and underwater motion perception capability of the mink (Mustela vison) as a function of stimulus radiant intensity and discrimination distance

The ability of mink to discriminate the direction of a fast, horizontally moving spot of light was investigated in air and underwater, over a range of stimulus radiant intensities (25–58×10⁴ μWsteradian^?1) and using discrimination distances from 10 cm to 50 cm. Threshold results indicated broadly equivalent motion preception capability in air and underwater, until low stimulus radiant intensity became limiting, when a more marked decline in perceptual ability underwater became apparent. The effect of changing discrimination distance was investigated in terms of the concomitant change in stimulus duration and angular displacement. The results are discussed with reference to the observed predatory behaviour of mink.     

The impact of American mink Mustela vison and European mink Mustela lutreola on water voles Arvicola terrestris in Belarus

In the U.K. the impact of introduced American mink Mustela vison , on water voles Arvicola terrestris , may be exacerbated by habitat loss and fragmentation. Pristine wetlands in Belarus, which American mink invaded in the early 1990s, provide a three-pronged opportunity to test this hypothesis. First, we examine the evidence that, even in the unmanaged wetlands of our Belarussian study site, American mink have reduced water vole populations. Second, we ask whether habitat size, type and isolation mitigate the impact of American mink predation. Thirdly, we explore whether water voles are at greater risk of predation from American than European mink because of their patterns of habitat use. Following the invasion of American mink, water voles were most abundant in small, still-water sites, far from river banks, while American mink were most active in large, running-water sites. Small mammal remains were found in a higher percentage of American than European mink scats, and of these, more were water vole in American mink scats. The occurrence of water voles in scats of both mink species declined after the American mink invaded and established. Our results provide at least circumstantial evidence that American mink limit water vole populations even in unmanaged wetland eco-systems, and that they have a greater impact than their European congener at least partly because they make greater use of isolated marshes. Although by no means providing complete protection, the configuration and dispersion of available habitat mitigated the impact of American mink on water voles. This raises the possibility that habitat restoration, especially through the establishment of isolated enclaves, could help reduce the effect of American mink in the U.K. These observations are of broader interest in the context of assessing the effect of multiple pressures on vulnerable species.     

Ecophysiological responses of two dominant grasses to altered temperature and precipitation regimes

Ecosystem responses to climate change will largely be driven by responses of the dominant species. However, if co-dominant species have traits that lead them to differential responses, then predicting how ecosystem structure and function will be altered is more challenging. We assessed differences in response to climate change factors for the two dominant C₄ grass species in tallgrass prairie, Andropogon gerardii and Sorghastrum nutans, by measuring changes in a suite of plant ecophysiological traits in response to experimentally elevated air temperatures and increased precipitation variability over two growing seasons. Maximum photosynthetic rates, stomatal conductance, water-use efficiency, chlorophyll fluorescence, and leaf water potential varied with leaf and canopy temperature as well as with volumetric soil water content (0–15 cm). Both species had similar responses to imposed changes in temperature and water availability, but when differences occurred, responses by A. gerardii were more closely linked with changes in air temperature whereas S. nutans was more sensitive to changes in water availability. Moreover, S. nutans was more responsive overall than A. gerardii to climate alterations. These results indicate both grass species are responsive to forecast changes in temperature and precipitation, but their differential sensitivity to temperature and water availability suggest that future population and community structure may vary based on the magnitude and scope of an altered climate.     

The influence of American mink odour on the spatial distribution and behaviour of water voles

The perception and assessment of predation risk often cause changes in the activities of animals and induce behavioural responses that may in turn affect their movements and distribution. To simulate high predation risk in a midfield pond riparian habitat, we used fresh faeces from ranch American mink Neovison vison and recorded behavioural responses of water voles Arvicola amphibius. In areas where mink odour was deployed, the numbers of captured vole individuals and their trappability were significantly lower than in control areas. Several voles migrated from the zones with deployed mink faeces to the areas without faeces, thus proving that increased predation risk affects the distribution of individuals in a population. The response to mink odour was much more pronounced in females than in males; in areas with deployed mink faeces, not a single female was trapped. We conclude that although American mink is a non‐native, invasive predator, water voles respond to mink odour by reducing their activity and/or by avoiding places with higher predation risk.     

Movements of radio-tracked American mink (<Emphasis Type="Italic">Neovison vison</Emphasis>) in extensive wetland in the UK,and the implications for threatened prey species such as the water vole (<Emphasis Type="Italic">Arvicola amphibius</Emphasis>)

In a number of countries around the world, introduced American mink are acknowledged to have had a negative effect on a number of native species, many of which are of particular conservation concern. In the UK, there has been an observed correlation between the spread of mink and the decline of the, once common and widespread, water vole. Large wetlands, such as extensive reed bed, appear to mitigate the impact of mink predation on water voles and some bird species. The present study was carried out to test the hypothesis that the observed refuge effect of reed beds arises from the way mink forage in this type of wetland. The results suggest that the interior of reed bed offers a spatial refuge for water voles, and other species, from predation by mink, because more than 60% of mink foraging activity occurred within 10 m of a main (>10 m wide) channel. Where mink ventured within the reed bed itself, they associated closely with scrub. The implication is that easily navigable channels and areas of scrub probably compromise the refuge effect of reed beds. This can be used to inform management recommendations at these sites.     

The impact of the American mink (Neovison vison) on native vertebrates in mountainous streams in Central Spain

The American mink (Neovison vison) is responsible for the widespread decline of its prey species in the regions where it is an invasive species. The current expansion of the mink in the Iberian Peninsula has aroused concern among conservationists about its negative impact on the rich native fauna. However, evidence for this is still scarce, although there are several studies establishing a direct causal relationship between declining native species and the presence of the American mink. Thus, it is important to further investigate the responses of native species to the American mink in several habitats and locations to enhance our knowledge about the patterns of the effect of the mink in Spain, as well as to inform conservation actions. A field study of the impact of the American mink on a mountainous vertebrate community in central Spain is presented. We studied six species: two fish, one amphibian, one bird, and two mammals. The general results showed a species-specific sensitivity to mink presence, with the Mediterranean water shrew (Neomys anomalus) and the southern water vole (Arvicola sapidus) being the most affected because their ranges were significantly decreased after the introduction of the mink. Regarding the other species, neither their abundance nor range was apparently affected by the American mink. The predatory behavior of the mink and interactions with other carnivores could account for these results. These data aid in shedding light about the current impact of the mink on invaded areas of the Iberian Peninsula and highlight the variability of its effects, as well as the urgent need to establish a general program of control of the mink to avoid negative effects upon native prey communities. Furthermore, given the different responses of native species, we propose that measures to protect native species should be based on species-specific goals and attributes.     

油松人工林SPAC水势梯度时空变化规律及其对边材液流传输的影响

 利用热扩散式边材液流茎流探针（TDP）和微型自动气象站组成的测定系统于2001年4月在北京林业大学妙峰山教学实验林场（39°54′N,116°28′E）对低山油松（Pinus tabulaeformis）人工林土壤-植物-大气体（SPAC）界面水势梯度及油松木质部边材液流传输速率的时空变化规律及其相关因子进行了连续测定。土壤水势随深度下降逐渐升高,日周期波动幅度减小,灌水后上层土壤水势迅速提高,但随着水分扩散和林地持续蒸散,土壤湿度迅速下降并逐渐与对照趋同;叶片水势连日逐渐降低,灌水后水势较对照有一定程度提高;林冠不同层次叶片水势在日周期内不同时间差异显著,但同一层次之间差异不明显;油松人工林土壤、叶片、大气水势梯度比约为1∶5∶30,灌水后SPAC相临界面水势差增大,水势梯度提高至1∶15∶90。大气水分饱和亏缺与土壤水势和叶片水势、以及土壤水势与叶片水势之间均有极显著相关性。干旱春季灌溉对油松木质部边材液流时空波动产生很大影响,灌水后连日树干上位边材液流峰值出现时间推迟1 h,连日平均液流速率提高48.59%,连日平均最大液流速率提高25.12%。木质部边材液流速率日变化和连日变化与SPAC水势和气象因子如空气相对湿度、空气温度、太阳辐射强度密切相关。与对照相比,灌水后边材液流速率与SPAC各介质水势和界面水势差的相关性下降。     

Risk induced by a native top predator reduces alien mink movements

1. Nonlethal predation effects may have stronger impacts on prey populations than direct predation impacts, and this should also apply to intraguild predation. The consequences of such interactions become especially important if invasive, and potentially destructive alien predators act as intraguild prey. 2. We studied the predation-risk impacts of a re-colonizing native top predator, Haliaeetus albicilla (white-tailed sea eagle), on the movements of Mustela vison (American mink), an alien predator in Europe. We radiocollared 20 mink in two study areas in the outer archipelago of the Baltic Sea, South-west Finland, during 2004 and 2005. In the archipelago, mink home ranges incorporate many islands, and mink are most predisposed to eagle predation while swimming between islands. Observed swimming distances of mink were compared to distances expected at random, and deviations from random swimming were explained by mink distance from nearest eagle nest, number of eagle observations near mink location, and mink home-range size. 3. Mink reduced their swimming distances with increasing sea eagle predation risk: for females, the reduction was 10% for an increase of 10 eagle observations, and 5% for each kilometre towards an eagle nest. Conclusions for males were restricted by their small sample size. 4. Our results suggest that female mink modify their behaviour according to eagle predation risk, which may reduce their population growth and have long-term cascading effects on lower trophic levels including bird, mammal and amphibian populations in the archipelago. Ecosystem restoration by bringing back the top predators may be one way of mitigating alien predator effects on native biota.     

Responses of mink to auditory stimuli: Prerequisites for applying the ‘cognitive bias’ approach

The aim of the study was to determine and validate prerequisites for applying a cognitive (judgement) bias approach to assessing welfare in farmed mink (Neovison vison). We investigated discrimination ability and associative learning ability using auditory cues. The mink (n = 15 females) were divided into two groups (High, n = 8; Low, n = 7, representing the frequency of the tone they were habituated to, 18 and 2 kHz respectively) and were tested using a habituation–dishabituation procedure in experiment 1. In experiment 2 one auditory stimulus was followed by an inter-trial-interval (safe/neutral situation), whereas another auditory stimulus was followed by an aversive stimulus (air blow) before the inter-trial-interval (danger situation). We observed behaviour including latencies to show a response during both experiments. The High mink showed significant habituation in experiment 1 but the Low mink only showed habituation in experiment 2. Regardless of the frequency used (2 and 18 kHz), cues predicting the danger situation initially elicited slower responses compared to those predicting the safe situation but quickly became faster. Using auditory cues as discrimination stimuli for female farmed mink in a judgement bias approach would thus appear to be feasible. However several specific issues are to be considered in order to successfully adapt a cognitive bias approach to mink, and these are discussed.     

Meteorology and hydrography of a shoaling reef flat on the Caribbean coast of Panama

We describe the seasonal patterns and frequency distributions of meteorological and hydrographic conditions on a windward, shoaling reef flat at Punta Galeta, Panama (9° 24 N lat.), between 1974 and 1985. The factors monitored were wind speed, wind direction, air temperature, rainfall, solar radiation, water level, water temperature, and salinity. All conditions showed strong seasonal periodicity; however, the timing, duration, and amplitude of the seasonal fluctuations differed among years. The greatest variation occurred in 1981 and 1982, leading into an El Niño event. Emergence of the reef flat and extremes of water temperature were the most apparent physiological stresses; both were dependent on mean water levels. The seasonal pattern of emergence time was inversely related to mean water level. Extreme water temperatures only occurred during low water tevels, ranging between 22° to >37°C in depths <15 cm, but staying between 25°C and 30.9°C in depths <35 cm. Water temperatures averaged 1.5°C higher than air temperatures. Although rainfall was 200 to 400 cm year^-1, salinity remained between 24 and 36 ppt, with more than 98% of the records 30 ppt. The relationship of water temperature to depth is consistent with the hypothesis that the physical environment becomes more stressful when a reef reaches sea level and forms a shoaling platform. Mailing address: Smithsonian Tropical Research Institute, APO Miami, Florida 34002-0011, USA     

Effects of early weaning and housing conditions on the development of stereotypies in farmed mink

Female mink pups were weaned at 6, 8 or 10 weeks of age and subjected to two different housing conditions. They were either kept together with a single male sibling in traditional mink cages (30x45x90 cm) or housed socially with all litter-mates in an alternative system consisting of three adjoining traditional cages (90x45x90 cm). All cages were supplied with nest boxes. At 5 months of age, the siblings were removed leaving the females socially isolated in the two different cage systems. Females' stereotypies were quantified by repeated scanning observations under the social housing conditions immediately before removal of the siblings, and again at the age of 7 and 9 months, when the animals had stayed solitary in the two systems for 2 and 4 months. Solitary females showed significantly more stereotypies than females under social housing conditions in both cage systems. Stereotypies were more frequent in the smaller traditional cages. Stereotypies declined from 7 to 9 months of age among solitary animals in traditional cages but not in alternative cages. Early-weaned solitary females in traditional cages showed more stereotypies than later-weaned animals, but only when measured at the age of 7 months. It is suggested that early weaning, individual housing and small cages promote the development of stereotypies in farmed mink. The influence of early weaning on stereotypies seems to decline with age, while effects related to individual housing and small cages appear to be more persistent.     

油蒿灌丛群落浅层土壤水分对不同降雨格局的响应

以库布齐沙漠东缘典型分布的油蒿灌丛为对象,使用微气象观测系统连续监测2016—2018年生长季降雨及多层次土壤含水量(0～10、10～30、30～50 cm),研究不同降雨格局下荒漠土壤水分的时空动态变化,分析降雨事件对土壤水分的补给作用和水分入渗特征。结果表明: 油蒿灌丛浅层土壤含水量在降雨脉动下产生明显的季节和垂直变化,雨量和雨前土壤含水量是影响土壤水分补给和入渗的主控因素。0～10 cm土层土壤对降雨反馈迅速,>3.8 mm降雨对该层产生补给作用;10～30 cm土层土壤对降雨反馈稍显迟滞,需8.6 mm以上降雨才能产生有效补给;30～50 cm土层土壤对降雨反馈更加滞后,降雨量超过11.8 mm后才能达到该补给深度。水分入渗速率随雨量增大而升高,随土层加深而减弱,入渗深度与雨量和雨前土壤含水量均呈显著正相关。研究期间,降雨事件以<10 mm降雨为主,占总降雨次数的78.4%,降雨对土壤的补给主要作用于30 cm以内土层,对深层土壤的补给十分有限,不利于深根性植物生长,降雨格局直接影响和改变了研究区植物群落的构成、分布和演替。     

Temporal distribution of transmissible mink encephalopathy virus in mink inoculated subcutaneously.

Information was sought on the temporal distribution of transmissible mink encephalopathy virus in royal pastel mink inoculated subcutaneously with 10(3.0) 50% intracerebral lethal doses of the Idaho strain. As determined by intracerebral assay in mink, extremely little replication of the virus occurred during the preclinical stage of infection. It seemed largely limited to lymph nodes draining the site of inoculation. Virus first appeared in the central nervous system (CNS) at 20 weeks, when all mink were still clinically normal. Early spongiform degeneration, limited to the posterior sigmoid gyrus of the frontal cortex, was first found at 28 weeks, or a few weeks before onset of clinical disease in most of the mink. Once virus reached the CNS, where greater concentrations occurred than elsewhere, it appeared in many extraneural sites (spleen, liver, kidney, intestine, mesenteric lymph node, and submandibular salivary gland). These seemingly anomalous findings, especially the limited extraneural replication of virus as a prelude to infection of the CNS, suggest that mink are not natural hosts of the virus. The results of this study support the generally held view that transmissible mink encephalopathy arises from chance or inadvertent infection of ranch mink with an exogenous virus, most likely feed-borne wild scrapie virus.     

Do alien North American mink compete for resources with native South American river otter in Argentinean Patagonia?

American mink Mustela vison , originally bred in fur farms, have become established in areas occupied by native endangered Southern river otter Lontra provocax , in Patagonia. In accordance with European experience, this biological invasion in South America raises questions about the interaction between invasive mink and native otter, from the viewpoints of both community assembly and conservation. We set out (1) to find which aspects of habitat structure were related to the distribution of signs of both this invasive species and Southern river otter Lontra provocax , in Argentinean Patagonia and their most common prey and (2) to test general predictions of niche partitioning between these two species. Based on surveys of 447 of 600 m transects for otter and mink scats/footprints along the waterside of lakes and rivers in the Andean Patagonian region, we compared diet composition (from scat analysis) and micro-habitat preferences (from field signs) of the two species. Otters were more specialist than mink in habitat use and diet. Mink used different habitats in other river basins where otters were absent. Where they occurred together in the basin of the Limay River, the distributions of their signs were similar, and mink diet was more similar to that of otters. There was no detectable difference in otter diet before and after mink arrival in the Limay basin. Contrary to the prediction of niche partitioning, and to the findings of European studies, resource use by mink was more similar to that of otters where the species occurred sympatrically than where they were allopatric.     

Concurrent changes in plant weight and soil water regimes in herbaceous communities in Central Australia

Two studies of arid zone plant communities are described. In the first, the perennial grass Eragrostis eriopoda was sampled over 8 months for dry weight and water stress of tops, and water content and tension of soil to a depth of 150 cm. In the second, lasting 2 years, pure Eragrostis and pure Aristida con-torta (annual) communities were sampled for dry weight of tops and roots and soil water content. Plots of naturally occurring mixtures of Eragrostis and Aristida were also studied. During periods of prolonged high soil water content, perennial communities greatly out-yielded annuals (1200 and 260gm^-2 respectively). During prolonged droughts all communities yielded less than 100 gm^-2. Perennial root systems were larger than for annuals. The weight of annual roots varied little with season as distinct from perennials which varied greatly. Maximum weight of annual roots occurred in the top 10 cm of soil; the zone of maximum rooting by perennials was 10–30 cm. Water loss from annual, perennial and bare plots was similar and extended throughout the measured profile. Two gradients of soil water tension of opposite signs developed during prolonged drought. The greater was due to evapo-transpiration and the lesser developed below the zone of recharge. On average. Eragrostis grew 4.6 times faster than the annuals which enjoyed a marginally more favourable water regime. In a mixture which had received one heavy simulated grazing the presence of annuals reduced the growth of Eragrostis by 68%, suggesting that the invasion of Eragrostis by annuals would seriously reduce productivity.     

RESPONSES OF LEAF SPECTRAL REFLECTANCE TO PLANT STRESS

Leaf spectral reflectances were measured to determine whether leaf reflectance responses to plant stress may differ according to the agent of stress and species. As a result of decreased absorption by pigments, reflectance at visible wavelengths increased consistently in stressed leaves for eight stress agents and among six vascular plant species. Visible reflectance was most sensitive to stress in the 535–640-nm and 685–700-nm wavelength ranges. A sensitivity minimum occurred consistently near 670 nm. Infrared reflectance was comparatively unresponsive to stress, but increased at 1,400–2,500 nm with severe leaf dehydration and the accompanying decreased absorption by water. Thus, visible rather than infrared reflectance was the most reliable indicator of plant stress. Visible reflectance responses to stress were spectrally similar among agents of stress and species.     

Some Factors Affecting Survival of Desiccation by Infective Juveniles of Orrina phyllobia

The survival of desiccation by J4 Orrina phyllobia was examined at controlled relative humidities. When nematodes were transferred from water to air at 10% relative humidity (rh), 80% died within 30 minutes. When nematodes were transferred from water to air with rh at 70% or greater for ca. 15 minutes prior to being transferred to 10% rh, more than 90% of them survived desiccation. This phenomenon is referred to as preconditioning and occurred at much faster rates (2-30 minutes) than has been observed for other nematode species (24 hours). Differences in preconditioning rates may be due to technique-dependent variations in boundary layer resistance around nematodes during desiccation.     

THE COMPARISON OF YELLOW CYLINDRICAL, FLAT AND WATER TRAPS, AND OF JOHNSON SUCTION TRAPS, FOR SAMPLING APHIDS

Different traps were compared to find the type most suitable for studying aphid vectors of plant viruses quantitatively.
A Moericke water trap caught more aphids than a flat sticky trap of equal area. A flat sticky trap (930 sq. cm.) caught half as many aphids as a cylindrical trap (945 sq. cm.), which caught about one-third as many as a water trap (1200 sq. cm.) or a Johnson suction trap (9 in. fan) when operated at between 2 and 3 ft. over bare soil.
Yellow traps caught proportionally more Tuberculoides annulatus , and in summer more Capitophorus species than a suction trap, but significantly fewer Anoecia corni, Sitobium spp. and Pemphigus bursarius. Traps with a level surface caught proportionally more Brevicoryne brassicae, Aphis fabae and Myzus persicae , but fewer Anoecia corni and Drepanosiphum plantanoides than vertical cylindical traps. Attraction by colour influences the catch on horizontal traps more than on cylindrical traps because there is less impaction by the wind.
Only suction traps indicate the number of aphids per unit volume of air and are non-selective, but they are expensive and require an electric power supply. Water traps effectively catch those aphids that are attracted to yellow, but they require frequent attention. Sticky traps catch fewer aphids than either suction or water traps, but they can be left unattended for about 2 weeks. Flat sticky traps catch aphids likely to land on a crop, and cylindrical traps show when aphids are in the air, but not if those aphids are able or wanting to land. For routine work cylindrical sticky traps have other advantages; they are cheap and do not require skilled handling, and their catches of alate Myzus persicae have been correlated with the spread of some plant viruses.     

Evaporative water loss, corporal temperature and the distribution of sympatric fiddler crabs (Uca) from south Texas

Desiccation and thermal stress are among the primary factors limiting terrestriality in crustaceans. Water loss was estimated as weight change in five sympatric species of Uca from south Texas for periods up to 7 hr in dry air. Simultaneously, corporal temperature was measured with a thermocouple placed under the carapace. To estimate integumental permeability to water, 115 mm2 portions of dorsal carapace were glued to U-shaped tubes containing a crab Ringer's solution. These were exposed to dry air and water permeability was estimated from weight change. In whole-animal studies, most rapid weight loss occurred in the first 5 min of exposure to dry air as the body temperature fell below ambient (25 degrees C) in all species. The three most terrestrial species exhibited significant survival over more aquatic congeners after prolonged desiccation. The greatest rate of water loss was observed in Uca subcylindrica which lost 22.9+/-3.0% body weight. Uca panacea and Uca spinicarpa lost 14.1+/-1.6% and 18.5+/-1.8%, respectively. Based on blood osmolarity changes, Uca longisignalis and Uca rapax were more resistant to water loss than Uca subcylindrica under these conditions. Water loss from sections of the dorsal carapace were highest in Uca spinicarpa (10.4 mg/hr/cm2) and Uca longisignalis (8.9 mg/ hr/cm2). Uca subcylindrica and Uca panacea were intermediate (4.5 and 4.2 mg/hr/cm2) while Uca rapax expressed the lowest value (2.9 mg/hr/cm2). These observations support the notion that water loss can effectively lower body temperature in fiddler crabs. However, an inverse relationship between terrestriality and integumental permeability was not evident in these sympatric congeners. Ultimately a balance between physiological and behavioral mechanisms must be achieved for adaptation to the semi-arid habitats in south Texas.