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1.
The records of one pack of Otter Hounds hunting in southwest England are examined for the period 1907 to 1971 as well as the records of all packs active in Britain between 1950 and 1976. The hunting success per unit effort varies from year to year depending on changes in hunting conditions but longer term changes can also be identified. The hunting success of the Culmstock Otter Hounds (hunting in parts of south-west England) increased steadily from 1907 to 1956 but in most of England and south Wales the success rate of the hunts declined rapidly after 1957. There was also a decline in success in northern England and southern Scotland but to a lesser extent, while in north Wales and Eire, there is no evidence for a decline.
These changes are considered to reflect changes in otter populations but the extent of the decline in hunting success (to between 37% and 55% of previous levels in the southern hunts) is probably less than the actual decline in otter numbers. There are no signs of a recovery in the population but indications of a continuing decline up to 1976.
The reason for the increasing population in the first half of the century in south-west England is probably the decrease in persecution since the nineteenth century. A variety of causes for the crash in the late 1950s are considered and the factor most likely to be responsible is the introduction of the dieldrin group of insecticides in 1956. Use of these compounds has been increasingly restricted since 1963 and the possible reasons for the failufe of the otter population to recover are listed but no firm conclusions can be drawn as yet.  相似文献   

2.
This paper considers shell-shape variation in samples of the dog-whelk/dog-winkle, ucella lapillus , from the southern half of its North American range, between 41 and 46N, and compares it with the pattern seen in Europe. At the extreme southern limit of its American range, to the south of Cape Cod, the species exhibits features to be expected in an animal close to an environmental limit. It is generally rare and has a patchy distribution. There is little variation in the shell: almost all adult individuals have rather large, thick, white, elongated shells. This contrasts sharply with the situation in Portugal, at the southern limit in Europe, where the animals have small thin, coloured shells of intermediate shape.
Away from the marginal situation, north of Nahant (42CN) in America, the species shows much the same range of variability in shell size, shape and colour on both sides of the Atlantic. Most populations appear to show the same pattern of shape variation in asociation with the exposure of their habitat to wave action. Animals from exposed sites tend to have shorter, squatter shells than their compatriots in shelter. However, in America as in some parts of Europe, there are occasional enclaves which do not fit the usual pattern. It is interesting to note that the form normally associated with extremely exposed shores from Brittany to Faroe in Europe is found in Atlantic Canada but is apparently absent from southern populations in both the U.S.A and the Iberian Peninsula.  相似文献   

3.
Isolation of Mediterranean species in the southern European peninsulas during the cold glacial phases often resulted in differentiation of several genetic lineages confined to the respective peninsulas. However, whilst there is good genetic evidence for multiple refugia in Iberia, there are only limited data available for the Balkans. Therefore, we wish to examine the hypothesis of a strong genetic structuring within southeastern Europe for the existence of multiple Balkan differentiation centres and/or several leading edges. As a model we use the marbled white butterfly, Melanargia galathea. We studied 18 allozyme loci of 564 individuals from 16 populations distributed over a large part of southeastern Europe. The single populations showed moderately high genetic diversity and no northward decline of genetic diversity was detected. The overall genetic differentiation between populations was considerable (F(ST) 7.0%). Cluster analysis discriminated three genetic groups: (i) a western flank in the former Yugoslavia, parts of eastern Austria and Hungary; (ii) an eastern flank with populations from Bulgaria and Romania (south of the southern Carpathians and eastern Carpathians); and (iii) the eastern Carpathian Basin. Hierarchical variance analysis distributed 53% of the variance among populations between these three groups. One sample from the Greek-Bulgarian border clustered within the eastern flank, but showed some tendency towards the eastern Carpathian Basin populations. Two populations from Carinthia clustered together with the eastern Carpathian Basin ones and a population from Styria showed an intermediate genetic composition between the three groups. Most probably, the eastern and the western flank groups are due to postglacial range expansion from the northeastern and the northwestern edges of the glacial differentiation centre (so-called leading edges). The eastern Carpathian Basin group may have resulted from postglacial expansion from northern Greece through valley systems of the central Balkan peninsula, maybe even expanding westwards north of the Balkan mountains reaching some parts of eastern Austria (e.g. Carinthia). Therefore, the Balkanic refugium of M. galathea may or may not have been continuous along the coastal areas of the Mediterranean, but must have been strongly genetically structured.  相似文献   

4.
M. H. Wise    I. J. Linn    C. R. Kennedy 《Journal of Zoology》1981,195(2):181-213
The feeding habits and prey selectivity of Mink Mustela vison and otters Lutra lutra were compared in two localities in Devon: a eutrophic lake and a moorland river, in which both species occurred and had access to the same prey populations. The effects of prey availability on the predators' diets were assessed by comparing prey consumed, as revealed by scat analysis, with estimates of prey abundance and size range. Otters specialized in fish at all times of year but showed seasonal variation in species taken. Selection for slow-moving fish and seasonal changes in behaviour of some fish species were the probable causes of this variation. Otters diversified more into non-fish food in summer, when fish availability was reduced. The main alternative prey in the lacustrine habitat was waterfowl, but in the riverine habitat, rabbits. Mink were more generalized carnivores, taking a variety of fish, waterside and terrestrial prey in all seasons. These three prey categories were taken to an almost equal extent in the lake but terrestrial prey dominated in the riverine habitat. Fish were taken most frequently in winter and birds and mammals in summer. Neither predator showed selection in respect of prey size. In each area, about one third of the otter and Mink diets was common to both species. Fish was the principal group of the shared component, and dietary overlap in respect of them was greatest in autumn and winter. In view of the dietary preferences of each predator, the existence of alternative prey items and limited degree of dietary overlap, it is considered unlikely that the two species competed for food to any extent. Other factors must therefore be responsible for the spread of feral Mink and the decline in otter populations in many parts of Britain.  相似文献   

5.
Aim  The aim of this study is to analyse the genetic population structure of Meum athamanticum Jacq. in order to explore the alternative hypotheses (1) that the central and northern highland populations are the result of post-glacial recolonization from southern refugia, and the disjunct distribution of M. athamanticum can be explained by modern ecological conditions, or (2) that extant populations north of the Alps and Pyrenees persisted in situ during glacial periods.
Location  Europe.
Methods  Variation of amplified fragment length polymorphisms (AFLPs) was analysed for 23 populations from the entire range of the species. We used band-based approaches and methods based on allele frequencies to measure genetic diversity and to identify population structure.
Results  Our analyses reveal a north–south differentiation within M. athamanticum . High levels of genetic diversity, as well as private fragments, are found in populations both north and south of the Alps. Differentiation among populations is lower in the northern than in the southern population group, and significant isolation-by-distance is found only in the latter group.
Main conclusions  Our results indicate that M. athamanticum survived the last ice age in multiple refugia throughout its contemporary range and did not expand into areas north of the Alps from southern refugia. We found evidence that regional-scale migration in northern, formerly periglacial, parts of the species range has resulted in the intermingling of populations. In contrast, southern populations are characterized by long-term isolation. The south-west Alps represent an area where immigration and mixing of populations from northern and southern refugia appears to have taken place.  相似文献   

6.
The Eurasian otter, Lutra lutra, has a Palaearctic distribution and has suffered a severe decline throughout Europe during the last century. Previous studies in this and other mustelids have shown reduced levels of variability in mitochondrial DNA, although otter phylogeographic studies were restricted to central-western Europe. In this work we have sequenced 361 bp of the mtDNA control region in 73 individuals from eight countries and added our results to eight sequences available from GenBank and the literature. The range of distribution has been expanded in relation to previous works north towards Scandinavia, east to Russia and Belarus, and south to the Iberian Peninsula. We found a single dominant haplotype in 91.78% of the samples, and six more haplotypes deviating a maximum of two mutations from the dominant haplotype restricted to a single country. Variability was extremely low in western Europe but higher in eastern countries. This, together with the lack of phylogeographical structuring, supports the postglacial recolonization of Europe from a single refugium. The Eurasian otter mtDNA control region has a 220-bp variable minisatellite in Domain III that we sequenced in 29 otters. We found a total of 19 minisatellite haplotypes, but they showed no phylogenetic information.  相似文献   

7.
The agricultural scene has changed over the past decades, resulting in a declining population trend in many species. It is therefore important to determine the factors that the individual species depend on in order to understand their decline. The landscape changes have also resulted in habitat fragmentation, turning once continuous populations into metapopulations. It is thus increasingly important to estimate both the number of individuals it takes to create a genetically viable population and the population trend. Here, population viability analysis and habitat suitability modeling were used to estimate population viability and future prospects across Europe of the Little Owl Athene noctua, a widespread species associated with agricultural landscapes. The results show a high risk of population declines over the coming 100 years, especially toward the north of Europe, whereas populations toward the southeastern part of Europe have a greater probability of persistence. In order to be considered genetically viable, individual populations must count 1,000–30,000 individuals. As Little Owl populations of several countries count <30,000, and many isolated populations in northern Europe count <1,000 individuals, management actions resulting in exchange of individuals between populations or even countries are probably necessary to prevent losing <1% genetic diversity over a 100‐year period. At a continental scale, a habitat suitability analysis suggested Little Owl to be affected positively by increasing temperatures and urban areas, whereas an increased tree cover, an increasing annual rainfall, grassland, and sparsely vegetated areas affect the presence of the owl negatively. However, the low predictive power of the habitat suitability model suggests that habitat suitability might be better explained at a smaller scale.  相似文献   

8.
The House Sparrow Passer domesticus is traditionally associated with human habitation. However, the species has undergone dramatic declines in many urban areas in north-western Europe. There are many theories as to why this decline has occurred, but the lack of data on House Sparrow numbers prior to their decline has hampered efforts to investigate these theories in detail. This review summarises the demographic changes in urban House Sparrow populations since the 1970s, and considers evidence that the current distribution of House Sparrows may reflect changes in urban habitats caused by socioeconomic change. Evidence is mounting that, within urban landscapes, House Sparrows appear to be more prevalent in areas with a relatively low human socioeconomic status. Here, we present evidence to suggest that House Sparrows may have disappeared predominantly from more affluent areas, and that these areas are more likely to have undergone changes to habitat structure. We also show how these changes in habitat could influence House Sparrow populations via impacts upon nesting success, foraging and predation risk.  相似文献   

9.
The importance of the marine environment to Eurasian otters is currently poorly understood. Wales is one of the few countries where coastal activity has been recorded and an increase in marine otter sightings could indicate remarkable developments within Welsh populations. The trophic niche of coastal otter populations around Pembrokeshire was investigated over a 12-month period. Marine activity was more widespread than previously thought and marine prey formed the largest component of otter diet, although, otters also consumed freshwater and terrestrial prey throughout the year. Otter diet was very diverse compared to other European coastal populations and a spring contraction in trophic niche width coincided with the estimated timing of breeding activity. Seasonal variation in prey composition was predominantly due to differences in the consumption of alternate prey types. In areas where wetlands are fragmented and populations of freshwater fish are declining, the marine environment may become an increasingly important habitat for otters. It is necessary to define the historical importance of coastal populations to otter conservation. Coastal areas are often subject to pressure from human activities, so the impact of disturbance needs to be assessed. Importantly, there is no verified otter survey method for coastal areas, so the use of marine habitat is likely to be underestimated.  相似文献   

10.
水獭是水生生态系统重要的指示种和旗舰种, 由于强烈的人为干扰, 中国的水獭种群数量大幅下降, 部分区域已局部灭绝。然而目前国内对水獭的调查和研究非常有限, 本底不清的状况已经严重影响到水獭的野外保育工作。本文以东北地区的欧亚水獭指名亚种(Lutra lutra lutra)为研究对象, 基于2016-2020年的调查数据, 使用组合建模的方法评估了水獭的潜在分布区; 利用地理信息系统和系统保护规划软件分析了水獭的保护优先区并计算了各省级行政区内水獭潜在分布区和保护优先区面临的人类压力; 结合国家级自然保护区的空间布局分析了水獭的保护现状, 并以内蒙古森工集团、大兴安岭林业集团、伊春森工集团三大国有林区为例分析了重点国有林区在水獭保护中的作用。结果表明: (1)水獭潜在分布区和保护优先区面积分别为104,515.04 km2和45,448.99 km2, 其中大兴安岭的水獭保护优先区集中连片, 并与小兴安岭的保护优先区相连, 栖息地之间没有明显地理隔离, 是维持东北地区水獭种群稳定的重中之重; (2)水獭面临的人类压力大小依次为: 辽宁 > 吉林 > 黑龙江 > 内蒙古; (3)研究区内110个国家级自然保护区中有63个包含水獭潜在分布区, 覆盖面积为12,168.93 km2, 仅占水獭潜在分布区面积的11.64%, 其中32个国家级自然保护区包含水獭保护优先区, 占水獭保护优先区面积的10.88%; (4)三大国有林区涵盖了71.18%的水獭潜在分布区和79.26%的保护优先区(面积分别为74,390.89 km2和36,022.22 km2)。由此可见, 尽管水獭潜在分布区中国家级自然保护区占比较低, 但是在天然林全面禁伐的背景下, 重点国有林区可能在未来东北地区的生物多样性保护中发挥更大作用, 因此我们建议将重点国有林区中具有重要保护价值的区域逐步纳入以国家公园为主体的自然保护地体系中, 以实现生物多样性的系统性和完整性保护。最后, 本文结合研究结果和实地调研提出以下保护建议: (1)加强对河流污染物的管理; (2)控制渔民捕鱼强度; (3)开展全面的水獭专项调查并建立长期的监测体系; (4)加大对水獭的科研投入; (5)加强宣传力度, 提升公众保护意识。  相似文献   

11.
艾怀森 《动物学研究》2006,27(4):427-432
根据高黎贡山地形和气候变化,将其分为南、中、北三段。通过查阅文献、访谈和野外调查,在该地区共记录到21种雉类。分布在海拔2500m以上的仅有9种,占45%;在海拔2500m以下的地域分布有雉类17种,占85%。北段有雉类13种,中段有11种,南段有12种。其中北、中、南段均有分布的仅有3种,北段和中段共有种为9种,中段和南段共有种为5种,北段和南段共有种也是5种。结果表明雉类多样性随海拔升高而降低,北段高于南段。生境破坏与狩猎是该区雉类生存的主要威胁因子。加强管理,恢复和建立生境走廊,加强宣传教育和执法力度以及开展观鸟旅游,可使该区雉类得到更好的保护。  相似文献   

12.
Human‐caused habitat destruction and modification constitute one of the largest threats to population persistence and biodiversity, and are also suspected to be the major cause behind the global decline of amphibian populations. We assessed the potential role of agriculture‐related habitat fragmentation on population size and genetic variability in the common frog (Rana temporaria) by recording the occurrence, population density and genetic diversity in three geographically disparate regions in Sweden – each containing landscapes of high and low agricultural activity – and related these to landscape variables extracted from digital maps. We found a highly significant region‐by‐landscape interaction in occurrence, population density and genetic diversity revealing a reversed response to agriculture from south to north: while the effects of agriculture on R. temporaria populations were negative in the south, there were no effects in the central region, whereas positive effects were observed in the north. Spatial autocorrelation analyses of genetic data revealed that populations in high agricultural activity areas were more isolated than populations in low activity areas both in the southern and central regions of Sweden. Landscape diversity showed a strong positive correlation with both density and occurrence of frogs in Sweden as a whole, as well as in the southern region. Also, negative effects of roads and positive effects of ditches on genetic diversity were found in the south. Overall, these results suggest clear but regionally opposite effects of habitat structure on the population size and genetic diversity of amphibian populations. This means that the management strategy aiming to maximize the size and genetic diversity of local common frog populations, and perhaps also those of other amphibian populations, should account for regional differences in existing land‐use patterns.  相似文献   

13.
张璐  范朋飞 《兽类学报》2020,40(1):71-80
顶级捕食者在生态系统中发挥着重要作用,受到研究者们的广泛关注。水獭作为很多淡水生态系统的顶级捕食者,在我国却长期处于被忽视的状态。我国分布有3种水獭--欧亚水獭、亚洲小爪水獭和江獭,曾经遍布我国中东部和东北地区,包括珠江口地区。但在20世纪,3种水獭均经历了大规模的种群下降,甚至区域性灭绝。在全球13种水獭中,已有3种(海獭、北美水獭和欧亚水獭)通过种群复壮和重引入实现了种群重建,这为其它水獭物种的种群重建提供了重要参考和建议。同国内其它地区类似,珠江口地区的水獭种群在20世纪后期大量减少,目前只在少数几个地点还有确切的欧亚水獭分布记录,亚洲小爪水獭和江獭已无近期记录。在珠江口重建水獭种群具有重要的生态意义和社会价值。本文对重建珠江口水獭种群的相关问题进行了分析。  相似文献   

14.
Aim Over the past three decades, evidence has been growing that many Afro‐Palaearctic migratory bird populations have suffered sustained and severe declines. As causes of these declines exist across both the breeding and non‐breeding season, identifying potential drivers of population change is complex. In order to explore the roles of changes in regional and local environmental conditions on population change, we examine spatial and temporal variation in population trajectories of one of Europe’s most abundant Afro‐Palaearctic summer migrants, the willow warbler, Phylloscopus trochilus. Location Britain and Ireland. Methods We use national survey data from Britain and Ireland (BBS: BTO/RSPB/JNCC Breeding Bird Survey and CBS: BWI/NPWS/Heritage Council Countryside Breeding Survey) from 1994 to 2006 to model the spatial and temporal variation in willow warbler population trends. Results Across Britain and Ireland, population trends follow a gradient from sharp declines in the south and east of England to shallow declines and/or slight increases in parts of north and west England, across Scotland and Ireland. Decreasing the spatial scale of analysis reveals variation in both the rate and spatial extent of population change within central England and the majority of Scotland. The rates of population change also vary temporally; declines in the south of England are shallower now than at the start of the time series, whereas populations further north in Britain have undergone periods of increase and decline. Main conclusion These patterns suggest that regional‐scale drivers, such as changing climatic conditions, and local‐scale processes, such as habitat change, are interacting to produce spatially variable population trends. We discuss the potential mechanisms underlying these interactions and the challenges in addressing such changes at scales relevant to migratory species.  相似文献   

15.
The recent commentary by Woinarski (2014, Global Ecology and Biogeography, doi: 10.1111/geb.12165) disagreed with our conclusions on the correlates of decline in the marsupials of tropical Australia (Fisher et al., 2014, Global Ecology and Biogeography, 23 , 181–190). We compared traits of species that were associated with range decline in southern and northern Australia. We found that habitat structure, climate and body size were correlated with range decline. In the north, declines of marsupials were most severe in savanna with moderate rainfall. In the south, the ranges of species in open habitat with very low rainfall have declined most. Also, the association between range decline and body mass differed between north and south: this is the main concern of Woinarski, who further disagreed with our choice of the Tropic of Capricorn as a boundary between north and south, our omission of rodents, how to treat timing of extinctions, and our inference that cats are major drivers of decline. We address these concerns in this response.  相似文献   

16.
We describe the genetic structure of a freshwater insect species and interpret it in terms of present-day population dynamics and possible postglacial colonization history. The sampling regime represented a large area of the species range in northwest Europe, particularly focusing on Britain, a region relatively neglected in molecular population genetic studies. Plectrocnemia conspersa generally showed low levels of genetic variation across the sampled populations (Nei's D = 0.0138) and subdivision was unrelated to the pattern of the drainage network. However, the results do suggest that populations across the region are not at equilibrium and that British populations still show effects of the recolonization of the species following the last glacial maximum. Levels of genetic diversity were lower in Britain than in mainland Europe. Two-dimensional scaling showed genetic differentiation between major regions and the pattern of genetic diversity indicates a more recent origin of populations in the north and west of the area compared with the south and east. We argue that, despite the highly fragmented larval habitat, dispersal over tens of kilometres is frequent. Over longer distances, however, P. conspersa does still show evidence of founder effects and postglacial range expansion into Britain.  相似文献   

17.
The nonmarine mammal fauna of the Maghreb region of north‐west Africa is related to that from three potential source areas: the northern Palaearctic (Europe and south‐west Asia; here referred to as the European fauna), subsaharan Africa (the African fauna) and the arid Palaearctic (Sahara Desert: the desert fauna). On the basis of geographical distribution patterns, this fauna divisible into two groups: the bats, whose affinities are most closely related to southern Europe and south‐west Asia, and nonflying species, most closely related to subsaharan Africa but with an appreciable northern Palaearctic element. These affinities are even more pronounced if desert fauna are removed from the analysis. The nonflying European fauna probably colonized via south‐west Asia and north Africa, rather than direct from western Europe. The results demonstrate that terrestrial habitat barriers are less of an impediment to dispersal, for all mammals except bats, than even narrow stretches of water. The fauna of the Maghreb may be undergoing faunal relaxation, following immigration from tropical Africa and south‐west Asia during mesic phases in the Late Pleistocene and early Holocene.  相似文献   

18.
Both the conversion of natural habitats to farmland and efforts at increasing the yield of existing crops contribute to a decline in biodiversity. As a consequence of land conversion, specialised species are restricted to remnants of original habitat patches, which are frequently isolated. This may lead to a genetic differentiation of the subpopulations. We used seven microsatellite markers to examine the genetic population structure of the grass snake, Natrix natrix (Linnaeus, 1758), sampled in remnants of pristine habitat embedded in an intensively used agricultural landscape in north‐western Switzerland. The study area, a former wetland, has been drained and gradually converted into an agricultural plain in the last century, reducing the pristine habitat to approximately 1% of the entire area. The grass snake feeds almost entirely on amphibians, and is therefore associated with wetlands. In Central Europe, the species shows severe decline, most probably as a result of wetland drainage and decrease of amphibian populations. We found no genetically distinct grass snake populations in the study area covering 90 km2. This implies that there is an exchange of individuals between small remnants of original habitat. Thus, gene flow may prevent any genetic differentiation of subpopulations distributed over a relatively large area. Our results show that a specialized snake species can persist in an intensively used agricultural landscape, provided that suitable habitat patches are interconnected. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 51–58.  相似文献   

19.
The little owl Athene noctua is a widespread species in Europe. This mainly sedentary owl experienced reduction in population sizes in some areas due to habitat loss and modification of the landscape. To assess the genetic structure of the populations of western and central Europe, we analysed 333 specimens from 15 geographical areas at 13 microsatellite loci. Statistical analyses and Bayesian clustering procedures detected two major genetically distinct clusters, the first distributed from Portugal to the Czech Republic and the second from the Balkans to Italy. The second cluster was further split into three groups, located in Italy, Sardinia and the Balkans. These groups match four previously‐described mtDNA haplogroups, and probably originated from the isolation of little owl populations in Sardinia and in three glacial refugia (Iberia, south Italy and Balkans) during the ice ages. High genetic admixture was recorded in central and northern Europe, probably as a consequence of the expansion from the refugia during interglacial. The main colonization route originated from the Iberian Peninsula towards central and northern Europe. Contact zones with colonization events from Italy and the Balkans were detected respectively in northern Italy and central Europe. Genetic indices show the existence of moderate levels of genetic variability throughout Europe, although evidence of recent evolutionary bottlenecks was found in some populations. Estimation of migration rates and approximate Bayesian computations highlighted the most likely phylogeographical scenario for the current distribution of little owl populations.  相似文献   

20.
Species with highly restricted ranges are disproportionately at risk of extinction, particularly where habitat loss occurs as a result of mining. Postmining restoration of rare species populations is considered as an appropriate response to counter such threats, but requires a careful, evidence‐based, and information‐driven approach. The economically important diamond mining at Sendelingsdrif in the southern Namib Desert occurs in the highly diverse Succulent Karoo Biome and threatens a significant part of the population of the narrow endemic succulent plant species Juttadinteria albata. To decrease the inherent risks of restoring such a rare species, we studied the habitat features of premining J. albata populations and experimentally tested whether some features could assist future reintroductions in postmining substrates. Plots where J. albata occurred were mostly south‐ to west‐facing and had among others higher rock cover and steeper slopes than plots where J. albata plants were absent. A revegetation experiment, with J. albata cuttings that were established on postmining substrate mounds, revealed that plants on steeper slopes, facing south to west, grew faster than plants on other slopes and aspects. Slope and aspect are therefore important habitat properties to recreate when restoring J. albata populations. These, and other preferred habitat properties such as higher levels of organic C, should now be tested in larger‐scale field trials. Validation of habitat requirements of J. albata through the revegetation experiment has decreased the risks at least partially and provides additional empirical evidence of the importance of establishing reference conditions to enhance ecological restoration.  相似文献   

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