首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Dispersal impacts on a range of population parameters making it a key piece of information in species conservation. Despite its importance, dispersal is poorly characterized for many species: pinnipeds are no exception. Understanding dispersal patterns of the New Zealand sea lion Phocarctos hookeri is crucial in the conservation management of the species as its recovery to a non-threatened status hinges on range recolonisation. In this study, we examined the movements of breeding adult male New Zealand sea lions within and following the breeding season of the 2002/03 austral summer using a novel multi colony approach. Based on resightings of 202 individually identifiable adult males, we found (1) a previously unappreciated, high level of dispersal by adult territorial males between breeding colonies during the pupping period and (2) that breeding males disperse to the extremes of the species’ range at the end of female oestrous. Our findings are contrary to the current paradigm of otariid breeding behaviour, which is believed to consist of prolonged, uninterrupted male territoriality based on intense male-male competition and sustained fasting. Adult male dispersal between colonies and across the species range has important implications for adult males as vectors of disease in three recent epizootics, species management and species recovery via recolonisation as males are apparently remaining part of a localized, vulnerable breeding population.  相似文献   

2.
This study presented evidence that creates a quandary for conservation management: predation by one threatened species, New Zealand sea lion (Phocarctos hookeri), threatens the viability of another threatened species, yellow-eyed penguin (Megadyptes antipodes), at Otago Peninsula, South Island, New Zealand. Otago Peninsula holds the largest population of yellow-eyed penguins on South Island and the only breeding population of New Zealand sea lions on the New Zealand mainland. New Zealand sea lions here represent the vanguard of re-colonisation within their prehistoric range, with nine females and 50-70 males resident in 2005. The initial indication of a potential problem was an attack on a yellow-eyed penguin by a New Zealand sea lion witnessed in 1996. The majority of 20 records for attacks were at two neighbouring sites, where they coincided with decreases in penguin nest numbers and adult annual survival. In contrast, penguin nest numbers increased at a third site, the main base for male sea lions at Otago Peninsula. Evidence from prey remains indicated that male sea lions did not eat yellow-eyed penguins but that females ate 20-30 annually, with one individual possibly responsible for most kills. Modelling indicated that the penguin population at any one site could not remain viable if it was the sole source of penguins killed. The dilemma is either to do nothing, and risk collapse of the Otago Peninsula population of yellow-eyed penguins, or to take action against known culprits, and risk failure in re-colonisation of the New Zealand mainland by New Zealand sea lions.  相似文献   

3.
Leopards (Panthera pardus) are endangered in South East Asia yet little is known about which resources need to be secured for their long-term conservation or what numbers of this species this region can support. This study uses radio telemetry to investigate seasonal variation in habitat selection and home range size of Leopards in Huai Kha Khaeng Wildlife Sanctuary, Thailand. Over a five year period, 3690 locations were recorded from nine individuals. The mean ± standard error of fixed kernel home range size for six adult females was 26 ± 8.2 km2, for two adult males was 45.7 ± 14.8 and for two sub-adult females was 29 km2 ± 5.5. Adult female wet and dry season home range sizes did not differ significantly. One adult male showed an increase in home range size from dry to wet seasons. Estimated density was 7 adult females/100 km2, which suggests 195 adult female leopards living in Huai Kha Khaeng alone, thus highlighting the larger Western Forest Complex’s potential contribution to leopard conservation. Compositional analysis of second and third order habitat selection suggested mixed deciduous and dry evergreen forest types, flat slope and areas close to stream channels are important landscape features for leopards. These results can help formulate a much needed conservation strategy for leopards in the region.  相似文献   

4.
Understanding metapopulation dynamics in large carnivores with naturally fragmented populations is difficult because of the large temporal and spatial context of such dynamics. We coupled a long-term database of visitor sighting records with an intensive 3-year telemetry study to describe population dynamics of recolonization by black bears (Ursus americanus) of Big Bend National Park in Texas during 1988-2002. This population, which occurs within a metapopulation in western Texas and northern Mexico, increased from a single pair of known breeding-age animals in 1988 to 29 bears (including 6 females of breeding age) in March 2000 (λ = 1.25/year). A migration and dispersal event in August-December 2000 reduced the population to 2 adult females and as few as 5-7 individuals. One-way movement distances from the study area during this event averaged 76 km for females (n = 7) and 92 km for males (n = 4), and 3 animals conducted migrations of at least 154, 178, and 214 km, respectively. Our observations exemplify the importance of stochastic events on demographics of small populations and highlight the potential scale of bear movement among montane islands of southwestern North America. They also provide insight into the use of dispersal data in parameterizing metapopulation models for large carnivores.  相似文献   

5.
Populations with small effective sizes are at risk for inbreeding depression and loss of adaptive potential. Variance in reproductive success is one of several factors reducing effective population size (Ne) below the actual population size (N). Here, we investigate the effects of polygynous (skewed) mating and variation in female breeding success on the effective size of a small population of the Gunnison sage-grouse (Centrocercus minimus), a ground nesting bird with a lek mating system. During a two-year field study, we recorded attendance of marked birds at leks, male mating success, the reproductive success of radio-tagged females, and annual survival. We developed simulations to estimate the distribution of male reproductive success. Using these data, we estimated population size () and effective population size Ne for the study population. We also simulated the effects of population size, skewed vs. random mating, and female breeding failure on Ne. In our study population, the standardized variance in seasonal reproductive success was almost as high in females as in males, primarily due to a high rate of nest failure (73%). Estimated Ne (42) was 19% of in our population, below the level at which inbreeding depression is observed in captive breeding studies. A high hatching failure rate (28%) was also consistent with ongoing inbreeding depression. In the simulations, Ne was reduced by skewed male mating success, especially at larger population sizes, and by female breeding failure. Extrapolation of our results suggests that six of the seven extant populations of this species may have effective sizes low enough to induce inbreeding depression and hence that translocations may be needed to supplement genetic diversity.  相似文献   

6.
The negative consequences of lead shot ingestion have been demonstrated in captive birds, and the prevalence of embedded shot has been measured in wild waterfowl several times. However, the long-term consequences of these two indirect outcomes of hunting on waterfowl survival have merely been investigated. Using data from about 40,000 X-rayed teals (Anas crecca), this study attempts to evaluate these effects. We used multivariate logistic regressions to model the probability of carrying shot in the flesh or in the gizzard while testing for various explanatory variables such as sex, age, time or morphological measures like mass and flattened wing length. Because of technical issues, we used a non-parametric sign test rather than a complete capture-recapture analysis to evaluate the effect of shot on teal survival. This test was applied to the differences in time between ringing and recovery for lead categories (no lead shot, ?1 shot in the flesh but none in the gizzard, ?1 shot in the gizzard but none in the flesh) compared two by two. We show that, overall, males are more likely to carry embedded shot than females whereas the latter are more likely to carry lead pellets in the gizzard. Similarly, adults are more likely to carry shot in the flesh whereas first year individuals are more likely to have pellets in the gizzard. Embedded shot tend to accumulate in the ducks body over time, i.e. with the number of encounters with hunters, with no significant effect on survival. Conversely, the probability of carrying shot in the gizzard decreases over time, because lead-poisoning quickly leads the individual to death. Several possible biological interpretations are put forward to explain those results. This study demonstrates that negative impacts of ingested lead on teal survival arise after only one single pellet is ingested, advocating the ban of lead ammunition.  相似文献   

7.
Management plans for threatened or recovering large vertebrate species that are increasing in population size and range focus on the establishment of viable populations within set temporal limits. New Zealand (Hookers) sea lions (Phocarctos hookeri) were declared a threatened species in 1997, and New Zealand legislation requires that threatened species of marine mammals must be managed to reduce human-induced mortality and achieve a non-threatened status within 20 years. The present breeding distribution of P. hookeri is highly localised, with over 95% of total annual pup production located at Auckland Islands and almost all of the remainder at Campbell Island. Breeding elsewhere has been ephemeral or restricted to <10 adult females. The only recorded sustainable breeding at a new location has been at Otago, South Island, New Zealand. This breeding population consisted of a total of four breeding females in 2002 and is derived from one immigrant female that gave birth to her first pup in the 1993/1994 breeding season. The New Zealand Department of Conservation management plan specifies that to achieve a non-threatened status P. hookeri (1) at Otago must increase in the number of breeding females to ?10, and (2) must establish ?two new breeding locations within the 20-year time frame, each with ?10 breeding females. This study 1) projects the population growth trends at a new location (Otago) to see if it will achieve ?10 breeding females within the legislated time frame, and (2) examines the likelihood that other breeding locations will establish elsewhere given the demographic information available for this species. We present 20 deterministic and three stochastic Leslie matrix model scenarios for female population growth for the initial years following the start of breeding at a new location. Our results indicate that (1) a new breeding population derived from one immigrant female is unlikely to reach 10 breeding females in 20 years; this duration is more likely to be 23-41 years (deterministic models) or 23-26 years (stochastic model), (2) the likelihood of two new sites establishing within 20 years is unquantifiable, but the probability is low, and (3) if the legislated outcome and time limit are not revised in the population management plan, the feasibility and effectiveness of re-locating young females could be investigated.  相似文献   

8.
Meadow breeding birds such as the whinchat Saxicola rubetra have been declining due to increased farming intensity. In modern grassland management, the first mowing and the bird’s breeding cycle coincide, causing high nest destruction rates and low productivity of grassland bird populations. However, it is virtually unknown whether the mowing process directly affects adult survival by accidentally killing incubating females. We studied adult survival of an Alpine whinchat population during two breeding seasons using either colour-ringing or radio-tracking of 71 adults. Assessing territories, mowing phenology and nest destruction from 1988 to 2007 allowed changes in the factors associated with female mowing mortality to be estimated. Adult survival over 5-day-periods was Φ = 0.986, but during the period of mowing female survival was strongly reduced (Φ = 0.946). As a result, 80.6% of the males, but only 68.4% of the females survived the breeding season. Mowing undoubtedly killed two of 20 radio-tagged females when they were laying or incubating. In the 20-year period, an increasing proportion of nests were destroyed before the chicks hatched and this change was associated with an increased distortion of the adult sex ratio. Modelling the population growth rate showed that including the additional effect of mowing on female mortality resulted in a 1.7 times faster local population decline. These results are consistent with the hypothesis that the extinction of whinchat populations in the lowlands of central Europe was caused not only by habitat degradation and low productivity, but also by increased man-made female mortality.  相似文献   

9.
In 1999, we published a report on how an introduction of 20 males into a severely inbred and isolated population of adders (Vipera berus) halted its decline towards extinction, induced a profound change in population genetic variability, resulted in a dramatic increase in offspring viability and thus in a rapid increase in numbers. Since the publication of our paper we have received numerous inquiries as to whether we have continued to monitor this population, as this is the case we herein present population demographic data gathered between 1981 and 2003. The population has continued to increase in numbers and in 2003, we collected 39 adult male adders, more than at any time over the 23-year study. Our continued work, hence, lends strong support to the importance of novel genes in enhancing the viability of inbred populations and supports the importance of preserving genetic variability in order to maintain viable wild populations.  相似文献   

10.
《Biological conservation》1992,61(2):107-116
We estimated the minimum size of the roan antelope Hippotragus equinus population in the Parc National de l'Akagera in Rwanda to be at least 144 animals, based on a two and a half year study of individually recognized stable social groups. Data from the same study were used to estimate the annual birth rate, and the survival rate of male calves, female calves, adult females and juvenile females; and to identify factors which would result in year-to-year variations in survival. The results of this analysis were incorporated into an age-structured model of the population's dynamics which took account of demographic and environmental stochasticity. This model was then used to determine the viability of the roan population in the park and to identify demographic characteristics whose occurrence could be used to predict when the population was most at risk of extinction.The risk of extinction could be predicted if the number of stable groups within the park was monitored in September of each year. This risk could be greatly reduced if a reciprocal arrangement was established with other protected areas such that the population in the park could be reinforced with new stable groups when the number of stable groups fell below three. However, the risks—particularly of disease transfer—associated with such reinforcement programmes should be clearly recognized.  相似文献   

11.
Within species habitat use may depend on age, season or sex of an individual. The distribution of males and females may vary both temporally and spatially due to differences in the costs of reproduction and the distribution of critical resources. Conservation of a species requires knowledge of the habitat use of both sexes in order to predict the population size and protect all habitats that a species requires. Adult dragonfly populations often have highly male-biased sex ratios at the breeding habitat. This bias has been attributed to females using alternative habitats to avoid male harassment, or to high female mortality. We monitored adult Hine’s emerald dragonfly (Somatochlora hineana Williamson) populations, in breeding and non-breeding habitats in Door County, Wisconsin and found significant differences in habitat use between males and females. Males primarily used wetland habitats, while females primarily used dry meadows and marginal breeding habitats, only coming into wetlands to lay-eggs or find mates. We assessed food resources in the different habitats and found that high quality insect prey (primarily adult Diptera) were more available in the wetland habitat, indicating that these areas were likely a more productive foraging area for adult dragonflies. The fact that females appear to avoid the wetland habitat is consistent with the hypothesis that male harassment alters female distribution patterns. Consideration of the patterns of habitat use by S. hineana indicates the need to develop a broader understanding of the importance of non-wetland areas in the conservation of wetland species.  相似文献   

12.
The kakapo (Strigops habroptilus) is a large, flightless, nocturnal parrot, endemic to New Zealand. It is critically endangered, with a world population of ca. 62 individuals and a male-biased adult sex ratio. The species has a polygynous “lek” mating system and adult males typically weigh 30-40% more than females. The kakapo is subject to intensive conservation efforts, including the provision of supplementary food to wild birds to encourage successful nesting. There is mounting evidence that, in polygynous species with large variance of male reproductive success, females in better condition may maximise their fitness by producing more offspring of the larger, more costly sex to be reared. We used data on the sex ratio of progeny of female kakapo that had or had not received supplementary food, to test the hypothesis that supplementary feeding might cause a male-biased offspring sex ratio. There was a significant excess of males in the clutches of females provided with supplementary food, suggesting that changes need to be made to the feeding regime to increase recruitment of females. This is an example of applying evolutionary theory to a practical conservation problem.  相似文献   

13.
The roosts of many IUCN-listed cave-roosting bat species are under threat from tourist development in SE Europe and other regions of the world. Much-needed conservation strategies require, among other information, an understanding of their roost movements and population dynamics, which can now be obtained relatively quickly using advanced models. We have studied the long-fingered bat, Myotis capaccinii, an obligate cave-dweller, in Dadia National Park, Greece. The species formed colonies of up to a few thousand individuals and was highly mobile, frequently switching summer roosts up to 39 km apart, even during late pregnancy. The bats migrated to distant hibernacula including a cave in Bulgaria 140 km NW of the Park. Adult recapture probabilities varied with season and sex: low female recapture rates in autumn, relative to spring and summer, indicated non-random temporary emigration following nursery colony dispersal. The opposite pattern was seen in males: increasing recapture rates in the autumn suggest that males gather in these roosts to mate with females in transit. Adult survival (0.86-0.94) was similar in females and males, similar in winter and summer, and comparable to recent estimates for other bats based on similar modelling techniques. Sex-based differences in juvenile recapture suggest female philopatry and male-biased dispersal. Our work shows that protection of M. capaccinii roosts must extend beyond the Park’s and indeed the country’s boundaries: its conservation requires large-scale, trans-national integrated conservation plans. Our results will apply to many other warm-temperate species with similar life history cycles.  相似文献   

14.
The hen harrier (Circus cyaneus) population on the Scottish Orkney Islands has declined dramatically since the end of the 1970s. We postulate that the cause of this decline was due to a reduction in the amount of available prey and predict that if this was the case the population would currently be limited by food. The evidence for this hypothesis is explored by examining the rates at which males deliver prey to their females in relation to breeding performance both among individuals within the declining population and also between this declining population and another, non-declining population in southern Scotland. Breeding performance within the Orkney population was related to male provisioning rates: males that provided more food to their females were more likely to initiate a breeding attempt and there was a tendency for males with the highest provisioning rates to breed with more females. Comparisons between the two populations revealed that harriers on Orkney had a lower breeding performance and also a lower rate of food provision. Changes in agriculture, in particular decreases in rough grazing and increases in sheep densities are thought to be the most likely cause for a reduction in food supply. Conservation measures should be aimed toward increasing the areas of rough grass habitat.  相似文献   

15.
Noninvasive genetic monitoring has the potential to estimate vital rates essential for conservation and management of many species. In a long-term genetic capture-mark-recapture study using scats we evaluated temporal variation in adult survival in a wolverine (Gulo gulo) population in southern Norway. In contrast to most previous studies of large mammals we found evidence for negative density dependence in adult survival in this large carnivore. Both sexes showed the same pattern of density dependence, with higher annual survival rates in adult females than males. In addition, we also found an additive mortality effect of harvesting in the population, resulting in the lowest adult survival rates at a combination of high population density and high harvest rate. The additive effects of density and harvest on adult survival of wolverines have relevance to the conservation and management of solitary carnivores with strong intrasexual territoriality, especially for species where combats among conspecifics can cause serious injury or even mortality.  相似文献   

16.
Capybaras (Hydrochoerus hydrochaeris) are the world’s largest rodent. Free-living populations are commercially harvested for their meat and leather in Colombia, Venezuela and Argentina; however, there is concern that legal and illegal harvesting is not sustainable. Since capybaras are considered an economic resource, there have been several attempts to explore the effect of different hunting strategies on its population dynamics. Two previous population models have been developed with this goal; however neither included capybara social behavior that may affect population dynamics. We developed an age-structured, density-dependent model of capybara herd dynamics to explore the demographic consequences of different hunting strategies. We then added infanticide and female reproductive suppression to explore the demographic consequences of such behavior. We conducted five different simulations and used ANOVA to estimate the effect of hunting females, hunting males, hunting both males and females, and the independent effects of reproductive suppression and infanticide on population size after 50 years. Our model suggests that suppression has the largest effect on population size, followed by hunting females and males hunting, female hunting, male hunting and infanticide. Thus, to develop more realistic harvesting models, managers should determine the degree of reproductive suppression and the frequency of infanticide by males.  相似文献   

17.
Ecotourism is a rapidly growing industry with unknown impacts on viewed wildlife that may require novel management action. We examined the impact of viewing activities on the behaviour of brown bears (Ursus arctos) in coastal British Columbia.Domination of the best feeding sites and human avoidance by large male bears has consistently been reported. We, however, saw displacement in time rather than space - during the viewing day large males were less active than at other times, while females with cubs tended to be more active.In each year, females with cubs spent similarly high proportions of their time fishing when people were present. In years with large male activity, less time was spent fishing when people were absent. When freed from the potential threat of large male bears, females with cubs showed no measurable impact of controlled human activity.Human presence at a feeding site impacts the behaviour of brown bears, but not as expected. Temporal avoidance of human activity by large males was observed; indications that they departed upon satiation, before the arrival of morning tours, however, suggests that there was little energetic impact. By displacing large males, viewing activities created a temporal refuge, enhancing feeding opportunities for subordinate age/sex classes. With the strong positive relationships between mean female mass and litter size, this may in turn increase population productivity.  相似文献   

18.
Conserving and managing populations of marine vertebrates can be complex when they occupy the waters of multiple nations, crossing heterogeneous legal and management landscapes. Hawksbill turtles (Eretmochelys imbricata) are subject to varying levels of use in Caribbean countries and their conservation and management is complicated by the extent to which they are a ‘shared’ resource. In 1997 and 2000, Cuba attempted to ‘downlist’ hawksbills from Cuban waters to CITES Appendix II to allow limited international trade. The research on movement and dispersal of hawksbills reported here was undertaken to better inform discussion about the impacts of their harvest. Flipper tagging and satellite tracking demonstrate that the majority of study turtles remained in Cuban territorial waters. Of 1170 hawksbills tagged (525 adults and 606 juveniles), 12% (n = 143) were recaptured. All recaptured adults (n = 16 males, 38 nesting females and 30 adult females in-water) were in Cuban waters. Of the 59 juveniles recaptured, only four recaptures were outside Cuban waters (Nicaragua = 2, Colombia = 1, USA = 1). Fourteen hawksbills tagged in the waters of other nations were recaptured in Cuban waters. We also satellite tracked 21 turtles (one adult male, ten nesting females and ten non-nesting adult females), of which five tags failed, 11 stayed in Cuban waters for the duration of transmissions (1–809 days) and five foraged in the waters of other nations (Mexico n = 1 an adult female; Honduras n = 2, both post-nesting turtles; Colombia n = 1 an adult female; and the eastern Lesser Antilles n = 1, an adult male), with differences for nesting and non-nesting turtles. Our results, demonstrating extended site fidelity within Cuban waters, suggest that strengthening national management within national jurisdictions that host hawksbill turtles is fundamental to improving regional conservation as a whole.  相似文献   

19.
Recently, European wild rabbit (Oryctolagus cuniculus) populations have undergone a sharp decline that may be exacerbated by hunting. We investigate the effects of the timing of hunting on the conservation of wild rabbit using a model for rabbit population dynamics. Scenarios with different hunting rates and age strategies were simulated for different population qualities. We interviewed hunters to ascertain the degree to which they would accept a change in the timing of hunting. We also investigated the hunting pressure applied by hunters and its relationship with rabbit abundance. Modelling results indicate that the current hunting season has the greatest impact on rabbit abundance. Hunting in late spring optimises hunting extraction while conserving rabbit populations. When the rabbit population quality is low the effects of age strategies and the timing of hunting are less important than the effect of the hunting rate applied. Almost half the hunters would agree to policy changes. More than 75% of hunters implemented self-imposed hunting restrictions to improve rabbit populations, that were more frequently applied in high rabbit abundance areas. Therefore, changing the timing of hunting and increasing the participation of hunters in low abundance areas could optimise both the exploitation and the conservation of wild rabbit populations in southwestern Europe.  相似文献   

20.
Little is known about the reproduction of the Iberian lynx (Lynx pardinus) even though it is the most endangered felid in the world. We studied during 9 years several reproductive parameters of the Iberian lynx in one of the subpopulations situated in Doñana National Park (south-western Spain), by means of radio-tracking, direct observations and photo-trapping. The potential breeding subpopulation was usually composed of 3 adult females, which bred 83% of the total possible 29 female-reproductive year. The minimum total number of cubs born during the study was 64 (7.7 ± 0.69 per year). There was no correlation between the number of cubs born or number of breeding females and population size of European rabbit (Oryctolagus cuniculus, the main prey of the lynx). All known births (n = 16) occurred in March except one in April and another in June. Mean litter size was 3.0 ± 0.16 (n = 16, range = 2-4). Sex-ratio (n = 59 cubs) was 1.03:1.00 (females:males). Nevertheless, the commonest picture was a female with 2 cubs older than 3 months. Altogether, at age of 3 months, 75% of cubs survived. Number of lynx alive at 10 months old and before dispersing was 69% and 57%, respectively. Sex did not affect survival for any age. Normally, it was not possible to know the causes of the death of cubs younger than 3 months. Survival at this age was not related with mother, mother age, or rabbit abundance. All females that bred were older than 3 years. The age of last reproduction was 9 years. For 3 females that were tracked during almost their complete reproductive life, the life time reproductive output was between 11 and 19 cubs. Iberian lynx reproductive parameters did not respond to wide changes in prey abundance during the study. Conservation plans considering the extraction of cubs with a low survival probability should be considered by managers, for instance, in translocation campaigns.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号