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 609 毫秒
1.
Many species of conservation concern are in decline due to threats from multiple sources. To quantify the conservation requirements of these species we need robust estimates of the impact of each threat on the rate of population decline. However, for the vast majority of species this information is lacking. Here we demonstrate the application of integrated population modelling as a means of deriving robust estimates of the impact of multiple threats for a rapidly declining koala (Phascolarctos cinereus) population in South-east Queensland, Australia. Integrated population modelling provides a basis for reducing uncertainty and bias by formally integrating information from multiple data sources into a single model. We quantify mortality rates due to threats from dog attacks, vehicle collisions and disease and the extent to which each of these mortality rates would need to be reduced, or how much habitat would need to be restored, to stop the population declining. We show that the integrated population modelling approach substantially reduces uncertainty. We also show that recovery actions that only address single threats would need to reduce those threats to implausibly low levels to recover the population. This indicates that strategies for simultaneously tackling multiple threats are necessary; a situation that is likely to be true for many of the world’s threatened species. This study provides an important framework for quantifying the conservation requirements of species undergoing declines due to multiple threats.  相似文献   

2.
Fire can be a catastrophic event which causes high mortality and injury in wildlife. While rehabilitation of injured animals is common, no studies have measured the success of rehabilitated wildlife following fire. This study compared the long-term survival and reproduction of a group of injured, rehabilitated and released koalas (n=16) with that of uninjured koalas (n=23) following fires in fragmented forest in Port Stephens, Australia, in 1994. Individual koalas were monitored for up to three years following release. Survival rates were calculated using the Kaplan–Meier estimate, modified for the staggered-entry of new animals. There was no significant difference in the survival of rehabilitated and uninjured koalas after fire. Annual survival, derived by fitting an exponential decay function to the data, was estimated to be 58% for rehabilitated koalas and 67% for the uninjured koalas. Predation by dogs was the major cause of mortality for both groups. Reproduction did not differ significantly between the two groups over two breeding seasons following fire. It was concluded that rehabilitation of injured koalas was successful from the perspective of the individuals. Furthermore, such efforts have the potential to contribute to the recovery of populations depleted after fire and thus contribute to the long-term survival of koala populations.  相似文献   

3.
The ocelot Leopardus pardalis population in the United States was listed as endangered in 1982, with only two known isolated breeding populations occurring in southern Texas. Conservation concerns for ocelots include loss of dense thornshrub habitat, mortality from ocelot-vehicle collisions, and genetic erosion. In this study, we used a population viability analysis (PVA) to evaluate four recovery strategies (i.e., supplementation of additional ocelots, reduced road mortality, habitat protection and restoration, and linkage of two breeding populations) for ocelot conservation management. We used the VORTEX (Version 9.42) program to conduct our PVA for an ocelot population located in Cameron County, Texas. Each scenario was simulated 500 times over 100 years. We compared the effectiveness of recovery strategies and combinations thereof with estimates of extinction probability and final population size. Model scenarios with no recovery strategies predicted an extinction probability of 0.65 for the Cameron population of ocelots over 100 years. The protection and restoration of thornshrub habitat was the most effective recovery strategy, followed by population linkage and reduced road mortality, with the supplementation of ocelots being the least effective strategy. Protection and restoration of ocelot habitat cannot be accomplished without the participation of private landowners. Using an adaptive management approach, future actions need to be taken to monitor ocelot populations and habitats and help to reduce the high probability of extinction predicted in our PVA for the ocelot population in Cameron County.  相似文献   

4.
VORTEX computer simulations were used to assess the viability of a small breeding flock of common cranes, recently established in Norfolk. Investigations were also conducted on the relative impact of various management options. Raising the carrying capacity of the site had little influence on the survival of the flock. However, great improvements were associated with increases in the size of the founder flock and reductions in the mortality rates of chicks and adults. Regularly supplementing the population increased flock survival times: for a fixed total number of birds added, frequently supplementing with few birds produced the best results. Immigration from the population in continental Europe also increased persistence of the flock, and it is possible that immigration rates will improve as the British flock expands. Strategies including captive breeding, and regular supplementation of the flock, may be the most effective means of ensuring the viability of the Norfolk cranes. The potential value of simulation models in guiding management of small populations is discussed.  相似文献   

5.
Catastrophic events, either from natural (e.g., hurricane) or human-induced (e.g., forest clear-cut) processes, are a well-known threat to wild populations. However, our lack of knowledge about population-level effects of catastrophic events has inhibited the careful examination of how catastrophes affect population growth and persistence. For the critically endangered short-tailed albatross (Phoebastria albatrus), episodic volcanic eruptions are considered a serious catastrophic threat since approximately 80% of the global population of ∼2500 birds (in 2006) currently breeds on an active volcano, Torishima Island. We evaluated how short-tailed albatross population persistence is affected by the catastrophic threat of a volcanic eruption relative to chronic threats. We also provide an example for overcoming the seemingly overwhelming problems created by modelling the population dynamics of a species with limited demographic data by incorporating uncertainty in our analysis. As such, we constructed a stochastic age-based matrix model that incorporated both catastrophic mortality due to volcanic eruptions and chronic mortality from several potential sources (e.g., contaminant exposure, fisheries bycatch) to determine the relative effects of these two types of threats on short-tailed albatross population growth and persistence. Modest increases (1%) in chronic (annual) mortality had a 2.5-fold greater effect on predicted short-tailed albatross stochastic population growth rate (lambda) than did the occurrence of periodic volcanic eruptions that follow historic eruption frequencies (annual probability of eruption 2.2%). Our work demonstrates that periodic catastrophic volcanic eruptions, despite their dramatic nature, are less likely to affect the population viability and recovery of short-tailed albatross than low-level chronic mortality.  相似文献   

6.
The construction of habitat models is a repeatable technique for describing and mapping species distributions, the utility of which lies in enabling management to predict where a species is likely to occur within a landscape. Typically, habitat models have been used to establish habitat requirements for threatened species; however they have equal applicability for modelling local populations of common species. Often, few data exist on local populations of common species, and issues of abundance and habitat selection at varying scales are rarely addressed. We provide a habitat suitability model for the common wombat (Vombatus ursinus) in southern New South Wales. This species is currently perceived as abundant throughout its extensive range across temperate regions of eastern Australia, yet little factual survey data exist and populations appear under threat. We use wombat burrows to reflect habitat selection and as our basis for ecological modelling. We found that environmental variables representing proximity to cover, measures of vegetation and proximity to watercourses are important predictors of burrow presence. Extrapolation of habitat models identified an abundance of habitat suitable for burrows. However, burrows in many suitable areas were abandoned. Our estimate of the population size was similar to the total annual mortality associated with road-kill. Theoretically, given the availability of suitable habitat, common wombat populations in the region should be thriving. It seems likely that this area once supported a much higher number of wombats; however limiting factors such as road mortality and disease have reduced the populations. The persistence of wombats in the study region must be supported by migration from other populations. Our findings challenge the perception that wombats are currently common and not in need of monitoring, suggesting that perceptions of abundance are often clouded by socio-political motives rather than informed by biological and ecological factors.  相似文献   

7.
Vaccination programs are occasionally used on wild mammal populations with conservation goals. In the case of the European wild rabbit Oryctolagus cuniculus, vaccination campaigns against rabbit hemorrhagic disease (RHD) have been widely applied to enhance rabbit populations, but their overall effects have not been compared. I used a modelling approach to compare the effects of several vaccination strategies on the growth rate of wild rabbit populations. For all simulated vaccination strategies, vaccination campaigns yielded positive or negative population growth rates, depending on rabbit population dynamics and subsequent RHD dynamics. Growth rate was negative when the proportion of RHD-seropositive adult rabbits was low or medium before vaccination, which occurred in populations at low rabbit density. Given that these low density populations are mainly targeted by vaccination campaigns, the model suggested that current immunization programs may be causing harmful effects on many rabbit populations. The best annual period to carry out vaccination campaigns was determined by the age-class targeted for immunization. If the RHD dynamics were not known, vaccination of only juvenile rabbits seemed to be the most conservative option, since it minimized the probability of yielding negative growth rates, whereas vaccination of only adult rabbits was the worst option. These findings suggest that prior knowledge of RHD dynamics in populations subject to immunization is essential to minimize the risk of harmful effects.  相似文献   

8.
Species that persist on a shifting mosaic of successional habitat offer particular challenges to conservation, to monitoring methods, and to population dynamic modelling. The conservation of the heath fritillary butterfly (Melitaea athalia) in woodland in England, for example, depends on the creation of woodland clearings by coppicing (rotational cutting). We have developed a simulation model to assist in the conservation of such populations, called MANAGE. We have parameterised the model for the M. athalia population in the Blean Woods in Kent, and used it to answer several management questions. We find that: (1) simulations predict that the observed rates of coppicing will not be enough to meet existing conservation (Biodiversity Action Plan) targets, except when the most generous modelling assumptions are made; (2) the greatest uncertainty in the model outcome arises from uncertainty in the colonisation parameters; (3) in the worst case scenario (using the most pessimistic model assumptions), a population would require 2.3% of the Blean Woods to be coppiced each year, which is around double the currently-observed rate; (4) the four management units of the Blean where coppicing is practised are not independent metapopulations– they support each other; and (5) to sustain a population in a smaller landscape would require less coppicing overall, but more as a percentage of the landscape. This modelling approach may prove useful in the development of conservation management plans for other species that inhabit successional habitats.  相似文献   

9.
Populations of threatened taxa in captivity within their natural ranges can make important contributions to conservation, but these may be compromised by the inappropriate application of population management goals developed in other contexts. We conducted demographic, genetic, and population viability analyses on the captive population of Andean bears (Tremarctos ornatus) in Venezuela to investigate the management of within-range captive populations in general, and to better integrate this population into the conservation of Andean bears in particular. We found that although the present population is very small and not internally self-sustaining, incorporation of confiscated wild individuals has resulted in a low average number of generations in captivity and low inbreeding, with moderate gene diversity and a high probability of future population persistence. However, past imports from extra-range populations have been from over-represented lineages of unknown origin, which have mixed with under-represented Venezuelan ones, reducing the future value of the Venezuelan population as a source for founder stock. Our analyses indicate that the rate of incorporation of wild recruits is a major factor influencing proxy measures of conservation value, and distinguishing within- from extra-range populations. This implies that, contrary to conventional wisdom, internal self-sustainability can be a misguided goal in within-range populations, which furthermore may not be suitable destinations for surplus animals from captive populations elsewhere.  相似文献   

10.
Since the early 1980s, the acidic deposition in the northern Europe has decreased substantially. This has resulted in corresponding improvements of the water quality in some acid sensitive small lakes of southern Finland. Among the fish of these lakes, the first signs of recovery were recorded in the early 1990s, when the European perch (Perca fluviatilis L.) started to reproduce in some sparse populations. Since then, the reproduction of perch has been successful in several years. The appearance of strong year-classes in lakes earlier almost empty of fish indicates recovery. This development has resulted in increased population densities, decreased mean sizes of fish and decreased growth rates. In a more acid sensitive species, roach (Rutilus rutilus (L.)), no clear indications of recovery have been recorded this far. However, schools of small roach (age 1+) were observed in the summer of 1998 in two acidic lakes that were inhabited by sparse roach populations during 1985–1995.  相似文献   

11.
The wolverine is a relatively long lived mustelid species with low average annual reproduction which in theory makes them sensitive to changes in survival rates. In a multi-year study we monitored 211 radio-marked wolverines to estimate age-specific survival rates and mortality causes in an endangered population. Our data suggests that poaching forms a substantial part of wolverine population dynamics in northern Scandinavia causing up to 60% of adult mortality. Average annual adult survival rate was 0.91. Male and female survival rates did not differ. Twenty-five adult wolverines were confirmed to have died during the study. Fifty-two percent of confirmed adult mortality was human caused. The most important cause of adult mortality was poaching (9). Annual adult survival was lower (0.86) when 15 adult resident wolverines that were assumed to have died due to poaching were included in the analyses. Natural mortality among subadults and adults was less frequent in our study population compared to North American wolverine populations. Adult survival was significantly lower during the snow season (December-May) than during the snow-free season (June-November), while natural mortality was more evenly distributed between seasons. We explain this by the frequency of poaching which is higher during snow season. Our results underline the need to frame the underlying human dimension factors behind poaching to facilitate conservation and management of endangered populations.  相似文献   

12.
The flesh-footed shearwater (Puffinus carneipes) is a medium-sized seabird (ca. 700 g) that is incidentally killed during longline fishing operations. We examined the levels of bycatch in Australia’s Eastern Tuna and Billfish Fishery and developed a model to examine the impact of this fishery on the eastern Australian population of flesh-footed shearwaters, which breeds at only one site, Lord Howe Island. Observed bycatch rates for flesh-footed shearwaters were 0.378 birds/1000 hooks for night sets, and 0.945 birds/1000 hooks for day sets. The mean number of birds killed from 1998 to 2002 was estimated to be 1794-4486 birds per year, with the estimated total killed over this period ranging from 8972 to 18,490 birds. Models incorporating both density-independent and density-dependent scenarios were applied to levels of bycatch representative of that observed in the fishery. Density-independent scenarios showed that fishing mortality levels caused declines in the majority of simulated populations. In contrast, density-dependent scenarios produced populations that were more resilient to fishing mortalities. Although some modelling scenarios led to population growth, under most stochastic simulations median population halving and quasi-extinction times were less than 55 and 120 years, respectively. We conclude that the level of bycatch observed in the fishery is most likely unsustainable and threatens the survival of the Lord Howe Island population. This situation can be improved only with the development and implementation of mitigation measures that will halt or greatly reduce the level of bycatch currently observed. Improved knowledge on a range of demographic parameters for the species, combined with a clearer idea of the at-sea distribution of breeding and non-breeding shearwaters, will greatly assist in improving understanding and the management of this population.  相似文献   

13.
Several predator species at risk of extinction in Southwestern Europe are dependent on the population density of European wild rabbits Oryctolagus cuniculus. Rabbit populations in the region, however, have recently undergone dramatic decreases in population density, which may be exacerbated by hunting. Current hunting policies set the autumn-winter season, just before the start of rabbit reproduction, as the main hunting season, and previous theoretical models have estimated that the current hunting season may have the greatest negative impact on rabbit abundance and should be changed. We utilised a model for rabbit population dynamics to determine the effects of the timing of hunting during two seasons, summer and autumn, on the tendency of rabbit populations to be over-harvested and on the number of rabbits hunted. This model included field estimates of age- and sex-selection biases of hunting by shotgun. Scenarios with different hunting rates and sex- and age-selection probabilities of hunting were simulated for populations with different turnover levels and with and without compensatory mortality mechanisms. Field estimations showed that hunting in summer was juvenile-biased whereas autumn hunting was juvenile- and male-biased. In contrast to previous findings, our modelling results suggested that hunting in autumn may be the most conservative option for harvesting of rabbit populations, since these populations were more prone to be over-harvested during the summer. The differences between the two seasons in number of rabbits hunted were dependent on population dynamics and hunting sex- and age-selection probabilities. Our findings suggest that altering of current hunting policies would not optimise the exploitation or conservation of wild rabbit populations, but that the latter may be improved by some changes in the timing of hunting.  相似文献   

14.
Predator populations with demographic cycles driven by multi-annual cycles of their key prey resource can be expected to be “cyclic phase sensitive” to management actions. We explored this by means of modelling in the case of the highly endangered Fennoscandian arctic fox population which is driven by 4-year population cycles in small rodent prey. By using a model in which the management action improved arctic fox vital rate through increased resource availability, we show that arctic fox population growth was most improved when management action was applied in the increase and decrease phase of the cycle. Except in the low phase of the cycle, the growth rate was more affected when the management action worked through improved reproduction than improved survival. There was a synergistic effect to be gained by performing management action during multiple phases during a demographic cycle. Thus we recommend that arctic fox conservation programs ought to be continuous in time, but with the highest intensities of management action in the phases of the cycle in which the target population is most prone to respond.  相似文献   

15.
An initial survey of breeding records of captive ungulates showed that juvenile mortality was higher in inbred than in non-inbred young in 15 of 16 species. Because of recent scepticism regarding the deleterious effects of inbreeding, we conducted a more detailed analysis of the 12 species for which adequate records were available to examine the possibility that the trend of higher mortality rates in inbred young was not due to inbreeding but rather to some other factor often associated with inbreeding.The factors considered were: birth season; birth order; management changes; population density; and differences between captive-born and wild-caught, and inbred and non-inbred dams.None of these possibly confounding factors could account for the higher mortality rates of inbred young. These results demonstrate the reality of the effects of inbreeding and emphasize that an awareness of the consequences of inbreeding is vital to the sound genetic management of small captive populations.  相似文献   

16.
Kokako (Callaeas cinerea wilsoni) population recovery on the North Island of New Zealand depends primarily on control of key introduced mammal pests, especially ship rats (Rattus rattus) and brushtail possums (Trichosurus vulpecula). Recovery can still occur if pest control is pulsed (x years ‘on’; y years ‘off’) because kokako sub-adults and adults are generally long-lived, although chick production is high only during ‘on’ years. Pulsing effort means that conservation resources can be extended to other sites or problems during ‘off’ years; that toxin input at any one site is reduced; and that project staff do not burn out by repeatedly working at a site. Mathematical modelling supports empirical evidence that pests need not be controlled every year in order to maintain or greatly increase kokako populations. It predicts that the total number of years during which there is pest control is the main factor determining population size. Three years of pest control in each 10 should be sufficient to at least maintain a population with 20 females when mean parameters apply, but pulsed control should still be effective with very pessimistic parameters. In the safest strategies, control should occur in minimum pulses of 2-3 years to avoid single poor years when few breeding attempts are made. Very small populations should first be increased to at least 20 females by translocation or continuous pest control. This will greatly reduce the probability of chance extinction, and increase the efficiency of subsequent pest control. The model will apply best to closed kokako populations below carrying capacity, in which pests are controlled over the entire block. Empirical data on the effects of habitat carrying capacity on kokako dispersal, and on the importance of stoats as predators of adult females are required to further strengthen the model.  相似文献   

17.
The increasing disturbances affecting marine communities highlight the need to examine restoration measures that can be added to other conservation efforts for threatened populations. The main goal of this study was to examine the usefulness of ecological restoration in the management of gorgonian populations damaged by diving activity in intensively visited marine protected areas (MPAs). We used field experiments as well as simulations from size-structured matrices to assess the utility of transplantation of living fragments from damaged colonies to increase the viability of threatened populations. Despite results showing that technique failure caused the loss of 40% of transplants, well-attached transplants achieved survival rates (80%) similar to those of natural colonies. Surprisingly, environmental conditions (light level and presence of algae) did not have a significant effect on the mortality of the transplants, but did affect methodological failure rates (37% of transplants were lost in the photophilous treatments in contrast to the 25% lost in sciaphilous treatment). The simulations showed a substantial increase in the annual population growth rate (λ) only when transplantation was performed every two years and under the most demanding conditions (recovering 75% of the detached colonies and obtaining 3 fragments from each one). Predictions from the size-structured matrix model suggest severe limitations of this technique at larger spatial scales. However, our study confirms the feasibility of this restoration measure to contribute to the recovery of populations in MPAs affected by local disturbances. The experimental and modelling approaches developed here may provide useful guidelines for future studies on the restoration of marine populations.  相似文献   

18.
Linking age-specific vital rates to population growth through demographic matrix models can enhance our understanding of crucial population processes, vital in a conservation context. The white-tailed eagle (Haliaeetus albicilla) population in the Federal State of Schleswig-Holstein, Germany, has been monitored since re-colonisation in 1947 and provides a well-documented example of a recovery. We test how demographic models capture growth trajectories of a recovering population and how applicable they are in guiding population management of endangered species. From 1947 to 1974, the population was stable but the growth rate predicted by an age-structured matrix model was −6.1% per annum. The small but stable population must have been maintained by immigration. From 1975 to 2008, observed and predicted population growths were very similar (6.7% and 4% per annum respectively). Elasticity and life-stage simulation analyses identified adult and pre-breeding survival as key vital rate elements. While the prospective analyses identified survival as the key vital rate influencing population growth, the increasing reproduction rate allowed the recovery to take place; thus caution is needed when prospective modelling makes management recommendations. Nevertheless, conservation efforts should address key mortality factors such as lead poisoning and collision with wind turbines. A logistic model predicted a maximum carrying capacity of 255 pairs for the Federal State, but using the highest currently observed density (1.4 pairs per 100 km2) and differences in habitat suitability, a more likely carrying capacity was estimated at 122 pairs. Under both scenarios, current population growth should slow soon.  相似文献   

19.
In population viability analysis we are often faced with a lack of knowledge of survival rates in animal populations. In particular, survival of recruits is usually hard to assess. However, data on population structure might be considered as patterns that contain valuable information to estimate missing parameters indirectly. As an example for this pattern-oriented modelling and parameterization, pre-breeding survival rate of the endangered Lesser Spotted Woodpecker (Picoides minor) was determined here using data on population structure (e.g. sex ratio) and reproductive success at the population level (e.g. nesting success). Therefore, an individual-based model was developed simulating the population dynamics for two different populations that had been empirically studied at Lake Möckeln, Sweden, and Taunus, Germany. For both populations, a small range for pre-breeding survival rates could be identified wherein all simulated patterns corresponded best to the empirical values. Pre-breeding survival rate was found to be higher in the German scenario than in the Swedish and geographical variation in life-history traits is discussed as a possible reason. It is concluded that the pattern-oriented approach is a valuable method for estimating missing demographic parameters, even when using weak patterns from empirical investigations. Furthermore, it was shown that the use of multiple patterns is necessary for this purpose.  相似文献   

20.
Allen Cays Rock Iguanas (Cyclura cychlura inornata) are native to two small islets (Leaf and U Cay) in the north-central Bahamas. These populations were nearly extirpated in the early 1900s because of heavy hunting pressure (for food), but increased to a total of ca. 150 lizards in 1970, and now number over 500 (not including juveniles). Over the past several decades poaching has declined, but tourist visitation (including nearly daily supplemental feeding of iguanas) has increased. To examine human impacts on the demography of these iguanas, survival, population growth rates, and population sizes for subadult and adult (>25 cm snout-vent length) males and females on the two cays were estimated based on mark-recapture data collected over a 25-year period (1980-2004). As predicted, annual survival probability was higher on U Cay (with less human visitation) than on Leaf Cay, was higher in females than in males (which are bolder), and exhibited a declining trend. Both populations more than doubled during this study, but population growth rates declined to near zero in recent years. These data reflect the importance of human impacts, but also suggest that the populations may be nearing carrying capacity. The rapid population growth observed on these cays, and that seen for several other translocated iguana populations, suggest that if unnatural causes of mortality are reduced or eliminated, island populations of iguanas are capable of rapid recovery. The inexpensive establishment of assurance colonies on undisturbed “islands” should be considered for any comprehensive management plan for endangered species of iguanas.  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