共查询到20条相似文献，搜索用时 31 毫秒
1.
Jeffrey A. Hostetler J. Walter McCown Elina P. Garrison Aletris M. Neils Mark A. Barrett Melvin E. Sunquist Stephanie L. Simek Madan K. Oli 《Biological conservation》2009,142(11):2456-2463
Anthropogenic habitat fragmentation poses a serious threat to conservation of large carnivores, due to their extensive movements and potential conflicts with humans. We studied the population ecology of Florida black bears (Ursus americanus floridanus) for 6 years in two study areas in north-central Florida: Ocala National Forest (ONF), a contiguous forested habitat, and an adjacent residential community of Lynne, a fragmented habitat with substantial human activities. We estimated age-specific survival and fecundity rates of bears using data from radio-collared bears, and parameterized and analyzed stage-structured matrix population models for the two study sites and also for data pooled from both sites. Annual survival rates of adult females were lower in Lynne (0.776 ± 0.074) than in ONF (0.966 ± 0.023). While cub survival rates were higher in Lynne (0.507 ± 0.135) than in ONF (0.282 ± 0.109), the rates at both sites were substantially lower than those reported for other black bear populations. Age-specific fecundities did not vary between sites. The asymptotic population growth rate for ONF was greater than one, whereas that for Lynne was less than one. Our results suggest that anthropogenic influences (primarily road density and vehicular traffic, through their effect on adult survival) can substantially affect the population dynamics of Florida black bears and other large carnivores with large home ranges. We recommend efforts such as constructing highway underpasses, which could reduce road-related mortalities, to ensure long-term persistence of Florida black bears facing threats from rapidly increasing human influences. 相似文献
2.
Simone Vincenzi Alain J. Crivelli Jean-Francois Rubin Giulio A. De leo 《Biological conservation》2008,141(1):198-210
While several population viability analyses (PVAs) have been performed on anadromous salmonids, less attention has been given to stream-living salmonids. In this work, we explore the role of PVA as a tool in the recovery of threatened stream-living salmonid species. The analysis has been performed with reference to marble trout Salmo marmoratus, a salmonid with a limited geographic distribution and at risk of extinction due to hybridization with the non-native introduced brown trout. Demographic parameters, such as survival, fecundity and density-dependent patterns were estimated from an eight year on-going monitoring program of two translocated marble trout populations in pristine, previously fishless streams (Zakojska and Gorska) in the Soca and Idrijca river basins (Slovenia). To explore the importance of disturbance events such as floods on marble trout population dynamics, we performed a PVA under three scenarios: (1) occurrence of both severe and moderate floods; (2) occurrence of only moderate floods; (3) no flood events. Our analysis shows that population viability is threatened only by severe flood events, otherwise the two populations prove to be fairly stable with population abundance fluctuating around stream carrying capacity. A sensitivity analysis performed on model parameters highlighted that density-dependence in first-year survival and the magnitude of reduction in population size after a severe flood are the two most crucial parameters affecting population abundance and quasi-extinction probability, respectively. While only extreme floods can drive the population to extinction, the increase in juvenile survival when population abundance collapses after a major flood may allow the populations to quickly recover from few reproductive individuals back to stream carrying capacity. 相似文献
3.
Many orchids are currently red-listed due to changes in land use, and their future persistence will depend on management. Traditional land use like mowing is believed to favour orchids through increased survival and reproduction of established individuals, but the lack of data connecting their complex life cycle presently limits our ability to evaluate effects of management. Here we used data from 16 years of demographic monitoring to study how mowing affects population dynamics in two populations of the rare orchid Dactylorhiza lapponica. Both populations were characterized by long-lived individuals, low adult mortality and high seedling mortality. The traditional regime of mowing every second year strongly increased recruitment and reduced seed production in both populations, but had moderate effect on adult survival, growth rate and flowering probability. Population growth rate was positive for all population × treatment combinations. Traditional mowing significantly increased growth rate in both populations, and LTRE-analyses revealed that this primarily was a result of increased recruitment. The results indicate that demographic rates commonly associated with orchid persistence may be insensitive to traditional management, and underscores the importance of seed production and recruitment to maintain population growth in this long-lived species. The combination of low establishment success and no seed bank makes D. lapponica dependent on high seed input. Our results suggest that D. lapponica would benefit most from traditional mowing performed after seed dispersal in the study areas, but also suggest a high probability of future survival in the absence of mowing. 相似文献
4.
Andr W.G. van der Wurff Rieta Gols Ger Ernsting Nico M. van Straalen 《Pedobiologia》2005,49(2):167-174
We studied genetic variation and population differentiation in the springtail Orchesella cincta L. An earlier approach, using allozymes, revealed extremely low variation among and within populations from NW Europe. Microsatellite marker analysis showed higher genetic variation than allozymes, and agreed with the previously reported low population differentiation in the species. Analysis of molecular variance showed that genetic variation within populations amounted to 96.5% of the total variation, whereas the remaining 3.5% is accounted for by population differentiation. Population differentiation, as described by microsatellite markers and with the exception of one population, can be explained by an isolation by distance. Although the microsatellites are short, viz. only up to 12 repeat units, they appear to be useful tools in revealing population genetic structures in O. cincta. 相似文献
5.
Poaching giant pandas (Ailuropoda melanoleuca) for their skins is a serious threat to the persistence of wild giant panda populations in China. An individual-based, age-structured stochastic simulation model was constructed to give a quantitative analysis of the effects of poaching. The model takes a total wild population of 1216 individuals divided among 16 ‘patches’. The model treats individual populations as being completely independent, with no dispersal, and density-dependence only enters into the model through local carrying capacity of patches. The model simulates three types of poaching: deterministic (constant) poaching, stochastic poaching with normal distribution and stochastic poaching with observed distribution. Results showed that, with a given initial population, poaching adult females produces lower average population size and higher average percentage extinction than poaching adult males or young. At the same poaching intensity, all three poaching simulations predicted a similar probability of extinction. However, they predicted different average population size and percentage extinction because of differences in the parameters in the three models. These results should therefore be treated with caution when constant poaching simulation or stochastic poaching with assumed normal distribution is used as a simplification of realistic poaching. Nevertheless, the results imply that giant pandas are threatened by any reduction in natural populations. Effective measures are essential to reduce poaching. It is also important to limit the capturing of wild animals for zoos or breeding facilities as this also has a serious effect on the total population. 相似文献
6.
Tropical rainforests are disappearing at a rapid rate. Although several studies have revealed the detrimental effects of forest fragmentation on tropical birds, the ecological mechanisms facilitating the decline of populations have been poorly documented. In the tropical rainforests of Africa and America, ant-following birds track the massive swarm raids of army ants and prey on animals which are flushed by the ants. We analyzed the persistence of five species of ant-following birds along a habitat fragmentation gradient in western Kenya and tested if bird populations are limited by the abundance of army ant colonies in forests. Abundances of four of five ant-followers declined by 52–100% in forest fragments 113 ha. Multi-model Bayesian inference suggests that the decline of the three most specialized ant-followers is facilitated by a decrease in the abundance of the army ant Dorylus wilverthi in small forest fragments. Our data suggests that a second, fragmentation-tolerant army ant species, Dorylus molestus, does not functionally compensate for the decline of D. wilverthi because, first, of a higher affinity of birds to D. wilverthi raids (found for one species). Second, because the daytime activity of D. molestus is dependent on high humidity conditions, a pattern which was not found for D. wilverthi. Consequently, specialized ant-followers in small fragments, where D. wilverthi is missing, probably suffer from food scarcity due to a cease of army ant foraging in the dry season. Our results suggest that a subtle alteration of army ant communities caused by habitat fragmentation may have large ecological consequences. 相似文献
7.
Olusegun O. Osunkoya 《Biological conservation》2003,114(1):39-51
Gardenia actinocarpa (Rubiaceae)—an endemic and dioecious shrub-small tree of the lowland rainforest of Cape Tribulation, NE Australia—is evaluated for its long-term population persistence using five-year demographic data from three permanent plots of the species. Two-sex, size-specific Lefkovitch matrices were constructed to evaluate the species’ vital rates and extinction thresholds. One site indicated a sign of significant population growth (annual λ=1.056), while the remaining two gave λs close to unity (λ=1.0102 and 1.007). Overall, λ was greater than 1 (λ=1.0281) indicating that G. actinocarpa will increase in population size with time, though male plants were projected to grow faster in number than female plants. Elasticity analyses indicated that the largest size class (>22 cm diameter) made the greatest contribution to population growth (28%), especially the male plants (23%). Also λ was equally sensitive to survival/stasis (45%) and growth (44%) and least sensitive to fecundity (11%). Stochastic simulations gave 0.505 probability of quasi-extinction to 10% of its initial size in 100 years of population growth projection- suggesting that the endemic G. actinocarpa, despite a positive rate of population increase, is indeed threatened. Sensitivity analyses and numerical simulations showed that to maintain population persistence of G. actinocarpa, efforts should concentrate, following cost-benefit analyses, on increasing seed production coupled with enhancing establishment of individuals in the seedling, juvenile and vegetative phases. 相似文献
8.
Seabirds such as albatrosses and petrels are frequently caught in longline and trawl fisheries, but limited demographic data for many species creates management challenges. A method for estimating the potential biological removal (the PBR method) for birds requires knowledge of adult survival, age at first breeding, a conservation goal, and the lower limit of a 60% confidence interval for the population size. For seabirds, usually only the number of breeding pairs is known, rather than the actual population size. This requires estimating the population size from the number of breeding pairs when important demographic variables, such as breeding success, juvenile survival, and the proportion of the adult population that engages in breeding, are unknown. In order to do this, a simple population model was built where some demographic parameters were known while others were constrained by considering plausible asymptotic estimates of the growth rate. While the median posterior population estimates are sensitive to the assumed population growth rate, the 20th percentile estimates are not. This allows the calculation of a modified PBR value that is based on the number of breeding pairs instead of the population size. For threatened albatross species, this suggests that human-caused mortalities should not exceed 1.5% of the number of breeding pairs, while for threatened petrel species, mortalities should be kept below 1.2% of the number of breeding pairs. The method is applied to 22 species and sub-species of albatrosses and petrels in New Zealand that are of management concern, of which at least 10 have suffered mortalities near or above these levels. 相似文献
9.
Uncertainty in parameter estimates from sampling variation or expert judgment can introduce substantial uncertainty into ecological predictions based on those estimates. However, in standard population viability analyses, one of the most widely used tools for managing plant, fish and wildlife populations, parametric uncertainty is often ignored in or discarded from model projections. We present a method for explicitly incorporating this source of uncertainty into population models to fully account for risk in management and decision contexts. Our method involves a two-step simulation process where parametric uncertainty is incorporated into the replication loop of the model and temporal variance is incorporated into the loop for time steps in the model. Using the piping plover, a federally threatened shorebird in the USA and Canada, as an example, we compare abundance projections and extinction probabilities from simulations that exclude and include parametric uncertainty. Although final abundance was very low for all sets of simulations, estimated extinction risk was much greater for the simulation that incorporated parametric uncertainty in the replication loop. Decisions about species conservation (e.g., listing, delisting, and jeopardy) might differ greatly depending on the treatment of parametric uncertainty in population models. 相似文献
10.
Contemporary fire patterns are considered the most likely cause for regional population decline amongst small to medium mammals in northern tropical Australia. Here we assess the extinction risk faced by a vulnerable north Australian native rodent, the Brush-tailed Rabbit-rat Conilurus penicillatus in relation to fire frequency. This species has recently suffered a significant contraction in range. We provide the first quantitative evidence to demonstrate the immediate threat destructive wildfires and regular annual fire pose to the long-term population persistence of C. penicillatus. We show that late-dry season fires cause a reduction in both juvenile and adult survival probabilities. However, abundance declined at the unburnt as well as a frequently burnt site, suggesting that fire exclusion alone does not guarantee the species’ long-term persistence. Our model projections indicate that the remaining populations of C. penicillatus on the Northern Territory mainland risk extirpation within the next ten years. Conservation requires decisive management action to ameliorate extensive and destructive fires. A multi-faceted management plan needs to focus on restoring a fire management regime which generates a fine-scale mosaic of burnt and unburnt habitat, and the release of captive bred animals into fenced reserves free of exotic predators. 相似文献
11.
Habitat fragmentation is often associated with reduced levels of fitness and local extinction of plant species, and consequently poses a major threat to the persistence of species worldwide. The majority of demography-based fragmentation studies to date have focussed primarily on fragmentation impacts on individual plant fecundity. Here we investigate the impact of habitat fragmentation on the demography (plant height classes and density) and key population dynamic processes for the rainforest tree species Macadamia integrifolia (Proteaceae). Raceme and fruit production and seedling emergence across fragmented sites exceeded that in more intact sites with no apparent difference in short-term mortality rates. Fecundity of flowering trees did not appear to be affected by fragmentation. Instead, overall reproductive output in fragmented sites was enhanced relative to undisturbed sites due to a higher proportion of reproductively active individuals. The probability of flowering and fruiting was negatively correlated with the projected foliage cover (PFC) surrounding individual trees, and average PFC was significantly lower in small and medium fragments, suggesting light availability as a potential contributor to the trends observed here.This study demonstrates that the short-term effects of habitat fragmentation on population viability may not necessarily be detrimental for some species, and highlights the importance of assessing not only the fecundity of flowering individuals but also the proportion of individuals reproducing within fragments. 相似文献
12.
Won Il Choi Daryl L. Moorhead Deborah A. Neher Mun Il Ryoo 《Biology and Fertility of Soils》2006,43(1):69-75
The effect of soil moisture on population dynamics of Paronychiurus kimi (Collembola) was examined by combining an empirical soil moisture model with a temperature-sensitive, stage-structured population model. Field observations of soil temperature were used to drive the population model, and simulations were compared to field observations of juvenile and adult densities. Simulations without soil moisture effects produced stable, interyear population dynamics and a significant correlation between simulations and observations (n=12, r
2=0.40, P<0.05) but overestimated densities during much of the year. Adding responses to soil moisture improved the fit between simulations and observations (n=13, r
2=0.40), suggesting that soil moisture is a major limiting factor on field populations of P. kimi. Moreover, an observed temporary decline in field populations during spring could be explained partly by the effects of an herbicide, paraquat (N,N′-dimethyl-gamma,gamma′-bipyridylium dichloride) (r
2=0.45), suggesting that paraquat imposes additional limits on collembolan populations. 相似文献
13.
Torbjörn Nilsson 《Biological conservation》2004,115(2):227-239
Focusing on the wolf Canis lupus in Scandinavia as an example, criteria are proposed and an analysis performed to assess the effect on extinction risk of various control policies, while accounting simultaneously for effects of inbreeding depression and potential catastrophic events. Each control policy is characterized by a hunting pressure (the increase caused by hunting of annual mortality rates) combined with a hunting threshold (the population size below which hunting is not permitted). Catastrophes are taken into account by including the persistence of a severe catastrophe in the criterion for population viability. Based on these criteria, the results suggest that only a very limited amount of hunting should be permitted at low population sizes. The results also illustrate the importance of including a long-term perspective in modelling threatened populations. 相似文献
14.
Rulon W. Clark Michael N. Marchand Brendan J. Clifford Randy Stechert Sierra Stephens 《Biological conservation》2011,(2):886-891
Extinction of populations from anthropogenic forces rarely has a single cause. Instead, population declines result from a variety of factors, including habitat loss, inbreeding depression, disease, and climate change. These impacts often have synergistic effects that can lead to rapid decline in isolated populations, but case studies documenting such processes are rare. Here, we describe the recent decline of the last known population of timber rattlesnakes (Crotalus horridus) in the state of New Hampshire. We used polymorphic nuclear DNA markers to compare genetic diversity of this population to other populations in the region that are not isolated. We also compare results from ongoing field monitoring of these populations. Genetic analyses reveal that the New Hampshire population lacks genetic diversity and exhibits signs of a recent bottleneck. New Hampshire snakes also exhibited high levels of morphological abnormalities (unique piebald coloration, amelanistic tongues) indicative of inbreeding depression. Furthermore, after a year with exceptionally high summer rainfall, a skin infection of unknown etiology caused significant mortality in the New Hampshire population, whereas other surveyed non-inbred populations were unaffected. This case study demonstrates how different anthropogenic impacts on natural environments can interact in unexpected ways to drive threatened populations toward extinction. 相似文献
15.
The influence of native vegetation clearing and different further soil managements on fungal propagule population diversity
was studied in the present work. In each of the 3 years (1998, 1999, and 2000), soil samples were collected at the depth of
0–7.5 cm from sites under native vegetation (V0); naturalized prairie, cleared in 1982 (P16); conventional tillage, cleared
in 1972 (T26); and direct drilling, cleared in 1958 (D40). Fungal population size and relative abundance of fungal genera
were studied by plate counts and further identification of isolates on potato dextrose agar. The undisturbed site and the
other sites with increasing time elapsed since native vegetation clearing and different management history showed a distinctive
distribution of fungal genera. There were significant differences (p<0.05) among the sites in the abundance of fungal genera analyzed in all the 3 years. Principal component analysis based on
relative fungal genus abundance differentiated the sites with 75% variance explained by the first and second components. Diversity
and abundance of isolated fungal genera were increased as density of Penicillium spp. decreased, suggesting a competitive effect of this fungal genus. The largest diversity was found in the site under no-till
management. The different distribution and relative abundance of the fungal genera studied seemed to be influenced strongly
by the management and the presence of surface residue in the no-tilled site. 相似文献
16.
Irshad Muzammil Sulaiman Cherakuri Raghavendra Babu 《Genetic Resources and Crop Evolution》1996,43(4):351-356
Populations of Meconopsis paniculata and M. sinuata inhabit open alpine slopes, while those of M. simplicifolia are restricted to alpine meadows of Sikkim Himalaya. These species are threatened and represented by very small populations. Three enzymes namely acid phosphatase, esterase, and glutamate dehydrogenase were tested for six populations each of M. paniculata and M. simplicifolia and single population of M. sinuata to analyse the genetic diversity of these species. In addition, alkaline phosphatases, glucose 6-phosphate dehydrogenase and malate dehydrogenase were tested for M. paniculata populations. The results on the electrophoretic variations revealed that genetic polymorphism is low to absent in all the populations of the three species of Meconopsis investigated, and the species are characterized by genetic homogeneity with fixed alleles. 相似文献
17.
John M. Tirpak William M. Giuliano John W. Edwards M. Seamster 《Biological conservation》2006,133(3):364-378
Ruffed grouse (Bonasa umbellus; hereafter grouse) populations in the central and southern Appalachians are in decline. However, limited information on the dynamics of these populations prevents the development of effective management strategies to reverse these trends. We used radiotelemetry data collected on grouse to parameterize 6 models of population growth to: (1) determine the pattern of growth in these populations, and (2) identify the demographic rates most important to growth. Trend estimates from population models were most similar to trend estimates derived from Breeding Bird Survey and Christmas Bird Count data when models incorporated either a reproductive or survival event. These events randomly increased fecundity or survival, respectively, to their empirical maxima on average once every 5 years. Reproductive events improved estimates on areas dominated by mixed mesophytic forest, while survival events characterized population growth on oak (Quercus spp.)-dominated sites. The finite rate of increase (λ) was most sensitive to brood survival followed by adult and juvenile non-breeding survival on most sites. However, brood survival was low (<0.35 female chicks/hen survived to week 5), and elasticity analyses indicated λ responded more strongly to proportionate change in non-breeding and breeding survival rates of adults and juveniles than any reproductive variable. Life stage analyses corroborated this result. At baseline values, survival of adults and juveniles may be the main determinants of growth in these populations, and reproduction may not be adequate to compensate for these losses. Therefore, population growth above baseline levels may be regularly needed to restock these populations. Researchers have hypothesized that population dynamics may differ between mixed mesopytic and oak-dominated sites due to differences in forage quality and quantity. Thus, a potential mechanism for the increases in λ needed to sustain populations on mixed mesophytic forest sites is the greater fecundity observed during years with high oak or beech (Fagus grandifolia) mast abundance. The availability of this high quality forage allows hens to enter the breeding season in better condition and realize higher fertility. Alternatively, on oak-dominated sites, population growth increases may also be a product of higher non-breeding survival of birds in mast years, when birds do not need to range as far to forage and can limit their exposure to predators. 相似文献
18.
Kebebew Assefa Hailu Tefera Arnulf Merker Tiruneh Kefyalew Fufa Hundera 《Genetic Resources and Crop Evolution》2001,48(1):53-61
One thousand and eighty tef, Eragrostis tef (Zucc.) Trotter, entries representing 36 populations collected from six central and northern regions of Ethiopia were evaluated at Debre Zeit Agricultural Research Center during the 1995 main season to assess the quantitative trait diversity in the germplasm with respect to collection regions and altitude zones. Hierarchical analysis of variance showed large (p 0.01) variations within populations, and among populations within regions and altitude zones in all the 14 traits studied. The variations among regions were significant (p 0.05) for number of main shoot culm nodes, and panicle branches and spikelets. But only days to maturity, number of culm nodes, diameters of the two basal culm internodes, and harvest index depicted discernible (p 0.05) clinal variability. The 36 populations clustered into six major (75% similarity level) groups consisting of two up to 15 populations. Five principal components (PCs) explained about 81% of the entire phenotypic diversity among the populations. Of these, the first three PCs accounted for about 65% of the gross variance. About 31% of the total variance explained by the first PC alone originated chiefly from variability in main shoot panicle grain yield and length, culm length and diameter of the two basal culm internodes. Likewise, about 23% the variance accounted for by the second PC was due mainly to variations in grain and shoot phytomass yield/plant, and harvest index. Overall, the study demonstrated that tef is a highly versatile crop species and the enormous wealth of quantitative trait diversity in the germplasm indicates immense potential for the genetic improvement of the crop through breeding. 相似文献
19.
Infectious diseases have the potential to play a role in the decline of threatened wildlife populations, as well as negatively affect their long-term viability, but determining which infectious agents present risks can be difficult. The southern resident killer whale, Orcinus orca, population is endangered and little is known about infectious diseases in this species. Using available reference literature, we identified 15 infectious agents (bacteria, viruses, and fungi) reported in free-ranging and captive killer whales, as well as 28 additional infectious agents reported in free-ranging and captive odontocete species sympatric to southern resident killer whales. Infectious agents were scored as having a high, medium, or low ability to affect fecundity or reproductive success, to cause disease in individual animals, and to cause epizootics. Marine Brucella spp., cetacean poxvirus, cetacean morbilliviruses, and herpesviruses were identified as high priority pathogens that warrant further study. Using identified pathogens to develop a standardized necropsy and disease testing protocol for southern resident killer whales and sympatric odontocetes will improve future efforts to better understand the impacts of priority and non-priority infectious agents on southern resident killer whales. This model can be used to evaluate potential infectious disease risks in other threatened wildlife populations. 相似文献
20.
Samuel Zschokke Georg F.J. Armbruster Sylvain Ursenbacher Bruno Baur 《Biological conservation》2011,144(11):2702-2709
The management of rare and endangered species in the wild and in captivity requires an understanding of the characterization of the genetic units within each species and their relationships to each other. The Indian rhinoceros (Rhinoceros unicornis) is an endangered species with a current population size of c. 2800 individuals. We analyzed 26 individuals of known origin kept in captivity and 21 wild ranging individuals of the two remnant large wild populations in Assam (India) and Nepal employing mitochondrial and microsatellite markers to determine whether the two geographically isolated populations show distinct patterns of genetic diversity, and whether the genetic diversity of the populations is influenced by past demographic bottlenecks. We identified 10 different mitochondrial D-loop haplotypes, of which 4 were specific to the Assam population (10 sequences examined) and 6 specific to the Nepal population (19 sequences). Similarly, the microsatellite analysis demonstrated a strong genetic differentiation between the Assam and Nepal populations and allowed to assign each individual to its origin with high confidence. Furthermore, our analyses revealed the occurrence of a bottleneck in the Assam population long before the reported bottleneck in 1908, and it revealed that the Nepal population is a recent (probably post-glacial) colonization. In summary, the extent of genetic divergence between the two remnant R. unicornis populations suggests separate conservation programs (even for captive individuals) as long as the persistence of the entire species is not severely threatened. The microsatellite markers can also be used to determine the origin of confiscated material such as horns. 相似文献