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1.
Without regular monitoring a rare species may slip into extinction unnoticed. We report a possible case from the Galápagos archipelago. The warbler finch (Certhidea fusca) has not been recorded by scientists on Isla Floreana in recent years, and we have been concerned about its status. On a two-day visit to prime habitat in the breeding season of 2004 we used playback of warbler finch song and calls recorded on another island to stimulate an approach of local birds. We failed to find a single warbler finch, whereas we encountered numerous small tree finches (Camarhynchus parvulus), medium tree finches (C. pauper) and yellow warblers (Dendroica petechia). Searches in 1979, 1983, 1997 and 1999 were also unsuccessful. Our continuing failure to find any warbler finches indicates the species must be extremely rare on the island, if not actually extinct. We discuss possible reasons for their demise and draw attention to other species that could be heading in the same direction.  相似文献   

2.
The aggregation of individuals into foraging flocks is one behavioural trait that, if disrupted, can cause the Allee effect, which is a slowing in population growth at low density or small population size, and this can greatly increase the risk of extinction. Here, I describe intraspecific flocking behaviour of a colour-banded population of speckled warblers, Chthonicola sagittata, a species that has declined across a large part of its range in the fragmented temperate woodlands of Australia. I make predictions about the context in which the Allee effect might be expressed and the consequences for the viability of populations living in small habitat remnants. Speckled warblers lived in discrete, stable social groups throughout winter, the nucleus of which was the residents from one or more adjacent breeding territories. The timing and mode of flock formation and the size of flocks varied between two winters, apparently in response to the severity of conditions; thus flocking probably facilitates increased foraging efficiency and predator detection, potentially leading to increased survival in harsh conditions. Because flock territories were up to 30 ha each, and larger territories are likely, birds living in remnants smaller than 40 ha may suffer increased mortality if there are too few birds available to form flocks of an appropriate size to facilitate the benefits of grouping when conditions are most extreme. Further, in small remnants where survival is reduced, dominance behaviour and male-male competition may act to compound the Allee effect by reducing reproductive success. Regardless of these predictions, speckled warbler populations may only be viable in remnants that are large enough to support multiple flocks, to enable rapid recruitment to breeding vacancies and thus provide adequate numbers of birds for flocking.  相似文献   

3.
The importance of seagrass beds and mangroves as a juvenile habitat as opposed to other shallow water habitat types is investigated using a single sampling method on four islands in the western Indian Ocean for Cheilinus undulatus, and on one island in the southern Caribbean Sea for Scarus guacamaia. Both species occur on the Red list of threatened species. Juveniles of Cheilinus undulatus were predominantly found on seagrass beds while adults were limited to the coral reef. The presence of seagrass beds resulted in significantly higher densities of the species on coral reefs in front of these habitats, indicating the importance of seagrass beds as a juvenile habitat. For Scarus guacamaia, juveniles were exclusively observed in mangroves while adults only occurred on the coral reef. Adult S. guacamaia occurred on all coral reefs along the sheltered coast of the island containing mangroves, but no relationship with distance to mangroves was observed. This could indicate the importance of mangroves for the occurrence of adults of this species on the scale of an entire island.  相似文献   

4.
A two-year tagging programme on Cousin Island, Seychelles showed that Hawksbills nested between September and March, each female nesting on average four times at intervals of 15 to 18 days. Females did not nest in successive years but the number of years between breeding attempts is not known. Twenty to thirty females now nest each year; the number of nests has increased markedly since the island became a nature reserve in 1968. Some females tried to nest on other islands in the same season, although those returning to Cousin usually did so within 50 m of their previous nest. The average clutch was 182, the largest recorded for any sea turtle, and the maximum estimate of average nest success was 86%. Present exploitation in the Seychelles is unsound from both biological and sociological points of view, exploiting the vulnerable breeding stock for a luxury product (‘tortoiseshell’) while wasting potentially valuable protein. It is recommended that future policy should concentrate instead on harvesting eggs for human consumption, while totally protecting adults, thus diverting valuable protein from natural predators to the local human population. This policy would exploit the stage of the turtle's life cycle best adapted to sustain high losses with minimum effect on breeding stocks, to the mutual benefit of turtle and local human populations.  相似文献   

5.
Although previous studies have demonstrated high use of shade coffee plantations by Neotropical migratory birds, we still have a poor understanding of the suitability of shade coffee plantations as habitat on the wintering grounds. We studied density, body condition, and survivorship of Neotropical migrants, with emphasis on cerulean warbler (Dendroica cerulea), in primary forest and shade coffee plantations in Venezuela. We worked in three primary forest sites and three shade coffee plantations on the western slope of the Cordillera de Mérida of the Andes Mountains. At each site, we surveyed migrants with distance-based line transects and mist-netted and banded migrants during November–February 2005/06 and 2006/07. In addition, we estimated apparent monthly survival for cerulean warbler based on 29 color-banded individuals. Densities of migrants were 3–14× higher in shade coffee plantations than primary forest sites, even after accounting for differences in detectability. Apparent monthly survival of cerulean warblers was estimated at 97% and overwinter persistence was similarly high. In addition, cerulean warblers demonstrated high between-season fidelity, with 65% of the birds banded the first year being resighted during the second year. Interestingly, immature birds returned at nearly half the rate as did adults. Banding data indicated that body condition increased significantly as the season progressed for cerulean warblers, Tennessee warblers (Vermivora peregrina), and American redstarts (Setophaga ruticilla). Collectively, these data provide evidence that shade coffee plantations offer high quality wintering habitat for Neotropical migrants, including cerulean warblers.  相似文献   

6.
The Seychelles giant millipede, Seychelleptus seychellarum, is abundant on Cousine Island, Seychelles (ca. 4.4 ind m−2), where there are no alien invasive mammals as predators. This study of its feeding behaviour and activity pattern showed that its dietary range is wide, feeding mostly on leaf litter and fallen fruit. There were quantitative differences in the feeding behaviour and activity patterns of both sexes and immatures. Its ingestion rate for its size was relatively low, but its role in litter breakdown was substantial. It ingested 4.55% of the litter standing crop, and 17.19% of the daily litter fall every 24 h. Total faecal production was 2.90% of the total litter standing crop and 10.96% of the daily litter fall. This has a highly significant effect on Cousine Island which, being small and granitic, depends on nutrient cycling to maintain its ecological integrity, especially when seabirds are absent and not contributing to soil nutrient input. As this Seychelles endemic millipede has been extirpated from several islands, its continued conservation on the islands where it still occurs is not simply about conserving an endemic species, but also about maintaining intact a tropical ecosystem, with a keystone species.  相似文献   

7.
In 1998, only 25 Tahiti Flycatchers (Pomarea nigra), a forest bird endemic to Tahiti (French Polynesia) remained. A recovery programme, aimed at nest protection through both rodent control and tree banding, was initiated. At this time it was supposed that the species was mainly the victim of island infestation by ship rats (Rattus rattus). In the 3 years of this study 54 nests were found and 17 fledged young produced, of which 12 survived the early stage of fledging. Despite an excellent 1999 breeding season and efficient nest protection against rodents, only five of 19 nests produced fledged young in 2000. This was related to higher (P=0.002 and 0.015 respectively) Indian Mynah (Acridotheres tristis) encounters and aggressive interactions in 2000 and 1998 than in 1999. Indian Mynah encounters and interactions were also higher during reproductive activities (and particularly at incubation and nestling stages) in comparison with the non breeding period (P <0.001). In contrast, Red-vented Bulbul (Pycnonotus cafer) encounters and interactions were more uniform throughout. Significantly more Indian Mynah and Red-vented Bulbul were observed in flycatcher territories which experienced nest failure or early fledgling death in comparison with those which experienced reproductive success (P=0.003 and 0.002 respectively). This strongly suggests that these two introduced species represent an important threat to the Tahiti Flycatcher’s survival. Currently, young birds (less than 4 years old) represent 42% of the population, an increase from 12% at the start of the recovery programme.  相似文献   

8.
Many wild reptile species are threatened by habitat loss. However, the way in which changes in landscape patterns influence intraspecific ecological processes is not completely understood. Boa constrictor occidentalis is an endangered species and has a special conservation value since it is endemic of dry forests in the Gran Chaco region. Because the Gran Chaco is largely threatened due to habitat loss it is necessary to know how landscape changes influence this species. Therefore, we evaluated the effects of forest loss and landscape composition on the reproductive life-history parameters. Landscape changes were assessed by analyzing satellite imagery and reproductive parameters were determined by ultrasound images of the reproductive structures. The obtained results indicate that habitat loss may affect body condition, clutch size and testicular volume of the Argentine boa constrictor. We also found that the spatial pattern of vegetation influences the distribution of females and males in the landscape. Matting aggregations are scarce in shrublands. Therefore, our study shows that forest loss could enhance vulnerability to extirpation through constraints placed on reproduction. We encourage resource managers to evaluate sensitive reproductive life-history parameters as well as habitat deterioration to asses the conservation status of the populations of the Argentine boa constrictor. Since the Gran Chaco forest, a key habitat to the species’ reproduction, is largely threatened, strong conservation action is needed to halt and reverse forest loss in this region.  相似文献   

9.
An important requirement for biologists conserving vulnerable species of wildlife and managing genetic problems associated with small population size is to evaluate existing evidence regarding what is known of a species’ recent population history. For endemic island species in particular, current genetic impoverishment could be due to either a recent population crash or a consequence of an evolutionary history of sustained isolation and small effective population size. Interpreting any given case can often be further complicated by incomplete or contradictory evidence from historical field surveys that might suggest a very different demographic history. Here, we use the case of the Seychelles kestrel (Falco araea), an island endemic previously listed as critically-endangered but now relatively common, to illustrate how genetic data from microsatellite genotypes of 100–150-year-old museum specimens reveals a recent and severe population crash since the 1940s to approximately eight individuals, before the population recovered. We re-interpret the historical population trajectory of the Seychelles kestrel in the light of the minimal intervention required for this species to recover. We examine different ecological explanations for the decline and apparently unassisted recovery of the Seychelles kestrel, review the evidence for similarly unaided recoveries elsewhere and discuss the implications of unaided population recoveries for future species conservation programmes. Demographic profiles from historical genetic signatures can provide highly informative evidence when evaluating past and future recovery efforts for endangered species.  相似文献   

10.
Montane grassland is a severely threatened habitat in Kenya. Despite a high level of faunal endemism, it has received very little conservation attention. We investigated habitat selection in a threatened grassland endemic bird species, Sharpe's longclaw (Macronyx sharpei) (family Motacillidae), in order to understand its likely response to land-use changes. Between November 1995 and May 1996, we studied 41 territories of this species on the Kinangop Plateau in central Kenya. With an overall density of 0.4 birds ha−1, longclaws lived in permanent groups of two to seven individuals. They were sedentary and territorial, with a mean home range size of 0.5 ha. The species avoided non-grassland areas entirely, and within grassland showed a strong preference for short grass with tussocks. Territory sizes and foraging ranges were smaller, and rates of pecking for food higher, in this grassland type than in open short grass or long grass. Land use changes, in particular conversion to cultivation or woodlots and ploughing up of grassland to remove tussocks, pose a serious and immediate threat to this species. Dairy farming is potentially compatible with grassland conservation, and conservation-friendly livestock rearing needs to be promoted through economic incentives, awareness-raising and technical advice.  相似文献   

11.
The effects of habitat fragmentation on the Australian avifauna have been widespread with species richness and abundance declining with reduced remnant size and habitat quality and increased habitat isolation. The speckled warbler, Chthonicola sagittata is one species from the highly fragmented temperate woodlands of eastern Australia that has declined across its range and populations that remain appear to be patchily distributed in habitat remnants. Specific causes of decline are unknown but several aspects of its biology make the species particularly vulnerable to decline in fragmented landscapes. Here, we analyse survey data (presence/absence) of speckled warblers in a large sample of habitat remnants from three regions to identify patterns of occupancy. We explore the effects of patch size on extinction risk using population viability analyses (PVA) and detailed demographic data from a behavioural study of individuals in the Australian Capital Territory, south-eastern Australia. Patch size was a strong predictor of the persistence of speckled warblers in habitat remnants. High density populations had higher probabilities of persisting, and inclusion of an Allee effect during drought decreased the probability of persistence. In the absence of an Allee effect, only high density populations in patches greater than 300 ha and low density populations in patches greater than700 ha had more than an 80% probability of persisting over 100 years. The accelerating decrease in population persistence below approximately 200-400 ha suggests that small populations were particularly vulnerable to stochastic demographic and environmental events. Adult female mortality was the single most important factor in driving population extinction. Our PVA model predictions matched the survey data for the Australian Capital Territory region remarkably well, but failed to predict occupancy rates in remnants in other regions. Differences in occupancy patterns between regions may, however, have resulted from inbreeding depression. This study demonstrates both the strengths and limitations of PVA analysis. PVA can predict occupancy patterns with reasonable accuracy, given good demographic data, but data for one region cannot be used universally for all regions. We highlight the need for studies of demography in different regions to interpret regional patterns of occupancy and to identify mechanisms of decline in remnant habitat.  相似文献   

12.
The pale-headed brush-finch (Atlapetes pallidiceps) is threatened with extinction due to habitat loss, but very little is known about its ecological requirements. We used multiple logistic regression to study habitat selection of this species at landscape, territory, and nest site scales in order to make recommendations about effective management. Habitat selection by the sympatric stripe-headed brush-finch (Buarremon torquatus) was examined with the same methods in order to analyse interspecific resource partitioning and potential competition. The pale-headed brush-finch selected semi-open habitat types with intermediate scrub heights, and avoided forests. Nest sites depended on the presence of vines or bamboo. By contrast, the stripe-headed brush-finch chose dense habitat with low ground cover under tall vegetation and avoided semi-open habitat. The two species had overlapping territories but differed significantly in microhabitat use and the use of vegetation strata. We found no convincing evidence that the stripe-headed brush-finch displaces the pale-headed brush-finch from optimal habitat. The preservation of semi-open scrubland maintained by low-intensity grazing is suggested for future conservation of the pale-headed brush-finch.  相似文献   

13.
We investigated the relationship between habitat quality, abundance, group size and breeding success in the threatened Kenyan endemic Hinde's babbler (Turdoides hindei; Family Timaliidae), a co-operative breeder mainly associated with riverine thickets in cultivated areas. At two intensively cultivated sites, significantly more Hinde's babbler groups occurred in areas retaining at least 3% thicket cover, while breeding outcome improved where cover exceeded 9%. Despite previous concerns over low breeding success, the percentage of young birds present (17%, n=424 birds aged) was similar to that of a sympatric congener, the northern pied babbler (T. hypoleucus) (12%, n=162), and comparable with that of two other African congeners. Although breeding outcome was positively correlated with adult group size, there was no evidence that larger groups monopolised more favourable habitat or defended larger territories. Group density showed a positive, non-linear relationship with adjacent cover, levelling out where this exceeded 15-20%. Our findings suggest that even a modest increase in thicket cover may significantly raise the density and productivity of Hinde's babblers at these sites.  相似文献   

14.
Habitat specialists are especially vulnerable to habitat alterations in vegetation structure and composition, making them difficult to protect and restore amidst agricultural landscapes. Protection strategies in such cases require information on species’ ability to survive and reproduce on marginal and modified habitat. We examined reproductive success, survival, and foraging efficiency of the Florida Scrub-Jay (Aphelocoma coerulescens), an extreme habitat specialist, in a human-modified habitat - regenerating pasture - along a pasture-native scrub interface. From 1985 to 2003, Florida Scrub-Jays were equally successful at producing young in regenerating pasture and native scrub. Production of eggs, nestlings, fledglings, independent young, and yearlings were not statistically different between territories containing pasture and those containing only scrub. Similar trends were observed for nest success and survival. When in pasture, individual jays were significantly more efficient at capturing small prey items, but significantly less efficient at capturing medium and large prey items. Availability of small prey items was significantly higher in pasture than in scrub; availability of medium and large prey items was not significantly different between habitat types. We conclude that regenerating pasture provides suitable supplemental habitat for Florida Scrub-Jays when in close proximity to native scrub, suggesting a novel conservation strategy for maintaining and potentially increasing local populations in fragmented agricultural settings. This case study illustrates how a broadened definition of ‘suitable habitat’ may augment existing conservation strategies for specialist species facing substantial and rapid modification of their native habitat.  相似文献   

15.
A population viability analysis (PVA) was conducted to assess the minimum viable population (MVP) of the Atlantic Forest spiny rat Trinomys eliasi, a species threatened by habitat loss and restricted geographical distribution. Objectives were to suggest quasi-extinction thresholds, estimate minimum areas of suitable habitat (MASH) and MVPs, and compare results with the species’ current status. The computer package VORTEX was used. The model predicted sizes of 200 animals to achieve demographic stability, but buffering declines in genetic variability required populations of 2000 animals. Estimated MASHs were approximately 250 and 2500 ha for demographic and genetic stability, respectively. Mortality rate and mean litter size were the most sensitive parameters to changes in model assumptions. The protection of known populations and the search for extant populations are the first steps in conservation. T. eliasi's issue could help protecting the coastal shrubland ecosystem of Rio de Janeiro state. Observing IUCN's criteria for listing threatened species, it is suggested that T. eliasi should be ranked as vulnerable in red lists.  相似文献   

16.
About twenty-five percent of all southern African Oxalis species are rare/endangered and highly localized, making them especially vulnerable to extinction through inbreeding, low genetic variation, disrupted biological interactions and stochastic events; all consequences of small population sizes. Moreover, Oxalis displays tristyly, which is a rare and specialized sexual system that includes a strong self-incompatibility component between three floral morphs to promote out-crossing within populations. As tristyly requires the availability of plants with different floral morphs as well as effective pollinators for seed production, this breeding system can affect small populations when fully expressed. Factors that may have an effect on rarity in Oxalis were investigated by focusing on the expression of tristyly, levels of natural seed production, clonality and the ecology of eight rare/highly localized Oxalis species. Field experiments revealed that the reproductive success of some Oxalis species may be hampered by tristyly, resulting in extremely low levels of natural seed production. Other species display a more relaxed expression of self-incompatibility, which in combination with the possibility of cross-pollinations provides reproductive assurance regardless of population structure and pollinator availability. Others are rare and endangered, but appear not to be negatively affected by the tristylous breeding system. Most species are limited by their highly specific habitat requirements and are particularly vulnerable to variation in rainfall patterns.  相似文献   

17.
Although edge effects often significantly alter abiotic habitat variables, and the performance and behaviour of plant and animal species, they are rarely taken into account when designing nature reserves or managing the movement of visitors within reserves. In this study, we examined the effects of proximity to a habitat edge, created by a visitor pathway, on reproductive success of the orchids Phaius delavayi and Ponerorchis chusua within the Huanglong National Park, China. Parallel transects were established at different distances from the pathway to test the effects of proximity to the pathway on male and female reproductive success in two consecutive years. For Phaius delavayi, percentage pollinarium removal and percentage fruit set showed significant variation between transects in both years, with plants in transects closer to the pathway having lower reproductive success. P. chusua showed the same trends except for pollinarium removal in one year. These results are consistent with the hypothesis that proximity to the pathway, which is used by a large number of visitors every day throughout the orchids’ flowering seasons, interfered with pollinator activity, depressing male and female reproductive success in both species. The impacts on reproductive success were significant for plants within approximately 10 meters of the pathway. Such edge effects may be common, and may need to be considered when designing nature reserves in which visitor activity is encouraged.  相似文献   

18.
Feral goats (Capra hircus) are implicated in habitat destruction, and alteration of species composition on sensitive insular ecosystems. In the absence of population control, goats have become the ecologically dominant species on many islands with the results that numerous endemic plant species have been extirpated, or are threatened by excessive grazing. It is demonstrated that removal of goats can lead to rapid recovery of suppressed vegetation. The problems associated with excessive numbers of feral goats have rarely been studied or formally recognised. Extensive and intensive research is critically needed if affected island ecosystem are to be preserved or restored.  相似文献   

19.
Understanding population differentiation and genetic diversity within population is critical to the development of conservation programmes for threatened species. The protected species, Anchusa crispa Viv. occurs on coastal sand dunes in three disjunct geographical groups of populations: two populations on the east coast of Corsica, several populations around a single estuary on the west coast of Corsica and at a number of sites in north-west Sardinia, where two different subspecies occur. In this study we quantify differentiation of reproductive traits and isozymes among regions and populations on Corsica and between subspecies on Sardinia. No isozyme variation was detected within any of the studied populations nor among populations from a given geographic region. Two loci showed geographic differentiation between regions on Corsica. On Sardinia, the two subspecies showed no isozyme differentiation, and, depending on the loci examined, are similar to one or other of the two regions on Corsica. Reproductive traits show significant differentiation between geographic regions on Corsica, but little variation among populations within a region. In populations on the west coast of Corsica, flowers are small and have a stigma situated at the same level as the apex of the anthers whereas on the east coast, flowers are larger and have the stigma below the anthers. On Sardinia, A. crispa subsp. crispa has a floral morphology similar to the Corsican plants, whereas subspecies maritima has larger flowers with the stigma positioned above the anthers (approach-herkogamy). Quantitative variation in floral morphology thus agrees with the separation of two taxonomic entities on Sardinia and geographic variation in reproductive traits and isozymes has important ramifications for the sampling of populations for conservation programmes.  相似文献   

20.
Understanding the decline and extinction of species has become critical to conservation biology. The five monarch species of the genus Pomarea, endemic to the southeastern Pacific, are all listed as threatened. Introduced mammals and birds are believed to be responsible for their rarefaction. We analyzed the historical and current distribution of monarchs and introduced animals and found no relation between presence of Polynesian rats (Rattus exculans) and monarch distribution. There was a highly significant correlation between the arrival of the black rat (Rattus rattus) and the decline and extinction of monarch populations. The extinction of monarch populations after colonization by black rats tended to take longer on larger islands than on smaller ones. On islands without black rats, monarchs persisted even where forests have been reduced by more than 75%. After an island was colonized by black rats the number of monarch pairs with young decreased dramatically. Eggs in artificial nests placed in sites used by monarchs were only preyed upon by black rats. No eggs were preyed upon by Polynesian rats (Rattus exulans) or introduced birds. Monarch nests were mainly placed on horizontal branches inside the canopy and were more accessible than nests of Polynesian warbler (Acrocephalus caffer), a species still locally abundant. Warbler nests were placed higher up on vertical branches near the top of trees. These studies suggest that nest predation by black rats has been the main cause of monarch decline. However observations of direct aggression of adult monarchs by introduced red-vented bulbuls (Pycnonotus cafer), especially when monarchs raise their young, suggest that introduced birds could aggravate the decline of monarch populations already weakened by black rats. We discuss the practical implications of these findings for monarch conservation.  相似文献   

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