We examine the abundance and distribution of Sumatran tigers (Panthera tigris sumatrae) and nine prey species in Bukit Barisan Selatan National Park on Sumatra, Indonesia. Our study is the first to demonstrate that the relative abundance of tigers and their prey, as measured by camera traps, is directly related to independently derived estimates of densities for these species. The tiger population in the park is estimated at 40-43 individuals. Results indicate that illegal hunting of prey and tigers, measured as a function of human density within 10 km of the park, is primarily responsible for observed patterns of abundance, and that habitat loss is an increasingly serious problem. Abundance of tigers, two mouse deer (Tragulus spp.), pigs (Sus scrofa) and Sambar deer (Cervus unicolor) was more than four times higher in areas with low human population density, while densities of red muntjac (Muntiacus muntjac) and pigtail macaques (Macaca nemestrina) were twice as high. Malay tapir (Tapirus indicus) and argus pheasant (Argusianus argus), species infrequently hunted, had higher indices of relative abundance in areas with high human density. Edge effects associated with park boundaries were not a significant factor in abundance of tigers or prey once human density was considered. Tigers in Bukit Barisan Selatan National Park, and probably other protected areas throughout Sumatra, are in imminent danger of extinction unless trends in hunting and deforestation are reversed.

The current extinction crisis is caused primarily by human impacts upon wild populations. Large carnivores are especially sensitive to human activity; because their requirements often conflict with those of local people, predators have been actively persecuted in most regions of the world. In this paper, the impact of people upon predators is analysed by relating local carnivore extinctions to past and projected human population densities. There are strong associations between high human density and the loss of carnivore populations from a region. Interspecific variation in ability to survive at high human densities probably reflects species' ability to adapt to human-modified habitats. However, regional and temporal variation in individual species' sensitivity to human density is more likely to reflect the activities of local people than the phenotypes of local carnivores. Local culture, government policy and international trade all influence human attitudes to predators and, therefore, the impact of people upon carnivore populations. The importance of these factors may mean that extinction risks for carnivores will continue to increase, even though human population growth is projected to deccelerate during the new millennium. This points to an urgent need for techniques to resolve conflicts between people and predators at either the local or landscape level.

Minimum convex polygons (convex hulls) are an internationally accepted, standard method for estimating species' ranges, particularly in circumstances in which presence-only data are the only kind of spatially explicit data available. One of their main strengths is their simplicity. They are used to make area statements and to assess trends in occupied habitat, and are an important part of the assessment of the conservation status of species. We show by simulation that these estimates are biased. The bias increases with sample size, and is affected by the underlying shape of the species habitat, the magnitude of errors in locations, and the spatial and temporal distribution of sampling effort. The errors affect both area statements and estimates of trends. Some of these errors may be reduced through the application of α-hulls, which are generalizations of convex hulls, but they cannot be eliminated entirely. α-hulls provide an explicit means for excluding discontinuities within a species range. Strengths and weaknesses of alternatives including kernel estimators were examined. Convex hulls exhibit larger bias than α-hulls when used to quantify habitat extent and to detect changes in range, and when subject to differences in the spatial and temporal distribution of sampling effort and spatial accuracy. α-hulls should be preferred for estimating the extent of and trends in species' ranges.

The monitoring and management of species depends on reliable population estimates, and this can be both difficult and very costly for cryptic large vertebrates that live in forested habitats. Recently developed camera trapping techniques have already been shown to be an effective means of making mark-recapture estimates of individually identifiable animals (e.g. tigers). Camera traps also provide a new method for surveying animal abundance. Through computer simulations, and an analysis of the rates of camera trap capture from 19 studies of tigers across the species' range, we show that the number of camera days/tiger photograph correlates with independent estimates of tiger density. This statistic does not rely on individual identity and is particularly useful for estimating the population density of species that are not individually identifiable. Finally, we used the comparison between observed trapping rates and the computer simulations to estimate the minimum effort required to determine that tigers, or other species, do not exist in an area, a measure that is critical for conservation planning.

In a recent analysis Woodroffe (2000) found a positive relationship between historical patterns of large carnivore extinction probability and human population density. However, much of the data in this analysis came from a period when carnivore extermination was a management objective. In order to explore the hypothesis that large carnivores can persist at high human densities when the management regime is more favourable we have repeated the analysis using up-to-date data from North America and Europe. In North America we found that large carnivore populations have increased after favourable legislation was introduced, despite further increases in human population density. In Europe we found no clear relationship between present carnivore distribution and human population density. We therefore believe that the existence of effective wildlife management structures is more important than human density per se.

Maintaining genetic variation for future evolutionary change is an important issue for conservation biology. However, there is controversy over the effective population size (Ne) required for endangered species to retain their evolutionary potential, with proposed sizes ranging from 500 to 5000. The highest estimate is based on the assumption that 90% of mutations are deleterious. We review the arguments for an effective size of 5000 and conclude that it assumes effective mutation rates that are too low, and heritabilities that are, in general, very high. We conclude that an Ne of 500–1000 is appropriate at this time.

It is necessary to look at the big picture when managing biological resources on the Qinghai—Xizang (Tibetan) plateau. Plateau pikas (Ochotona curzoniae) are poisoned widely across the plateau. Putative reasons for these control measures are that pika populations may reach high densities and correspondingly reduce forage for domestic livestock (yak, sheep, horses), and because they may be responsible for habitat degradation. In contrast, we highlight the important role the plateau pika plays as a keystone species in the Tibetan plateau ecosystem. The plateau pika is a keystone species because it: (i) makes burrows that are the primary homes to a wide variety of small birds and lizards; (ii) creates microhabitat disturbance that results in an increase in plant species richness; (iii) serves as the principal prey for nearly all of the plateau's predator species; (iv) contributes positively to ecosystem-level dynamics. The plateau pika should be managed in concert with other uses of the land to ensure preservation of China's native biodiversity, as well as long-term sustainable use of the pastureland by domestic livestock.

To ensure the effective conservation of biodiversity the distribution of species needs to be accurately characterized and areas of high species richness located. For many taxa this can be achieved only by experienced taxonomists. Taxonomic research has a large input from non-professional or amateur researchers, in addition to professionals working at museums or universities. The decline of taxonomy and the number of taxonomists within the professional community has been widely publicized, but the trends in the activities of amateur taxonomists are unclear. Because amateurs contribute many valuable records of species occurrence this may have a disproportionate impact upon the information available for conservation planning and represents an underappreciated threat to conservation planning. We use taxonomic research by UK entomologists in order to evaluate the changing role of both amateur and professional taxonomists. We reviewed contributions by British-based authors to Entomologist's Monthly Magazine over the past century. Our results show that both amateur and professional taxonomy have undergone a long and persistent decline since the 1950s, in terms of both the number of contributors and the number of papers contributed. It is argued that the conservation community needs to help try and reverse the decline of taxonomy.

Reintroduction of captive-bred animals is a key approach in conservation attempts for many endangered species, however, post-release survival is often low. Rearing conditions may be unlike those encountered upon release and the animals may not have had experiences necessary for survival in the wild. Animals may also habituate in captivity to stimuli that may pose a danger after release and/or there may be selection for behavioural traits, in particular reduced fearfulness, that may not be suited for the wild. Here, variation in boldness was assessed in captive-bred swift fox (Vulpes velox) and tested for influence on survival after release. Radio-tracked individuals that died in the 6 months following release were those judged previously as bold. In the presence of novel stimuli in captivity, they had left their dens more quickly, approached more closely to the stimuli and shown more activities indicating low fear than did those that survived. These individuals were less suited for release. Future selection of release-candidates on the basis of behavioural variation should enhance the success of reintroduction programmes.

Taxonomic bias has been documented in general science and conservation research publications. We examined whether taxonomic bias is similarly severe in actual conservation programmes as indicated by the focus of species reintroduction projects worldwide. We compiled a database of reintroduction projects worldwide, yielding a total of 699 species of plants and animals that are the focus of recent, current or planned reintroductions. Using IUCN (World Conservation Union) data for total numbers of known species worldwide, we found that vertebrate projects were over-represented with respect to their prevalence in nature. Within vertebrates, mammals and, to a lesser extent, birds, were over-represented, whereas fish were under-represented. This over-representation extended to two mammal orders, artiodactylids and carnivores, and to four bird orders, anseriforms, falconiforms, gruiforms and galliforms. For neither mammals nor birds was reintroduction project bias related to any differences between orders in vulnerability to threat. Bird species that are the focus of reintroduction efforts are more likely to be categorised as ‘Threatened’ than expected on the basis of the distribution of all known species over all threat categories, however, nearly half of all bird species being reintroduced are classified as ‘Least Concern’. The selection of candidates for reintroduction programmes is likely to consider national priorities, availability of funding and local community support, over global conservation status, While a focus on charismatic species may serve to garner public support for conservation efforts, it may also divert scarce conservation resources away from taxa more in need of attention.

It is commonly held that species loss is linked to human population size but there are surprisingly few quantitative studies that measure the strength and nature of this linkage. In a study of about 150 nations, a highly significant positive relationship (P << 0.01) was found between population size and threat levels of birds and mammals. For continental nations, log population explains 16-33% of the variation in threat level among nations. The pattern of the continental population-threat correlation indicates that per capita human impacts are initially very high and asymptotically diminish with increasing population size. No population-threat correlation was found for island nations, since human impacts are apparently so catastrophic that human population size is largely irrelevant. Surprisingly, for both islands and continents, area does not affect the level of threat after human population size is accounted for. Thus, even on continents the harmful impacts of humans, for a given population size, are evidently so profound that no amount of added area provides compensatory refugia for native species. Major regional differences in levels of threat are shown, with nations in Asia and the Middle East having generally higher proportions of threatened species than nations in Africa. The causes of these differences are only partly related to population size. Other factors not related to population size are that Asian nations tend to have much higher rates of mammal over-harvesting and Middle Eastern nations tend to have statistically lower percentages of area set aside as preserves. Threat proportions are correlated between birds and mammals among nations implying that one group may be a proxy indicator of impacts on the other. The slope of this relationship indicates that mammals suffer more losses during initial human impacts but proportions of threatened birds increase more rapidly than mammals as human impacts become more widespread.

Single locus neutralist models predict that population size bottlenecks will reduce genetic variation and increase inbreeding, thereby reducing evolutionary potential. However, experimental evaluations of the effects of bottlenecks on quantitative genetic variation do not always follow predictions, especially for characters related to reproductive fitness. Populations of Drosophila melanogaster were subjected to population bottlenecks of a single pair for one or three generations, and their ability to tolerate increasing concentrations of NaCl was compared with those of their outbred base populations, and related highly inbred lines. Bottlenecked populations became extinct at significantly lower concentrations of NaCl than their non-bottlenecked base populations. Population bottlenecks should be avoided in managing species of conservation concern.

Large carnivores have declined worldwide, largely through conflict with people. Here, we quantify the impact of lethal control, associated with livestock depredation, on a population of African lions (Panthera leo) living outside protected areas. Farmers shot lions only in response to livestock attacks. Nevertheless, adult mortality was high and a simple model predicted that the population was marginally stable or slowly declining. Mortality was four times higher among lions radio-collared in association with attacks on livestock, than among lions with no known history of stock killing, suggesting that some animals were habitual stock killers. Known stock killers also experienced lower reproductive success; hence there was strong artificial selection against stock-killing behaviour. In addition, mortality was higher among lions whose home ranges overlapped a property where non-traditional livestock husbandry was associated with chronic depredation by lions. This 180 km2 ranch acted as a sink that directly affected lions over more than 2000 km2 and may have undermined the viability of the study population. Our results suggest that sustainable coexistence of lions and people demands livestock husbandry that effectively deters predators from acquiring stock-killing behaviour, but that lethal control may play an important role in avoiding the spread of such behaviours through the population.

We synthesize the results of empirical studies of marine reserves to assess the potential benefits of protection for fish populations. Our meta-analyses demonstrate that the overall abundance of fishes inside reserves is, on average, 3.7 times higher than outside reserve boundaries. This enhancement is mainly a result of a significant increase in abundance of species that are the target of fisheries. Non-target species are equally abundant inside and outside reserves. Large-bodied species also respond more to protection, irrespective of their fishery status. Species within genera show great heterogeneity in their response to protection despite similarities in their life histories. Our study confirms that marine reserves benefit fish populations and highlights the need for monitoring prior to reserve establishment to provide more accurate, habitat-controlled studies of the effects of marine reserves on fish populations.

The conservation of migratory species can be problematic because of their requirements for large protected areas. We investigated this issue by examining the annual movements of the migratory wildebeest, Connochaetes taurinus, in the 25000 km2 Serengeti-Mara Ecosystem of Tanzania and Kenya. We used Global Positioning System telemetry to track eight wildebeest during 1999–2000 in relation to protected area status in different parts of the ecosystem. The collared wildebeest spent 90% of their time within well-protected core areas. However, two sections of the wildebeest migration route – the Ikoma Open Area and the Mara Group Ranches – currently receive limited protection and are threatened by poaching or agriculture. Comparison of current wildebeest migration routes to those recorded during 1971–73 indicates that the western buffer zones appear to be used more extensively than in the past. This tentative conclusion has important repercussions for management and needs further study. The current development of community-run Wildlife Management Areas as additional buffer zones around the Serengeti represents an important step in the conservation of this UNESCO World Heritage Site. This study demonstrates that detailed knowledge of movement of migratory species is required to plan effective conservation action.

Population models incorporating demographic, environmental and genetic stochasticity were created from long-term data on natural populations of 30 species of vertebrates. The probability of extinction for a single population in a continuous habitat was compared to that of multiple isolated, or semi-isolated, populations occupying a fragmented landscape with an equivalent total carrying capacity. Populations occupying a fragmented landscape were modelled for a range of dispersal rates and levels of asynchrony in the effects of environmental disturbances. Dispersal among subpopulations in the fragmented landscape partially alleviates the effect of fragmentation on extinction rates, despite the models explicitly incorporating disease epidemics which spread between subpopulations through dispersal. Even moderate environmental correlations among subpopulations greatly reduces the viability of the metapopulation relative to the case where the populations are totally independent. Whether a population performed better as a single population or as a metapopulation was strongly affected by the carrying capacity assumed, the time frame examined and the initial fitness of the population. A single population always fared better when the total habitat available was capable of supporting ≤1000 adults. Thus, continued habitat fragmentation can be expected to fuel the ongoing global extinction crisis and conservation efforts should be aimed at interconnecting isolated habitat patches.

Although the massive organized slaughter of African wild dogs, Lycaon pictus, largely ended several decades ago, this endangered canid continues to decline and faces extinction. Several lines of evidence suggest that this arises from obligate cooperative breeding, which makes Lycaon more sensitive to anthropogenic mortality. A number of behaviours in this species are characterized by a reliance on helpers. These include cooperative hunting, defence from kleptoparasitism, pup feeding and baby-sitting. As a result, there are strong, positive relationships between pack size and the production and survival of pups, and pairs of wild dogs are often unsuccessful at raising offspring without the assistance of helpers. Consequently, a pack in which membership drops below a critical size may be caught in a positive feedback loop: poor reproduction and low survival further reduce pack size, culminating in failure of the whole pack. Here, we review the literature to reveal the importance of pack size in the African wild dog. Most importantly, we argue that there is a critical minimum threshold, below which packs face an increasing probability of extinction - an Allee effect with consequences for the conservation of this species, and of other obligate cooperators.

For practical reasons, managers and policy-makers have to make rapid decisions with limited information on the status of endangered species. Because of its relative ease of acquisition, the most common surrogate used to derive inferences about the risk of extinction is population size. This is not to say that population size is the best indicator of risk; other considerations, such as the recent rate of population decline, are of clear importance (Mace & Lande, 1991). A popular rule of thumb for the critical population size necessary for the maintenance of adequate genetic variance for adaptive evolution in quantitative traits, originally espoused by Franklin (1980) and Soulé (1980), has been an effective population size (Ne) of 500 individuals. More recent assessments, based on both empirical and theoretical developments, suggest that this number should be revised upwards to Ne≃1000–5000 (Lande, 1995a; Lynch, 1995; National Research Council, 1995; Bürger & Lynch, 1997). Here we address the arguments of Franklin & Frankham (1998) that a critical Ne≃500–1000 is adequate for conservation purposes.

Habitat loss and fragmentation are main causes for Asian elephant population declines. We mapped wildlands - large, unfragmented and undeveloped areas - asking: (1) Where are the largest wildlands that constitute elephant habitats? (2) What proportion of these wildlands is protected? (3) What is their potential for elephant conservation? Our study demonstrates that wildlands constitute only 51% of the Asian elephant range. Myanmar has the largest wildland (∼170,000 km2), followed by Thailand and India. In Principal Components Analysis (PCA), the first two components explained 73% of the variation in fragmentation among ranges. We identified three fragmentation clusters from the PCA. Cluster A contains large ranges with unfragmented wildlands; cluster B includes ranges with well-developed transportation networks and large human populations; and cluster C contains ranges with severely fragmented wildlands. In cluster A, we identified four ranges with elephant populations >1000 animals: ARYO, MYUC, BNMH and BITE. Together with ranges that support >1000 elephants in cluster B, these A ranges have great potential for long-term elephant conservation. We propose that fragmentation clusters and population size can be used to identify different elephant monitoring and management zones.

While subsidised populations of feral cats are known to impact their prey populations, little is known about the ecological impact of inside/outside hunting cats (IOHC). We studied IOHC around a suburban nature preserve. Mail surveys indicated an average of 0.275 IOHC/house, leading to a regional density estimate of 0.32 IOHC/ha. A geographical model of cat density was created based on local house density and distance from forest/neighbourhood edge. IOHC hunted mostly small mammals, averaging 1.67 prey brought home/cat/month and a kill rate of 13%. Predation rates based on kills brought home was lower than the estimate from observing hunting cats (5.54 kills/cat/month). IOHC spent most outside time in their or their immediate neighbours' garden/yard, or in the nearby forest edge; 80% of observed hunts occurred in a garden/yard or in the first 10 m of forest. Radio-tracked IOHC averaged 0.24 ha in home-range size (95% minimum convex polygon (MCP)) and rarely entered forest. Confirming this, scent stations detected cats more often near the edge and more cats were detected in smaller forest fragments. There was no relationship between the number of cats detected in an area and the local small mammal abundance or rodent seed predation rates. Cold weather and healthy cat predator populations are speculated to minimise the ecological impact of IOHC on this area.