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In addition to habitat loss and fragmentation, demographic processes—the vagaries of births, deaths and sex ratio fluctuations—pose substantial threats to wild giant panda populations. Additionally, climate change and plans for the Giant Panda National Park may influence (in opposing directions) the extinction risk for wild giant pandas. The Fourth National Giant Panda Census showed pandas living in 33 isolated populations. An estimated 259 animals live in 25 of these groups, ~14% of the total population. We used individual-based models to simulate time series of these small populations for 100 years. We analysed the spatial pattern of their risk of extinction under current conditions and multiple climate change models. Furthermore, we consider the impact of the proposed Giant Panda National Park. Results showed that 15 populations face a risk >90%, and for 3 other populations the risk is >50%. Of the 15 most at-risk populations, national parks can protect only 3. Under the Representative Concentration Pathway 8.5 climate change scenario, the 33 populations will probably further divide into 56 populations. Some 41 of them will face a risk >50% and 35 face a risk >90%. Although national parks will probably connect some fragmented habitats, 26 populations will be outside national park planning. Our study gives practical advice for conservation policies and management and has implications for the conservation of other species in the world that live in isolated, fragmented habitats. The authors model likely outcomes for the 33 isolated populations reported in the Fourth National Giant Panda Census under multiple RCP scenarios and with the provision of the planned Giant Panda National Park. They find that, although the National Park may connect some fragmented habitats, most of the populations with high extinction risk fall outside the current plans.

Conservation science is a new and evolving discipline, so it seems prudent to explore different approaches. That said, we should examine what we know and, vitally, what works to conserve biodiversity and what does not. Ecosystem processes determine the fate of many species, but many attempts to theorise about ecosystems have led to ever more fanciful descriptions of nature. All conservation is local. It will only succeed if we find ways to accommodate people and nature. That does not mean indigenous knowledge acquired over millennia will be sufficient to our ever more overcrowded planet. Observational and experimental studies of small populations of wild species, however, do provide practical insights into how to manage biodiversity across much larger geographical extents.

Estimates of global forest area vary widely; this discrepancy is now shown to originate primarily from ambiguity in the definition of ‘forest’. Monitoring and reporting should focus on measures more directly relevant to ecosystem function. Deforestation is a major driver of climate change1 and the major driver of biodiversity loss1,2. Yet the essential baseline for monitoring forest cover—the global area of forests—remains uncertain despite rapid technological advances and international consensus on conserving target extents of ecosystems3. Previous satellite-based estimates4,5 of global forest area range from 32.1 × 106 km2 to 41.4 × 106 km2. Here, we show that the major reason underlying this discrepancy is ambiguity in the term ‘forest’. Each of the >800 official definitions6 that are capable of satellite measurement relies on a criterion of percentage tree cover. This criterion may range from >10% to >30% cover under the United Nations Framework Convention on Climate Change7. Applying the range to the first global, high-resolution map of percentage tree cover8 reveals a discrepancy of 19.3 × 106 km2, some 13% of Earth’s land area. The discrepancy within the tropics alone involves a difference of 45.2 Gt C of biomass, valued at US$1 trillion. To more effectively link science and policy to ecosystems, we must now refine forest monitoring, reporting and verification to focus on ecological measurements that are more directly relevant to ecosystem function, to biomass and carbon, and to climate and biodiversity.

Stuart Pimm on the tragic tale of a hobbyist, a heist and a great scientific legacy. Stuart Pimm on the tragic tale of a hobbyist, a heist and a great scientific legacy.

Stuart Pimm considers the obsessive, sometimes dark side to the joyous pursuit of watching birds.

Elephant are increasing across some areas of Africa leading to concerns that they may reduce woodlands through their feeding. Droughts may help limit elephant numbers, but they are generally both episodic and local. To explore more general impacts of rainfall, we examine how its annual variation influences elephant survival across ten sites. These sites span an almost coast-to-coast transect of southern Africa that holds the majority of the ~500,000 remaining savanna elephants. Elephants born in high rainfall years survive better than elephants born in low rainfall years. The relationship is generally weak, except at the two fenced sites, where rainfall greatly influenced juvenile survival. In these two sites, there are also extensive networks of artificial water. Rainfall likely affects elephant survival through its influence on food. The provision of artificial water opens new areas for elephants in the dry season, while fencing restricts their movements in the wet season. We conclude that the combination of these factors makes elephant survival more susceptible to reductions in rainfall. As a result, elephants living in enclosed reserves may be the first populations to feel the impacts of global warming which will decrease average rainfall and increase the frequency of droughts. A way to prevent these elephants from damaging the vegetation within these enclosed parks is for managers to reduce artificial water sources or, whenever practical, to remove fences.

Darwin used the metaphor of a 'tangled bank' to describe the complex interactions between species. Those interactions are varied: they can be antagonistic ones involving predation, herbivory and parasitism, or mutualistic ones, such as those involving the pollination of flowers by insects. Moreover, the metaphor hints that the interactions may be complex to the point of being impossible to understand. All interactions can be visualized as ecological networks, in which species are linked together, either directly or indirectly through intermediate species. Ecological networks, although complex, have well defined patterns that both illuminate the ecological mechanisms underlying them and promise a better understanding of the relationship between complexity and ecological stability.

Stuart Pimm examines E. O. Wilson's grand vision for an Earth shared equally between humanity and nature.

We tested the prediction that we are more likely to create persistent, species-rich plant communities by increasing the number of species sown and allowing communities to assemble over six or seven growing seasons. Treatments consisted of four initial seed mixtures comprising 4, 8, 12 and 16 species that represent four functional groups (C3 graminoids, C4 grasses, N-fixing species, and late-flowering composites) that predominate within North American prairies. Once seeded, half of the plots were left alone to develop without subsequent reseeding. To provide multiple opportunities for establishment, we reseeded the remaining plots with any target species that failed to establish after two growing seasons. There were two 16 x 16 m (256 m2) replicates per treatment established in 1994 and 1996 on former agricultural land. Annually, we measured total species richness and evenness, total cover, and establishment success defined as target species richness and total percentage cover by target species, collectively. In some instances, significant treatment x year interactions indicated that treatment effects on variables varied among years. Both richness and rate of establishment of target communities were higher in the more species-rich mixtures. Moreover, richness of resident species in the plots declined with increasing target species richness. Reseeding had no measurable effect on any of the variables, nor on the eventual establishment of target communities or individual target species. Our results, indicating that establishment of species-rich plant communities can be enhanced by starting with larger numbers of species at the outset, have implications for projects in which community biodiversity creation and maintenance are key goals.

Greater numbers and higher proportions of recent species extinctions have been on islands rather than on continents. In contrast, predictions of massive future extinctions stem from the current clearing of continental, tropical forests1. For instance, since 1600, 97 out of 108 bird extinctions have been on islands2. However, 452 of the total 1,111 species currently considered to be threatened are continental3. Island flora and fauna are uniquely vulnerable to the human introduction of previously absent predators, diseases and other menaces4, whereas species on continents are not so ecologically naive. So could predictions of future continental extinctions based on island histories be exaggerated1? Most threatened species have small geographic ranges5, and the ranges of island species are inevitably smaller than those of continental species. For a given range size, how do the proportions of threatened island and continental species compare? Here we compile the ranges of thepasserine (perching) birds of the Americas. Corrected for range size, continental species are more—not less—likely to be threatened. We use this unexpected vulnerability of continental species with small ranges to produce a map showing where species losses might occur in the long term.

During their colonization by Polynesians and later by Europeans, the Hawaiian islands suffered a massive loss of species. All the extinctions are indirectly attributable to human impact. Nonetheless, it has proved extremely difficult to specify which of several possible mechanisms caused each particular extinction. This seems to admit defeat in the battle to understand past extinctions. Such understanding could guide our efforts to protect species that are now threatened with extinction. Will it be easier to understand the causes of future extinctions? Surveys of future extinctions stress habitat destruction as the simple and dominant mechanism. This contrasts to its secondary (and generally confused) role in past extinctions. I argue that this contrast between the complexity of the past and the apparent simplicity of the future arises because extinction mechanisms are inherently synergistic. Once extensive species losses begin, it may be impossible to separate the mechanisms and thus manage an individual species as if its decline had a single cause.

Much ecology considers only the typical size of a population, yet extreme values may be of particular importance. Unusually low numbers may doom a population to extinction and unusually high numbers may pose an economic threat. Extreme values may also determine the evolutionary traits that predominate. Obviously, even for a fixed variance in annual numbers, the observed maximum and minimum population size will increase the more years that we count the population. Interestingly, over the time scales of available data (

Stuart Pimm enjoys a fellow naturalist's first visit to sub-Saharan Africa, and the global lessons drawn from it.

Habitat fragmentation continues to be a leading threat for our global future. Methods to quantify fragmentation of habitat landscapes, particularly for endangered species, would be especially useful in conservation planning. Using the principles of metapopulation theory, we updated and devised two methods for analyzing fragmented landscapes: metapopulation capacity and abandonment rate. Our version of metapopulation capacity includes a self-colonization component to counteract the issue metapopulation theory experiences with single large patches. We then tested these methods on satellite image range maps of endemic birds in the highland forests of northern Central America.The metapopulation capacity method proved to be a better measure in that it highlighted which patches would be the most successful habitat in the landscape, based on size and connectivity to surrounding patches, thus allowing for species persistence. Unexpectedly, the abandonment rate method proved useful in providing a way of measuring each individual patch’s support to the rest of the landscape system. This could then be used to rank the remaining patches in order of their greatest contribution. Finally, by using a historical satellite map that showed previously forested habitat in the now deforested landscape, we were able to generate optimal restoration sequences by ranking each 1 km squares’ potential contribution.

Habitat destruction, especially of the humid forests in the tropics, is the main cause of the species extinctions happening now. New work documents the uneven, highly clumped distribution of vulnerable species on the Earth, and pinpoints 25 so-called ‘biodiversity hotspots’. Seventeen of them are tropical forest areas, and here reduction of natural habitat is disproportionately high. Nonetheless, identification of this pattern should enable resources for conservation to be better focused.

A food web is a map that describes which kinds of organisms in a community eat which other kinds. A web helps picture how a community is put together and how it works. Although webs were often initially reported in despair at ever understanding ecological complexity, recently discovered widespread patterns in the shapes of webs, and theoretical explanations for these patterns, indicate that webs are orderly and intelligible, and have some foreseeable consequences for the dynamics of communities.

Many models of animal populations show complex yet predictable patterns of density changes under simple and plausible assumptions. Yet one previous attempt to determine the extent and importance of complex dynamics concluded that they were likely only in some laboratory populations, but not in field populations. Ecologists have treated changes more complex than a return to a simple equilibrium, such as the cyclical changes in populations of lynx and voles in the arctic, as special cases. Highly variable populations, such as insects, are usually thought to be driven by unpredictable changes in the weather. Here, we assemble 71 populations counted for over 50 years, and suggest that complex yet predictable population changes are more common than previously thought.

Stuart Pimm follows a fellow biologist's evolution from wide-eyed wonder to a life chasing snakes in the field.

Stuart Pimm enjoys an exploration of what we can learn from rare species, if we care enough to keep them.

Our actions have driven top predators from much of the world, resulting in complex consequences for many ecosystems, explains Stuart Pimm.

Given that humans are here to stay on Earth for some time yet, what can we do to lessen our impact?

Stuart Pimm applauds eminent biologist E. O. Wilson's pragmatic and passionate career advice.

The subtitle gives the book away. It rehashes books such as Ronald Bailey's The True State of the Planet (Free Press, 1995). As Bjorn Lomborg tells us, the book's origin was a class he taught in 1997. The original Danish version appeared a mere year later —remarkably fast, given the delays of academic publishing. It shows, too. This survey of global environmental problems — food, forests, energy, water, pollution, biodiversity, global warming — reads like a compilation of term papers from one of those classes from hell where one has to fail all the students. It is a mass of poorly digested material, deeply flawed in its selection of examples and analysis.

Twenty years ago a unique ecological experiment was set up, to monitor the effects of a rapid influx of people into one of the most sparsely populated areas in the world — the Amazon. Scientists have now met in Manau, Brazil, to discuss the results of this experiment. They conclude that of the two questions that caused controversy back in 1978, only one — that of forest edge effects — is still relevant.

Wheat, maize and the other grains constitute some 85% of global food production. But these plants are annuals, and they are usually grown in monoculture. The consequences are that harvesting them leaves the earth vulnerable to erosion; extra fertilizers are required for their growth; and they are especially prone to attack by pests and diseases. Could a more natural agricultural system, based on several perennial species, be both productive and avoid some of these problems? The prospects for such systems were discussed at a meeting last month.

Economists and ecologists have Joined forces to estimate the annual value of the services that Earth's ecosystems provide. Most services lie outside the market and are hard to calculate, yet minimum estimates equal or exceed global gross national product.

Nature's Keepers: The New Science of Nature Management. By Stephen Budiansky. Free Press/Weidenfeld and Nicolson: 1995. Pp. 310. $25, £18.99.

From Coastal Wilderness to Fruited Plain: A History of Environmental Change in Temperate North America from 1500 to the Present. By Gordon G. Whitney Cambridge University Press: 1994. Pp. 451. £45, $54.95.

Scarcity or Abundance? A Debate on the Environment. By Norman Myers and Julian L. Simon. Norton: 1994. Pp. 254. $21, £16.95.

Protected from hunting and provided with access to water-holes during droughts, elephant numbers can double in a decade, severely damaging natural vegetation and the many species dependent upon it. Culling is an effective but controversial control strategy, so Fayrer-Hosken et al.1 have assessed the efficacy of using immunocontraception through vaccination, concluding that this could be a practical way of controlling elephant numbers. However, an intervention feasible in reproductive physiology may not be a practical way to control a population. Fayrer-Hosken et al. have not considered calculations2,3 that undermine the practicality of their method, nor alternative management strategies.

Betrayal of Science and Reason. By Paul R. Ehrlich and Anne H. Ehrlich. Island Press:1996. Pp. 320. $24.95.

A History of the Ecosystem Concept in Ecology: More than the Sum of the Parts. By Frank Benjamin Golley. Yale University Press: 1993. Pp. 254. £25, $30.

The Expendable Future: US Politics and the Protection of Biological Diversity. By Richard Tobin. Duke University Press: 1991. Pp.325. Hbk £42.50, $45; pbk £17, $18.75

Early studies suggested that simple ecosystems were less stable than complex ones, but later studies came to the opposite conclusion. Confusion arose because of the many different meanings of ‘complexity’ and ‘stability’. Most of the possible questions about the relationship between stability–complexity have not been asked. Those that have yield a variety of answers.

To evaluate the role of competition in structuring communities, we conducted morphological analyses on the surviving species of passerine birds that were successfully introduced to the Hawaiian islands. Forty-nine species have been introduced a total of 111 times to five of the six main islands. There have been 33 extinctions. Our analyses were done at two separate organizational levels: all species introduced to an island; and all forest-dwelling species. If competition determines which species can coexist, and the intensity of competition is correlated with morphological similarity, then the surviving species should be overdispersed in morphological space. Further, sets of surviving species that coexist should be regularly positioned in morphological space. At the island-wide organizational level, the surviving species were neither overdispersed nor regularly positioned in morphological space. However, at the forest-wide level the surviving species were not only highly overdispersed, they were also regularly positioned when compared to randomly assembled communities.