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Journal: Conservation biology : the journal of the Society for Conservation Biology


A key measure of humanity’s global impact is by how much it has increased species extinction rates. Familiar statements are that these are 100-1000 times pre-human or background extinction levels. Estimating recent rates is straightforward, but establishing a background rate for comparison is not. Previous researchers chose an approximate benchmark of 1 extinction per million species per year (E/MSY). We explored disparate lines of evidence that suggest a substantially lower estimate. Fossil data yield direct estimates of extinction rates, but they are temporally coarse, mostly limited to marine hard-bodied taxa, and generally involve genera not species. Based on these data, typical background loss is 0.01 genera per million genera per year. Molecular phylogenies are available for more taxa and ecosystems, but it is debated whether they can be used to estimate separately speciation and extinction rates. We selected data to address known concerns and used them to determine median extinction estimates from statistical distributions of probable values for terrestrial plants and animals. We then created simulations to explore effects of violating model assumptions. Finally, we compiled estimates of diversification-the difference between speciation and extinction rates for different taxa. Median estimates of extinction rates ranged from 0.023 to 0.135 E/MSY. Simulation results suggested over- and under-estimation of extinction from individual phylogenies partially canceled each other out when large sets of phylogenies were analyzed. There was no evidence for recent and widespread pre-human overall declines in diversity. This implies that average extinction rates are less than average diversification rates. Median diversification rates were 0.05-0.2 new species per million species per year. On the basis of these results, we concluded that typical rates of background extinction may be closer to 0.1 E/MSY. Thus, current extinction rates are 1,000 times higher than natural background rates of extinction and future rates are likely to be 10,000 times higher. Estimación de la Tasa Normal de Extinción de Especies.

Concepts: Conservation biology, Approximation, Plant, Normal distribution, Speciation, Extinction, Species, Evolution


Hybridization between endangered species and more common species is a significant problem in conservation biology because it may result in extinction or loss of adaptation. The historical reduction in abundance and geographic distribution of the American plains bison (Bison bison bison) and their recovery over the last 125 years is well documented. However, introgression from domestic cattle (Bos taurus) into the few remaining bison populations that existed in the late 1800s has now been identified in many modern bison herds. We examined the phenotypic effect of this ancestry by comparing weight and height of bison with cattle or bison mitochondrial DNA (mtDNA) from Santa Catalina Island, California (U.S.A.), a nutritionally stressful environment for bison, and of a group of age-matched feedlot bison males in Montana, a nutritionally rich environment. The environmental and nutritional differences between these 2 bison populations were very different and demonstrated the phenotypic effect of domestic cattle mtDNA in bison over a broad range of conditions. For example, the average weight of feedlot males that were 2 years of age was 2.54 times greater than that of males from Santa Catalina Island. In both environments, bison with cattle mtDNA had lower weight compared with bison with bison mtDNA, and on Santa Catalina Island, the height of bison with cattle mtDNA was lower than the height of bison with bison mtDNA. These data support the hypothesis that body size is smaller and height is lower in bison with domestic cattle mtDNA and that genomic integrity is important for the conservation of the American plains bison. Efectos Fenotípicos del ADN Mitocondrial de Ganado en el Bisonte Americano.

Concepts: Beef, Cattle, Bos, Gaur, Bovinae, Extinction, American Bison, Bison


Indian Himalayan basins are earmarked for widespread dam building, but aggregate effects of these dams on terrestrial ecosystems are unknown. We mapped distribution of 292 dams (under construction and proposed) and projected effects of these dams on terrestrial ecosystems under different scenarios of land-cover loss. We analyzed land-cover data of the Himalayan valleys, where dams are located. We estimated dam density on fifth- through seventh-order rivers and compared these estimates with current global figures. We used a species-area relation model (SAR) to predict short- and long-term species extinctions driven by deforestation. We used scatter plots and correlation studies to analyze distribution patterns of species and dams and to reveal potential overlap between species-rich areas and dam sites. We investigated effects of disturbance on community structure of undisturbed forests. Nearly 90% of Indian Himalayan valleys would be affected by dam building and 27% of these dams would affect dense forests. Our model projected that 54,117 ha of forests would be submerged and 114,361 ha would be damaged by dam-related activities. A dam density of 0.3247/1000 km(2) would be nearly 62 times greater than current average global figures; the average of 1 dam for every 32 km of river channel would be 1.5 times higher than figures reported for U.S. rivers. Our results show that most dams would be located in species-rich areas of the Himalaya. The SAR model projected that by 2025, deforestation due to dam building would likely result in extinction of 22 angiosperm and 7 vertebrate taxa. Disturbance due to dam building would likely reduce tree species richness by 35%, tree density by 42%, and tree basal cover by 30% in dense forests. These results, combined with relatively weak national environmental impact assessment and implementation, point toward significant loss of species if all proposed dams in the Indian Himalaya are constructed. Efectos Potenciales del Desarrollo Hidroeléctrico Actual y Propuesto sobre la Diversidad Biológica Terrestre en el Himalaya Hindú

Concepts: Impact assessment, Hydroelectricity, Himalayas, River, Extinction, Environmental impact assessment, Biodiversity, Dam


That at least some aspects of nature possess intrinsic value is considered by some an axiom of conservation. Others consider nature’s intrinsic value superfluous or anathema. This range of views among mainstream conservation professionals potentially threatens the foundation of conservation. One challenge in resolving this disparity is that disparaging portrayals of nature’s intrinsic value appear rooted in misconceptions and unfounded presumptions about what it means to acknowledge nature’s intrinsic value. That acknowledgment has been characterized as vacuous, misanthropic, of little practical consequence to conservation, adequately accommodated by economic valuation, and not widely accepted in society. We reviewed the philosophical basis for nature’s intrinsic value and the implications for acknowledging that value. Our analysis is rooted to the notion that when something possesses intrinsic value it deserves to be treated with respect for what it is, with concern for its welfare or in a just manner. From this basis, one can only conclude that nature’s intrinsic value is not a vacuous concept or adequately accommodated by economic valuation. Acknowledging nature’s intrinsic value is not misanthropic because concern for nature’s welfare (aside from its influence on human welfare) does not in any way preclude also being concerned for human welfare. The practical import of acknowledging nature’s intrinsic value rises from recognizing all the objects of conservation concern (e.g., many endangered species) that offer little benefit to human welfare. Sociological and cultural evidence indicates the belief that at least some elements of nature possess intrinsic value is widespread in society. Our reasoning suggests the appropriateness of rejecting the assertion that nature’s intrinsic value is anathema to conservation and accepting its role as an axiom. Evaluar si el Valor Intrínseco de la Naturaleza es un Axioma o un Anatema para la Conservación.

Concepts: Morality, Intrinsic value, Logic, Ethics, Value theory, Endangered species, Sociology, Meaning of life


Conservation of sea snakes is virtually nonexistent in Asia, and its role in human-snake interactions in terms of catch, trade, and snakebites as an occupational hazard is mostly unexplored. We collected data on sea snake landings from the Gulf of Thailand, a hotspot for sea snake harvest by squid fishers operating out of the ports of Song Doc and Khanh Hoi, Ca Mau Province, Vietnam. The data were collected during documentation of the steps of the trading process and through interviewers with participants in the trade. Squid vessels return to ports once per lunar synodic cycle and fishers sell snakes to merchants who sort, package, and ship the snakes to various destinations in Vietnam and China for human consumption and as a source of traditional remedies. Annually, 82 t, roughly equal to 225,500 individuals, of live sea snakes are brought to ports. To our knowledge, this rate of harvest constitutes one of the largest venomous snake and marine reptile harvest activities in the world today. Lapemis curtus and Hydrophis cyanocinctus constituted about 85% of the snake biomass, and Acalyptophis peronii, Aipysurus eydouxii, Hydrophis atriceps, H. belcheri, H. lamberti, and H. ornatus made up the remainder. Our results establish a quantitative baseline for characteristics of catch, trade, and uses of sea snakes. Other key observations include the timing of the trade to the lunar cycle, a decline of sea snakes harvested over the study period (approximately 30% decline in mass over 4 years), and the treatment of sea snake bites with rhinoceros horn. Emerging markets in Southeast Asia drive the harvest of venomous sea snakes in the Gulf of Thailand and sea snake bites present a potentially lethal occupational hazard. We call for implementation of monitoring programs to further address the conservation implications of this large-scale marine reptile exploitation. Cosecha de Serpientes Marinas en el Golfo de Tailandia.

Concepts: Viperidae, Hydrophis, Vietnam, Venomous snake, Elapidae, Sea snakes, Sea snake, Snake


It is widely accepted that the main driver of the observed decline in biological diversity is increasing human pressure on Earth’s ecosystems. However, the spatial patterns of change in human pressure and their relation to conservation efforts are less well known. We developed a spatially and temporally explicit map of global change in human pressure over 2 decades between 1990 and 2010 at a resolution of 10 km(2) . We evaluated 22 spatial data sets representing different components of human pressure and used them to compile a temporal human pressure index (THPI) based on 3 data sets: human population density, land transformation, and electrical power infrastructure. We investigated how the THPI within protected areas was correlated to International Union for Conservation of Nature (IUCN) management categories and the human development index (HDI) and how the THPI was correlated to cumulative pressure on the basis of the original human footprint index. Since the early 1990s, human pressure increased 64% of the terrestrial areas; the largest increases were in Southeast Asia. Protected areas also exhibited overall increases in human pressure, the degree of which varied with location and IUCN management category. Only wilderness areas and natural monuments (management categories Ib and III) exhibited decreases in pressure. Protected areas not assigned any category exhibited the greatest increases. High HDI values correlated with greater reductions in pressure across protected areas, while increasing age of the protected area correlated with increases in pressure. Our analysis is an initial step toward mapping changes in human pressure on the natural world over time. That only 3 data sets could be included in our spatio-temporal global pressure map highlights the challenge to measuring pressure changes over time. Mapeo del Cambio en la Presión Humana Global en Tierra y Dentro de Áreas Protegidas.

Concepts: American Human Development Report, 1990s, Developed country, Population density, Natural environment, Category theory, Human Development Index, Nature


The recent extnction of the Caribbean monk seal Monachus tropicalis has been considered an example of a human-caused extinction in the marine environment, and this species was considered a driver of the changes that have occurred in the structure of Caribbean coral reef ecosystems since colonial times. I searched archaeological records, historical data, and geographic names (used as a proxy of the presence of seals) and evaluated the use and quality of these data to conclude that since prehistoric times the Caribbean monk seal was always rare and vulnerable to human predation. This finding supports the hypothesis that in AD 1500, the Caribbean monk seal persisted as a small fragmented population in which individuals were confined to small keys, banks, or isolated islands in the Gulf of Mexico and the Caribbean Sea. This hypothesis is contrary to the assumption that the species was widespread and abundant historically. The theory that the main driver of monk seal extinction was harvesting for its oil for use in the sugar cane industry of Jamaica during the 18th century is based primarily on anecdotal information and is overemphasized in the literature. An analysis of reported human encounters with this species indicates monk seal harvest was an occasional activity, rather than an ongoing enterprise. Nevertheless, given the rarity of this species and its restricted distribution, even small levels of hunting or specimen collecting must have contributed to its extinction, which was confirmed in the mid-20th century. Some sources had been overlooked or only partially reviewed, others misinterpreted, and a considerable amount of anecdotal information had been uncritically used. Critical examination of archaeological and historical records is required to infer accurate estimations of the historical abundance of a species. In reconstructing the past to address the shifting baseline syndrome, it is important to avoid selecting evidence to confirm modern prejudices.

Concepts: Mediterranean Monk Seal, Caribbean Monk Seal, Coral reef, Gulf of Mexico, Caribbean Sea, Cuba, Baseline, Caribbean


For decades conservation biologists have proposed general rules of thumb for minimum viable population size (MVP); typically, they range from hundreds to thousands of individuals. These rules have shifted conservation resources away from small and fragmented populations. We examined whether iteroparous, long-lived species might constitute an exception to general MVP guidelines. On the basis of results from a 10-year capture-recapture study in eastern New York (U.S.A.), we developed a comprehensive demographic model for the globally threatened bog turtle (Glyptemys muhlenbergii), which is designated as endangered by the IUCN in 2011. We assessed population viability across a wide range of initial abundances and carrying capacities. Not accounting for inbreeding, our results suggest that bog turtle colonies with as few as 15 breeding females have >90% probability of persisting for >100 years, provided vital rates and environmental variance remain at currently estimated levels. On the basis of our results, we suggest that MVP thresholds may be 1-2 orders of magnitude too high for many long-lived organisms. Consequently, protection of small and fragmented populations may constitute a viable conservation option for such species, especially in a regional or metapopulation context. Reexaminando el Concepto de Población Mínima Viable para Especies Longevas Resumen.

Concepts: Population, Population genetics, Minimum viable population, Conservation biology, Population ecology, Species, Biology, Demography


Despite widespread recognition of the major threat to tropical forest biological diversity and local food security posed by unsustainable bushmeat hunting, virtually no long-term studies tracking the socioecological dynamics of hunting systems have been conducted. We interviewed local hunters and collected detailed hunting data to investigate changes in offtake and hunter characteristics over 10 years (2001-2010) in Dibouka and Kouagna villages, central Gabon, in the context of hunter recollections of longer term trends since the 1950s. To control for changes in hunter behavior, such as trap location and characteristics, we report hunting offtake data per trap. Our results suggest the hunting area was already highly depleted by 2001; local hunters reported that 16 large-bodied prey species had become rare or locally extirpated over the last 60 years. Overall, we observed no significant declines in hunting offtake or changes in species composition from 2001 to 2010, and offtakes per trap increased slightly between 2004 and 2010. However, trapping distance from the villages increased, and there was a switch in hunting techniques; a larger proportion of the catch was hunted with guns in 2010. The number of hunters declined by 20% from 2004 to 2010, and male livelihood activities shifted away from hunting. Hunters with the lowest hunting incomes in 2004 were more likely than successful hunters to have moved away from the village by 2010 (often in response to alternative employment opportunities). Therefore, changes in trap success (potentially related to biological factors) were interacting with system-level changes in hunter number and composition (related to external socioeconomic factors) to produce a relatively static overall offtake. Our results highlight the importance of understanding the small-scale context of hunting to correctly interpret changes or apparent stasis in hunting effort and offtake over time. Cambio Social y Ecológico a lo Largo de Una Década en un Sistema de Cacería Aldeana, Gabón Central.

Concepts: Biodiversity, Poaching, Animal trapping, Sustainability, Game, Bushmeat, Predation, Hunting


Failure to account for interactions between endangered species may lead to unexpected population dynamics, inefficient management strategies, waste of scarce resources, and, at worst, increased extinction risk. The importance of species interactions is undisputed, yet recovery targets generally do not account for such interactions. This shortcoming is a consequence of species-centered legislation, but also of uncertainty surrounding the dynamics of species interactions and the complexity of modeling such interactions. The northern sea otter (Enhydra lutris kenyoni) and one of its preferred prey, northern abalone (Haliotis kamtschatkana), are endangered species for which recovery strategies have been developed without consideration of their strong predator-prey interactions. Using simulation-based optimization procedures from artificial intelligence, namely reinforcement learning and stochastic dynamic programming, we combined sea otter and northern abalone population models with functional-response models and examined how different management actions affect population dynamics and the likelihood of achieving recovery targets for each species through time. Recovery targets for these interacting species were difficult to achieve simultaneously in the absence of management. Although sea otters were predicted to recover, achieving abalone recovery targets failed even when threats to abalone such as predation and poaching were reduced. A management strategy entailing a 50% reduction in the poaching of northern abalone was a minimum requirement to reach short-term recovery goals for northern abalone when sea otters were present. Removing sea otters had a marginally positive effect on the abalone population but only when we assumed a functional response with strong predation pressure. Our optimization method could be applied more generally to any interacting threatened or invasive species for which there are multiple conservation objectives. Definición de Metas de Recuperación Realistas para Dos Especies en Peligro Interactuantes, Enhydra lutris y Haliotis kamtschatkana.

Concepts: Extinction, Lotka–Volterra equation, Endangered species, Biodiversity Action Plan, Mustelidae, Predation, Otter, Sea otter