High Probability Of Extinction Research Articles

Flow Field and Scalar Measurements in a Series of Turbulent Partially-Premixed Dimethyl Ether/Air Jet Flames

We present a series of benchmark flames consisting of six partially-premixed piloted dimethyl ether (DME)/air jet flames. These flames provide an opportunity to understand turbulence-flame interactions for oxygenated fuels and to develop predictive models for these interactions using a canonical burner geometry. The development of accurate models for DME/air flames would establish a foundation for studies of more complex oxygenated fuels. The flames are stabilized on a piloted jet burner similar to that of the partially-premixed methane/air jet flames that have been studied extensively within the context of the TNF Workshop. This series of six jet flames spans jet exit Reynolds numbers, ReD, from 29,300 to 73,300 and stoichiometric mixture fractions, ξst, from 0.35 to 0.60. Flame conditions range from very low probability of localized extinction to a high probability of localized extinction and subsequent re-ignition. Measurements in the flames are compared at downstream locations from 5 to 25 diameters above the nozzle exit. Mean and fluctuating velocity components are measured using stereo particle image velocimetry (SPIV). Simultaneous laser-induced fluorescence (LIF) imaging of OH and CH2O provides insights into the distribution of these intermediate species in partially-premixed DME/air flames. OH LIF imaging is also combined with SPIV to investigate the strain rate field across the reaction zone.

Characterization of extinction/reignition events in turbulent premixed counterflow flames using strain-rate analysis

We investigate extinction/reignition events in two contrasting turbulent premixed flames of the Yale turbulent counterflow flame (TCF) burner, that are both qualitatively and quantitatively different. One of the two chosen flames is a high-burning (HB) flame with a low probability of local extinction while the other flame is a low-burning (LB) flame with a high probability of local extinction. In recent work, we successfully studied the turbulent premixed flames of the Yale TCF burner using the large-eddy simulation/probability density function (LES/PDF) methods. In this present study, the main motivation is to investigate how the compositional structure of the two turbulent flames are related to that of laminar flames. To this end, steady, one-dimensional, strained, opposed-jet laminar flame calculations are performed to investigate the effect of strain rates K on the laminar counterparts of HB and LB, and to evaluate the extinction strain rates Sext for the two flames. Subsequently, a normalized distance Z is defined in terms of the mixture fraction ξ, which is calculated based on the mass fraction of N2. The scatter plots from the particle data of (a) CH2O mass fraction YCH2O*vs. progress variable p* and (b) temperature T*vs. the normalized distance Z* are quite different for the two flames with more samples close to the extinguished laminar profile for the LB flame than for the HB flame. The cell-mean profiles of T vs. Z resemble the laminar profiles at different strain rates even though the LES/PDF are non-trivially 3D and unsteady. These cell-mean profiles are used to evaluate the instantaneous equivalent steady strain rate (ESSR) S for the two flames. The cumulative distribution function (CDF) of S, conditional on S < Sext (i.e., burning samples), is somewhat similar, with the distributions being broad without a peak close to the bulk strain rate. However, comparatively, more samples of the LB flame have the ESSR values above the extinction strain rate, i.e., S > Sext. The scatter plots of the ESSR S vs. the fresh product layer thickness Δf quantify the thinning of the product layer as the strain rate S increases. The scatter for the HB flame follow the corresponding laminar profile quite closely, whereas, the thicknesses observed for the LB flame are higher compared to its laminar prediction.

Use of Simulation Modeling to Evaluate Management Strategies for Reintroduced Riparian Brush Rabbits in California

Abstract The riparian brush rabbit Sylvilagus bachmani riparius is restricted to areas of dense cover along rivers and tributaries in the Central Valley of California, USA, and is considered endangered under the U.S. Endangered Species Act. An approved recovery plan for this subspecies recommended establishment of three additional self-sustaining populations within its historical range. Concurrent with habitat restoration efforts that included revegetation of levees and provision of flood refugia, we reintroduced 325 captive-bred individuals to the San Joaquin River National Wildlife Refuge between July 2002 and July 2005, and monitored their survival with radiotelemetry. Using available survival estimates and estimated reproductive parameters, we developed a population viability analysis model to determine the risk of extinction of the reintroduced population under a series of alternate scenarios including different release strategies. All model scenarios resulted in high probabilities of extinction over 20 y in the absence of either ongoing supplementations or significant improvements to vital rates. Extinction risks over 20 y appeared independent of initial release strategies. The risk of extinction remained high (&amp;gt;99%) even when the initial founder population was supplemented with captive-bred brush rabbits for up to 10 y. Supplementing the population annually for the entire 20-y period would be required for the population to persist given current estimates of vital rates. These results suggest that the reintroduced population is not self-sustaining and continued releases will not provide the anticipated long-term benefits. Additionally, our understanding of the integral components of habitat and potential limiting factors should be refined to address their influence on demographics and the cause of brush rabbit declines at the release site in a comprehensive way. These results underscore the importance of viability analyses and developing testable hypotheses about potential limiting factors early in reintroduction efforts to more efficiently guide data-gathering and monitoring criteria, identify data deficiencies, and refine reintroduction techniques in the early stages of management.

Communal nesting under climate change: fitness consequences of higher incubation temperatures for anocturnal lizard.

Communal nesting lizards may be vulnerable to climate warming, particularly if air temperatures regulate nest temperatures. In southeastern Australia, velvet geckos Oedura lesueurii lay eggs communally inside rock crevices. We investigated whether increases in air temperatures could elevate nest temperatures, and if so, how this could influence hatching phenotypes, survival, and population dynamics. In natural nests, maximum daily air temperature influenced mean and maximum daily nest temperatures, implying that nest temperatures will increase under climate warming. To determine whether hotter nests influence hatchling phenotypes, we incubated eggs under two fluctuating temperature regimes to mimic current 'cold' nests (mean=23.2°C, range 10-33°C) and future 'hot' nests (27.0°C, 14-37°C). 'Hot' incubation temperatures produced smaller hatchlings than did cold temperature incubation. We released individually marked hatchlings into the wild in 2014 and 2015, and monitored their survival over 10months. In 2014 and 2015, hot-incubated hatchlings had higher annual mortality (99%, 97%) than cold-incubated (11%, 58%) or wild-born hatchlings (78%, 22%). To determine future trajectories of velvet gecko populations under climate warming, we ran population viability analyses in Vortex and varied annual rates of hatchling mortality within the range 78- 96%. Hatchling mortality strongly influenced the probability of extinction and the mean time to extinction. When hatchling mortality was >86%, populations had a higher probability of extinction (PE: range 0.52- 1.0) with mean times to extinction of 18-44years. Whether future changes in hatchling survival translate into reduced population viability will depend on the ability of females to modify their nest-site choices. Over the period 1992-2015, females used the same communal nests annually, suggesting that there may be little plasticity in maternal nest-site selection. The impacts of climate change may therefore be especially severe on communal nesting species, particularly if such species occupy thermally challenging environments.

Experimental study of vorticity-strain rate interaction in turbulent partially premixed jet flames using tomographic particle image velocimetry

In turbulent flows, the interaction between vorticity, ω, and strain rate, s, is considered a primary mechanism for the transfer of energy from large to small scales through vortex stretching. The ω-s coupling in turbulent jet flames is investigated using tomographic particle image velocimetry (TPIV). TPIV provides a direct measurement of the three-dimensional velocity field from which ω and s are determined. The effects of combustion and mean shear on the ω-s interaction are investigated in turbulent partially premixed methane/air jet flames with high and low probabilities of localized extinction as well as in a non-reacting isothermal air jet with Reynolds number of approximately 13 000. Results show that combustion causes structures of high vorticity and strain rate to agglomerate in highly correlated, elongated layers that span the height of the probe volume. In the non-reacting jet, these structures have a more varied morphology, greater fragmentation, and are not as well correlated. The enhanced spatiotemporal correlation of vorticity and strain rate in the stable flame results in stronger ω-s interaction characterized by increased enstrophy and strain-rate production rates via vortex stretching and straining, respectively. The probability of preferential local alignment between ω and the eigenvector of the intermediate principal strain rate, s2, which is intrinsic to the ω-s coupling in turbulent flows, is larger in the flames and increases with the flame stability. The larger mean shear in the flame imposes a preferential orientation of ω and s2 tangential to the shear layer. The extensive and compressive principal strain rates, s1 and s3, respectively, are preferentially oriented at approximately 45° with respect to the jet axis. The production rates of strain and vorticity tend to be dominated by instances in which ω is parallel to the s1¯-s2¯ plane and orthogonal to s3¯.

Extinction probabilities and stationary distributions of mobile genetic elements in prokaryotes: The birth–death-diversification model

Theoretical approaches are essential to our understanding of the complex dynamics of mobile genetic elements (MGEs) within genomes. Recently, the birth–death-diversification model was developed to describe the dynamics of mobile promoters (MPs), a particular class of MGEs in prokaryotes. A unique feature of this model is that genetic diversification of elements was included. To explore the implications of diversification on the longterm fate of MGE lineages, in this contribution we analyze the extinction probabilities, extinction times and equilibrium solutions of the birth–death-diversification model. We find that diversification increases both the survival and growth rate of MGE families, but the strength of this effect depends on the rate of horizontal gene transfer (HGT). We also find that the distribution of MGE families per genome is not necessarily monotonically decreasing, as observed for MPs, but may have a peak in the distribution that is related to the HGT rate. For MPs specifically, we find that new families have a high extinction probability, and predict that the number of MPs is increasing, albeit at a very slow rate. Additionally, we develop an extension of the birth–death-diversification model which allows MGEs in different regions of the genome, for example coding and non-coding, to be described by different rates. This extension may offer a potential explanation as to why the majority of MPs are located in non-promoter regions of the genome.

Status assessment of the Endangered snow leopardPanthera unciaand other large mammals in the Kyrgyz Alay, using community knowledge corrected for imperfect detection

AbstractThe Endangered snow leopardPanthera unciaoccurs in the Central Asian Mountains, which cover c. 2 million km2. Little is known about its status in the Kyrgyz Alay Mountains, a relatively narrow stretch of habitat connecting the southern and northern global ranges of the species. In 2010 we gathered information on current and past (1990, the last year of the Soviet Union) distributions of snow leopards and five sympatric large mammals across 14,000 km2of the Kyrgyz Alay. We interviewed 95 key informants from local communities. Across 49 400-km2grid cells we obtained 1,606 and 962 records of species occurrence (site use) in 1990 and 2010, respectively. The data were analysed using the multi-season site occupancy framework to incorporate uncertainty in detection across interviewees and time periods. High probability of use by snow leopards in the past was recorded in &gt; 70% of the Kyrgyz Alay. Between the two sampling periods 39% of sites showed a high probability of local extinction of snow leopard. We also recorded high probability of local extinction of brown bearUrsus arctos(84% of sites) and Marco Polo sheepOvis ammon polii(47% of sites), mainly in regions used intensively by people. Data indicated a high probability of local colonization by lynxLynx lynxin 41% of the sites. Although wildlife has declined in areas of central and eastern Alay, regions in the north-west, and the northern and southern fringes appear to retain high conservation value.

InSTREAM-Gen: Modelling eco-evolutionary dynamics of trout populations under anthropogenic environmental change

Current rates of environmental change are exceeding the capacity of many populations to adapt to new conditions and thus avoid demographic collapse and ultimate extinction. In particular, cold-water freshwater fish species are predicted to experience strong selective pressure from climate change and a wide range of interacting anthropogenic stressors in the near future. To implement effective management and conservation measures, it is crucial to quantify the maximum rate of change that cold-water freshwater fish populations can withstand. Here, we present a spatially explicit eco-genetic individual-based model, inSTREAM-Gen, to predict the eco-evolutionary dynamics of stream-dwelling trout under anthropogenic environmental change. The model builds on a well-tested demographic model, which includes submodels of river dynamics, bioenergetics, and adaptive habitat selection, with a new genetic module that allows exploration of genetic and life-history adaptations to new environments. The genetic module models the transmission of two key traits, size at emergence and maturity size threshold. We parameterized the model for a brown trout (Salmo trutta L.) population at the warmest edge of its range to validate it and analyze its sensitivity to parameters under contrasting thermal profiles. To illustrate potential applications of the model, we analyzed the population's demographic and evolutionary dynamics under scenarios of (1) climate change-induced warming, and (2) warming plus flow reduction resulting from climate and land use change, compared to (3) a baseline of no environmental change. The model predicted severe declines in density and biomass under climate warming. These declines were lower than expected at range margins because of evolution towards smaller size at both emergence and maturation compared to the natural evolution under the baseline conditions. Despite stronger evolutionary responses, declining rates were substantially larger under the combined warming and flow reduction scenario, leading to a high probability of population extinction over contemporary time frames. Therefore, adaptive responses could not prevent extinction under high rates of environmental change. Our model demonstrates critical elements of next generation ecological modelling aiming at predictions in a changing world as it accounts for spatial and temporal resource heterogeneity, while merging individual behaviour and bioenergetics with microevolutionary adaptations.

Spatial occupancy models for predicting metapopulation dynamics and viability following reintroduction

SummaryThe reintroduction of a species into its historic range is a critical component of conservation programmes designed to restore extirpated metapopulations. However, many reintroduction efforts fail, and the lack of rigorous monitoring programmes and statistical models have prevented a general understanding of the factors affecting metapopulation viability following reintroduction.Spatially explicit metapopulation theory provides the basis for understanding the dynamics of fragmented populations linked by dispersal, but the theory has rarely been used to guide reintroduction programmes because most spatial metapopulation models require presence–absence data from every site in the network, and they do not allow for observation error such as imperfect detection.We develop a spatial occupancy model that relaxes these restrictive assumptions and allows for inference about metapopulation extinction risk and connectivity. We demonstrate the utility of the model using six years of data on the Chiricahua leopard frogLithobates chiricahuensis, a threatened desert‐breeding amphibian that was reintroduced to a network of sites in Arizona USA in 2003.Our results indicate that the model can generate precise predictions of extinction risk and produce connectivity maps that can guide conservation efforts following reintroduction. In the case ofL. chiricahuensis, many sites were functionally isolated, and 82% of sites were characterized by intermittent water availability and high local extinction probabilities (0·84, 95% CI: 0·64–0·99). However, under the current hydrological conditions and spatial arrangement of sites, the risk of metapopulation extinction is estimated to be &lt;3% over a 50‐year time horizon.Low metapopulation extinction risk appears to result from the high dispersal capability of the species, the high density of sites in the region and the existence of predator‐free permanent wetlands with low local extinction probabilities. Should management be required, extinction risk can be reduced by either increasing the hydroperiod of existing sites or by creating new sites to increase connectivity.Synthesis and applications. This work demonstrates how spatio‐temporal statistical models based on ecological theory can be applied to forecast the outcomes of conservation actions such as reintroduction. Our spatial occupancy model should be particularly useful when management agencies lack the funds to collect intensive individual‐level data.

Are genetic data relevant in the conservation of species in imminent danger? The case of a critically endangered endemism from the Canary Islands Helianthemum juliae Wildpret (Cistaceae)

Genetic data could be considered irrelevant to the conservation of species in imminent danger, and that habitat protection and ex situ conservation strategies should be carried out regardless of the existence of estimates of genetic diversity. However, genetic data are needed to determine the current state of diversity of the species, the genetic structure and the genetic differentiation between populations and therefore to establish the most suitable management strategy. We compared genetic diversity and differentiation estimated from allozymes and random amplified polymorphic DNA (RAPD) in the three known natural populations of the critically endangered endemism from the Island of Tenerife (Canary Islands) Helianthemum juliae Wildpret. There were discrepancies in levels and structuring of genetic diversity measured with both molecular markers due to genome sampling. So, whereas allozymes allele frequency revealed a low genetic differentiation between natural populations (F ST = 0.034), the presence/absence of RAPD data matrix showed a considerable level of genetic differentiation (F ST = 0.397) between these populations. Genetic data identify 20 unique genotypes distributed within H. juliae populations, which supposes an important finding for conservation management of this endangered species. Considering that the three populations showed unique genotypes, management strategies should be focused on strengthening these genotypes in the whole of the species. So, although considerable genetic differentiation has been detected between the natural populations, bearing in mind the high extinction probabilities described for the species, genetic data would support the establishing of new localities with individuals from different natural populations in a conservation genetics strategy.

High-speed tomographic PIV measurements of strain rate intermittency and clustering in turbulent partially-premixed jet flames

The effects of combustion on the strain rate field in turbulent jets were studied using 10kHz tomographic particle image velocimetry (TPIV). Measurements were performed in three turbulent jets: a well-studied, piloted partially-premixed methane/air jet flame, Sandia flame C, with low probability of localized extinction; a second piloted jet flame, analogous to flame C but with a reduced pilot flow rate and a high probability of localized extinction; and a non-reacting air jet. Since the jet exit Reynolds number of approximately 13000 was nearly identical in the three jets, differences in the strain rate fields were attributed to the effects of combustion. Spatiotemporal characteristics of the strain rate field were analyzed. Overall, the strain rate norm was larger in the flames than in the non-reacting jet with the most stable flame having the largest values. In all three jets, the compressive strain rate was on average the largest of the three principal strain rates. At high strain rates, the ratios of the compressive and extensive strain rate to the intermediate strain rate were similar to those found in isotropic incompressible turbulent flows. The three-dimensional velocity measurements were used to analyze the spatial distribution of strain rate clusters, defined as singly-connected groups of voxels where the strain rate magnitude exceeded a threshold value. The presence of a stable flame significantly attenuated the number of clusters of intermediate strain rate. Strain rate bursts, corresponding to sudden increases in the number of clusters, were identified in the three jets. Bursts in the non-reacting jet and the unstable flame contained up to twice as many clusters as in the stable flame. The temporal intermittency of intense strain rate clusters was analyzed using the time-series measurements. Clusters with strain rates greater than five times the standard deviation of the strain rate norm were highly intermittent.

Population Genetic Consequences of the Allee Effect and the Role of Offspring-Number Variation

A strong demographic Allee effect in which the expected population growth rate is negative below a certain critical population size can cause high extinction probabilities in small introduced populations. But many species are repeatedly introduced to the same location and eventually one population may overcome the Allee effect by chance. With the help of stochastic models, we investigate how much genetic diversity such successful populations harbor on average and how this depends on offspring-number variation, an important source of stochastic variability in population size. We find that with increasing variability, the Allee effect increasingly promotes genetic diversity in successful populations. Successful Allee-effect populations with highly variable population dynamics escape rapidly from the region of small population sizes and do not linger around the critical population size. Therefore, they are exposed to relatively little genetic drift. It is also conceivable, however, that an Allee effect itself leads to an increase in offspring-number variation. In this case, successful populations with an Allee effect can exhibit less genetic diversity despite growing faster at small population sizes. Unlike in many classical population genetics models, the role of offspring-number variation for the population genetic consequences of the Allee effect cannot be accounted for by an effective-population-size correction. Thus, our results highlight the importance of detailed biological knowledge, in this case on the probability distribution of family sizes, when predicting the evolutionary potential of newly founded populations or when using genetic data to reconstruct their demographic history.

Multi-season occupancy analysis reveals large scale competitive exclusion of the critically endangered European mink by the invasive non-native American mink in Spain

Understanding changes over time in the distribution of interacting native and invasive species that may be symptomatic of competitive exclusion is critical to identify the need for and effectiveness of management interventions. Occupancy models greatly increase the robustness of inference that can be made from presence/absence data when species are imperfectly detected, and recent novel developments allow for the quantification of the strength of interaction between pairs of species.We used a two-species multi-season occupancy model to quantify the impact of the invasive American mink on the native European mink in Spain through the analysis of their co-occurrence pattern over twelve years (2000–2011) in the entire Spanish range of European mink distribution, where both species were detected by live trapping but American mink were culled. We detected a negative temporal trend in the rate of occupancy of European mink and a simultaneous positive trend in the occupancy of American mink. The species co-occurred less often than expected and the native mink was more likely to become extinct from sites occupied by the invasive species. Removal of American mink resulted in a high probability of local extinction where it co-occurred with the endemic mink, but the overall increase in the probability of occupancy over the last decade indicates that the ongoing management is failing to halt its spread. More intensive culling effort where both species co-exist as well as in adjacent areas where the invasive American mink is found at high densities is required in order to stop the decline of European mink.

Extinction in a branching process: why some of the fittest strategies cannot guarantee survival

Biological fitness is typically measured by the expected rate of reproduction, but strategies with high fitness can also have high probabilities of extinction. Likewise, gambling strategies with a high expected payoff can also have a high risk of ruin. We take inspiration from the gambler’s ruin problem to examine how extinction is related to population growth. Using moment theory we demonstrate how higher moments can impact the probability of extinction and how the first few moments can be used to find bounds on the extinction probability, focusing on s-convex ordering of random variables. This approach generates “best case” and “worst case” scenarios to provide upper and lower bounds on the probability of extinction.MSC Codes92D15, 60J80, 60E15

Sturgeon and paddlefish research focuses on low risk species and largely disregards endangered species

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 22:95-97 (2013) - DOI: https://doi.org/10.3354/esr00543 FEATURE ARTICLE AS WE SEE IT: Sturgeon and paddlefish research focuses on low risk species and largely disregards endangered species Jörn Gessner1,2, Ivan Jarić3,*, Eric Rochard4, Mohammad Pourkazemi5 1Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany 2Society to Save the Sturgeon, Fischerweg 408, 18069 Rostock, Germany 3Institute for Multidisciplinary Research, University of Belgrade, Kneza Viseslava 1, 11000 Belgrade, Serbia 4IRSTEA, EPBX, 50 avenue de Verdun, 33612 Cestas, Cedex, France 5International Sturgeon Research Institute, PO Box 41635-3464, Rasht, Gilan, Iran *Corresponding author. Email: ijaric@imsi.rs ABSTRACT: Sturgeons and paddlefish are among the most commercially valuable groups of fishes and include both low risk and highly endangered species. However, a recent bibliometric study on sturgeon and paddlefish research revealed that disproportionately little attention has been paid to those species that are endangered or face a high probability of extinction. With the exception of European sturgeon Acipenser sturio, all of the 8 species that are highly threatened with extinction or functionally extinct, were each addressed in less than 1% of the publications dealing with sturgeons or paddlefishes. Information on the biology and sensitive life-cycle phases of threatened sturgeon and paddlefish species, as well as knowledge of their interactions with their respective habitats, is especially deficient or lacking, thus rendering the planning and execution of protection measures even more difficult. We argue that a more stringent focus has to be placed upon conservation research and management for vulnerable species and populations that are threatened with a high risk of extinction. This also makes it a necessity to overcome the apparent lack of commitment which has been observed in some regions to developing and/or implementing effective and concerted regional actions which address sturgeon and paddlefish rehabilitation. KEY WORDS: Sturgeon · Paddlefish · Acipenser · Extinction risk · Endangered · IUCN · Bibliometric Full text in pdf format Information about this Feature Article NextCite this article as: Gessner J, Jarić I, Rochard E, Pourkazemi M (2013) AS WE SEE IT: Sturgeon and paddlefish research focuses on low risk species and largely disregards endangered species. Endang Species Res 22:95-97. https://doi.org/10.3354/esr00543 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 22, No. 2. Online publication date: December 02, 2013 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2013 Inter-Research.

Island mammal extinctions are determined by interactive effects of life history, island biogeography and mesopredator suppression

AbstractAimUnderstanding extinction on islands is critical for biodiversity conservation. Introduced predators are a major cause of island extinctions, but there have been few large‐scale studies of the complexity of the effects of predators on island faunas, or how predation interacts with other factors. Using a large database of island mammal populations, we describe and explain patterns of island mammal extinctions as a function of introduced predators, life history and geography.LocationThree hundred and twenty‐three Australian islands.MethodsWe built a database of 934 island mammal populations, extinct and extant, including life history and ecology, island geography and the presence of introduced predators. To test predictors of extinction probability, we used generalized linear mixed models to control partially for phylogenetic non‐independence, and decision trees to more fully explore interactive effects.ResultsThe decision trees identified large mammals (&gt; 2.7 kg) as having higher extinction probabilities than small species (&lt; 2.7 kg). In large species, extinction patterns are consistent with island biogeography theory, with distance from the mainland being the primary predictor of extinction. For small species, the presence of introduced black rats is the primary predictor of extinction. As predicted by mesopredator suppression theory, extinction probabilities are lower on islands with both black rats and a larger introduced predator (cats, foxes or dingoes), compared with islands with rats but no larger predator. Similarly, extinction probabilities are lower on islands with both a mid‐sized (cats or foxes) and a larger (dingoes) predator, compared with islands with cats or foxes only.Main conclusionsIsland mammal extinctions result from complex interactions of introduced predators, island geography and prey biology. One conservation implication of our results is that eradication of introduced apex predators (cats, foxes or dingoes) from islands could precipitate the expansion of black rat populations, potentially leading to extinction of native mammal species whose remaining populations are confined to islands.

Conserving tropical biodiversity via strategic spatiotemporal harvest planning

Summary Tropical timber production forests have the potential to harbour many species, but landscape‐level management strategies for minimizing extinctions are lacking. To develop relevant conservation guidelines, we investigated how harvest plans with different spatiotemporal patterns affected the persistence of sessile species with different traits and preharvest characteristics. We confronted this problem via an individual‐based simulation model. We explored several harvest plans with different levels of spatiotemporal aggregation, but equivalent total harvest area, and found that extinction probabilities for each plan varied with species traits and predisturbance characteristics. Most notably, plans with large contiguous harvest units yielded particularly high extinction probabilities for dispersal‐limited habitat specialists with clustered preharvest distributions. Differences between plans were small for some types of species, but highly aggregated plans yielded the highest extinction rates for all extinction‐prone groups. Synthesis and applications. Our simulations suggest that reducing the size of contiguous harvest units, even while total harvest area remains constant, may reduce extinction rates in tropical production forests (assuming that road‐related threats can be effectively managed). Our findings have important implications for tropical conservation efforts and also provide general insight into the compositional effects of disturbances with different spatiotemporal characteristics.

Método de valoración de la viabilidad de corredores biológicos para mamíferos: análisis preliminar del corredor biológico San Juan-La Selva en Costa Rica

Biological corridors are fundamental strategies for biodiversity conservation in fragmented landscapes. However, few evidence exist respecting their functionality or the population viability of its species on long term especially for the tropics. We performed a theoretical-descriptive approach to determine mammals’ risk of extinction based on three main parameters: species vulnerability and area and habitat requirements, each one of these categories were classified in levels of high, medium and low. For large mammals there is a high probability of extinction, while for medium and small mammals there is a low probability of extinction and a high probability of permanence of viable populations with high habitat availability.

Caught in the middle: Asymmetric competition causes high variance in intermediate trait abundances

In asymmetric competition between two individuals of the same or different species, one individual has a distinct advantage over the other due to a particular beneficial trait. An important trait that induces asymmetric competition is size (body size in animals, height in plants). There is usually a trade-off between fecundity and the trait that leads to competitive superiority (e.g. seed number vs seed size), enabling coexistence of populations with different trait values. These predictions on coexistence are based on classic deterministic models. Here, we explore the behaviour of a stochastic model of asymmetric competition where stochasticity is assumed to be demographic. We derive approximations for the temporal variance and covariance of the population sizes of the coexisting species. The derivations highlight that the variability of the population size of a species strongly depends on the stochastic fluctuations of species with higher trait values, while they are less influenced by species with lower trait values. Particularly, species with intermediate trait values are strongly affected resulting in relatively high variability. As a result these species have a relative high probability of extinction even though they have a larger population size than species with high trait values. We confirm these approximations with individual-based simulations. Thus, our analysis can explain gaps in size distributions as an emergent property of systems with a fecundity–competition trade-off.

Patterns of molecular evolution in dioecious and non‐dioecious Silene

Dioecy (i.e. having separate sexes) is a rather rare breeding system in flowering plants. Such rareness may result from a high probability of extinction in dioecious species because of less efficient dispersal and the costs of sexual selection, which are expected to harm dioecious species' survival on the long term. These handicaps should decrease the effective population size (Ne) of dioecious species, which in turn should reduce the efficacy of selection. Moreover, sexual selection in dioecious species is expected to specifically affect some genes, which will evolve under positive selection. The relative contribution of these effects is currently unknown and we tried to disentangle them by comparing sequence evolution between dioecious and non-dioecious species in the Silene genus (Caryophyllaceae), where dioecy has evolved at least twice. For the dioecious species in the section Melandrium, where dioecy is the oldest, we found a global reduction of purifying selection, while on some, male-biased genes, positive selection was found. For section Otites, where dioecy evolved more recently, we found no significant differences between dioecious and non-dioecious species. Our results are consistent with the view that dioecy is an evolutionary dead end in flowering plants, although other scenarios for explaining reduced Ne cannot be ruled out. Our results also show that contrasting forces act on the genomes of dioecious plants, and suggest that some time is required before the genome of such plants bears the footprints of dioecy.