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Forecasting Extinction

By Claire Asher, on 5 January 2015

Classifying a species as either extinct or extant is important if we are to quantify and monitor current rates of biodiversity loss, but it is rare that a biologist is handy to actually observe an extinction event. Finding the last member of a species is difficult, if not impossible, so extinction classifications are usually estimates based on the last recorded sightings of a species. Estimates always come with some inaccuracy, however, and recent research by GEE academics Dr Ben Collen and Professor Tim Blackburn aimed to investigate how accurate our best estimates of extinction really are.

Using data from experimental populations of the single-celled protist Loxocephalus, as well as wild populations of seven species of mammal, bird and amphibian, the authors tested six alternative estimation techniques to calculation the actual date of extinction. In particular, they were interested in whether the accuracy of these estimates is influenced by the rate of population decline, the search effort put in to find remaining individuals and the total number of sightings of the species. The dataset included very rapid declines (40% a year in the Common Mist frog) and much slower ones (16% per year in the Corncrake), and different sampling regimes.

Their results showed that the speed of decline was a crucial factor affecting the accuracy of extinction estimates – for experimental laboratory populations, estimates were most accurate for rapid population declines, however slow population declines in wild populations tended to produce more accurate results. The sampling regime was also important, with larger inaccuracies occurring when sampling effort decreased over time. This is probably a common situation for many species – close monitoring is common for species of high conservation priority, but interest may decrease as the species becomes closer and closer to extinction. The total number of sightings was also an important factor – a larger number of sightings overall tended to produce more accurate estimates.

Finally, the estimation technique also influenced accuracy, but only in interaction with the other variables mentioned above. Some methods fared best for rapid population declines, others for slower ones. Many of the methods fare poorly when sampling effort changes over time, particularly if it decreases, although they were relatively robust to sporadic, opportunistic sampling regimes. Overall, optimal linear estimation, a statistical method which makes fewer assumptions about the exact pattern of sightings, produced the most accurate results in cases where more than 10 sightings were recorded in total.

This study highlights the challenges faced by ecologists trying to determine whether a species has gone extinct or not. Sightings of rare species are often opportunistic, and only rarely are they part of a systematic, long-term monitoring program. Thus, methods that produce accurate results in the face of changing or sporadic search efforts are of key importance to conservationists. If the history of a species’ population declines and of the sampling effort are known, then statistical estimates can be selected which provide the best estimates for the particular situation. However, this information is rarely available and so using techniques that can provide accurate estimates for a range of different historical scenarios are likely to be of most use in predicting extinction status. Ultimately, it is extremely useful for conservationists to know whether a species is extinct or not, but estimates will always be subject to error except in rare cases (such as the passenger pigeon, for example) where the extinction event is observed first hand. There will always be cases of species turning up years after they were declared extinct, and no estimate will ever be perfect, but understanding the sources of error and the best methods to use to minimise it can be of great benefit in reducing the frequency with which that happens.

Original Article:

() Conservation Biology

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This research was made possible by funding from the Natural Environment Research Council (NERC).

Applying Metabolic Scaling Laws to Predicting Extinction Risk

By Claire Asher, on 25 September 2014

The Earth is warming. That much were are now certain of. A major challenge for scientists hoping to ameliorate the effect of this on biodiversity is to predict how temperature increases will affect populations. Predicting the responses of species living in complex ecosystems and heterogenous environments is a difficult task, but one starting point is to begin understanding how temperature increases affect small, laboratory populations. These populations can be easily controlled, and it is hoped that the lessons learned from laboratory populations can then begin to be generalised and applied to real populations. Recent research from GEE academics attempted to evaluate the predictive power of a simple metabolic model on the extinction risk of single-celled organisms in the lab. Their results indicate that simple scaling rules for temperature, metabolic rate and body size can be extremely useful in predicting the extinction of populations, at least in laboratory conditions.

Current estimates suggest that over the next 100 years we can expect a global temperature rise of between 1.1°C and 6.4°C. This change will not be uniformly distributed across different regions however, with some areas expected to experience warming at twice the global average rate. Temperature is known to be a crucial component in some of the most basic characteristics of life – metabolism, body size, birth, growth and mortality rates. These characteristics have been shown to scale with temperature in an easily predictable way, formalised in the Arrhenius equation. This equation yields a roughly 3/4 scaling rule, so that as temperature increases, metabolism increases around 75% as fast. This relationship appears to hold true for a variety of taxa with different life histories and positions in the food chain. Models based upon this rule can be designed that are very simple, which makes it easy for scientists to collect the data needed to plug into the model. But are they accurate in predicting extinction?

Recent research conducted by GEE and ZSL academics Dr Ben Collen and Prof. Tim Blackburn, in collaboration with the University of Sheffield and The University of Zurich, investigated the predictive power of simple metabolic models on extinction risk in a single-celled protist Loxocephallus. They first collected data on the population and extinction dynamics of a population held at constant temperature. This data was fed into a model based on scaling laws for metabolic rates and temperature, which in turn attempted to predict extinction risk under different temperature changes. The researchers tested how real protists responded to temperature changes – for 70 days they monitored populations of the protist Loxocephallus under either decreases or increases in temperature. Populations began at 20°C and increased to 26°C or decreased to 14°C at different rates (0.5°C, 0.75°C, 1.5°C or 3°C each week). Most populations eventually went extinct, but these extinctions happened sooner in hotter environments, and mean temperature showed a strong correlation with the date at which the population went extinct. Extinction tended to happen sooner in populations subjected to more rapid warming.

None of this is particularly surprising, but what the researchers found when they ran their models was that, even with relatively minimal data to start out with (population dynamics under constant ‘normal’ conditions), and using only simple scaling laws to predict extinction, their model was able to accurately predict when populations would go extinct under different warming or cooling conditions, with an accuracy of 84%. One important factor was the specifics of the temperature changes that were input into the model – using average temperature across the experiment rather than actual temperature changes produced much less accurate results.

This research is a first step in creating models that may help us predict the future extinction dynamics of wild populations subjected to unevenly distributed climatic warming over coming decades. It is a long way from a simple model of a laboratory population to a model that can accurately predict the future of complex assemblages of wild animals that are also subject to predation, disease and a healthy dose of luck. But the fact that these models can work for simple systems in laboratory conditions is a great first start – if they didn’t work for these populations, we could be fairly sure they wouldn’t generalise to natural populations. This shows that simple phenomenological models based on basic metabolic theory can be useful to understand how climate change will effect populations.

Original Article:

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This research was made possible by funding from the Natural Environment Research Council (NERC).

Extinction and Species Declines:
Defaunation in the Anthropocene

By Claire Asher, on 18 August 2014

We are in the grips of a mass extinction. There have been mass extinctions throughout evolutionary history, what makes this one different is that we’re the ones causing it. A recent review paper from GEE’s Dr Ben Collen discusses the current loss of biodiversity and suggests that our main concerns are species and population declines, which alter ecosystem dynamics and threaten our food, water and health. Understanding the drivers of local declines is more complex than understanding species extinction, but may be more pertinent to our ongoing health and survival.

The history of life on Earth has been punctuated by five mass-extinction events; from the Ordovician-Silurian extinction that killed 85% of sea life 443 million years ago, to the famous Cretaceous-Tertiary extinction that wiped out the dinosaurs 65 million years ago, mass extinctions have been a part of life. However, we are now in the middle of the sixth mass extinction event, and we’re the ones who are causing it. The last 500 years has seen humans cause a wave of extinctions of such speed and magnitude that it rivals the big five extinction events of the past.

Defaunation in the Anthropocene

Like other mass extinctions, the Anthropocene extinction event is affecting all taxonomic groups, although some are being hit harder than others. Since 1500, over 300 terrestrial vertebrates, 90 fish and nearly 400 are known to have been driven to extinction (although the real figures are likely much higher!). A conservative estimate suggests that we may be losing anywhere between 10,000 and 60,000 species each year. Many of these species go extinct before we ever even get a chance to identify them. Extinction is not evenly distributed, though – amphibians appear to be worse affected than birds, for example. Perhaps more worrying, many remaining species are suffering severe population declines. Globally, terrestrial vertebrate populations show declines of 25%, and 67% of monitored invertebrate populations are declining by 45%! The loss of species from ecosystems, either through local population declines or species extinction, will undoubtedly disrupt ecosystem function and the key ecosystem services humans rely on for survival and well being.

Scientists have coined the term ‘defaunation’ to include the extinction of species and populations as well as local declines in abundance. Defaunation can be thought of as deforestation for animals. It is an important point to make that although species extinctions are conspicuous and striking, the real damage to ecosystem function happens a long time before the final extinction event. Declines in populations will alter community composition far more than the final loss of the few remaining individuals of a population, and further, population declines have the potential to be reversed, if we act quickly enough!

Predicting Patterns of Defaunation

If we are to halt or even slow the current mass extinction, we need to identify both the causes of defaunation and the traits that make certain species so vulnerable to human disruption. The main drivers of defaunation are overexploitation of species, habitat destruction and introduced invasive species. These threats have all increased in severity over the past decade and look set to continue. In addition to these long-term threats, climate change is rapidly becoming the biggest threat to biodiversity. Most threatened species are under pressure from multiple human threats, but our understanding of the complex interactions and feedback loops between different threats is still in it’s infancy. It’s clear though that these threats do not act in isolation; a species trying to track suitable habitat as it moves with climate change will find that task much harder if habitat loss and fragmentation is also occurring.

Researchers have highlighted a number of life history and biological traits that tend to make species more vulnerable to human impacts. For example, species that have a small geographic range, large body size and produce just a few offspring after a long-development process, are more likely to be threatened with extinction due to human activities. However, our understanding of the traits that influence species’ extinction risk doesn’t help conservation as much as you might expect, because the relationship between these traits and extinction risk is often idiosyncratic and highly context-dependent. These relationships may also be more variable and weaker for individual populations than for whole species, making population declines more difficult to predict than whole-species extinctions. Defaunation, ultimately, is a synergistic function of the traits a species possess and the nature of the threat(s) it is exposed to.

Disrupting Ecosystems and Communities

The loss of biodiversity through defaunation is not just a concern because of the aesthetic appeal of an individual species, or of a world rich in diversity in general. It is also a major concern because defaunation will likely have a negative impact on the ecosystem goods and services upon which we rely upon for our wellbeing and survival. In fact, biodiversity loss is thought to be comparable to other threats such as pollution in terms of it’s impact on ecosystem function. Defaunation can be expected to have a negative impact on our food, water and health, as well as our psychological wellbeing.

Food

Insect pollination is required for the continued production of 75% of the World’s crops, and is responsible for 10% of the economic value of the entire World’s food supply. Declines in pollinators are now a major problem, particularly in Northern Europe and the USA, and have been linked to declines in insect-pollinated plants. Biodiversity, particularly of small vertebrates, is provides crucial pest control services, valued at around $4.5 billion a year in the USA alone. Declines in small vertebrate populations are linked to cascading changes in the whole ecosystem which allow increases in pest abundance and, consequently, a loss of plant biomass. If the plant in question is a crop or food source, the results can be catastrophic.

Nurtient Cycling and Decomposition

Invertebrates are also very important for their roles in decomposition and nutrient cycling. Defaunation can reduce these important services, and cause changes in the patterns of nutrient cycling that can have knock-on effects on a huge variety of ecosystems. Likewise, large vertebrates that roam large home ranges are important in connecting ecosystems and transferring energy between them, and yet these species are often the most severely impacted by human activities.

Water

Another key ecosystem service is the provision of clean, fresh water. Research has shown that declines in amphibian populations can result in increases in algae, reduced nitrogen uptake and changes to oxygen availability in the water. This too will likely have major knock-on effects for other species (including ourselves!).

Health and Medicine

Finally, we can expect defaunation to negatively affect our health. Species that are more robust to human disturbance are often also better at carrying and transmitting zoonotic diseases (diseases that are carried by animals and transferred to humans), and altering ecosystem dynamics can change behaviours that influence transmission rates. Defaunation is likely to also reduce the availability of pharmaceutical compounds and alter the dynamics of disease regulation. All of this may mean that defaunation leads to an increase disease and a reduction in the availability of therapeutic compounds.

The impact of defaunation is less about the absolute loss of biodiversity and more about the local shifts in species composition and functional groups, which alter ecosystem function and ultimately, our food, water and health. However, reductions in species exploitation and land-use change are two feasible actions that can be achieved rapidly and may buy us enough time to address other drivers of defaunation such as climate change. Globally, we need to reduce and more evenly distribute our consumption if we are to change current trends in defaunation, and open the possibility for refaunation.

Original Article:

() Science

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This research was made possible by funding from the Natural Environment Research Council (NERC), the National Council for Scientific and Technological Development (CNPQ), the Foundation for the Development of UNESP, the Sao Paolo Research Foundation, the Joint Nature Conservation Committee (JNCC), the National Science Foundation (NSF) and the National Autonomous University of Mexico/a>.

Predicting Extinction Risk:
The Importance of Life History and Demography

By Claire Asher, on 28 July 2014

The changing climate is no longer simply a concern for the future, it is a reality. Understanding how the biodiversity that we share our planet with will respond to climate change is a key step in developing long-term strategies to conserve it. Recent research by UCL CBER’s Dr Richard Pearson identifies the key characteristics that are likely to influence extinction risk due to climate change, and shows that existing conservation indicators such as the IUCN red list may contain the data necessary to make these predictions.

Human activities have been negatively impacting biodiversity for centuries, and conservationists have developed a number of different indicator lists which attempt to classify species’ extinction risk. However, these lists were created to measure human impacts such as as habitat loss, hunting and introduction of invasive species. These impacts will continue to be a major issue for biodiversity, but may be dwarfed in the future as climate change takes hold. Can the indices and data we already have be used to predict extinction risk from climate change? Or does climate change represent a new type of threat, needing new indices?

Studies have previously identified the ecological and biological traits that are characteristic of threatened or declining species. However, it is not clear how well these traits predict the future risk of climate-induced extinction. In February this year, GEE’s Dr Richard Pearson, in collaboration with colleagues at the American Museum of Natural History, Stony Brook University and the University of Adelaide, published a paper in Nature which attempted to address these questions. Most studies that have considered the impact of climate change on species’ extinctions have attempted to predict changes in the distribution of suitable habitats and measure extinction risk in terms of whether the species is likely to be able to find habitat to live in. However, such studies rarely consider how a species’ traits such as life history and spatial characteristics will influence their ability to persist through changes in climate. In this study, Pearson and colleagues coupled ecological niche models with demographic models, and developed a generic life history method to estimate extinction risk over the coming century.

Modelling Extinction
The authors then tested their models on ecological and spatial traits for 36 reptile and amphibian species in the USA. Using commonly available life history variables, they found that their models could accurately predict extinction risk between 2000 and 2010. They then utilised the same traits and models to predict future extinction risk under two climate models – a high emissions scenario and a policy scenario aimed at curbing emissions. Average extinction risk for the 36 species studied was 28% under the high emissions scenario, dropping to 23% under strict policy intervention. This seems like a very small difference for a significant intervention – it’s important to note that the same estimates indicated an average extinction risk of just 1% in the absence of any climate change at all.

One of the most important determinants of extinction risk in reptiles and amphibians was occupied area, which represents the range of climatic and habitat conditions the species can survive in. Species with a larger occupied area tended to be more robust to climate change, presumably because they are already adapted to a wider range of habitats and climates. Other key variables influencing extinction risk include population size and generation length. In many cases, traits interacted to determine species risk, for example extinction risk was strongly influenced by interactions between occupied area and generation length. Including many different traits can therefore greatly improve the accuracy of predictions. Recent trends tended to be less informative than spatial, demographic and life history traits, particularly under the high emissions scenario, suggesting that the impacts of climate change we have observed so far are likely to become less and less relevant as climate change accelerates.

The majority of variables that showed a significant impact on extinction risk are already included in major conservation assessments and indices, meaning that data and monitoring programs already in place may be better at predicting extinction risk under climate change than we might have expected. Climate change may not be fundamentally different from other human threats such as habitat loss and hunting, at least in terms of our ability to assess extinction risk. Conservation initiatives should focus on species who currently occupy a small and declining area and have a small population size. Regardless of the policy future, conservation actions will need to consider and account for climate change if they are to prove effective.

Original Article:

() Life History and Spatial Traits Predict Extinction Risk Due to Climate Change Nature

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This research was made possible by funding from the National Aeronautics and Space Administration (NASA) and the Australian Research Council

Predicting the Future of Biodiversity

By Claire Asher, on 14 August 2013

As human populations expand and use the land differently, they are having an impact on the plants and animals that share that land with them. Conservation biologists have been working for decades to try and document the ways in which these changes are affecting species, and to try and develop indicators that can be used to monitor these changes over time. However, previous work has tended to focus on certain species (e.g. bats, birds), neglecting other important groups such as insects, and have been biased towards certain habitats (e.g. tropical rainforest).

A new project in partnership between University College London, Imperial College London, the University of Sussex, UNEP World Conservation Monitoring Center and Microsoft Research, aims to improve on previous studies and develop a model for understanding how whole biological communities respond to human pressures across the globe. Collating high-quality data from hundreds of peer-reviewed papers, in addition to unpublished data direct from field researchers, the PREDICTS team hope to investigate local patterns of biodiversity at a global scale, and improve our understanding of how whole ecosystems respond to human pressures such as land-use change.

Biodiversity Declines
IMG_5921Major global loss of biodiversity is underway, and we have good reason to believe humans are responsible. The current extinction rate of species is estimated to be 1000 times higher than long-term historical averages, although large fluctuations in this in the past were also common. Humans have altered the world enormously, converting forests and savannas into farmland and housing. Virtually all ecosystems have been changed substantially – most biomes have lost between 20 and 50% of land to human uses. Humans have also exploited natural resources for wood, food, medicine and social reasons, and in many cases overexploitation has lead to major species declines and extinctions. Globally, it is estimated that 12% of bird species, 23% of mammals and 32% of amphibians are threatened with extinction, with many of these species suffering population declines and a reduction in genetic diversity, which may exacerbate the effect of human impacts. Even optimistic projections indicate continued human pressure on biodiversity from a range of different sources including hunting and habitat destruction. Many of the pressures currently placed on global biodiversity, such as land-use change, pollution and the introduction of invasive species, are set to continue or intensify over coming decades.

Ecosystem Services
Biodiversity is a valuable asset to humans for many reasons, not least its considerable economic value. Biodiversity contributes to human well-being by providing ecosystem services such as food (crops and livestock), fresh water, timber, natural hazard protection, air quality, climate regulation, prevention of erosion, as well as cultural benefits such as the aesthetic and recreational use of biodiversity. The exact relationship between biodiversity and ecosystem services is still relatively poorly understood, as it represents a complex interaction of many factors, which may vary from habitat to habitat. Many researchers suspect there may be threshold effects, with a sudden collapse of ecosystems, and a consequent loss of the services they provide, once a threshold number of species is lost. Others suggest certain ‘keystone’ species may be more important for ecosystem function. What is clear, however, is that healthy, functioning ecosystems are key to human health and well being. A greater understanding both of how biodiversity contributes to ecosystem function and ecosystem services, and of how biodiversity is likely to respond to continued anthropogenic pressures is sorely needed.

Improving Indicators
DSC_1216_watermarkOne central issue to studying and increasing our understanding of how ecosystems respond to human pressures is selecting species, populations or ecosystems to act as indicators of overall trends. It is simply not possible to monitor all populations of all species, and conservationists have traditionally relied upon indicator species and ecosystems as a measure of the overall health of biodiversity. In many cases these indicators were initially selected out of convenience meaning that well-studied species, communities and biomes are hugely overrepresented in the data available. However, species’ traits are likely to influence how they respond to human pressures, and a broader geographical and taxonomic view is needed to take the next step in our understanding.

Projecting Responses of Ecological Diversity in Changing Terrestrial Systems
The PREDICTS project aims to address some of these issues by performing a meta-analysis of species responses to different human pressures, covering as broad a taxonomic and geographical data set as is available. The PREDICTS team are collecting data from published papers; however, they also hope to draw on rich datasets held by ecologists which are simply too large to have been published in full. If you are an ecologist and believe you may have data that could be used for this project, please visit the PREDICTS website to find out more. They have already collated over 800,000 biodiversity records covering more than 15,000 species. These data are being combined to form a database that will be used to answer a number of key questions about biodiversity and anthropogenic change. In particular, the PREDICTS project is interested in investigating how different taxonomic groups respond, how responses differ in different biomes and with different intensities of human pressure. They also plan to investigate how different measures of biodiversity (e.g. species richness, evenness, abundance etc) may respond differently in different species, regions and for different human pressures.

_DSC3418_watermarkBy combining data from many species and sites, across a variety of different intensities of human pressure, PREDICTS hopes to develop a deeper understanding of how different factors interact to determine species responses. From this they hope to make predictions about how biodiversity may respond to different projected future scenarios, and thus provide insights for science policy.

Turning Science into Policy
We are faced with an increasingly difficult global situation, as human populations expand, the climate changes and biodiversity declines. What makes this situation more difficult still is that we need to make decisions now and over the next few years that will impact a generation, but for which we still have insufficient data to know for sure what’s best. Making projections for climate change, human population expansions and changes in the exploitation of biodiversity is difficult. Making projections for how biodiversity will respond to those changes is even more difficult still, but it is a task we must attempt if we are to make informed decisions about the future of our planet. PREDICTS hopes to utilise what data we do have to make synthesise a more in depth and holistic understanding of how ecological communities respond to human impacts, which can be used to make predictions that will help inform science policy makers globally.

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The Dynamics of Population Declines

By Claire Asher, on 2 July 2013

Widespread declines in wildlife populations are a major concern, but global and regional targets to reduce the rate of biodiversity loss have so far not been met. Conservation practitioners are faced with an increasingly difficult task of balancing limited funding against increasing human pressures on wild populations. Methods for identifying detrimental human activities, identifying and classifying declines and prioritising species for conservation interventions are critical to ensure conservation efforts are invested wisely over the coming decades. Researchers at the Institute of Zoology (IOZ), Imperial College London and GEE have been working towards developing innovative methods for identifying pressures and determining conservation priorities in wild mammal populations.

Theoretical work suggests that different human pressures may result in different types of population decline, leaving a fingerprint of anthropogenic stress on the history of a population. Human activity might cause a constant pressure, or one that changes in proportion to the abundance of a species. Pressures may become more extreme as populations become smaller, for example when the value of a species to hunters increases as it becomes rarer. By contrast, a constant hunting effort would create a declining pressure over time, as individuals become increasingly difficult to find. Previous work by CBER’s Georgina Mace has suggested that the shape of the population decline curve observed may be characteristic of certain types of human pressure. A recent paper in Ecology and Evolution by IOZ’s Martina Di Fonzo, and Ben Collen and Georgina Mace from GEE, uses computer simulations and long-term monitoring data from nearly 60 species of mammal worldwide to test these theoretical predictions.

Different Population Decline Curve Shapes for Different Types of Human Pressure

Different Population Decline
Curve Shapes for Different Types
of Human Pressure

Taking a number of biological traits into account, such as life-history speed (e.g. generation time) and the carrying capacity of the environment, Di Fonzo, Collen and Mace (2013) simulated population size trends under a number of different types of human pressure. They looked at threats that are constant, increase or decrease in intensity as the population declines, and threats that act in proportion to the population size or that remain fixed as population size changes. They then statistically characterised the shape of the resulting curves using three different statistical models (linear, exponential, quadratic) and different curve shapes (concave or convex). This produced mixed results. Some types of pressure consistently produced the same type of decline curve regardless of the biological and environmental characteristics of the population, but others were more strongly influenced by generation length and habitat carrying capacity. This makes sense, since populations with a short generation time are likely to be better able to cope with and recover from human pressure. For most types of pressure, however, some tell-tale signs were usually identifiable. For example, pressures that are proportional to population size and increase over time tended to produce convex declines, whilst proportional pressure that decreases over time is more likely to produce a concave curve.

From Simulation to the Wild
That’s all very well and good, but how well does the simulated data match up to real-world wildlife populations? Using data from the Living Planet Index, the authors attempted to characterise the shape of real population declines and compared the model predictions with data about real human pressures impacting on these populations. Across 124 populations for 57 different species of mammal, they found that populations were most commonly experiencing concave declines, suggesting human pressures that are in proportion to population size, but decrease in intensity over time. There was some association between curve-shape and the actual sources of pressure, with exponential concave declines being associated with habitats suffering from exploitation, habitat loss, invasive species and pollution, and quadratic convex declines being more characteristic of disease-affected populations. However, most populations were subject to multiple human-pressures simultaneously, which may have partly obscured the relationship predicted by theory.

Population decline curves may not enable us to identify specifically which threats are affecting a population, however they can reveal important details of how those pressures are changing over time. The International Union for the Conservation of Nature (IUCN) Red list attempts to categorise species’ conservation status. Currently, the Red List includes population size decline when assessing conservation status, however this does not take into account whether those declines are accelerating or decelerating over time. Incorporating information about the shape of the decline curve can provide important insights for conservation – species experiencing accelerating declines may be prioritised when determining how to use limited funding. Population-level data can highlight the impact of human activities more rapidly than studying species-level information, as populations are likely to show more rapid responses to human change, and may act as an early warning of longer-term species decline.

The dynamics of real populations are complex, and species’ biological traits in combination with multiple human pressures acting on a population simultaneously can mean that reality does not always match perfectly with theory. However, studying the shape of population declines can reveal characteristics of the pressure being exerted on the population, may provide an early-warning system for species-level declines, and can be used to inform conservation priorities. This relatively simple method for assessing the type of decline a population is experiencing can provide valuable information to conservationists about which types of pressures are most influential, and how to act to prevent extinction.

Original Article:

() Ecology and Evolution

This project was made possible by funding from the Natural Environment Research Council (NERC)

Biological Traits Influence Vulnerability to Climate Change in Birds, Amphibians and Corals

By Claire Asher, on 25 June 2013

Climate change is fast becoming a reality, and with temperature rises of between 0.8°C and 2.6°C predicted over the next 35 years, biodiversity will certainly be impacted, with many species set to suffer declines or potential extinction. But all species are not equal and certain traits may make species more or less vulnerable to climate change than others. A new model presented in PLOS one this month investigates the impact of biological traits, such as physiology, ecology and evolutionary history, on vulnerability to climate change for some of the most threatened groups: birds, amphibians and corals. Around 10% of species are both highly vulnerable to climate change, and already listed as threatened with extinction. The model also identifies potentially vulnerable species for future conservation priorities, giving biologists a head-start in trying to slow the inevitable loss of biodiversity that climate change will bring.

Many researchers are interested in predicting how biodiversity might respond to climate change. Biodiversity is essential to human survival – diverse, functional ecosystems provide us with food, water and medicine. However, predicting how ecosystems might respond to changes in temperature and rainfall is a complicated matter. Most previous models have considered the availability of suitable habitat for species based upon their current range and predictions of temperature changes. However, not all species are created equal – biological traits of individual species are likely to play an important role in determining species survival. For example, some species are adapted to a very specialised habitat or are poor as dispersal and so may struggle to find alternative habitats even if they are available. Other species have long generation times and produce few young, or have very limited genetic diversity in the population, making adaptation to new habitats more difficult. Species like these are likely to be more vulnerable to climate change than generalists who are good at dispersal and produce lots of offspring. Not considering the biology of a species when modelling responses to climate change can lead to under- or over-estimations of how vulnerable a species actually is.

Accounting for Biology
To address this issue, Foden and colleagues, working in collaboration with Professor Georgina Mace from CBER, developed a systematic framework for assessing species vulnerability to climate change, and applied this model to three of the best-studied, and most endangered groups of animals: birds, amphibians and corals. They considered three factors – sensitivity (whether a species can survive where it is), exposure (the predicted extent of change under climate models), and adaptive capacity (whether a species can avoid the negative impacts of climate change by moving or evolving).

The components of species vulnerability - sensitivity, adaptive capacity and exposure

Components of species
vulnerability – sensitivity, adaptive
capacity and exposure

In consultation with extinction risk specialists, they identified 90 biological, ecological, phsyiolocial and environmental traits which are likely to influence vulnerability to climate change. In particular, they identified habitat specialisation, rarity, environmental tolerance, disruption of environmental triggers and interactions with other species as key components of species sensitivity to climate change. Adaptive capacity is composed of dispersal ability, barriers to dispersal, genetic diversity, generation length and reproductive output. They assessed these traits for each of 16,857 species of bird, amphibian and coral, across the globe.

The proportion of species in a region that are sensitive or have limited adaptive capacity (blue), high exposure to climate change (yellow) or both (maroon).

The proportion of species in a region that are sensitive or have limited adaptive capacity (blue), high exposure to climate change (yellow) or both (maroon).

Armed with these traits, they were able to determine sensitivity, adaptive capacity and exposure for each species, and generated maps of where species may be particularly vulnerable. They found that around 24% – 50% of bird species, 22% – 44% of amphibians and 15% – 32% of corals are both sensitive and exposed, and have limited capacity to adapt. They identified the Amazon region as containing many highly vulnerable birds and amphibians. Many bird species were also highly vulnerable in central Eurasia, the Congo basin, the Himalayas, Malaysia and Indonesia, with amphibians most vulnerable in north Africa, eastern Russia, and the northern Andes. The waters around Malaysia, Indonesia and the Philippines were hot-spots for highly vulnerable corals.

A Silver Lining
It’s not all doom and gloom, though. The study also identified some species and regions where species’ traits may make them more able to cope with climate change. Around 28% -53% of bird species, 23% – 59% of amphibians and 30% – 55% of corals may survive projected climate changes because of their inherent ability to disperse or adapt to change. In particular, southern Asia and North America may see less severe biodiversity declines than previously thought.

The interplay between climate change and biodiversity is complex, and unlikely to be uniform across taxonomic groups. It is important to consider the physiological, ecological and evolutionary traits of individual species when making predictions about the impact of climate change. This study considered the effects of temperature and rainfall changes, as well as ocean acidification and sea-level rise, on global biodiversity. However, many other factors will influence whether species survive over the long-term – habitat destruction, invasive species and pollution are also major drivers of extinction which need to be taken into account when predicting the future of a species. Taking into account the biology of a species, and it’s interaction with other species, is a major step forward in our understanding of how biodiversity will respond to the impending climate changes that are now inevitable.

Original Article:

This research was made possible by funding from the MacArthur Foundation.

Farewell to One of Darwin’s Frogs
…but it’s not too late for another

By Claire Asher, on 18 June 2013

Amphibian declines are one of the biggest conservation concerns of the 21st century. In a paper last week in PLOS ONE, Claudio Soto-Azat at the Universidad Andrés Bello in Chile, in collaboration with Ben Collen from GEE’s Centre for Biodiversity and Environmental Research (CBER), and colleagues at ZSL, reported some sad news about two species of Darwin’s frog in South American. They announce the exctintion of the Chile Darwin’s Frog and substantial declines in the closely related species, Darwin’s Frog.

Using published data and archived specimens, Soto-Azat and colleagues reconstructed the historical range of these two species across Chile and Argentina, and went looking for the frogs right across their original range. Not a single Chilea Darwin’s frog (Rhinoderma rufum) was found. They used modeling based upon recorded sightings to predict whether the Chile Darwin’s frog truly is extinct. Unfortunately, this model confirmed the worst, that Chile Darwin’s frog is now extinct in the wild, and probably vanished over 30 years ago.

Darwin’s Frog (Rhinoderma darwinii)
Image from ARKive. Photograph used with permission from (Universidad Andrés Bello)

Populations of the closely related Darwin’s frog (Rhinoderma darwinii) were found, however these populations are much smaller and more fragmented than previously thought. The authors recommend classifying Darwin’s only remaining frog as Endangered. No frogs were found in or near urban environments – the surviving populations exist in primary forest. The populations that have gone extinct had been put under strain from human pressures. In Chile, loss of native forest as it is chopped down to make way for pine plantations to satisfy a growing global demand for wood and paper may be reducing the availability of habitat for these colourful little frogs.

The same frog captured twice during the study - identifiable by it's unique underbelly patterning

Darwin’s Frog (Rhinoderma darwinii)
The same frog captured twice – identifiable by it’s unique underbelly patterning

Darwin’s frogs aren’t just colourful, they also have a rather remarkable way to care for their young. The male waits patiently until the eggs he fertilised are ready to hatch, when he swallows the eggs and holds them in his vocal sac as they hatch. The tadpoles remain their at least until they are able to feed by themselves, but in Darwin’s frog (R.darwinii), the young stay until they can hop out, as tiny froglets. Chile Darwin’s frog is lost forever, but it may not be too late to save Darwin’s frog, and this unusual strategy for rearing offspring.

Original Article:

() PLOS ONE

Sexy Mates Ensure Survival in Stalk-Eyed Flies

By Claire Asher, on 30 May 2013

Attracting a female can be expensive, and females may use this cost to weed out poor quality males. Male ornaments such as antlers are a reliable indicator of nurture, but what about nature? Recent research into in male ornamentation in stalk-eyed flies reveals a key role for genetics, and highlights the importance of mate choice in species survival.

Males throughout the animal kingdom go to some weird and wonderful lengths to try and attract females. This might involve an elaborate dance, a carefully wrapped gift, or an ornate head-dress, and these adverts are often costly to the male who performs them. A peacock’s tail makes him conspicuous to predators; a red deer’s antlers require food and energy to grow. And a female finds all of this very sexy, because it informs her about the quality of the male; only the highest calibre males can afford the handicap.

Stalk-Eyed Flies
This phenomenon isn’t limited to birds and mammals, of course, even flies need to attract a mate, and stalk-eyed flies have a rather odd form of ornamentation: their eyes sit on the end of long stalks that protrude out horizontally from their head. Clearly this makes their lives difficult; long eye stalks take more energy to grow, and make the males more cumbersome during flight. So why do males grow these impractical eye stalks? Because, despite the costs, males with longer stalks have more luck with the ladies.

D. meigenii

A male Stalk-Eyed Fly (D. meigenii)
Photography by

Females are thought to be attracted to males with longer stalks because they are reliable indicators of the quality of the male. Males with good genes, who grew up in plentiful environments, produce the largest ornaments and consequently get their pick of the ladies. In other words, these traits are strongly dependent on environmental conditions (e.g. food availability, temperature) and genetics. Or so the theory goes. There is good evidence that the appearance of male sexual traits is influenced by the environment in which the male grew up, but few empirical tests have been conducted to see whether ornaments also reflect genetic quality. And until recently, we had little idea of what impact this might have at the population level.

Nature and Nurture
Recent research in GEE has taken a major step towards answering these questions. Bellamy and colleagues conducted a long-term inbreeding experiment with the African stalk-eyed fly (Diasemopsis meigenii) to investigate how eye stalk length is influenced by genetic stress. Inbreeding is known to be harmful to populations, causing inbreeding depression by increasing the frequency of rare and damaging mutations, and thereby reduce the fitness of individuals. If long eye stalks are a sign of high genetic quality, then we would expect inbreeding to reduce the size of eye stalks over time. And this is just what 11 generations of mating with siblings: eye span decreased significantly during the experiment, more so than other traits such as wing size, which are not considered sexy. Thus, male traits important for attracting a female are more sensitive to genetic quality than non-sexy traits, supporting previous theory about why females are attracted to these traits in the first place.

Surviving the Genetic Storm
One rather unexpected result, however, was that male eye span at the start of the experiment was also a strong predictor of whether the line went extinct or not before the end of the experiment. Less than half the original lines survived the entire 11-generation experiment, and those who did survive were descended from males with longer eye-stalks. This again supports the idea that male eye span in stalk-eyed flies is linked closely to genetic quality; males with long eye stalks carried fewer deleterious mutations when the experiment began and so were more robust against inbreeding depression and less likely to go extinct. This result may have intriguing implications for conservation and for population dynamics in general. It shows that individual decisions such as mate choice may influence the fate of a whole population. Conservationists should take mate choice and sexual selection into account when designing programmes to conserve species, especially those with small or declining populations.

Original Article:

This project was made possible by funding from the Natural Environment Research Council (NERC), the Biotechnology and Biological Sciences Research Council (BBSRC) and the Engineering and Physical Sciences Research Council (EPSRC)