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Archive for the 'Biodiversity and Environmental Biology' Category

PREDICTS Project: Global Analysis Reveals Massive Biodiversity Losses

By Claire Asher, on 21 May 2015

The changing climate is only one of a myriad of pressures faced by global biodiversity – we are also changing habitats and altering land-use on an unprecedented scale. The first global analysis published from the PREDICTS project reveals the striking global effect of land-use change on local biodiversity patterns, and highlights the importance of future climate-mitigation strategies in shaping the future of biodiversity and the vital ecosystem services it provides.

Human activities are causing widespread change to and degradation of habitats, which has been linked to serious biodiversity declines globally. Land-use change comes in many forms, from deforestation and agriculture to urban development and road-building, and previous work by the PREDICTS project has shown how different types of land-use influence different types of species differently. We are interested in biodiversity loss at a global scale, and many metrics aim to quantify this, but viewing global patterns can obscure local-scale changes that are likely to be more important for the resilience of ecosystem services. Ecosystem services include clean air and water, food, medicine and nutrient cycling, among others, and are vital both for biodiversity and for human survival and well-being. The PREDICTS project considers local-scale changes to biodiversity in response to land-use change, to produce a powerful model that can be used to project the impact of future land-use and climate change. In their latest paper, published in Nature last month, the PREDICTS team reveal their most comprehensive analysis to date, showing massive reductions in local biodiversity since 1500, and projecting further widespread losses under several future climate and land-use scenarios. There is still hope, however, and strategies to mitigate greenhouse gas emissions without major land-use change could offer the opportunity for global biodiversity to recover.

Understanding the Past and Present

The PREDICTS team have assembled a database of over 1,130,000 records of species abundance and nearly 330,000 records of species richness across more than 11,000 sites worldwide. The database includes results from 284 scientific publications, and represents over 25,000 species. Using this incredible resource, the team compared species richness and abundance between sites with different land-use types and produced a statistical model to quantify local biodiversity responses to land-use change. This enabled them to infer changes in species assemblages since the year 1500.They found that species richness and total abundance were both strongly influenced by land-use type and intensity, with reductions in biodiversity outside of primary vegetation and the worst losses seen in intensively used areas. Local biodiversity was also negatively impacted by human population density and accessibility (measured by the distance to the nearest main road). In the worst-affected habitats, changing land-use away from primary vegetation reduced species richness and abundance by an average of about 40%, and globally, land-use change was responsible for an average reduction in species richness and abundance of around 9%. The value of secondary vegetation (forest recovering from past damage) for biodiversity depended strongly on how mature the habitat was, with species diversity increasing over time, and mature secondary vegetation most closely resembling primary habitats. Restoration projects do, therefore, have the power to return biodiversity to damaged habitats, but (unsurprisingly!) it will take time.

Previous estimates have suggested that local losses of species richness and diversity greater than 20% are likely to substantially impair ecosystem services contributed to by biodiversity and reduce overall ecosystem function. Some scientists believe biodiversity loses at this scale may push populations towards ‘tipping points’ where ecosystem function declines lead to further species loss. Thus, in the worst-affected habitats considered by the PREDICTS team, which experienced on average a 31% loss of local species richness, ecosystem function is likely to be substantially impaired.

Changes in species richness and abundance may underestimate the real impact of land-use change because the measure fails to capture the composition of a community. The team therefore compared the species composition between sites and found that communities tended to be similar under similar land-use. Communities living in primary and secondary vegetation were most alike, while more disturbed habitats such as plantation forest, pasture and cropland tended to support a different cluster of more human-tolerant species. Human-dominated landscapes lost far more natural local diversity than more pristine sites where natural vegetation remains.

Reconstructing past biodiversity loss indicated that the greatest reductions in species richness occurred in (unsurprisingly) the 19th and 20th centuries, and that by 2005 local species richness worldwide had reduced by 13.6% due to land-use change and related anthropogenic pressures. How will this trend continue into the future?

Projecting the Future

The PREDICTS team then went on to combine their analysis of current species’ responses to land-use change with four climate scenarios produced by the Intergovernmental Panel on Climate Change, to project future changes in biodiversity under different socioeconomic scenarios of land-use change. Projecting as far as 2095, the PREDICTS model projects rapid biodiversity losses under a ‘business-as-usual’ land-use scenario, with species richness projected to drop a further 3.5%. These loses are not likely to be uniformly distributed, however, with the largest loses predicted to occur in economically poor but highly biodiverse regions, such as Southeast Asia and Sub-Saharan Africa. Buisness-as-usual results in rapid human population growth and agricultural expansion, and most closely matches recent trends, and yields the most severe losses in biodiversity of any scenario considered by the PREDICTS team. Continuing on as we have been does not bode well for biodiversity or the vital ecosystem services it provides us.

Projected net change in local richness from 1500 to 2095. Source: http://www.nature.com/nature/journal/v520/n7545/abs/nature14324.html.

Projected net change in local richness from 1500 to 2095. Source: http://www.nature.com/nature/journal/v520/n7545/abs/nature14324.html.

Perhaps surprisingly, the second-worst scenario for biodiversity is in fact the scenario with the least climate change (IMAGE2.6). This is because this scenario achieved reduced emmisions and climatic change by rapidly converting the world’s forests (primary vegetation) to crops and biofuel. In contrast, the IPCC scenario MiniCAM 4.5, which mitigates climate change through the use of carbon markets, crop improvements and diet shifts, however, is projected to increase average species richness. Not all our possible solutions to curb greenhouse gas emissions and reduce climate change will necessarily spell good news for biodiversity.

It isn’t all bad news, though. The right strategies can promote biodiversity globally, even producing increases in species richness by 2095 of up to 2%, and the PREDICTS team say widespread biodiversity loss is not inevitable. Concerted efforts and the right socioeconomic choices can make long-term global sustainability of biodiversity an achievable goal.

Original Article:

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This research was made possible by funding from the Natural Environment Research Councik (NERC) and the Biotechnology and Biological Sciences Research Council (BBSRC).

Planning for the Future – Resilience to Extreme Weather

By Claire Asher, on 15 January 2015

As climate change progresses, extreme weather events are set to increase in frequency, costing billions and causing immeasurable harm to lives and livelihoods. GEE’s Professor Georgina Mace contributed to the recent Royal Society report on “Resilience to Extreme Weather”, which predicts the future impacts of increasing extreme weather events, and evaluates potential strategies for improving our ability to survive, even thrive, despite them.

Extreme weather events, such as floods, droughts and hurricanes, are predicted to increase in frequency and severity as the climate warms, and there is some evidence this is happening already. These extreme events come at a considerable cost both to people’s lives, health and wellbeing, and the economy. Between 1980 and 2004, extreme weather is estimated to have cost around US$1.5 trillion, and costs are rising. A recent report by the Royal Society reviews the future risks of extreme weather and the measures we can take to improve our resilience.

The global insured and uninsured economic losses from the two biggest categories of weather-related extreme events. Royal Society (2014)

The global insured and uninsured economic losses from the two biggest categories of weather-related extreme events. Royal Society (2014)

Disaster risk is a combination of the likelihood of a particular disaster occurring and the impact on people and infrastructure. However, the impact will be influenced not only by the severity of the disaster, but by the vulnerability of the population and its infrastructure, a characteristic we have the potential to change. Thus, while it may be possible to reduce the frequency of disasters by reducing carbon emissions and slowing climate change, another key priority is to improve our own resilience against these events. Rather than just surviving extreme weather, we must adapt and transform.

The risks posed by climate change may be underestimated if exposure and vulnerability to extreme weather are not taken into account. Mapped climate and population projections for the next century show that the number of people exposed to floods, droughts and heatwaves will both increase and become more concentrated.

Exposure risk to floods and droughts in 2090. Royal Society (2014)

Exposure risk to floods and droughts in 2090. Royal Society (2014)

In their recent report, the Royal Society compared different approaches to increasing resilience to coastal flooding, river flooding, heatwaves and droughts. Overall, they found that a portfolio of defence options, including both physical and social techniques and those that utilise both traditional engineering solutions and more ecosystem based approaches. Broadly, approaches can be categorised as engineering, ecosystem-based, or hybrids of the two. Resilience strategies that incorporate natural ecosystems and processes tend to be more affordable and deliver wider societal benefits as well as simply reducing the immediate impact of the disaster.

Ecosystem-based approaches can take a variety of different forms, but often involve maintaining or improving natural ecosystems. For example … Large, intact tropical forests are important in climate regulation, flood and erosion management and … Forests can also act as a physical defence, and help to sustain livelihoods and provide resources for post-disaster recovery. Ecosystem-based approaches often require a lot of land and can take a long time to become established and effective, however in the long-term they tend to be more affordable and offer a wider range of benefits than engineering approaches. For this reason, they are often called ‘no regret’ options. Evidence for the effectiveness of different resilience strategies is highly varied. Engineered approaches are often well-established, with decades of strong research to back them up. In contrast, ecosystem approaches have been developed more recently and there is less evidence available on their effects. The Royal Society report indicates that for coastal flooding and drought, some of the most affordable and effective solutions are ecosystem-based, such as mangrove maintenance as a coastal defence and agroforestry to mitigate the effects of drought and maintain soil quality. In many situations, hybrid solutions may offer the best mixture of affordability and effectiveness.

It is crucial for governments to develop and implement resilience strategies and start building resilience now. This will be most effective if resilience measures are coordinated internationally, resources shared and where possible, cooperative measures implemented. By directing funds towards resilience-building, governments can reduce the need for costly disaster responses later. Governments can reduce the economic and human costs of extreme weather by focussing on minimising the consequences of infrastructure failure, rather than trying to avoid failure entirely. Prioritising essential infrastructure and focussing on minimising the harmful effects of extreme weather are likely to be the most effective approaches in preparing for future increases in extreme weather events.

Original Article:

() Resilience to
extreme weather

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).

The Best of Both Worlds:
Planning for Ecosystem Win-Wins

By Claire Asher, on 16 November 2014

The normal and healthy function of ecosystems is not only of importance in conserving biodiversity, it is of utmost importance for human wellbeing as well. Ecosystems provide us with a wealth of valuable ecosystem services from food to clean water and fuel, without which our societies would crumble. However it is rare that only a single person, group or organisation places demands on any given ecosystem service, and in many cases multiple stakeholders compete over the use of the natural world. In these cases, although trade-offs are common, win-win scenarios are also possible, and recent research by GEE academics investigates how we can achieve these win-wins in our use of ecosystem services.

Ecosystem services depend upon the ecological communities that produce them and are rarely the product of a single species in isolation. Instead, ecosystem services are provided by the complex interaction of multiple species within a particular ecological community. A great deal of research interest in recent years has focussed on ensuring we maintain ecosystem services into the long term, however pressure on ecosystem services worldwide lis likely to increase as human demands on natural resources soars. Ecosystem services are influenced by complex ecosystem feedback relationships and food-web dynamics that are still relatively poorly understood, and increased pressures on ecosystems may lead to unexpected consequences. Although economical signals respond rapidly to global and national changes, ecosystem services are thought to lag behind, often by decades, making it difficult to predict and fully understand how our actions are influences the availability of crucial services in the future.

Trade-offs in the use of ecosystem services occur when the provision of one ecosystem service is reduced by increased use of another, or when one stakeholder takes more of an ES at the expense of other stakeholders. However, this needn’t be the case – in some scenarios it is possible to achieve win-win outcomes, preserving ecosystem services and providing stakeholders the resources they need. Although attractive, win-win scenarios may be difficult to achieve without carefully planned interventions, and recent research from GEE indicates they are not as common as we might like.

In a comprehensive meta-analaysis of ecosystem services case studies from 2000 to 2013, GEE academics Prof Georgina Mace and Dr Caroline Howe show that trade-offs are far more common than win-win scenarios. Across 92 studies covering over 200 recorded trade-offs or synergies in the use of ecosystem services, trade-offs were three times more common than win-wins. The authors identified a number of factors that tended to lead to trade-offs rather than synergies. In particular, if one or more of the stakeholders has a private interest in the natural resources available, trade-offs are much more likely – 81% of cases like this resulted in tradeoffs. Furthermore, trade-offs were far more common when the ecosystem services in question were ‘provisioning’ in nature – products we directly harvest from nature such as food, timber, water, minerals and energy. Win-wins are more common when regulating (e.g. nutrient cycling and water purification) or cultural (e.g. spiritual or historical value) ecosystem services are in question. In the case of trade-offs, there were also factors that predicted who the ‘winners’ would be – winners were three times more likely to hold private interest in the natural resource in question, and tended to be wealthier than loosing stakeholders. Overall, there was no generalisable context that predicted win-win scenarios, suggesting that although trade-off indicators may be useful in strategic planning, the outcome of our use of ecosystem services is not inevitable, and win-wins are possible.

They also identified major gaps in the literature that need to be addressed if we are to gain a better understanding of how win-win scenarios may be possible in human use of ecosystems. In particular, case studies are currently only available for a relatively limited geographic distribution, and tend to focus of provisioning services. Thus, the lower occurrence of trade-offs for regulating and cultural ecosystem services may be in part a reflection of a paucity of data on these type of services. Finally, relatively few studies have attempted to explore the link between trade-offs and synergies in ecosystem services and the ultimate effect on human well-being.

Understanding how and why trade-offs and synergies occurs in our use of ecosystem services will be valuable in planning for win-win scenarios from the outset. Planning of this kind may be necessary if we are to achieve and maintain balance in our use of the natural world in the future.

Original Article:

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This research was made possible by support from the Ecosystem Services for Poverty Alleviation (ESPA) programme, which is funded by the Natural Environment Research Council (NERC), the Economic and Social Research Council (ESRC), and the UK Department for International Development (ERC)

Life Aquatic:
Diversity and Endemism in Freshwater Ecosystems

By Claire Asher, on 6 November 2014

Freshwater ecosystems are ecologically important, providing a home to hundreds of thousands of species and offering us vital ecosystem servies. However, many freshwater species are currently threatened by habitat loss, pollution, disease and invasive species. Recent research from GEE indicates that freshwater species are at greater risk of extinction than terrestrial species. Using data on over 7000 freshwater species across the world, GEE researchers also show a lack of correlation between patterns of species richness across different freshwater groups, suggesting that biodiversity metrics must be carefully selected to inform conservation priorities.

Freshwater ecosystems are of great conservation importance, estimated to provide habitat for over 125,000 species of plant and animal, as well as crucial ecosystem services such as flood protection, food, water filtration and carbon sequestration. However, many freshwater species are threatened and in decline. Freshwater ecosystems are highly connected, meaning that habitat fragmentation can have serious implications for species, while pressures such as pollution, invasive species and disease can be easily transmitted between different freshwater habitats. Recent work by GEE academics Dr Ben Collen, in collaboration with academics from the Institute of Zoology, investigated the global patterns of freshwater diversity and endemism using a new global-level dataset including over 7000 freshwater mammals, amphibians, reptiles, fishes, crabs and crayfish. Many freshwater species occupy quite small ranges and the authors were also interested in the extent to which species richness and the distribution threatened species correlated between taxonomic groups and geographical areas.


The study showed that almost a third of all freshwater species considered are threatened with extinction, with remarkably little large-scale geographical variation in threats. Freshwater diversity is highest in the Amazon basin, largely driven by extremely high diversity of amphibians in this region. Other important regions for freshwater biodiversity include the south-eastern USA, West Africa, the Ganges and Mekong basins, and areas of Malaysia and Indonesia. However, there was no consistent geographical pattern of species richness in freshwater ecosystems.

Freshwater species in certain habitats are more at risk than others – 34% of species living in rivers and streams are under threat, compared to just 20% of marsh and lake species. It appears that flowing freshwater habitats may be more severely affected by human activities than more stationary ones. Freshwater species are also consistently more threatened than their terrestrial counterparts. Reptiles, according to this study, are particularly at risk from extinction, with nearly half of all species threatened or near threatened. This makes reptiles the most threatened freshwater taxa considered in this analysis. The authors identified key process that were threatening freshwater species in this dataset – habitat degradation, water pollution and over-exploitation are the biggest risks. Habitat loss and degradation is the most common threat, affecting over 80% of threatened freshwater species.

That there was relatively little congruence between different taxa in the distribution of species richness and threatened species in freshwater ecosystems suggests that conservation planning that considers only one or a few taxa may miss crucial areas of conservation priority. For example, conservation planning rarely considers patterns of invertebrate richness, but if these groups are affected differently and in different regions than reptiles and amphibians, say, then they may be overlooked in initiatives that aim to protect them. Further, different ways to measure the health of populations and ecosystems yield different patterns. The metrics we use to identify threatened species, upon which conservation decisions are based, must be carefully considered if we are to suceeed in protecting valuable ecosystems and the services the provide.

Original Article:

() Global Ecology and Biogeography

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This research was made possible by funding from the Rufford Foundation and the European Commission

PREDICTS Project: Land-Use Change Doesn’t Impact All Biodiversity Equally

By Claire Asher, on 13 October 2014

Humans are destroying, degrading and depleting our tropical forests at an alarming rate. Every minute, an area of Amazonian rainforest equivalent to 50 football pitches is cleared of its trees, vegetation and wildlife. Across the globe, tropical and sub-tropical forests are being cut down to make way for expanding towns and cities, for agricultural land and pasture and to obtain precious fossil fuels. Even where forests remain standing, hunting and poaching are stripping them of their fauna, degrading the forest in the process. Habitat loss and degradation are the greatest threats to the World’s biodiversity. New research from the PREDICTS project investigates the patterns of species’ responses to changing land-use in tropical and sub-tropical forests worldwide. In the most comprehensive analysis of the responses of individual species to anthropogenic pressures to date, the PREDICTS team reveal strong effects of human disturbance on the geographical distribution and abundance of species. Although some species thrive in human-altered habitats, species that rely on a specific habitat or diet, and that tend to have small geographical ranges, are particularly vulnerable to habitat disturbance. Understanding the intricacies of how different species respond to different types of human land-use is crucial if we are to implement conservation policies and initiatives that will enable us to live more harmoniously with wildlife.

Red Panda (Ailurus fulgens)

Habitat loss and degradation causes immediate species losses, but also alters the structure of ecological communities, potentially destabilising ecosystems and causing further knock-on extinctions down the line. As ecosystems start to fall apart, the valuable ecosystem services we rely on may also dry up. There is now ample evidence that altering habitats, particularly degrading primary rainforest, has disastrous consequences for many species, however not all species respond equally to land-use change. The functional traits of species, such as body size, generation time, mobility, diet and habitat specificity can have a profound impact on how well a species copes with human activities. The traits that make species particularly vulnerable to human encroachment (slow reproduction, large body size, small geographical range, highly specific dietary and habitat requirements) are not evenly distributed geographically. Species possessing these traits are more common in tropical and sub-tropical forests, areas that are under the greatest threat from human habitat destruction and loss of vegetation over the coming decades. The challenge in recent years, therefore, has been developing statistical models that allow us to investigate this relationship more precisely, and collecting sufficient data to test hypotheses.

There are three key ways we might chose to investigate how species respond to land-use change. Many studies have investigated species-area relationships, which model the occurrence or abundance of species in relation to the size of available habitat. These studies have revealed important insights into the damage caused by habitat fragmentation, however they rarely consider how different species respond differently. Another common approach uses species distribution models to predict the loss of species in relation to habitat and climate suitability. These models can be extremely powerful, but require large and detailed datasets that are not available for many species, particularly understudied creatures such as invertebrates. The PREDICTS team therefore opted for a third option to investigate human impacts on species. The PREDICTS project has collated data from over 500 studies investigating the response of individual species to land-use change, and their database now includes over 2 million records for 34,000 species. Using this extensive dataset, the authors were able to model the relationship between land-use type and both the occurrence and abundance of species. One of the huge benefits of this approach is that their dataset enabled them to investigate these relationships in a wide range of different taxa, including birds, mammals, reptiles, amphibians and the often neglected invertebrates.

Modelling Biodiversity

Sunbear (Helarctos malayanus)
image used with permission from
Claire Asher (Curiosity Photographic)

The resulting model included the responses of nearly 4000 different species across four measures of human disturbance; lang-use type, forest cover, vegetation loss and human population density. The vast dataset, the PREDICTS team were able to compare the responses of species in different groups (birds, mammals, reptiles and amphibians, invertebrates, between habitat specialists and generalists and between wide- and narrow-raging species. Their results revealed a complex interaction between these factors, which influenced the occurrence and the abundance of species in different ways.

In general human-dominated habitats, such as urban and cropland environments, tended to harbour fewer species than more natural, pristine habitats. Community abundance in disturbed habitats was between 8% and 62% of the abundance found in primary forest, and urban environments were consistently the worst for overall species richness. In these environments, human population density and a lack of forest cover were key factors reducing the number of species. Human population density could impact species directly through hunting, or more indirectly through expanding infrastructure. However, these factors impact different species in different ways, so the authors next investigated different taxa separately.

Birds appear to be particularly poor at living in urban environments, most likely because they respond poorly to increases in human population. Forest specialists and narrow-ranged birds fare especially badly in urban environments; only 10% of forest specialists found in primary forest are able to survive in urban environments. Although the effect was less extreme, mammals were also less likely to occur in secondary forest and forest plantations than primary forest, and forest specialists were particularly badly affected.

Urban Pests
Although many species were unable to exist in disturbed habitats, those species that persisted were often more abundant in human-modified habitats than pristine environments. This isn’t particularly surprising – some species happen to possess characteristics that make them well suited to urban and disturbed landscapes; these are often the species that we eventually start to consider a pest because they are so successful at living alongside us (think pigeons, rats, foxes). These species tend to be wide-ranging generalists, although sometimes habitat specialists do well in human-altered habitats if we happen to alter the habitat in just the right. Pigeons, for example, are adapted to nesting on cliffs, which our skyscrapers and buildings inadvertently mimic extremely well. The apparent success of some species in more open habitats such as cropland and urban environments might also be partly caused by increased visibility – it’s far easier to see a bird or reptile in an urban environment than dense primary forest! This doesn’t explain the entire pattern, however, and clearly some species are simply more successful in human-altered habitats. They are in the minority, though.

Do Reptiles Prefer Altered Habitats?
One interesting finding was that for herptiles (reptiles and amphibians), more species were found in habitats with a higher human population density. This rather unexpected relationship might reflect a general preference in herptiles for more open habitats. Consistent with this, the authors found fewer species in pristine forest than secondary forest. However, upon closer inspection the authors found that herptiles do not all respond in the same way. Reptiles showed a U-shaped relationship with human population density – the occurrence of species was highest when there were either lots of people or no people at all. By contrast, amphibians showed a straight relationship, with increases in human population density being mirrored by increases in the number of species present. This highlights the importance of investigating fine-scale differences between species in their responses to human activities.

Filbert Weevil (Curculio occidentis)

Consistent with previous studies, the traits of species were very important in determining whether a species was found in human-altered habitats. Narrow-ranging species were much less likely to occur in any habitat than wide-ranging ones, but this difference was particularly clear for croplands, plantation forests and urban habitats. The extent of human impact was also a key factor determining the occurrence of species in different habitats. Forest cover, human population density and NDVI (a measure of vegetation loss taken from remote sensing) all reduced the number of species present. Measures of disturbance and species characteristics do not act in isolation – the best models produced by the PREDICTS team included interactions between these variables. Invertebrate numbers were lowest in areas of high human population density and high rates of vegetation loss.

This study is the first step in more detailed, comprehensive analyses of the responses of species to human activities. The power of this study comes not only from it’s large dataset and broad spectrum of taxonomic groups, but also from it’s ability to directly couple land-use changes with species’ traits such as range-size and habitat specialism. The authors say that the next major step would be to incorporate interactions between species in these models – the community structure of an ecosystem can have profound effects on the species living in it, and changes in the abundance of any individual species does not happen in isolation from the rest of the community.

Check out the PREDICTS Project for more information!

Original Article:

() Proc. R. Soc. B

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This research was made possible by funding from the Natural Environment Research Council (NERC), and the Biotechnology and Biological Sciences Research Council (BBSRC).

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).

The Importance of Size in the Evolution of Complexity in Ants

By Claire Asher, on 16 September 2014

Ants are amongst the most abundant and successful species on Earth. They live in complex, cooperative societies, construct elaborate homes and exhibit many of the hallmarks of our own society. Some ants farm crops, others tend livestock. Many species have a major impact on the ecosystems they live in, dispersing seeds, consuming huge quantities of plant matter and predating other insect species. One of the major reasons for their enormous success is thought to be the impressive division of labour they exhibit. Theory suggests that, during the evolution of ants, increases in colony size drove increases in the complexity of their division of labour. However, there have been few previous attempts to test the hypothesis. A recent paper by GEE’s Professor Kate Jones and Phd student Henry Ferguson-Gow tested this hypothesis across the Attine ants, a large neotropical group including the famous leaf-cutter ants.

Ants, along with other social insects such as some bees, wasps and termites, are eusocial. This means that reproduction in their societies is dominated by just one or a few queens, while most of the colony members never reproduce, but instead perform other important tasks such as foraging, nest construction and defence. This system initially puzzled evolutionary biologists, because it poses the question, “how do non-reproductive workers pass on their genes?”. More specifically, “how can genes evolve to generate different morphology and behaviour in workers if they never reproduce and pass those genes on?”. This question was resolved in the 1960s, when W.D. Hamilton proposed the concepts of inclusive fitness and kin selection. He pointed out that although members of the non-reproductive worker caste do not directly pass on their genes, they are helping to ensure the survival of their siblings. Closely related individuals, such as siblings, share a large percentage of their genetic information, so by helping relatives, you are indirectly passing on your genes. Inclusive fitness is a measure of the total reproductive success of an individual, including direct fitness (gained by producing your own offspring) and indirect fitness (gained by helping relatives to reproduce). Kin selection, a form of natural selection, can therefore favour genes that cause sterility in the worker caste through it’s positive effects on the reproductive success of relatives.

When eusociality first began to evolve, colonies were probably small and although the worker caste likely refrained from reproduction most of the time, they weren’t completely sterile. In small colonies, keeping your reproductive options open makes a lot of sense – if the queen dies you may have a good chance of taking over the colony and reproducing yourself. Through evolutionary time, however, colony size increased in some lineages, and it is thought this may have driven increasing specialisation and commitment of individuals to their queen and worker roles. As colony size increases, your chances for gaining any kind of direct fitness start to decrease very rapidly. As a worker it’s a much better bet to do what you can to maximise your indirect fitness benefits in large colonies, and this can be achieved by becoming increasingly specialised for your particular role. Increases in division of labour, for example, as individuals specialise more in particular tasks, may lead to increase colony efficiency and success. In turn, this may allow for the evolution of larger colonies, resulting in a positive feedback loop whereby increases in colony size lead to increases in division of labour which lead to increases in colony size, and so on. This force may have lead to the evolution of ant species with enormous colonies – over a million workers can be found in some leaf-cutter colonies!

GEE Researchers Professor Kate Jones and Henry Ferguson-Gow, along with colleagues at the University of East Anglia and the University of Bristol, produced a phylogenetic tree for the Attine Ants (a group containing over 250 species), and mapped social and environmental data onto this tree in order to test for the effects of colony size and environment on the evolution of more sophisticated division of labour. The Attini are a good group of ants to test this hypothesis in, as they show large variation in colony size and the extent of morphological divergence between the queen and worker caste.

They collected published data on social traits (colony size, worker size, queen size) and environmental conditions (daytime temperature, seasonality in temperature and precipitation) for over 600 observations of populations for 57 species of Attine ant, including every single Attine genus. Using supertree methods, they constructed a phylogeny for the attine ants, which enabled them to control for evolutionary relationships and to estimate the speed at which evolutionary changes occurred.

Colony size ranged from 16 to 6 million individuals, with the largest colonies exhibited by the fungus growing leaf-cutter ants Atta and Acromyrmex. The authors found that increases in colony size through evolution are strongly associated with increases in both worker size variation (representing division of labour within the worker caste) and queen worker dimorphism (representing reproductive division of labour). Colony size showed a positve correlation with variation in size within the worker caste, and a weaker, but positive correlation with queen-worker dimorphism. Environmental factors such as temperature, rainfall and seasonality did not have any effect on colony size, indicating that climate and other environmental variables have not been an important factor in driving the evolution of increased colony size.

This study finds strong support for the size-complexity hypothesis, which suggests that during the evolution of eusociality, increases in colony size both drove and were driven by increases in division of labour and in specialisation of the queen and worker castes to their respective roles. This pattern may have also occurred during other major transitions in evolution, such as the evolution of multicellularity, which shares many similarities with the evolution of eusociality (e.g closely related group members, division of labour). The relationship between group size and complexity may therefore have been a crucial force in the evolution of complex life, and in the major evolutionary innovations that have generated the diversity of life we see today.

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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.

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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>.

Evolving Endemism in East Africa’s Sky Islands

By Claire Asher, on 8 August 2014

The World’s biodiversity is not evenly distributed. Some regions are hot spots for species richness, and biologists have been trying better to understand why these regions are special and what drives evolution and diversification. A recent paper by GEE’s Dr Julia Day and recent PhD graduate Dr Siobhan Cox, investigated the diversification of White-Eye Birds in East Africa’s Afromontane Biodiversity hotspot. Their results indicate that speciation in these birds has likely been driven by adaptation to a gradient of environmental conditions.

The East Afromontane Biodiversity Hotspot (EABH) is one of the most biodiverse regions on Earth, but it is under constant threat from increasing urbanisation in the area, which is predicted to continue over coming decades. It is therefore crucial to quantify what biodiversity is found in this hotspot, and understand the evolutionary processes that have made it a hotspot. The geography in this region is quite special, and is thought to have been a key factor driving high levels of species richness here. The Afromontane region is formed of a chain of ancient massifs (mountains created by faults and flexures in the Earth’s crust) and relatively young volcanoes. The low-lying regions between these peaks are covered in arid savannah, but montane forests appear on the peaks above about 800m. These forests exists as “ecological islands”, isolated from each other since the early Oligocene around 33 million years ago. Before this, conditions in the region were less arid and continuous forests covered the mountains and the valleys. As the forests retracted and fragmented, their inhabitants became isolated from one another, and this may have led to the emergence of new species, unique to each isolated montane fragment.

A Brief Introduction to Speciation
The processes by which new species arise depend upon the circumstances. Traditionally, speciation was thought to occur as a result of geographic separation of populations of a single ‘parent’ species. Once isolated and unable to interbreed, the two populations would slowly diverge from each other both due to random genetic change and adaptation to differing conditions. If enough time passed before the two populations came into contact with each other again, then they would eventually be so distinct that they were unable to interbreed even if they were reunited, and therefore should be classified as separate species. This is the standard model of speciation, known as allopatric speciation. It is now appreciated that new species can arise even without geographical isolation in a process known as sympatric speciation, often this can be caused by isolation of other kinds, such as behavioural isolation or through selective mate choice. It is generally accepted, however, that speciation requires, at least, a massive reduction in the rates of interbreeding between two populations or subspecies. Interbreeding will tend to restrain divergence as it mixes genes between the populations.

Evolving Endemism
There are two main hypotheses for how the extraordinarily high levels of endemism arose on the montane forest ‘islands’:

  1. The Montane Speciation Model suggests that montane ‘islands’ became refugia for species as they tracked suitable conditions up the mountain. This idea is based on a general theory for speciation and divergence known as ‘niche conservatism’, which suggests that geographical isolation of populations is driven by an inability to adapt to changing conditions. Once isolated, populations begin to diverge from one-another and over time this generates very high species richness.
  2. The Gradient Speciation Model by contrast, hypotheses that new species emerge as a result of adaptation to different conditions along a gradient. In this model, adaptation and niche divergence drive speciation, and we expect to find related species living in adjacent habitats.

The EABH is home to over 1300 described species of bird, of which 110 are known to exist nowhere else on Earth. In a recent paper in Molecular Ecology, Dr Day, along with colleagues at the Natural History Museum (Tring, Hertfordshire), the Technical University of Munich and the National Museums of Kenya, investigated the pattern of divergence in African montane white-eyes (Zosterops), a group of small, gregarious birds. Each montane forest fragment houses a single, endemic species, while other species live on real islands, and others live in other habitats on the mainland. This makes them an ideal group to test the competing hypotheses of niche conservatism and niche divergence.

The authors collected mitochondrial and genomic DNA samples for 148 birds from 15 species found across the EABH and elsewhere. They estimated the evolutionary timing of each species’ divergence based on both geological and molecular data, to investigate whether the montane taxa speciated in their current habitat or elsewhere, and whether they speciated before or after the climatic changes that isolated forest fragments.

A Late Pleistocene Colonisation
Based on molecular data, the authors estimate that White-eyes colonised Africa in the late Pleistocene, around 1.55 million years ago, and then exhibited brief pulses of diversification from 0.9 million years ago until around 0.3 million years ago. The genus Zosterops therefore colonised the region long after the montane forest habitat had fragmented into ecological islands, discounting the montane speciation hypothesis. Montane species diverged from their lowland sisters around 1 million years ago, during the last major wet phase. In some cases, montane species were found to be older than species found in neighbouring lowland areas, indicating colonisation in the other direction. They found no evidence that diversification of the White-eyes corresponded with volcanic activity in the region, which has previously been suggested.

They found that many of the so-called ‘species’ of Zosterops in fact include multiple sub-species, and they found strong support for already identified subspecies. This suggests that different species and subspecies independently colonised the montane habitat, and have remained more or less the same since. That the lowland savannahs that exist between the montane islands is a strong barrier that isolates montane populations is strongly supported by their results – species on neighbouring sky islands are very different from each other genetically, indicating they have not interbred for a great deal of evolutionary time. This is similar to the pattern of colonisation and diversification seen in White-eye species that live on real islands, which likely present similar evolutionary pressures to the ecological islands found in fragmented habitats.

Overall, their results support a niche divergence explanation of speciation in Montane White-Eyes, consistent with the gradient hypothesis, and ruling out niche conservatism models, such as the montane speciation hypothesis. However, the authors point out that their results do not distinguish between the gradient hypothesis and similar alternative, the vanishing refugia model, which suggests that speciation occurs through adaptation to less favourable habitats as suitable habitat contracts and refugia become unable to maintain viable populations. Further research is needed to conclusively distinguish between these models. The relative climatic stability of the highland montane habitats, couples with frequent climatic fluctuations in low-land areas may have played a key role in diversification in White-eyes, and may be a key driver of endemism in this region.

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