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Global biodiversity outlook 31

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Invasive alien species continue to be a major threat to all types of ecosystems and species. There are no signs of a significant reduction of this pressure on biodiversity, and some indications that it is increasing. Intervention to control alien invasive species has been successful in particular cases, but it is outweighed by the threat to biodiversity from new invasions.
In a sample of 57 countries, more than 542 alien species, including vascular plants, marine and freshwater fish, mammals, birds and amphibians, with a demonstrated impact on biodiversity have been found, with an average of over 50 such species per country (and a range from nine to over 220)223.). This is most certainly an underestimate, as it excludes many alien species whose impact has not yet been examined, and includes countries known to lack data on alien species.
It is difficult to get an accurate picture of whether damage from this source is increasing, as in many areas attention has only recently been focused on the problem, so a rise in known invasive species impacts may partly reflect improved knowledge and awareness. However, in Europe where introduction of alien species has been recorded for many decades, the cumulative number continues to increase and has done so at least since the beginning of the 20th century. Although these are not necessarily invasive, more alien species present in a country means that in time, more may become invasive. It has been estimated that of some 11,000 alien species in Europe, around one in ten has ecological impacts and a slightly higher proportion causes economic damage [See Box 18]. Trade patterns worldwide suggest that the European picture is similar elsewhere and, as a consequence, that the size of the invasive alien species problem is increasing globally.

Box 18: Documenting Europe’s alien species

The Delivering Alien Invasive Species Inventories for Europe (DAISIE) project provides consolidated information aimed at creating an inventory of invasive species that threaten European biodiversity. This can be used as the basis for the prevention and control of biological invasions, to assess the ecological and socio-economic risks associated with most widespread invasive species, and to distribute data and experience to member states as a form of early warning system.

Currently about 11,000 alien species have documented by DAISIE. Examples include Canada geese, zebra mussels, brook trout, the Bermuda buttercup and coypu (nutria)224.). A recent study based on information provided by DAISIE indicated that of the 11,000 alien species in Europe, 1,094 have documented ecological impacts and 1,347 have economic impacts. Terrestrial invertebrates and terrestrial plants are the two taxonomic groups causing the greatest impacts225.

Eleven bird species (since 1988), five mammal species (since 1996) and one amphibian (since 1980) have substantially had their risk of extinction reduced due primarily to the successful control or eradication of alien invasive species226. Without such actions, it is estimated that the average survival chances, as measured by the Red List Index, would have been more than 10% worse for bird species and almost 5% worse for mammals [See Box 19]. However, the Red List Index also shows that almost three times as many birds, almost twice as many mammals, and more than 200 times the number of amphibian species, have deteriorated in conservation status due largely to increased threats from invasive animals, plants or micro-organisms227. Overall, birds, mammals and amphibian species have on average become more threatened due to invasive alien species. While other groups have not been fully assessed, it is known that invasive species are the second leading cause for extinction for freshwater mussels and more generally among endemic species228.

Box 19: Successful control of alien invasive species

  • The Black vented Shearwater (Puffinus opisthomelas) breeds on six islands off the Pacific coast of Mexico, one of which is Natividad.  Predation from approximately 20 feral cats reduced the population of the bird by more than 1,000 birds per month while introduced herbivores such as donkeys, goats sheep and rabbits damaged habitat of importance to the bird. With the assistance of a local fishing community goats and sheep were removed from the island in 1997-1998 while cats were controlled in 1998 and eventually eradicated in 2006. As a result the pressure on this species has decreased, the population has begun to recover and the species was reclassified from Vulnerable to Near Threatened in the IUCN Red List of 2004229.

  • The Western Brush Wallaby (Macropus irma) is endemic to south western Australia. During the 1970 the wallaby began to decline as a result of a dramatic increase in the Red Fox (Vulpes vulpes) population. Surveys conducted in 1970 and 1990 suggested that population had declined from approximately 10 individuals per 100 kilometers to about 1 per 100 kilometers. Since the introduction of fox control measures the wallaby population has recovered and currently stands at approximately 100,000 individuals. As a result the Western Brush Wallaby has been reclassified from Near Threatened to Least Concern on the IUCN Red List of 2004230.

Combined Pressures and Underlying Causes of Biodiversity Loss

    The direct drivers of biodiversity loss act together to create multiple pressures on biodiversity and ecosystems. Efforts to reduce direct pressures are challenged by the deep-rooted underlying causes or indirect drivers that determine the demand for natural resources and are much more difficult to control. The ecological footprint of humanity exceeds the biological capacity of the Earth by a wider margin than at the time the 2010 target was agreed.

The pressures or drivers outlined above do not act in isolation on biodiversity and ecosystems, but frequently, with one pressure exacerbating the impacts of another. For example:

  • Fragmentation of habitats reduces the capacity of species to adapt to climate change, by limiting the possibilities of migration to areas with more suitable conditions.

  • Pollution, overfishing, climate change and ocean acidification all combine to weaken the resilience of coral reefs and increase the tendency for them to shift to algae-dominated states with massive loss of biodiversity.

  • Increased levels of nutrients combined with the presence of invasive alien species can promote the growth of hardy plants at the expense of native species. Climate change can further exacerbate the problem by making more habitats suitable for invasive species.

  • Sea level rise caused by climate change combines with physical alteration of coastal habitats, accelerating change to coastal biodiversity and associated loss of ecosystem services.

An indication of the magnitude of the combined pressures we are placing on biodiversity and ecosystems is provided by humanity’s ecological footprint, a calculation of the area of biologically-productive land and water needed to provide the resources we use and to absorb our waste. The ecological footprint for 2006, the latest year for which the figure is available, was estimated to exceed the Earth’s biological capacity by 40 per cent231. This “overshoot” has increased from some 20 per cent at the time the 2010 biodiversity target was agreed in 2002.

As suggested above, specific measures can and do have an impact in tackling the direct drivers of biodiversity loss: alien species control, responsible management of farm waste and habitat protection and restoration are some examples. However, such measures must compete with a series of powerful underlying causes of biodiversity loss. These are even more challenging to control, as they tend to involve long-term social, economic and cultural trends. Examples of underlying causes include232:

  • Demographic change

  • Economic activity

  • Levels of international trade

  • Per capita consumption patterns, linked to individual wealth

  • Cultural and religious factors

  • Scientific and technological change

Indirect drivers primarily act on biodiversity by influencing the quantity of resources used by human societies. So for example population increase, combined with higher per capita consumption, will tend to increase demand for energy, water and food – each of which will contribute to direct pressures such as habitat conversion, over-exploitation of resources, nutrient pollution and climate change. Increased world trade has been a key indirect driver of the introduction of invasive alien species.
Indirect drivers can have positive as well as negative impacts on biodiversity. For example, cultural and religious factors shape society’s attitudes towards nature and influence the level of funds available for conservation. The loss of traditional knowledge can be particularly detrimental in this regard, as for many local and indigenous communities biodiversity is a central component of belief systems, worldviews and identity. Cultural changes such as the loss of indigenous languages can therefore act as indirect drivers of biodiversity loss by affecting local practices of conservation and sustainable use [See Box 20233]. Equally, scientific and technological change can provide new opportunities for meeting society’s demands while minimizing the use of natural resources – but can also lead to new pressures on biodiversity and ecosystems.
Strategies for decreasing the negative impacts of indirect drivers are suggested in the final section of this synthesis. They centre on “decoupling” indirect from direct drivers of biodiversity loss, primarily by using natural resources much more efficiently; and by managing ecosystems to provide a range of services for society, rather than only maximizing individual services such as crop production or hydro-electric power.
The trends from available indicators suggest that the state of biodiversity is declining, the pressures upon it are increasing, and the benefits derived by humans from biodiversity are diminishing, but that the responses to address its loss are increasing [See Figure 17]. The overall message from these indicators is that despite the many efforts taken around the world to conserve biodiversity and use it sustainably, responses so far have not been adequate to address the scale of biodiversity loss or reduce the pressure.

Box 20: Trends in indigenous languages


Indigenous languages transmit specialized knowledge about biodiversity, the environment and about practices to manage natural resources. However, determining the status and trends of indigenous languages at the global level is complicated by the lack of standardized methodologies, the absence of shared definitions for key concepts and limited information. Where such information exists there is evidence that the extinction risk for the most endangered languages, those with few speakers, has increased. For example: 

  • Between 1970 and 2000, 16 of 24 indigenous languages spoken by less than 1,000 people in Mexico lost speakers234.

  • In the Russian Federation, between 1950 and 2002, 15 of 27 languages spoken by less than 10,000 people lost speakers235.

  • In Australia, 22 of 40 languages lost speakers between 1996 and 2006236.

  • In an assessment of 90 languages used by different indigenous peoples in the Arctic, it was determined that 20 languages have become extinct since the 19th century. Ten of these extinctions have occurred since 1989, suggesting an increasing rate of language extinctions. A further 30 languages are considered to be critically endangered while 25 are severely endangered237.

Continuing species extinctions far above the historic rate, loss of habitats and changes in the distribution and abundance of species are projected throughout this century according to all scenarios analyzed for this Outlook. There is a high risk of dramatic biodiversity loss and accompanying degradation of a broad range of ecosystem services if the Earth system is pushed beyond certain thresholds or tipping points. The loss of such services is likely to impact the poor first and most severely, as they tend to be most directly dependent on their immediate environments; but all societies will be impacted. There is greater potential than was recognized in earlier assessments to address both climate change and rising food demand without further widespread loss of habitats.
For the purposes of this Outlook, scientists from a wide range of disciplines came together to identify possible future outcomes for biodiversity change during the rest of the 21st century. The results summarized here are based on a combination of observed trends, models and experiments. They draw upon and compile all previous relevant scenario exercises conducted for the Millennium Ecosystem Assessment, the Global Environment Outlook and earlier editions of the Global Biodiversity Outlook, as well as scenarios being developed for the next assessment report of the Intergovernmental Panel on Climate Change (IPCC). They pay particular attention to the relationship between biodiversity change and its impacts on human societies. In addition to the analysis of existing models and scenarios, a new assessment was carried out of potential “tipping points” that could lead to large, rapid and potentially irreversible changes. The analysis238 reached four principal conclusions:

  • Projections of the impact of global change on biodiversity show continuing and often accelerating species extinctions, loss of natural habitat, and changes in the distribution and abundance of species, species groups and biomes over the 21st century.

  • There are widespread thresholds, amplifying feedbacks and time-lagged effects leading to “tipping points”, or abrupt shifts in the state of biodiversity and ecosystems. This makes the impacts of global change on biodiversity hard to predict, difficult to control once they begin, and slow, expensive or impossible to reverse once they have occurred [See Box 21 and Figure 18].

  • Degradation of the services provided to human societies by functioning ecosystems are often more closely related to changes in the abundance and distribution of dominant or keystone species, rather than to global extinctions; even moderate biodiversity change globally can result in disproportionate changes for some groups of species (for example top predators) that have a strong influence on ecosystem services.

  • Biodiversity and ecosystem changes could be prevented, significantly reduced or even reversed (while species extinctions cannot be reversed, diversity of ecosystems can be restored) if strong action is applied urgently, comprehensively and appropriately, at international, national and local levels. This action must focus on addressing the direct and indirect factors driving biodiversity loss, and must adapt to changing knowledge and conditions.

Box 21: What is a tipping point?

A tipping point is defined, for the purposes of this Outlook, as a situation in which an ecosystem experiences a shift to a new state, with significant changes to biodiversity and the services to people it underpins, at a regional or global scale. Tipping points also have at least one of the following characteristics:

  • The change becomes self-perpetuating through so-called positive feedbacks, for example deforestation reduces regional rainfall, which increases fire-risk, which causes forest dieback and further drying.

  • There is a threshold beyond which an abrupt shift of ecological states occurs, although the threshold point can rarely be predicted with precision.

  • The changes are long-lasting and hard to reverse.

  • There is a significant time lag between the pressures driving the change and the appearance of impacts, creating great difficulties in ecological management.

Tipping points are a major concern for scientists, managers and policy–makers, because of their potentially large impacts on biodiversity, ecosystem services and human well-being. It can be extremely difficult for societies to adapt to rapid and potentially irreversible shifts in the functioning and character of an ecosystem on which they depend. While it is almost certain that tipping points will occur in the future, the dynamics in most cases cannot yet be predicted with enough precision and advance warning to allow for specific and targeted approaches to avoid them, or to mitigate their impacts. Responsible risk management may therefore require a precautionary approach to human activities known to drive biodiversity loss.

The projections, potential tipping points, impacts and options for achieving better outcomes are summarized on the following pages:

Terrestrial ecosystems to 2100
Current path: Land-use change continues as the main short-term threat, with climate change, and the interactions between these two drivers, becoming progressively important. Tropical forests continue to be cleared, making way for crops and biofuels. Species extinctions many times more frequent than the historic “background rate” - the average rate at which species are estimated to have gone extinct before humans became a significant threat to species survival - and loss of habitats continue throughout the 21st century. Populations of wild species fall rapidly, with especially large impacts for equatorial Africa and parts of South and South-East Asia. Climate change causes boreal forests to extend northwards into tundra, and to die back at their southern margins giving way to temperate species. In turn, temperate forests are projected to die back at the southern and low-latitude edge of their range. Many species suffer range reductions and/or move close to extinction as their ranges shift several hundred kilometres towards the poles. Urban and agricultural expansion further limits opportunities for species to migrate to new areas in response to climate change.
Impacts for people: The large-scale conversion of natural habitats to cropland or managed forests will come at the cost of degradation of biodiversity and the ecosystem services it underpins, such as nutrient retention, clean water supply, soil erosion control and ecosystem carbon storage, unless sustainable practices are used to prevent or reduce these losses. Climate-induced changes in the distribution of species and vegetation-types will have important impacts on the services available to people, such as reduced wood harvests and recreation opportunities
In addition, there is a high risk of dramatic loss of biodiversity and degradation of services from terrestrial ecosystems if certain thresholds are crossed. Plausible scenarios include:

  • The Amazon forest, due to the interaction of deforestation, fire and climate change, undergoes a widespread dieback, changing from rainforest to savanna or seasonal forest over wide areas, especially in the East and South of the biome. The forest could move into a self-perpetuating cycle in which fires become more frequent, drought more intense and dieback accelerates. Dieback of the Amazon will have global impacts through increased carbon emissions, accelerating climate change. It will also lead to regional rainfall reductions that could compromise the sustainability of regional agriculture.

  • The Sahel in Africa, under pressure from climate change and over-use of limited land resources, shifts to alternative, degraded states, further driving desertification. Severe impacts on biodiversity and agricultural productivity result. Continued degradation of the Sahel has caused and could continue to cause loss of biodiversity and shortages of food, fibre and water in Western Africa.

  • Island ecosystems are afflicted by a cascading set of extinctions and ecosystem instabilities, due to the impact of invasive alien species. Islands are particularly vulnerable to such invasions as communities of species have evolved in isolation and often lack defences against predators and disease organisms. As the invaded communities become increasingly altered and impoverished, vulnerability to new invasions may increase.

Alternative paths: Alleviating pressure from land use changes in the tropics is essential, if the negative impacts of loss of terrestrial biodiversity and associated ecosystem services are to be minimized. This involves a combination of measures, including an increase in productivity from existing crop and pasture lands, reducing post-harvest losses, sustainable forest management and moderating excessive and wasteful meat consumption.
Full account should be taken of the greenhouse gas emissions associated with large-scale conversion of forests and other ecosystems into cropland. This will prevent perverse incentives for the destruction of biodiversity through large-scale deployment of biofuel crops, in the name of climate change mitigation [See Figures 19 and 20]. When emissions from land-use change rather than just energy emissions are factored in, plausible development pathways emerge that tackle climate change without widespread biofuel use. Use of payments for ecosystem services, such as Reducing Emissions from Deforestation and Degradation (REDD) mechanisms may help align the objectives of addressing biodiversity loss and climate change. However, these systems must be carefully designed, as conserving areas of high carbon value will not necessarily conserve areas of high conservation importance – this is being recognized in the development of so-called “REDD-Plus” mechanisms.
Tipping points are most likely to be avoided if climate change mitigation to keep average temperature increases below 2 degrees Celsius is accompanied by action to reduce other factors pushing the ecosystem towards a changed state. For example, in the Amazon it is estimated that keeping deforestation below 20-30% of the original forest extent will greatly reduce the risk of widespread dieback. As current trends will likely take cumulative deforestation to 20% of the Brazilian Amazon at or near 2020, a programme of significant forest restoration would be a prudent measure to build in a margin of safety. Better forest management options in the Mediterranean, including the greater use of native broad-leaf species in combination with improved spatial planning, could make the region less fire-prone. In the Sahel, better governance, poverty alleviation and assistance with farming techniques will provide alternatives to current cycles of poverty and land degradation.
Avoiding biodiversity loss in terrestrial areas will also involve new approaches to conservation, both inside designated protected areas and beyond their boundaries. In particular, greater attention must be given to the management of biodiversity in human-dominated landscapes, because of the increasingly important role these areas will play as biodiversity corridors as species and communities migrate due to climate change.
There are opportunities for rewilding landscapes from farmland abandonment in some regions – in Europe, for example, about 200 000 square kilometers of land are expected to be freed up by 2050. Ecological restoration and reintroduction of large herbivores and carnivores will be important in creating self-sustaining ecosystems with minimal need for further human intervention.

Inland water ecosystems to 2100
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