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Natural or human-induced factors that directly or indirectly cause a change in biodiversity are referred to as drivers.
Some direct drivers of change are easier to measure than others, for instance, fertilizer usage, water consumption, irrigation, and harvests. For other drivers, indicators are not as well developed and measurement data is less readily available. This is the case for non-native species, climate change, land cover conversion, and landscape fragmentation.
Changes in biodiversity are driven by combinations of drivers that work over time, on different scales, and that tend to amplify each other. For example, population and income growth combined with technological advances can lead to climate change. More...
Five major indirect drivers that influence biodiversity are:
Different direct drivers are critical in different ecosystems. Historically, habitat and land use change have had the biggest impact on biodiversity in all ecosystems, but climate change and pollution are projected to increasingly affect all aspects of biodiversity. Overexploitation and invasive species have been important as well and continue to be major drivers of changes in biodiversity.
Over the past 50 years, the most important direct drivers of change have been:
In terrestrial ecosystems:
land cover change, mainly by conversion to cropland. Only areas unsuited to crop plants, such as deserts, boreal forests, and tundra, remain relatively intact. Deforestation and forest degradation are currently particularly extensive in the tropics. Nearly a quarter of the Earth's surface is currently covered by cultivated systems.
In marine ecosystems:
fishing is the major direct human pressure affecting the structure, function, and biodiversity of the oceans. In all oceans, a number of fish stocks targeted in fisheries have collapsed because they have been overfished or fished above their maximum sustainable levels. After a peak in the late 1980s, the global amount fished has been declining.
In freshwater ecosystems:
water regime changes, such as those following the construction of large dams; invasive species, which can lead to species extinction; and pollution, such as high levels of nutrients. More...
4.4.1 Natural disturbances (such as fires) or changes in land use (such as road construction) lead to the fragmentation of forests. Such habitat changes have a significant impact on biodiversity, as small fragments of habitat can only support small populations that tend to be more vulnerable to extinction. More...
Click on any continent below to view maps which estimate the amount of:
Forest fragmentation induced by human activities
4.4.2 Invasive alien species that establish and spread outside their normal distribution have been a major cause of extinction. This has particularly affected islands and freshwater habitats and continues to be a problem in many areas, as effective preventive measures are lacking. In New Zealand, for example, plants have been introduced at a rate of 11 species per year since European settlement in 1840. More...
4.4.3 Overexploitation remains a serious threat to many species, such as marine fish and invertebrates, trees, and animals hunted for meat. Most industrial fisheries are either fully or overexploited, while destructive fishing techniques harm estuaries and wetlands. The overexploitation of bushmeat is in a similar situation, where sustainable levels of exploitation are poorly understood, and the catches difficult to manage effectively. The trade in wild plants and animals and their derivatives is estimated to reach nearly $160 billion annually. Because this trade crosses national borders, the effort to regulate it requires international cooperation to safeguard certain species from overexploitation. More...
4.4.4 Over the past four decades, excessive levels of nutrients in soil and water have emerged as one of the most important drivers of ecosystem change in terrestrial, freshwater, and coastal ecosystems. More than half of all the synthetic nitrogen fertilizers ever used on Earth have been used since 1985, and phosphorous uses are now three times what they were in 1960.
The total amount of nitrogen made available to organisms by human activities now exceeds that from all natural sources combined. Excessive additions of nitrogen and phosphorous to freshwater or coastal marine systems can lead to excessive plant and algae growth (eutrophication) and a lack of oxygen as well as to other environmental problems. More...
Recent changes in climate, such as warmer temperatures in certain regions, have already had significant impacts on biodiversity and ecosystems. They have affected species distributions, population sizes, and the timing of reproduction or migration events, as well as the frequency of pest and disease outbreaks. Projected changes in climate by 2050 could lead to the extinction of many species living in certain limited geographical regions. By the end of the century, climate change and its impacts may become the main direct driver of overall biodiversity loss.
While the growing season in Europe has lengthened over the last 30 years, in some regions of Africa the combination of regional climate changes and human pressures have led to decreased cereal crop production since 1970. Changes in fish populations have also been linked to large-scale climate variations such as "El Nio". As climate change will become more severe, the harmful impacts on ecosystem services will outweigh the benefits in most regions of the world. The Intergovernmental Panel on Climate Change (IPCC) project that the average surface temperature will rise by 2 to 6.4C by 2100 compared to pre-industrial levels. This is expected to cause global negative impacts on biodiversity.
According to the projections:
Today many drivers of extinction, such as land use change, emerging disease, and invasive species, are all occurring together and at a greater intensity than in the past. Because exposure to one threat often makes a species more susceptible to a second, and so on, multiple threats may have unexpectedly dramatic impacts on biodiversity.
Drivers affecting biodiversity range from local to global and from immediate to long-term,. Climate change may operate on a spatial scale of a large region, whereas political change may operate at the scale of a nation or a municipal district. Socio-cultural changes typically occur slowly, on a time scale of decades, while economic changes tend to occur more rapidly.
Many impacts of management interventions on ecosystems are slow to become apparent. For example, a population cannot recover more quickly than the time needed to give birth to a new generation, and recovery will often take several generations. Moreover, human institutions are often slow to reach decision and to implement them. In addition, none of the drivers appears to be slowing or well controlled and we have not yet seen all of the consequences of changes that occurred in the past.
The extinction of species due to habitat loss has a significant lag time. For some species this process can be rapid, but for other sit may take 100 to 10 000 years. Time lags between habitat reduction and extinction provide an opportunity for humans to restore habitats and rescue species from extinction. Notwithstanding this, habitat restoration measures will not be likely to save the most sensitive species, which will become extinct soon after habitat loss. More...
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