In some areas, it has recently been partly driven by the demand for biofuels. The IUCN Red List assessments show habitat loss driven by agriculture and unsustainable forest management to be the greatest cause of species moving closer towards extinction. The sharp decline of tropical species populations shown in the Living Planet Index mirrors widespread loss of habitat in those regions.
As noted above, birds face an especially high risk of extinction in South-east Asia, the region that has seen the most extensive development of oil palm plantations, driven in part by the growing demand for biofuel. Infrastructure developments, such as housing, industrial developments, mines and transport networks, are also an important contributor to conversion of terrestrial habitats, as is afforestation of non-forested lands.
With more than half of the world's population now living in urban areas, urban sprawl has also led to the disappearance of many habitats, although the higher population density of cities can also reduce the negative impacts on biodiversity by requiring the direct conversion of less land for human habitation than more dispersed settlements. Even though there are no signs at the global level that habitat loss is declining significantly as a driver of biodiversity loss, some countries have shown that, with determined action, historically persistent negative trends can be reversed.
An example of global significance is the recent reduction in the rate of deforestation in the Brazilian Amazon, mentioned above. For inland water ecosystems, habitat loss and degradation is largely accounted for by unsustainable water use and drainage for conversion to other land uses, such as agriculture and settlements. The major pressure on water availability is abstraction of water for irrigated agriculture, which uses approximately 70 per cent of the world's withdrawals of fresh water, but water demands for cities, energy and industry are rapidly growing.
The construction of dams and flood levees on rivers also causes habitat loss and fragmentation, by converting free-flowing rivers to reservoirs, reducing connectivity between different parts of river basins, and cutting off rivers from their floodplains. In coastal ecosystems, habitat loss is driven by a range of factors including some forms of mariculture, especially shrimp farms in the tropics where they have often replaced mangroves.
Coastal developments, for housing, recreation, industry and transportation have had important impacts on marine ecosystems, through dredging, landfilling and disruption of currents, sediment flow and discharge through construction of jetties and other physical barriers.
As noted above, use of bottom-trawling fishing gear can cause significant loss of seabed habitat. Climate change is already having an impact on biodiversity, and is projected to become a progressively more significant threat in the coming decades. Loss of Arctic sea ice threatens biodiversity across an entire biome and beyond. The related pressure of ocean acidification, resulting from higher concentrations of carbon dioxide in the atmosphere, is also already being observed.
Ecosystems are already showing negative impacts under current levels of climate change an increase of 0. In addition to warming temperatures, more frequent extreme weather events and changing patterns of rainfall and drought can be expected to have significant impacts on biodiversity. Impacts of climate change on biodiversity vary widely in different regions of the world.
For example, the highest rates of warming have been observed in high latitudes, around the Antarctic peninsula and in the Arctic, and this trend is projected to continue. The rapid reduction in the extent, age and thickness of Arctic sea ice, exceeding even recent scientific forecasts, has major biodiversity implications [See Box 15 and Figure 14]. Already, changes to the timing of flowering and migration patterns as well as to the distribution of species have been observed worldwide.
In Europe, over the last forty years, the beginning of the growing season has advanced by 10 days on average. These types of changes can alter food chains and create mismatches within ecosystems where different species have evolved synchronized inter-dependence, for example between nesting and food availability, pollinators and fertilization. Climate change is also projected to shift the ranges of disease-carrying organisms, bringing them into contact with potential hosts that have not developed immunity.
Freshwater habitats and wetlands, mangroves, coral reefs, Arctic and alpine ecosystems, dry and subhumid lands and cloud forests are particularly vulnerable to the impacts of climate change.
Some species will benefit from climate change. However, an assessment looking at European birds found that of widespread species assessed, about three times as many were losing population as a result of climate change as those that were gaining numbers.
The specific impacts of climate change on biodiversity will largely depend on the ability of species to migrate and cope with more extreme climatic conditions. Ecosystems have adjusted to relatively stable climate conditions, and when those conditions are disrupted, the only options for species are to adapt, move or die.
It is expected that many species will be unable to keep up with the pace and scale of projected climate change, and as a result will be at an increased risk of extinction, both locally and globally. In general climate change will test the resilience of ecosystems, and their capacity for adaptation will be greatly affected by the intensity of other pressures that continue to be imposed. Those ecosystems that are already at, or close to, the extremes of temperature and precipitation tolerances are at particularly high risk.
Over the past years, the oceans have absorbed approximately a quarter of the carbon dioxide produced from human activities, which would otherwise have accumulated in the atmosphere. This has caused the oceans which on average are slightly alkaline to become more acidic, lowering the average pH value of surface seawater by 0.
Because pH values are on a logarithmic scale, this means that water is 30 per cent more acidic. The impact on biodiversity is that the greater acidity depletes the carbonate ions, positivelycharged molecules in seawater, which are the building blocks needed by many marine organisms, such as corals, shellfish and many planktonic organisms, to build their outer skeletons. Concentrations of carbonate ions are now lower than at any time during the last , years.
For example, invasive plants can alter the fire regimen, nutrient cycling, and hydrology in native ecosystems. Invasive species that are closely related to rare native species have the potential to hybridize with the native species. Harmful effects of hybridization have led to a decline and even extinction of native species. For example, hybridization with introduced cordgrass, Spartina alterniflora , threatens the existence of California cordgrass in San Francisco Bay.
Invasive species cause competition for native species. Four hundred of the endangered species under the Endangered Species Act are at risk due to this competition. Global decline in amphibian species : This Limosa Harlequin Frog Atelopus limosus , an endangered species from Panama, died from a fungal disease called chytridiomycosis.
The red lesions are symptomatic of the disease. Lakes and islands are particularly vulnerable to extinction threats from introduced species.
In Lake Victoria, as mentioned earlier, the intentional introduction of the Nile perch was largely responsible for the extinction of about species of cichlids.
The accidental introduction of the brown tree snake via aircraft from the Solomon Islands to Guam in has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened.
The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas.
Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors. It now appears that the global decline in amphibian species recognized in the s is, in some part, caused by the fungus Batrachochytrium dendrobatidis , which causes the disease chytridiomycosis.
There is evidence that the fungus, native to Africa, may have been spread throughout the world by transport of a commonly-used laboratory and pet species: the African clawed toad Xenopus laevis.
It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana , which has also been widely introduced as a food animal, but which easily escapes captivity, survives most infections of Batrachochytriumdendrobatidis and can act as a reservoir for the disease. The global warming trend is recognized as a major biodiversity threat, especially when combined with other threats such as habitat loss.
Climate change, specifically, the anthropogenic caused by humans warming trend presently underway, is recognized as a major extinction threat, particularly when combined with other threats such as habitat loss. Scientists disagree about the probable magnitude of the effects, with extinction rate estimates ranging from 15 percent to 40 percent of species by Scientists do agree, however, that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them.
Grizzly-polar bear hybrid : Since , grizzly bears Ursus arctos horribilis have been spotted farther north than their historic range, a possible consequence of climate change. As a result, grizzly bear habitat now overlaps polar bear Ursus maritimus habitat. The two kinds of bears, which are capable of mating and producing viable offspring, are considered separate species as historically they lived in different habitats and never met.
However, in a hunter shot a wild grizzly-polar bear hybrid known as a grolar bear, the first wild hybrid ever found. The warming trend will shift colder climates toward the north and south poles, forcing species to move with their adapted climate norms while facing habitat gaps along the way.
The shifting ranges will impose new competitive regimes on species as they find themselves in contact with other species not present in their historic range. One such unexpected species contact is between polar bears and grizzly bears. Previously, these two species had separate ranges.
Now, with their ranges are overlapping, there are documented cases of these two species mating and producing viable offspring. Many contemporary mismatches to shifts in resource availability and timing have recently been documented.
Range shifts are already being observed. The same study suggests that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, and mammals. Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations.
Some climates will completely disappear. The rate of warming appears to be accelerated in the arctic, which is recognized as a serious threat to polar bear populations that require sea ice to hunt seals during the winter months; seals are the only source of protein available to polar bears.
A trend to decreasing sea ice coverage has occurred since observations began in the mid-twentieth century. The rate of decline observed in recent years is far greater than previously predicted by climate models.
Finally, global warming will raise ocean levels due to glacial melt and the greater volume of warmer water. Shorelines will be inundated, reducing island size, which will have an effect on many species; a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher elevation mountains, a cycle that has provided freshwater to environments for centuries, will also be jeopardized. This could result in an overabundance of salt water and a shortage of fresh water.
Privacy Policy. Skip to main content. Conservation Biology and Biodiversity. Search for:. Threats to Biodiversity. Habitat Loss and Sustainability Through increased adoption of sustainable practices, we can reduce habitat loss and its consequences. It helps us fight climate change and adapt to it as well reduce the impact of natural hazards. Since living organisms interact in dynamic ecosystems, the disappearance of one species can have a far-reaching impact on the food chain.
It is impossible to know exactly what the consequences of mass extinctions would be for humans, but we do know that for now the diversity of nature allows us to thrive. They want the targets to be binding and implemented by EU countries at national level, in cooperation with regional and local authorities. More information about what the EU does to preserve biodiversity. Launch the search.
Biodiversity loss: what is causing it and why is it a concern? Created: - Share this page:. What is biodiversity? Find out facts and figures about endangered species in Europe Why is biodiversity important? Main reasons for biodiversity loss. Changes in land use e.
0コメント