Reasons of Biodiversity Loss
The Millennium Ecosystem Assessment identifies the following primary drivers leading to loss of biodiversity:
- Habitat change
- Climate change
- Invasive species
- Over-exploitation
- Pollution
They have been discussed briefly here.
Habitat change
Humans have had an effect on every habitat on Earth, particularly due to the conversion of land for agriculture. Cultivated systems (areas where at least 30% of the landscape is used in cultivation) now cover one quarter of Earth’s terrestrial surface. Habitat loss also occurs in coastal and marine systems, though these changes are less documented. One example is the Trawling of the seabed, which can significantly reduce the diversity of benthic habitats.
Climate Change
Observed recent changes in climate, especially warmer regional temperatures, have already had significant impacts on biodiversity and ecosystems, ncluding causing changes in species distributions, population sizes, the timing of reproduction or migration events, and an increase in the frequency of pest and disease outbreaks. By the end of the twenty-first century, climate change and its impacts are likely to be the dominant direct driver of biodiversity loss and changes in ecosystem services globally.
Invasive Species
The spread of invasive alien species has increased because of increased trade and travel. While increasingly there are measures to control some of the pathways of invasive species, for example, through quarantine measures and new rules on the disposal of ballast water in shipping, several pathways are not adequately regulated, particularly with regard to introductions into freshwater systems.
Overexploitation of bioresources
For marine systems, the dominant direct driver of change globally has been overfishing. 50% of the world’s commercial marine fisheries are fully exploited whilst 25% are being overexploited.
Pollution and nutrient loading
Since 1950, human mediated increases in nitrogen, phosphorus, sulphur, and other nutrients (nutrient loading) has emerged as one of the most important drivers of ecosystem change in terrestrial, freshwater, and coastal ecosystems, and this driver is projected to increase substantially in the future. For example, humans now produce more biologically available nitrogen than is produced by all natural pathways combined. Aerial deposition of reactive nitrogen into natural terrestrial ecosystems, especially temperate grasslands, shrub-lands, and forests, leads directly to lower plant diversity; excessive levels of reactive nitrogen in water bodies, including rivers and other wetlands, frequently leads to algal blooms and eutrophication in inland waters and coastal areas. Similar problems have resulted from phosphorus, the use of which has tripled between 1960 and 1990. Nutrient loading will become an increasingly severe problem, particularly in developing countries and particularly in East and South Asia.
