Habitat loss through changes of land use in particular the conversion of natural ecosystems to cropland, continues to be the biggest direct cause of biodiversity loss. Already, more than half of the Earth’s 14 terrestrial biomes have had between 20% and 50% of their total area converted to cropland.

Unsustainable use of ecosystems and over-exploitation of biodiversity continue to be major threats. Many species are used by humans to fulfill basic needs. Many species are in a state of decline because they are being used at unsustainable levels or are being harvested in such a way that threatens the ecosystems on which they depend. These declines are widespread.

Climate change is projected to become a progressively more significant threat to biodiversity in the coming decades. 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.

Plants, animals and micro-organisms transported deliberately or accidentally to an area outside their natural geographical ranges can cause great damage to native species by competing with them for food, eating them, spreading diseases, causing genetic changes through inter-breeding with native species or populations, and disrupting various aspects of the food web and the physical environment. More than 530 alien species with a demonstrated impact on biodiversity have been found across 57 countries for which data were collated, with an average of over 50 such species per country (and a range from nine to over 200)

The accumulation of pollution such as phosphorus and nitrogen, largely from excess fertilizers running off farmland, and from sewage and other effluents, causes the build-up of algae able to benefit from the added nutrients. The algae themselves can be toxic and therefore create a health hazard, but the greatest damage to biodiversity is caused when they decompose and use up large quantities of oxygen in the water, creating “dead zones” where other forms of life cannot survive. The number of such dead zones increased from 149 in 2003 to over 200 in 2006. The continuing release pollutants from urban and agricultural sources combined with projected growth in coastal development and agricultural intensification may lead to a multiplication of the number of dead zones in the coming decades, unless substantial changes in policy are implemented.

Here are some videos about the loss of Biodiversity.