A recent report Living Planet Report 2014 (http://www.wwf.org.uk/about_wwf/other_publications/living_planet_report_2014/#.VJ4WbcPaA), published jointly by WWF and the Zoological Society of London, contains many disturbing facts about the state of our planet's species. The most shocking, no doubt, is the fact that over the past 40 years, the number of mammals, birds, reptiles, amphibians and fish decreased on average by 52%.
The biggest victim of the disaster - a freshwater species, with an average reduction of 76% according to the Living Planet Report. "The main threats to freshwater species is the loss and fragmentation of habitat, pollution, and changes in the levels of water and growth of fresh water consumption. For example, irrigation and hydropower dams - have a great impact on the habitat of freshwater. "
Terrestrial species declined by 39% over 4 decades from 1970 to 2010. This trend is evidenced by the loss of habitat for the benefit of man. Remains one of the major threats to agriculture, and urban development, mining and energy production, all of this is exacerbated by hunting. "For some poaching is a huge problem ...”
Populations of marine species also decreased by 39% since 1970. "The greatest reduction can be seen in the tropics and the Southern Ocean - among the most significant loss of sea turtles, lots of sharks and large sea birds such as the wandering albatross." Some stability was recorded in the mid-1980s, but it was gone, and we now see another period of sharp decline.
In general, there two main causes of this tragedy, human activity and the degradation / alteration/ destruction of habitat, for all 3 categories of species.