If we lose the insects then everything is going to collapse." In 2006, many species were formally classified as rare or endangered or threatened; moreover, scientists have estimated that millions more species are at risk which have not been formally recognized. About 40 percent of the 40,177 species assessed using the IUCN Red List criteria are now listed as threatened with extinction—a total of 16,119. Jared Diamond describes an "Evil Quartet" of habitat destruction, overkill, introduced species and secondary extinctions. Edward O. Wilson prefers the acronym HIPPO, standing for Habitat destruction, Invasive species, Pollution, human over-Population and Over-harvesting. The most authoritative classification in use today is IUCN's Classification of Direct Threats ("version 2.0 released in 2016") which has been adopted by major international conservation organizations such as the US Nature Conservancy, the World Wildlife Fund, Conservation International and BirdLife International. The 11 main direct threats to conservation are:  1. residential & commercial development 2. farming activities 3. energy production & mining 4. transportation & service corridors 5. biological resource usages 6. human intrusions & activities that alter, destroy, simply disturb habitats and species from exhibiting natural behaviors 7. natural system modifications 8. invasive & problematic species, pathogens & genes 9. pollution 10. catastrophic geological events 11. climate changes  Habitat destruction has played a key role in extinctions, especially in relation to tropical forest destruction. Factors contributing to habitat loss include: overconsumption, overpopulation, land use change, deforestation, pollution (air pollution, water pollution, soil contamination) and global warming or climate change. Habitat size and numbers of species are systematically related. Physically larger species and those living at lower latitudes or in forests or oceans are more sensitive to reduction in habitat area. Conversion to "trivial" standardized ecosystems (e.g., monoculture following deforestation) effectively destroys habitat for the more diverse species that preceded the conversion. Even the simplest forms of agriculture affect diversity – through clearing/draining the land, discouraging weeds and "pests", and encouraging just a limited set of domesticated plant and animal species. In some countries, property rights  or lax law/regulatory enforcement are associated with deforestation and habitat loss. A 2007 study conducted by the National Science Foundation found that biodiversity and genetic diversity are codependent—that diversity among species requires diversity within a species and "vice versa". "If anyone type is removed from the system, the cycle can break down and the community becomes dominated by a single species." , the most threatened ecosystems occur in fresh water, according to the Millennium Ecosystem Assessment 2005, which was confirmed by the "Freshwater Animal Diversity Assessment" organised by the biodiversity platform and the French "Institut de recherche pour le développement" (MNHNP).