The main factor currently driving biodiversity loss is habitat destruction—on land; in streams, rivers, and lakes; and in the oceans. Human activities such as: deforestation; bottom trawling in the oceans; the damming and dredging of streams, rivers, and lakes; and the draining and degradation of wetlands, estuaries, and mangroves are responsible.
Other threats to biodiversity and to ecosystems include: the over-harvesting of plant and animal species; the introduction of non-native species; and pollution. Many types of human-caused pollution are a threat—the release of excessive amounts of nitrates and phosphates from sewage and agricultural run-off; persistent organic pollutants that can concentrate in food webs (and in our own tissues) and adversely affect hormonal and reproductive function; pharmaceuticals used by people and in livestock production that are toxic to wildlife; acid rain; heavy metals; herbicides and pesticides; and plastics.
Still further threats come from: excessive ultraviolet radiation from depletion of the stratospheric ozone layer that can damage the DNA and proteins of land-based, freshwater, and marine organisms; war and conflict that can result in habitat destruction, over-hunting, and pollution; and climate change.