In part because the value of biodiversity and the resulting ecosystem services are poorly understood by a lot of people, nature's “cogs and wheels” are going missing at an alarming rate — on the order of 100 to 1000 times the background rate, estimated from fossil records to be from one to ten species/year . Some estimates of current rates are much higher. There have been five mass extinctions in the past 500 million years, the most recent about 65 million years ago . We appear to be in the sixth, with the major difference being that for this one, the cause appears to be not a major physical catastrophe such as severe volcanism or a meteor strike, but a single species: us.
The Millennium Ecosystem Assessment (2005) reports that there has been a substantial and largely irreversible loss in the earth's biodiversity, with some 10-30% of mammal, bird and amphibian species currently threatened with extinction, and 15 of 24 ecosystem services being degraded. Fortunately, it comes at a time when the earth probably contains more species than ever before , and there's some redundancy built into the system. We can lose some species — some — before things start to really unravel.
The causes of these losses are varied and can be encompassed in the term HIPPO(C):
Habitat loss. Habitat loss, alteration and fragmentation directly affect the species that rely on the habitat that is being changed. Habitat loss is particularly serious in southern Ontario where urbanization, agriculture and road density are greatest.
Invasive species. Invasive species are harmful non-native species whose introduction or spread threatens the environment, the economy and society, including human health. Invasive species originate from other continents, adjacent countries or from other ecosystems within Canada. Free from predation and competition that would normally limit their distribution and abundance in their natural habitats, many invasive species reproduce rapidly and damage, displace or destroy native species in our forests (e.g., emerald ash borer), agricultural areas (e.g., plum pox virus), wetlands (e.g., purple loosestrife) and lakes and rivers (e.g., zebra mussel). The zebra mussel disrupts ecosystem composition and structure, clogs water intake pipes, and affects public beaches.
Pollution. Pollution is emitted in many different forms, including atmospheric pollution, soil and water pollution, pesticides,
"The loss of biological diversity is second only to nuclear warfare in its threat to human and other life on this planet."
— U.S. Environmental Protection Agency
particulate matter, and heavy metals. There are thousands of pollutants circulating through the Earth's ecosystems, and many of these materials have significant, large-scale impacts on forests and aquatic ecosystems. Acid precipitation, for example, has had a significant impact on Ontario's maple forests and industrial pollutants such as DDT is known to have caused significant declines in populations of many bird species including Peregrine Falcon and Bald Eagles. Pollution can also disrupt ecological processes. For example, scientists are now linking light pollution to declines in migratory songbirds.
Population growth. Human population growth adds to the impact of all the other causes because more people require more space and more resources. There are now about 6 billion people on Earth, more than twice as many as in 1950. While the rate of increase is slowing, it still adds more than 90 million people each year. Habitats, even healthy ones, can support just so
many of anything, including people.
Over-consumption or unsustainable use. Over-consumption is the harvest of species at a rate higher than can be sustained by the natural reproduction of the population. In Ontario, for example, wild American ginseng has been over-harvested from its natural rich woodland habitat to the point of being Endangered.
Climate Change and other Cumulative impacts (the "C" in HIPPOC). Ontario's Biodiversity Strategy adds an additional letter. People have added carbon dioxide, nitrous oxide, methane and other greenhouse gases to the atmosphere by extracting and burning fossil fuels such as coal, oil and natural gas. The effect of these gases has been to trap heat and accelerate the rate of global warming and climate change. Climate change is a major threat to the world's biodiversity. The cumulative impacts of pollution, habitat modification, the global redistribution of species and over-harvesting place many ecosystems at risk. These cumulative impacts cause alteration, reduction and loss of ecosystem function, populations and species, degradation, loss and fragmentation of habitat. They also damage human health.