Why are Species Disappearing?
Clear-cut in Spotted owl habitat, east side of Harrison Lake, BC Photo: Jeremy Sean Williams
Habitat loss – habitat loss is the primary reason for the decline in species both in Canada and worldwide. The loss or alternation of forests, meadows, grasslands, marshes, lakes and rivers through logging, urban sprawl, mineral extraction and agricultural development has led to the loss of areas where species breed, forage, rest and raise their young. An example of habitat loss and the negative impact it has on species can be seen in southern Ontario where over 60% of wetlands have been drained and filled , resulting in a dramatic decline in bird species that traditionally used these areas.
Climate change – Climate change is another component of the sixth wave of extinction. Species of Canada’s far north such as polar bears, Peary caribou and musk ox will be especially hard hit by increasing temperatures and the severe weather patterns that accompany climate change. Already unusual winter storms have devastated the ability of peary caribou herds to reach their winter food source: lichens, and shrinking ice fields have reduced the ability of polar bears to hunt ringed seals, an important prey species.
White-headed woodpecker Photo: Doug Herr
Invasive species – The introduction of non-native species into local environments can be devastating to indigenous species who do not have time to develop survival mechanisms against alien species that compete with or even crowd out indigenous species. In Canada, invasive species such as the gypsy moth, zebra mussel, knapweed, bullfrog, purple loosestrife, Dutch elm disease and the ubiquitous starling are well known examples of introduced species that have wreaked havoc on local ecosystems (16).
“When alien species enter into an ecosystem, they can disrupt the natural balance, reduce biodiversity, degrade habitats, alter native genetic diversity, transmit exotic diseases to native species, and further jeopardize endangered plants and animals. When there are no established natural controls, such as predators to keep the non-native harmful species in check, there can be a population explosion of the invasive non-native species causing an ecological catastrophe.” (17).
Over-harvesting – Over-harvesting, or over-exploitation, is another reason why species worldwide are rapidly disappearing. Historically we can look to the near radication of the right and blue whales through whaling the dramatic decline of black-tailed prairie dogs through indiscriminate poisoning and pest control programs and the extinction of the great auk through hunting. Today over-harvesting is particularly stark in our oceans. Globally, over the past 30 years consumption of fish has increased by 240%, and today more than 70% of the world’s commercial fish stocks are over-exploited or depleted (18).
Pollution – Pollution is an insidious threat to species because it is often invisible, ignores national boundaries, lingers in the environment for decades and can travel thousands of kilometers from its place of origin. In Canada toxins such as PCBs (poly- chlorinated biphenyls), mercury and other heavy metals, have gradually crept into our food chain, devastating British Columbia’s killer whale populations (19) and heavily contaminating the beluga whales of the St. Lawrence Estuary (20).
Web of Life
White-headed woodpecker and ponderosa pines
The relation between plants, animals, microbes, fungi, bacteria, climate and the geography of a particular area is both essential and fragile, for the whole of these disparate components make up the web of life – a living breathing ecosystem where all parts are interconnected.
The connection between healthy ecosystems and healthy species is profound - simply put, wild species need the wild spaces in which they have evolved and adapted to over millennia.
An excellent example of the interconnection between wild species and wild places can be seen between the endangered white-headed woodpecker and the mature ponderosa pine tree ecosystem in southern British Columbia. Today, less than 100 white-headed woodpeckers are believed to exist in Canada, all of which are found in southern BC. Dependent on the large pine seeds that come from the mature ponderosa pine trees that are found in open grassy areas, this regal woodpecker also relies on these mature low-elevation pines for roosting and nesting.
So specially adapted is the woodpecker to this ecosystem that over 50% of the birds’ diet is composed of ponderosa pine seeds. Unfortunately, logging which has targeted mature trees, and a misguided fire suppression policy has altered this ecosystem to the point where mature, open pine tree savannahs are disappearing, and the white- headed woodpecker which relies upon them is also vanishing (21).
