Threats to Biodiversity

Extinction is a natural event and most species that have ever lived have gone extinct. The average duration of a species is 2-10 million years (based on the period over the last 200 million years). Scientists estimate that over the past 200 million years, and average of 1-2 species went extinct per year. Present day human activities, however, are endangering species worldwide and accelerating the rate of extinction. Estimates for modern day extinctions are 1-2 species per hour. Species are now vanishing faster than at any other time in Earth’s history.


The human activities that cause the most damage to biodiversity include habitat destruction, over-harvesting, invasion of non-native species, environmental degradation, and climate change. Species may be threatened by more than one cause, and together the above threats form the cumulative impacts on biodiversity. Ultimately, the root cause of the above threats is an increase in the global human population, whose needs for resources continue to increase exponentially. Some of these threats can be reduced in the short-term, such as stopping over-harvesting. Other threats, such as climate change, will take concerted effort over a long term.

Habitat Destruction, which includes habitat loss and fragmentation, is the greatest threat to biodiversity. The loss and fragmentation of habitat, through activities such as deforestation, agriculture, and urbanization, eliminates or alters the environmental conditions necessary for the survival of species. Species that have very specific habitat needs are more vulnerable to habitat loss and fragmentation. On the contrary, generalist species that are adaptable to human activities, thrive in degraded habitat conditions. Human alteration of landscapes creates simpler habitats that appeal to fewer species, creating biodiversity poor landscapes with reduced ecosystem functions and services. Habitat loss has occurred in Chelsea, primarily in the form of urban development. The construction of buildings eliminates native habitat. Urban sprawl is considered one of the most critical threats facing endangered species in southern Quebec and southern Ontario, where close to half of Canada`s threatened and endangered species occur.

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Habitat Fragmentation occurs when native vegetation, such as a forest, is cleared for agriculture, logging, or urban development. Habitats that were continuous become divided into separate fragments. After intensive clearing, the separate fragments become very small patches, isolated from each other by a matrix of other types of habitat, such as crop land and pasture.

Small patches of habitat support only small populations of animals, and small populations are more vulnerable to extinction. Some species do not travel through the matrix to colonize other patches. Small patches of habitat do not contain interior habitat, and habitat along the edge of a patch has different environmental conditions and favours different species. Some interior species do not breed in patches under a certain size. Small fragments are therefore unfavourable for those species that require interior habitat and may lead to the endangerment of those species. In Chelsea, the red-shouldered hawk is an example of an interior species. Red-shouldered hawks are vulnerable to habitat fragmentation. They require interior forest with closed canopy. Open canopy and forest fragmentation enables Red-tailed Hawks and Great Horned Owls to displace or kill Red-shouldered Hawks.


Route 105 Extension

Roads cause habitat fragmentation, and many roads exist in Chelsea. Not all roads are alike, though. High volume and high-speed roads have the greatest effect on wildlife. They cause more road kills and create a barrier or filter to movement for many animals. Highway 5 has the biggest impact on wildlife, followed by highway 105, then secondary roads. Some species are very sensitive to roads, and some species will not cross even narrow access roads.

Urban sprawl or ex-urban development is occurring in Chelsea, creating a fragmented condition of the forest. As development becomes increasingly diffuse and dispersed, the distinction between “suburb” and “forest” becomes less clear.

Over-harvesting includes over-hunting animals and over-harvesting plants. Over-harvesting for food, fashion and commercial hunting has caused the extinction or endangerment of hundreds of species. The pet trade and trade in decorative plants are part of the commercial hunting category, and include legal and illegal activities. In Chelsea, the pet trade may affect some rare turtle species, and over-harvesting of certain plant species, such as wild ginseng, wild garlic, and some orchid and fern species, have caused them to be rare or threatened.

Dog Strangling Vine

Dog Strangling Vine

Invasion of Non-Native species. Invasive alien species are species whose introduction or spread outside their natural distribution threatens biological diversity. When a foreign species is introduced to an area, intentionally or by accident, it can spread rapidly and become invasive because their native predators or competitors do not exist in its new environment. Consequently, it can outcompete native species for habitat and food. The dog strangling vine is an example of an alien invasive species that is advancing through Chelsea and threatening to take over the habitat of many native plant species.

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Environmental Degradation, including pesticides and pollution, impact biodiversity across the planet. There are many sources of pollution that affect wildlife. In Chelsea, pollutants such as road salt and used motor oil may form surface water pollution. Malfunctioning septic systems may leach nutrients into the water table and impact the quality of local habitats and water sources. The use of pesticides and herbicides has increased worldwide over the past several decades, and are pervasive in wildlife habitat and threaten the survival or recovery of some species. Pesticides have been linked to the decline of amphibians, birds, mammals, and insect pollinators. Some pesticides have demonstrated to be toxic to humans. For these reasons, Chelsea adopted a by-law banning the use of pesticides for aesthetic purposes in 1998.

Climate Change is recognized by the Convention on Biodiversity as a major threat to biodiversity. Changes in the climate recorded by scientists include increased concentrations of carbon dioxide in the atmosphere, higher land and ocean temperatures, rise in sea levels, and changes in precipitation levels. Changes in climate over the last few decades have affected the timing of plant and animal reproduction, the timing of animal migration, the length of the growing season, species distributions and population sizes, and the frequency of pest and disease outbreaks. Climate change in the future is likely to reduce the capability of species to migrate and the ability of species to persist in fragmented habitats. Species with restricted habitat requirements or small and fragmented populations are the most vulnerable to climate change effects.