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,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.

So the correct option is all of these.