Canada has over 140 000 species, only 70 000 of which have been identified. Half of these species are terrestrial, a quarter freshwater and the other quarter marine. In the figure, the terrestrial component (land) is represented by green, marine by dark blue, and freshwater by light blue. Compared to the relative amounts of Canada's territory that are in these three environmental types ("Area" in the figure), the marine environment has fewer species than expected, while freshwater has more. This trend reverses itself at higher levels of classification; two-thirds of phyla (one of the highest levels of classification) are mostly or exclusively marine, while only a third are primarily terrestrial or freshwater (enough phyla have enough members both on land and in freshwater that it is difficult to assign them to one environment or the other, so they are grouped together in the figure). The large number of phyla that are marine isn't very surprising, given that life has existed in the oceans far longer than it has on land.
Within these three broad environmental types, the proportion of species in any given group will vary widely from group to group. For instance, although overall 25% of species are found in freshwater systems, 80-98% of algae, 32% of bacteria, 15% of native flowering plants and only 7% of fungi species in Canada are freshwater.
Only one to five percent of Canadian species are endemic (i.e. are only found in Canada). Much of this is due to the periodic glaciation that the land endures. The glaciers force populations and species to move south or be destroyed, and the 10 000 years since the Wisconsin ice age hasn't been enough time for many new species to arrive.
The patterns of Canadian biodiversity follow a definite trend, largely following the increasingly hostile environment as one heads north, and this pattern has been taken into account in the borders and definitions of Canada's ecozones. What follows is a summary of the patterns that different groups of organisms follow in Canada. For more detail on the land and specific species found on it, see the Ecozones and Canada's Species sections.
Diversity is in general highest to the south, and the further north one goes, the fewer the number of species one encounters. North of the tree line, trees species can no longer grow as full-grown trees, and if they are present they are found in dwarf forms.
Patterns from west to east depend largely on rainfall. British Columbia's coast receives so much rainfall due to the mountains that temperate rain forests can be found there. The plant species found on the Rocky and Coastal mountains vary depending on the mountain face one is looking at; slopes facing south receive much more sun than those facing north, and those facing west are far wetter than those that face east. Continuing eastward, the plains past the mountain ranges are too dry for most tree species, resulting in the grasslands that are characteristic of the area. Southern Ontario's fertile soil, high precipitation and temperate climate produces the highest plant diversity in Canada.
Diversity of vertebrates (fish, amphibians, reptiles, birds and mammals) decreases towards the north. Freshwater fish species diversity fades out towards the north, with only a fifth of freshwater fish species being found in the Northwest Territories and Nunavut. Amphibians and reptiles have highest diversity in southern Ontario for many of the same reasons as plants. They lack the ability to survive in the extreme cold of Canada's north, and most species have not yet expanded the northern extent of their ranges back to pre-glaciation latitudes. Birds can also be found extremely far north, although their presence varies remarkably depending upon the season. In spring and summer northern Canada is filled with bird species, many of whom fly south as winter approaches. Mammals are found on land and in the water to almost the very northern tip of the continent. They are well suited to the west and especially the western mountains, which have a higher mammal diversity than flatter areas to the east.
While invertebrates (animals without backbones) are far more plentiful and diverse than vertebrates, their distributions are much more poorly known. There are many reasons for this: invertebrates tend to be small, making them hard to find; the great number of species and their small size makes them difficult to identify; they are not as popular as plants and vertebrates, meaning that fewer people are likely to study them.
Land invertebrates such as insects and spiders disappear to the north, unable to deal with the cold. Aquatic invertebrates are more plentiful in the south, but even in the frigid arctic waters sea stars, sea urchins, and crustaceans can be found, having found ways to adapt to the low temperatures.
The distribution of invasive species follows the pattern of trade and population more than any climatic trend. Species have entered the country mainly in cargo and ships from around the world (e.g. Dutch elm disease, zebra mussels), as crops to be grown (most of our staple agricultural crops), and as ornamental species (e.g.purple loosestrife). Most invasive species into Canada came through the St. Laurence seaway, and have spread outward from there.
Aquatic species, such as fish, are usually easier to control than land-based species, and many have had their spread limited. This isn't always the case; the sea lamprey was accidentally introduced to the upper Great Lakes through the construction of the Welland Canal, and zebra mussels have spread throughout the Great Lakes and beyond. On the other hand, deliberately introduced game fish can be found all through the country.
Some introduced species, such as the starling, have spread to virtually anywhere they can survive. Agricultural plants have been introduced all through the south, and in the Prairies they have replaced most of the natural ecosystems.
Like invasive species, endangered species are found in areas of high population density and intensive human activity. The Mixedwood Plains, for example, contain much of Canada's species and population as well as, unsurprisingly, much of its endangered species. Cities themselves take up relatively little space when compared to the entire country, but many species are nonetheless threatened by the sprawl, roads, and pollution that cities create. Agriculture takes up huge tracts of land and is the main threat to the south, while forestry is the major threat slightly to the north. Fisheries are a potential threat anywhere they exist.