Amphibians

am / phib / i / an: an amphibious organism; especially : any of a class (Amphibia) of cold-blooded vertebrates (as frogs, toads, or salamanders) intermediate in many characters between fishes and reptiles and having gilled aquatic larvae and air-breathing adults

Comprising mostly frogs, toads, and salamanders, much about amphibians is captured in their name: “double life.” This refers to the complex life cycle of amphibians, with most having an aquatic stage as a gilled “tadpole” before going through a remarkable metamorphosis to become air-breathing, four-limbed adults. The transition from water to air is also reflected in amphibian history. Amphibians are thought to have been the first vertebrate group to colonize land some 350 million years ago, their ancestors ultimately giving rise to modern amphibians on the one hand and to reptiles, birds, and mammals on the other hand. Despite success in colonizing the land, amphibians have never completely lost their dependence on water. Most species deposit jelly-like eggs in water, where the tadpoles then hatch and mature. Even amphibian species that lead largely terrestrial lives never escape the requirement to maintain a moist skin. This is because amphibians use their porous skin to supplement breathing, a feat that requires moisture to be efficient.

Amphibians play the role of both prey and predator in the ecosystems of which they are a part, these being predominantly wetlands and forests. At all life stages, amphibians are food for fish, birds, reptiles, mammals, and even invertebrates and other amphibians. In their turn, amphibians consume vast quantities of insects and other invertebrates, many considered pests by humans. Yet, despite their importance in nature, amphibians frequently escape our notice, probably because they are less conspicuous than other animals (e.g., mammals, birds). Moreover, because differences among amphibian species are often subtle, few people have any idea of their astounding species richness. Recent estimates indicate that the number of described amphibian species globally (4 780) exceeds that of mammals (4 629).

Canada boasts 45 species of amphibians: 21 salamanders and 24 frogs and toads. While all provinces and territories are home to some amphibians, the distribution of species is by no means even. Ontario has the most species (23), followed closely by Quebec (21) and British Columbia (21). A substantial number of the species in British Columbia, including seven salamander species, occur in no other region of Canada. Most amphibian species found in Canada have the majority of their range in the United States. However, 14 amphibian species have 50% or more of their range in Canada. Four of these, the Canadian Toad, Mink Frog, Wood Frog, and Blue-spotted Salamander, have upwards of 75% of their range in Canada. All amphibians in Canada meet the northern limits of their range here. As such, Canada offers opportunities to study the ability of these animals to adapt their physiology to our severe winters and short summers. Perhaps the best example of this exceptional physiological adaptation is the phenomenal ability of Wood Frogs to survive freezing solid over winter.

While 64% (29 species) of amphibians are Secure, nearly a quarter (22%, 10 species) are designated At Risk or May Be At Risk. This precarious state may in part be explained by living a life at their ecological and geographic limits. Yet human-caused factors, like draining of wetlands and forest clearing or fragmentation, are also threats to the persistence of amphibian species in Canada. Besides loss of habitat, amphibians are also thought to be more sensitive and more widely exposed to a host of environmental stresses by virtue of their aquatic and terrestrial life stages and porous skins. Indeed, many scientists regard them as “canaries in the coal mine,” a reference to their potential value as indicator species of environmental decline. For this reason, reports of a number of bizarre morphological deformities in amphibians, such as extra eyes or legs, are particularly unsettling. This, joined by an apparent global decline in amphibian populations, even in seemingly pristine habitats, has sparked a great deal of interest in the status of these animals the world over. Surveys, based on the calls of breeding male toads and frogs, have provided valuable data with which to monitor population sizes and changes in species distribution. Incorporating survey information into this report has resulted in the most up-to-date assessment of the general status of these species in Canada.