Castor canadensis: Keystone Species and Canadian National Symbol

The beaver (Castor canadensis) is one of North America’s most fascinating, beautiful, and industrious species (and super tasty). Many of my posts relate directly to hunting, but the goal is to discuss a range of issues and topics relevant to conservation. This one is an endorsement for giving the beaver our full respect and appreciation as an integral component of the ecosystems we cherish and as an honourable national animal for Canada. Seriously, I think the beaver is one of the most incredible animals in North America.

The North American beaver
The North American beaver

Currently, there are only two species of beaver in the world, the North American beaver that most of us are familiar with, and the Eurasian beaver (Castor fiber). However, during the Pleistocene, there was a genus of giant beavers (Castoroides) that lived in North America, from Florida to the Yukon. Giant beavers were not actually related to modern beavers, but shared a close physical resemblance, with larger, sharper front teeth. They were much larger than modern beavers, measuring upwards of six feet long and weighing over 200 pounds. The giant beaver went extinct sometime during the megafaunal collapse at the end of the Pleistocene, the period from roughly 2.5 million years ago to 12,000 years ago, which marked the end of the last ice age.

Skeleton of a giant beaver
Skeleton of a giant beaver

One thing I hear a lot from landowners and outdoors people is that beavers are nuisances, flooding or drying up land without regard for how inconvenient this may be for humans. My first, admittedly callous reaction, is that’s what beavers do, and they’ve been doing it for a lot longer than you’ve been feeling personally affronted by it. On a more engaging level, I also suggest to those people that it’s not exactly without regard for human needs. In fact, the resulting ecological changes from beaver activity provide important services that benefit humans.

Beavers are considered a keystone species for their roles in altering and creating habitat. What this means is that if we remove beavers from an ecosystem, it changes the entire structure and function of that ecosystem. Numerous other species lose habitat, food and water sources, and with those changes there is a reduction in local biodiversity. Beaver activity creates critical habitat for fish, birds, turtles, frogs, ducks, and some of these are in turn important food sources for many other species, including otters, foxes, and birds of prey. The ecological interactions that are created by beavers are literally too numerous to fully describe here.

Beaver lodge
Beaver lodge

In addition, the wetland habitats created from beaver flooding provide ecosystem services that are crucial to maintaining healthy environments and provide direct benefits to humans. Wetlands filter and purify water, refill aquifers, mitigate erosion, prevent droughts, and control floods (seems counterintuitive perhaps since beavers flood land, but this actually provides a form of flood control for other areas). Wetlands are one of the world’s most critical and productive habitats, and they are being destroyed at alarming rates.

But the beaver hasn’t always enjoyed the gratitude and platitudes it deserves. In 2011, Canadian Senator Nicole Eaton offered her opinion that Canada should trade in a “19th-century has-been for a 21st-century hero”, suggesting that the beaver is not worthy of being Canada’s national animal. Instead, Senator Eaton proposed the polar bear replace the beaver. It’s not that I don’t have tremendous respect for the polar bear (in fact, my graduate work is focused on Arctic marine species, including polar bears). What troubles me is Ms. Eaton’s clear lack of knowledge about beaver ecology and biology, yet her belief that she is suitably positioned to make such strong statements about the value of the beaver and whether it possesses the qualities with which Canadians should be proud to be associated (she literally reduced the animal to a “dentally defective rat”).

In addition to the deliberate work to create and continuously maintain critical habitat, scientists have discovered some unintended benefits of beaver activity. Beaver ponds (the area of land flooded by the creation of dams) may be the answer to our nitrogen problems.

The massive expansion of agriculture in North America over the last century created a demand for increased productivity and yields. Nitrogen is a key nutrient for plant growth and agricultural processes eventually lead to nitrogen depletion in soils. In 1888, two scientists discovered that leguminous plants remove nitrogen from the air and add it to soils, a process known as nitrogen fixation. In 1909, two German chemists created a process through which nitrogen could be artificially produced for addition to soils, eventually leading to the invention of soil fertilizers.

Although fertilizers lead to substantially increased crop yield, the addition of massive amounts of nitrogen to soils has created problems for marine ecosystems. Rain water washes fertilizers containing nitrogen from agricultural fields into nearby streams and rivers. When nitrogen eventually flows into estuaries it stimulates algal blooms. The decomposition that results from increased algal growth eventually de-oxygenates marine ecosystems (a state known as hypoxia) and creates massive dead zones. One of the more famous dead zones is in the Gulf of Mexico.

Don’t worry. Beavers are here to save the day. Researchers from the University of Rhode Island have discovered that the ecology of beaver ponds makes them quite effective at removing nitrogen. In a paper published this past September, Julia G. Lazar and co-authors explain that bacteria found in the organic material and soil of beaver ponds  transform nitrate into nitrogen gas which then bubbles to the surface and mixes with the air. In their experiments, the researchers found that beaver ponds were able to remove up to 45% of the nitrogen from the system.

I hope that discoveries like this encourage more appreciation for the important ecological functions of beavers. We already knew that the habitat created by beavers performs valuable ecosystem services benefitting humans, but now we can add a service that benefits environmental health many miles downstream of beaver habitat. Beavers are complex animals, quietly and diligently going about their work. People may not think they are the most charismatic species, but I think they possess all the qualities that we should value and measure ourselves against.

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