Invasive cousins trade intercontinental swamp destruction
Intercontinental swamp munching cousins Mr. Coypu and Ms. Beaver
by Len Bahr, PhD*
On June 17 The Washington Post published a story by Juan Forero, in which he described the destruction of forested aquatic ecosystems in Argentina’s Tierra del Fuego province** by the beaver Castor canadensis, a large furry rodent native to North America. On June 24, NPR’s All Things Considered featured a separate account on the beaver invasion, also by Mr. Forero.
In 1946 the beaver, with its webbed feet, flat hairless tail and huge incisors, was purposely imported into Argentina by entrepreneurial furriers. As could have been predicted, some beavers escaped captivity and established a successful invasive population that became a warm blooded forest wetland-destroying machine.
In Louisiana this story sounds uncannily familiar. During the 1930s Louisiana Tabasco tycoon L.A. McIlhenny imported the beaver’s South American cousin, the coypu (nutria) from Argentina to establish a fur ranch on Avery Island. This large immigrant rodent has webbed feet, striking orange buck teeth and a round hairless tail. Just eight years before beavers were brought to Argentina, between 12 and 20 nutria escaped from Avery Island during a hurricane in 1938 and in 1940 another storm freed about 150 additional animals.
Fur trappers formerly kept the newly established invasive population under some control but an explosion of nutria in south Louisiana followed a global decline in the fur trade partly spurred during the ’80s and since by People for the Ethical Treatment of Animals (PETA). The prolific breeding rate and voracious appetite of the nutria have become disastrous for America’s Delta.
The W-P article about beavers included the following passage reminiscent of the nutria recipes ‘cooked up’ by John Folse and other Cajun chefs and Jefferson Parish nutria sharpshooters hired by the late Sheriff Harry Lee:
(Argentine) authorities…have tried just about everything to stop the beavers, including a campaign to get locals to acquire a taste for beaver meat. Now there’s even talk about hiring professional riflemen to search and destroy every last one of them, perhaps even from helicopters.
These parallel stories in south Argentina and south Louisiana almost perfectly mirror each other and this intercontinental swap of invasive furry cousins is having simultaneous and eerily similar outcomes in ecosystems separated by thousands of miles. This represents an ironic ecological turnabout and an angle that the Washington Post story totally missed.
As has been pointed out here, an anti-science attitude dominates Louisiana coastal policy, which seems to be controlled by deniers of evolution, as well as climate change. Nevertheless, those who understand evolutionary ecology recognize that each of the millions of species of life forms currently alive on Terra Firma occupies a unique niche from which all other creatures are normally excluded by a process known as competitive exclusion. Members of species populations compete among themselves and entire populations both compete and cooperate, in a perpetual iterative correction process that may be ‘upgraded’ in hours for microbes…or it may take millions of years for visible life forms.
Competition includes struggles for light or other forms of free energy, physical and temporal space, metabolic requirements, disease-resistance, defense against predators and many other potentially limiting factors. The principle of competitive exclusion doesn’t apply to invasive or imported species; it only works for ‘native’ creatures that have co-evolved and adapted with their neighbors.
If organisms whose ancestors have long been isolated, for example by continental drift, suddenly find themselves transported into foreign ecosystems, unpredictable and usually destructive things result. Ecosystem scientists understand this lesson but those who believe that all land animals that ever lived floated along with Noah on the Ark continue to believe they can outsmart Mother Nature.
The beaver and the nutria are evolutionary cousins, with similar anatomy, aquatic lifestyle and wetland feeding habits. Nevertheless, their respective lineages have been isolated for so long that they belong to separate suborders as well as families in the order Rodentia (see classification below). This means that they have distinct niches and that each species has different natural population controls.
When these distant cousins were coincidentally relocated to each other’s continents during the 30s and 40s, their respective natural controls were lacking or ineffective and ecosystem destruction was almost inevitable.
Beavers (and muskrats) are natives in south Louisiana, where they live within their means. Nutria, on the other hand, are profligate wasters. They clearly reduce habitat quality for their native cousins, although this impact would be difficult to assess. At any rate they are extremely destructive to forested coastal wetlands and freshwater marshes of south Louisiana. Some scientists believe that their impact throughout the coast is highly underestimated.
Classification for three rodent cousins, the North American beaver, the South American coypu and the native North American muskrat
Kingdom Animalia; Phylum Chordata; Class Mammalia; Order Rodentia (from Latin, rodere, to gnaw)
Beaver (Castor Canadensis)
Suborder Castorimorpha; Family Castoridae
Description: The North American beaver is primarily a nocturnal, large, semi-aquatic rodent. Beavers are known for building dams, canals, and lodges (homes).
Nutria (Myocastor coypus)
Suborder Hystrichomorpha; Family Myocastoridae
Description: The coypu (or nutria) is a large, herbivorous, semi-aquatic rodent. Coypus live in burrows alongside stretches of water. They feed on river plants, and waste close to 90% of the plant material while feeding on the stems.
Muskrat (Ondata zibethicus)
Suborder Myomorpha; Family Cricetidae
Description: a medium-sized semi-aquatic rodent native to North America and introduced in parts of Europe, Asia and South America The muskrat is found in wetlands and is a very successful animal over a wide range of climates and habitats.
*Founding editor leonardbahr@gmx.com
**One of Charles Darwin’s field laboratories during his extended travels on The Beagle.
Such an ironic turn of events. If only the hunters and furriers had been happy with their own homegrown rodents!
I’m not sure how beaver meat tastes, but I believe that officials from Baton Rouge explored the idea of exporting nutria meat from Louisiana to clients abroad. We linked to a story on the piece in a post we wrote last fall on Restoration and Resilience:
http://blogs.edf.org/restorationandresilience/2010/10/05/neutralizing-nutria-how-cost-effective-rodent-control-is-saving-coastal-wetlands/
Muskrat (Ondatra zibethicus)