Guest post by John
Cherkas
Fifty
years ago, Dr. Walter Howard presented his thoughts on invasive mammals at a
symposium on colonizing (invasive) species, which was later turned into the
volume "The Genetics of Colonizing Species." He speculated on the
nature of predator-prey interactions, population growth limits and habitat
disruptions. His ideas still resonate, but how well do they match up with a
certain invasive mammal today.
May
I bring your attention to some invasive beavers? Our national creature has been making quite a mess is the Southern
most reaches of the Western Hemisphere. In the 1940s, Argentina was seeking
economic improvements and imported beavers, mink and muskrat to Tierra
del Fuego in an attempt to establish a fur
trade. That fur trade didn't turn out as expected. Within a few years, beavers
had colonized the entire island and were soon crossing channels to reach other
Chilean islands, including Cape Horn, a UNESCO
Biosphere Reserve.
 |
| Angry beaver -roar! |
The
ecological effects have been pretty well researched recently by Dr.
Christopher B. Anderson. In seeing if
beavers behave differently in their new habitat than back home, he’s been
finding a few differences in the environment and beavers here. One of the most
obvious changes is that the beaver colonies are at least twice as dense in Cape
Horn. Is this for lack of predators or an abundance of food? So far, I couldn’t
say, but I’d lean toward the latter. The Cape Horn forests are entirely
southern beeches, which provide ample resources for the beavers’ engineering
projects.
But
how disruptive have beavers been to the environment: and environment that has
no animal that makes such a massive environmental impact as the beaver. Howard
suggested that an animal moving into a habitat where its niche doesn’t exist
would have wider impacts than one who’s niche does exist. It’s fairly clear
that the beaver’s landscaping projects is not something that other animals
(except humans) partake in.
In
the beaver situation this ecological disruption holds true. The floral
assemblage in Cape Horn has never had to deal with beaver-like behaviour. The
beavers foraging and building habits prevent forest regrowth, and provide a
pathway for other plants to invade. It seems this beaver introduction might be
a good example of invasional
meltdown. The Chilean archipelago is home to
quite a few invasive species already, and this synergistic effect is definitely
concerning.
All the beaver-induced worries come with a grave concern for the
natural environment. Cape Horn is referred to as pristine quite a bit by
Anderson. Is this the place to have a deep political, socio-economic discussion
about “pristine” environments? No, not today; you’ll have to read elsewhere for that. Cape Horn is certainly already at risk from invasive species. Beavers
have a tremendous impact on the ecological structure of streams and forests. I
am certainly one to wonder whether the eradication effort can be truly successful and both removing the beavers and
reversing the environmental changes.
I surely hope that the environmental disruption can be reversed. Unfortunately
we cannot look back to Howard to speculate on what happens when we remove an
alien species. Just fifty years ago, species invasions were seen as a great
research opportunity, not something to be extensively managed or eradicated.
Further Reading:
C.B. Anderson et al.
(2006), The effects of invasive North American beavers on riparian plant
communities in Cape Horn, Chile. Do exotic beavers engineer differently in
sub-Antarctic ecosystems? Biological
Conservation, 128: 467-474.
doi:10.1016/j.biocon.2005.10.011
C. Choi, (2008) Tierra del Fuego: the beavers must die. Nature 453: 968. doi:10.1038/453968a
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