Monday, November 5, 2012

The Origin of (Exotic) Species

My friend Leighton’s comment on last week’s post – that beaver reintroduction to their native ranges by parachute outdoes dumping fish from airplanes – sparked my idea for this week’s post. Over the course of the past few centuries, there have been many intentional and inadvertent introductions of exotic (non-native) species to areas throughout North America. Some of these exotic species can be beneficial (depending on your viewpoint), some harmless, and some turn into invasives (i.e. non-native species that negatively impact the native ecosystem). Current estimates of the number of exotic species in the U.S. are around 50,000; around 4300 of these are considered invasives.

However, while we often hear about the impacts of exotic species, we don’t usually hear the interesting back-story that brought many of these species to their new homes in the first place. How did they spread? Was it on purpose or by accident? I’ve looked into the stories of several high-impact species that were introduced to North America to find out how they were first introduced, and what their impact has been.

European Honeybees: What’s all the buzz?
Honeybees first arrived in the U.S. in 1622, carried by ship with European settlers determined to have honey in their new home (I don’t blame them there). The only documentation that exists of this first bee introduction is found in a letter from the Virginia Company in London to the Governor of Virginia:
“Wee haue by this Shipp and the Discouerie sent you diurs [diverse] sortes of seedes, and fruit trees, as also Pidgeons, Connies, Peacockes Maistiues [Mastiffs], and Beehives, as you shall by the invoice pceiue [perceive]…”  (Goodwin 1956; Kingsbury 1906:532).
Along with the honeybees, settlers brought many of the agricultural crops that honeybees thrive on and pollinate, thus facilitating a change in the face of the American landscape. As European settlers moved west, many of the plant species with which they were familiar already abounded.  
Honeybees are crucial for pollinating many of the non-native agricultural crops that we rely on today. The advent of Colony Collapse Disorder is therefore extremely concerning, because it threatens the existence of many mainstay crops. However, there are also around 4000 species of (often overlooked) native bees in North America, and many native plants—such as tomatoes, eggplant, pumpkin, blueberries and cranberries—are more efficiently pollinated by these native bees than by honeybees.

Earthworms vs. Ovenbirds
European Earthworms: An Unlikely Suspect
For a species that most of us associate with good garden soil, the earthworm has a surprising dark side to its story. It was first introduced to the U.S. around 1620 in ship ballast (soil and gravel) that was dumped around Jamestown, Pennsylvania to make room for transporting popular American tobacco back to Europe. Earthworms are not native to the post-glacial forests of North America, which are characterized by thick layers of leaf litter. Once introduced to these forests, the silent underground invaders eat their way through the leaf litter, completely changing the face of the forest floor and the entire microbial cycle. This can have serious impacts on everything from native seedling success and tree species composition to native bird populations. One interesting case is the decline of the Ovenbird in the Midwest, which is being blamed on the earthworm; the Ovenbird is a ground-nester, and the decrease in leaf litter abundance is linked to increased predation risk (less shelter) and decreased food availability (bugs in leaf litter) for the Ovenbird. As earthworms continue to spread (mostly through bait-fishing, composting, and other means of human transport), they could potentially have large impacts on our forest ecosystems.

Shakespeare’s Songbirds: The Starling Saga
In 1890 a drug manufacturer (and Shakespeare fanatic) named Eugene Scheiffelin thought it would be romantic to introduce all the songbirds mentioned in Shakespeare’s works to New York City. Over the course of two years, he released 100 European starlings into Central Park. By 1942, their descendants had reached California. (He tried with thrushes and skylarks as well, but these birds failed to thrive).
Starlings are now a common sight in almost every city in the U.S. – they build their nests in cavities and vents, and thrive in urban landscapes. They are now mostly considered pests, and are linked to the spread of various diseases to both livestock and humans, mostly through their droppings. They can also pose serious safety risk to airplanes, as they fly in large murmurations (perhaps the best word ever for a group of animals), which can be quite visually impressive. Efforts to eradicate them have included artificial owls, electric wires, chemicals, broadcasted alarm calls, and recipes for Starling Pie. And yet they remain, perhaps even in your yard at this moment.

“Crazy Jumping Fish” (aka Asian Carp)
Asian Carp were first introduced to the United States by the U.S. Fish and Wildlife Service – this is an interesting example of how the mission and practices of environmental organizations can change as our understanding of and relationship to the environment changes. These fish were brought to the southern U.S. (Mississippi River in Arkansas) in 1963 as a tool to help aquaculture farms keep vegetation in check. By the 1970s, the carp had escaped the farms and spread northwards into the Illinois River.

Asian Carp jump up to 3m out of the water when startled (often by motor noise)
Asian Carp have become a huge problem in the rivers of the Mississippi basin, and currently threaten to invade the Great Lakes. They have a voracious appetite, and can consume up to 20% of their body weight per day in phytoplankton, which is significant considering they can reach 4 feet and 100 pounds. They also have a high reproduction rate, and compete with native fish species for habitat. In addition, these “crazy jumping fish” can be physically threatening to boaters (see YouTube video). And they have even inspired an important cultural contribution to America, in the form of the Redneck Fishing Tournament of Bath, Illinois.
The possibility of Asian Carp invading the Great Lakes is a serious threat – the Great Lakes support a large commercial fisheries industry – and both government and private agencies are working to come up with solutions to keep them out. One recent innovation is the use of an electrical barrier, implemented by the U.S. Army Corps of Engineers, to keep the carp out of Lake Michigan. So far it seems to be working, although there have been some reports of DNA evidence for carp above the barrier.

As with the case of the beavers mentioned earlier, a recent phenomenon is the re-introduction of native species back to natural historic ranges from which they have been extirpated (e.g. made locally extinct). The goal of these reintroductions is to restore the natural ecosystem, and often to bring back charismatic species that people feel “belong” in the landscape for sentimental (as well as environmental) reasons. This can become controversial in the case of large predators (wolf reintroduction to Yellowstone National Park, for example). But it has also inspired some interesting studies on the success of these reintroduced species (check out my friend's blog on Fishers in the Sierra), and success stories such as the reintroduction of California Condors to the Big Sur region of California. 


  1. That Asian carp video is the funniest thing I've seen all day! Good eating? ~Aiyana

    1. You'd hope they're good! I've never had them myself, but it looks like Illinois is taking advantage of them..