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Are humans an invasive species? (photo courtesy of flickr user Mike PD)

Some readers of recent Smithsonian stories on wild pigs in Texas and the world’s worst invasive mammals list have argued that we may have left out the worst invasive species of them all: Homo sapiens. But are humans really an invasive species?

Let’s start with the definition of an invasive species. It turns out, it’s not so simple. The legal definition in the United States is “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” The International Union for Conservation of Nature (IUCN), which developed the list of the 100 world’s worst from which our invasive mammals piece originated, defines them as “animals, plants or other organisms introduced by man into places out of their natural range of distribution, where they become established and disperse, generating a negative impact on the local ecosystem and species.” And a 2004 paper in Diversity and Distributions that examines the terminology of invasiveness notes that their is a lack of consensus on this topic and lists five dominant definitions for ‘invasive,’ the most popular of which is “widespread [nonindigenous species] that have adverse effects on the invaded habitat.”

Despite the lack of a single definition, however, we can pull from these definitions some general aspects of an invasive species and apply those to Homo sapiens.

1) An invasive species is widespread: Humans, which can be found on every continent, floating on every ocean and even circling the skies above certainly meet this aspect of invasiveness.

2) An invasive species has to be a non-native: Humans had colonized every continent but Antarctica by about 15,000 years ago. Sure, we’ve done some rearranging of populations since then and had an explosion in population size, but we’re a native species.

3) An invasive species is introduced to a new habitat: Humans move themselves; there is no outside entity facilitating their spread.

4) An invasive species had adverse effects on its new habitat and/or on human health: Humans meet this part of the definition in too many ways to count.

Verdict: We’re not an invasive species, though we’re certainly doing harm to the world around us. If you think about it, all of the harm done by invasive species is by definition our collective faults; some kind of human action led to that species being in a new place where it then causes some harm. And so I’m not at all astonished to find people arguing that we’re the worst invasive species of them all.

A female striped plateau lizard shows off her mothering potential (credit: University of Puget Sound)

Good moms make sure their kids eat well. Lizard moms only get one chance to do that; in most species, their mothering ends when they lay their eggs. So their one and only chance to be a good mom is to create high-quality eggs, and particularly ones with higher levels of antioxidants. But lizard dating isn’t particularly drawn out and a female lizard needs a quick way to tell a potential mate she’d make a good mom. How does she do it?

Female striped plateau lizards (Sceloporus virgatus), which live on the rocky slopes of mountains in southeastern Arizona, do this with bright orange patches underneath the jaw. Scientists from the University of Puget Sound and elsewhere, reporting in the Journal of Animal Ecology, found that the size of those patches correlates with the concentration and amount of antioxidants in the yolk of her eggs, and the richness of color with antioxidant concentration.

“Thus, in female S. virgauts, female ornaments [the orange patches] may advertise egg quality. In addition these data suggest that more-ornamented females may produce higher-quality offspring, in part because their eggs contain more antioxidants,” said lead author Stacey Weiss, of the University of Puget Sound.

That advertising appears to work; previous research has shown that male striped plateau lizards prefer females with darker orange spots.

Cold this winter? At least you're not in Antarctica. (Photograph by: Kristina 'Kricket' Scheerer, courtesy of National Science Foundation)

With another frigid winter, complete with a snowstorm dumping on D.C. this week, I’m trying to remind myself that there are far worse places for someone like me who can’t stand the cold. Take the South Pole, where winter temperatures can reach more than 100 degrees Fahrenheit below zero. Even summer rarely sees temperatures in positive numbers. Strong winds blow across the plateau, and the night lasts for six months. Captain Robert Scott, who died in his attempt to reach the South Pole, wrote in 1912: “Great God! this is an awful place and terrible enough for us to have laboured to it without the reward of priority.”

But a team of scientists and support personnel now lives at the South Pole around the year, weathering even the depths of the polar winter. What advice might they give about surviving life in such a cold and barren place?

1)  Be prepared: Everyone who leaves the McMurdo Research Station and heads out to somewhere else on Antarctica, like the South Pole, must first complete the “Happy Camper” training course. Trainees spend two days and a night out on the ice learning about potential threats, such as frostbite and hypothermia, and how to protect themselves by building things like wind walls and survival trenches. Having the right gear helps, but it’s no use without knowing what to do with it.

2)  Dress warmly: Layers, layers and more layers. When writer Richard Panek visited scientists studying dark energy at the South Pole, he described them wearing “thermal underwear and outerwear, with fleece, flannel, double gloves, double socks, padded overalls and puffy red parkas, mummifying themselves until they look like twin Michelin Men.”

3)  Don’t get wet: Water is a better conductor of heat than air is, so if a person falls into water, even relatively warm water, they are at risk of developing hypothermia—when the body’s core temperature falls below 95 degrees—if they don’t get out and get warm and dry quickly. At least the South Pole is far away from any liquid bodies of water.

4)  Stay hydrated: Antarctica is a desert; low humidity and high winds sap the moisture out of a person. Chapped skin is common. But more importantly, dehydration can contribute to hypothermia and frostbite.

5)  Eat well: Even with all those layers or just staying indoors, keeping warm requires more energy than normal. Residents at the South Pole Station eat the same kinds of food they eat at home (they even have a hydroponic garden for fresh veggies), but outdoor snacks have to be something that can be eaten frozen. One resident wrote:

When I first arrived in Antarctica, I was surprised that whenever any one went out for a trip—a few hours or all day—they only ever took chocolate bars to eat. I was most unimpressed with how unhealthy this was, so when I went on my first trip I made some wholesome and nutritious sandwiches (tuna and mayonnaise on wholemeal bread—I remember it well).

Come lunch time, my companion got out his chocolate bar and proceeded to eat it, I got out my sandwiches and after 5 minutes of sucking a frozen corner gave up and resorted to chocolate. Thankfully my companion didn’t ROFL, but I didn’t bother with my healthy option again!

6) Mark your path: In the dark and blinding winds, it’s possible to lose your way, even if your way is relatively short. At the South Pole, paths from research facilities to the base station where everyone lives are marked with lines of flags on poles.

7)  Have a warm place to stay: A tent or igloo will do in a pinch, but as of 2008, South Pole residents make their home in a modern base station complete with private rooms, computers and televisions, even a gym with a basketball court.

Visitors to the National Museum of Natural History framed by the megalodon jaw (photo courtesy of flickr user Ryan Somma)

If the movie Jaws scared you away from swimming, perhaps you should avoid the “Journey through Time” section of the Sant Ocean Hall at the National Museum of Natural History. There you’ll find a collection of fossil marine life dating back as far as 500 million years ago. In one case is possibly the scariest item in the place—the jaw of a giant great white shark, Carcharadon megalodon, opened wide enough to take in a few adult humans at once and with rows of teeth as big as my hand. It’s no wonder that these fossils have inspired a series of bad sci-fi films.

We can all sleep easy, though; megalodon lived 25 to 1.5 million years ago and is long gone from today’s oceans.

Megalodon was the world’s largest shark, growing to 60 or 70 feet in length and 77 tons in weight. It roamed warm oceans (fossils have been found all over the world) eating around 2,500 pounds of food each day, scientists have estimated, including fish and whales. One 2008 study calculated that this giant shark had a bite force of 12 to 20 tons, about 6 to 10 times that of modern great whites.

What led to their demise? Scientists aren’t sure, but the chief suspect is shrinking habitat. When this shark lived, the world was forming into the one we now recognize—the Himalayas and Rockies were growing, the Isthmus of Panama rose from the sea to separate the Atlantic and Pacific, then massive glaciation locked much of the world’s water in ice. Everything was changing for the big sharks, possibly including what they ate and where they raised their kids, and they just couldn’t survive in the new world.

Rumors of megalodon’s survival persist on the Internet. But no live specimen, or even fresh teeth, has ever been found, making it pretty unlikely that this shark still exists.

A Sunda clouded leopard caught in a camera trap on Borneo (photo courtesy of Wilting & Mohamed, Sabah Wildlife Department, Sabah Forestry Department)

Clouded leopards—named for their large, cloud-like spots—are rare. They are medium-sized (a bit bigger than a housecat) tree dwellers with big teeth and big paws that let them hang upside down among the foliage. In 2006, scientists used DNA studies to determine that there were two species of clouded leopards: Neofelis nebulosa, which lives on the Asian mainland and is the subject of a breeding program at the National Zoo (producing some of the world’s most adorable kittens), and Neofelis diardi, the Sunda clouded leopard, found on the islands of Borneo and Sumatra.

Now a group of researchers led by the Leibniz Institute for Zoo and Wildlife Research in Germany has determined the the Borneo and Sumatra populations are really two separate subspecies, splitting this rare kitty into two even rarer varieties. The scientists, reporting in Molecular Phylogenetics and Evolution, analyzed DNA from 15 leopards on Borneo and 16 on Sumatra and also examined the skulls and coats of museum specimens. They found that the kitties on the two islands looked very similar on the outside but had significant differences in skull shape and in their genetics.

The scientists aren’t certain about the events that led to the evolution of the various species and sub-species, but here’s what they propose: The ancestor species to all modern clouded leopards was living in Southeast Asia when the super-volcano Toba erupted on Sumatra around 75,000 years ago, possibly plunging the Earth into a years-long volcanic winter. Two populations of clouded leopards survived—one in southern China, which evolved into the modern-day clouded leopard, N. nebulosa, and one on Borneo, which became the Sunda clouded leopard, N. diardi. When sea level was low, some of those Sunda clouded leopards were able to travel back to Sumatra, but when the last Ice Age ended, around 10,000 years ago, and sea levels rose, Borneo and Sumatra were once again isolated from each other and the two populations were left to evolve into sub-species apart from each other.