What triggers mass extinctions? Study shows how invasive species stop new life
Collapse of Earth's marine life 378 to 375 million years ago holds key
An influx of invasive species can stop the dominant natural process of new species formation and trigger mass extinction events, according to research results published today in the journal PLoS ONE.
The study of the collapse of Earth's marine life 378 to 375 million years ago suggests that the planet's current ecosystems, which are struggling with biodiversity loss, could meet a similar fate.
Although Earth has experienced five major mass extinction events, the environmental crash during the Late Devonian was unlike any other in the planet's history.
The actual number of extinctions wasn't higher than the natural rate of species loss, but very few new species arose.
"We refer to the Late Devonian as a mass extinction, but it was actually a biodiversity crisis," said Alycia Stigall, a scientist at Ohio University and author of the PLoS ONE paper.
"This research significantly contributes to our understanding of species invasions from a deep-time perspective," said Lisa Boush, program director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research.&
"The knowledge is critical to determining the cause and extent of mass extinctions through time, especially the five biggest biodiversity crises in the history of life on Earth. It provides an important perspective on our current biodiversity crises."
The research suggests that the typical method by which new species originate--vicariance--was absent during this ancient phase of Earth's history, and could be to blame for the mass extinction.
Vicariance occurs when a population becomes geographically divided by a natural, long-term event, such as the formation of a mountain range or a new river channel, and evolves into different species.
New species also can originate through dispersal, which occurs when a subset of a population moves to a new location.
In a departure from previous studies, Stigall used phylogenetic analysis, which draws on an understanding of the tree of evolutionary relationships to examine how individual speciation events occurred.
She focused on one bivalve, Leptodesma (Leiopteria), and two brachiopods, Floweria and Schizophoria (Schizophoria), as well as a predatory crustacean, Archaeostraca.
These small, shelled marine animals were some of the most common inhabitants of the Late Devonian oceans, which had the most extensive reef system in Earth's history.
The seas teemed with huge predatory fish such as Dunkleosteus, and smaller life forms such as trilobites and crinoids (sea lilies).
The first forests and terrestrial ecosystems appeared during this time; amphibians began to walk on land.
As sea levels rose and the continents closed in to form connected land masses, however, some species gained access to environments they hadn't inhabited before.
The hardiest of these invasive species that could thrive on a variety of food sources and in new climates became dominant, wiping out more locally adapted species.
The invasive species were so prolific at this time that it became difficult for many new species to arise.
"The main mode of speciation that occurs in the geological record is shut down during the Devonian," said Stigall. "It just stops in its tracks."
Of the species Stigall studied, most lost substantial diversity during the Late Devonian, and one, Floweria, became extinct.
The entire marine ecosystem suffered a major collapse. Reef-forming corals were decimated and reefs did not appear on Earth again for 100 million years.
The giant fishes, trilobites, sponges and brachiopods also declined dramatically, while organisms on land had much higher survival rates.
The study is relevant for the current biodiversity crisis, Stigall said, as human activity has introduced a high number of invasive species into new ecosystems.
In addition, the modern extinction rate exceeds the rate of ancient extinction events, including the event that wiped out the dinosaurs 65 million years ago.
"Even if you can stop habitat loss, the fact that we've moved all these invasive species around the planet will take a long time to recover from because the high level of invasions has suppressed the speciation rate substantially," Stigall said.
Maintaining Earth's ecosystems, she suggests, would be helped by focusing efforts and resources on protection of new species generation.
"The more we know about this process," Stigall said, "the more we will understand how to best preserve biodiversity."
The research was also funded by the American Chemical Society and Ohio University
Thursday, December 30, 2010
Looking through my frost covered windows into the snowy backyard, the plump red squirrels looked more like fancy Gund stuffed toys than the animate creatures they are. This was a banner fall for red oak acorns, and autumn’s invasion of red squirrels and ground-feeding yellow-shafted flickers into my pin oak-black oak-chinquapin oak urban backyard signaled a good mast year for the city block. Mast production of red oaks was great throughout the Ozark Highlands this year, and in some parts of the state white oaks fared well also.
Squirrels like fatty red oak acorns, but if the white oak acorns are more abundant, they will eat more of them just after acorn drop. Recent research has shown that squirrels will only eat the top part of the red oak acorn (about 60% of it) to avoid the concentrated tannins at the embyronic end. Even though squirrels eat the bulk of an acorn, the remaining part can still produce a tree. Estimates suggest that 74% of all buried acorns are never found again. White oaks send out taproots days and weeks after they fall, while red oaks sprout the following spring. Since the tannins in white oak acorns are concentrated in the taproot, squirrels tend to eat them first, and store red oak acorns for the winter; so, in good mast years like this one in parts of the Ozarks, squirrels are fattening up for a productive spring.
Historically, before the age of active fire suppression and livestock grazing in the woods (followed by annual burning and grazing), much of the Ozarks was dominated by white oak, white oak-black oak, or even white oak-post oak associations. Due directly to the lack of fire and a long history of grazing following European settlement, tree associations in the Ozarks favored a red oak-black oak dominance. Livestock are very hard on white oaks. It has been suggested that the now-extinct passenger pigeons played a significant role in the propagation of white oaks in Ozark woodlands, and it is widely accepted that squirrels and blue jays are largely responsible for planting the woodlands in red oak and black oak. Good for flooring, but not as desirable as white oaks for wildlife food.
Today, nodding a backwards glance towards the early days of the age of extraction, some in agribusiness and conservation industry suggest that grazing cattle in woodlands is beneficial for both woodlands and for growing protein. Grazing cattle in Missouri's native ecosystems is terribly destructive, and because of a long history of grazing following settlement, we have thousands and thousands of acres of out-of-context, destroyed, jacked up, trashed out, depauperate, unrestorable landscapes (that aren't even worth burning unless you're managing for buckbrush, annual weeds, poison ivy and oak sprouts). Grazing has changed the face of Missouri's native ecosystems forever, and not positively. Grazing cattle in woodlands is as conscientious for biodiversity as clearcutting Amazonian rainforests to grow steak.
Wednesday, December 22, 2010
I recognized several years ago that biodiversity in Missouri is doomed, totally unsustainable. It's very sad, actually, and on those dark winter days when birds aren't around (but hunkered into cedar boughs to wait out the clouds) it's nice to still be able to go to decent enough (but vast in scale) post oak woodlands managed for their highest and best use, for ecosystem protection above all else.
And winter botany is only fun when there's a biodiverse understory around: tall and rangy Lespedeza hirta, big, strapping Aster linariifolius stalks, Solidago juncea , switch grass and Indian grass and the bluestems, sweet everlasting with that distinctive scent, and a strange Muhlenbergia I've never seen before. A nice winter day in nice burned-5-times-in-15-years woods....
Saturday, December 18, 2010
Thick, crisp white snow carpeted the landscape during the Christmas Bird Counts today. Assigned to Section 6 of the COMO circle, I was treated to song sparrows by the droves, and thousands--around 9,000, actually--of waterfowl hanging out in the artificial wetlands outside of town. Among the 9,000 birds in the marsh were shovelers, pintail, thousands of mallards whose wingbeats above sent chills down my spine, wigeons, wood ducks, green-wing teal (about 200), coots, Virginia rails clucking in the yellow cattails, marsh wrens and swamp sparrows.
Highlights from the day came from the woodlands, my favorite landscape in all Missouri:
A hermit thrush flitting from branch to branch in a fencerow along the KATY Trail, the only speckled thrush that winters in Missouri in significant numbers. Wonderful birds with big, baleful eyes and a trim little beak
Super sleek and elegant multi-colored Lincoln sparrows eating monarda seeds
We spent so much time with the waterfowl that we didn't hit the woodlands until 10 am. We were imnmediately greeted by three darling golden-crowned kinglets offering their little meager pip! high up in a sycamore, finally moving down the tree so we could see them up close.
Bluebirds. It's hard to find a more brilliant blue in nature than the plumage of Eastern bluebirds. Four (3 males, one female) were seen in the canopy along a wooded section of Hinkson Creek, all basking in the bright late afternoon sun that literally electrified their colors.
The stark white chest of a brown creeper moved into view at the bottom of a hickory snag. He quickly danced up the tree, skirting from side to side.
One lone fox sparrow, the largest of the sparrows on our list, revealed himself to us in a tangle of vines along Perche Creek.
So it begins, the Christmas Bird Count season. Next up this week is the western Ozarks and hopefully so many red-headed woodpeckers that I start counting them by fives.
Monday, December 13, 2010
For the past few years, once, twice or thrice a week, I have had the great fortune to travel one of Missouri's deadliest roads, Highway 63, to head deep into the heart of the Ozarks. There's no way around traveling Hwy. 63 to do what I do during the week, and every time I do it, I end up with white knuckles, but grateful to arrive at my destination alive.
Among the highlights of the drive are small German Catholic communities that advertise on big plywood boards their Fall Suppers, Visitations (I don't know what those are, but I don't think they're associated with funerals), Holiday Suppers, and Festivals too numerous to count. I don't mind at all slowing down to 35 mph through Westphalia, home to one of the state's finest Nortons, and Freeburg, the town with the old general store that still functions quite well in its original 1800s white clapboard building.
But when you roll through Vienna at 35 mph between October and January, it's hard to miss the ranch style house located at the bottom of a gentle slope whose owners populate their mowed lawn with plastic figurines lit with small incandescent bulbs. In October, they set out pumpkins of all sizes, big black cats, and more pumpkins. As December rolls around, they pull out all the stops to celebrate Christmas.
I first noticed the army of Santas several years ago. Oh, there were 50 or more Santas, some clutching candy canes, others with an arm around a reindeer. The next year, there were more. A growing army of Santas and nativity scenes, more reindeer and candy canes all aglow with little single bulbs. Now, in 2010, I think the family of Christmas cheer has pulled out all the proverbial stops. Standing erect on this 5 degree night with snow on the ground and the Geminids ready to pierce the early morning sky, there must be 200 Santas in the front yard of all shapes and sizes, some duplicates, some vintage, but all happy Santas waving to the slow drivers on Hwy. 63. (Don't speed through these towns. The friendly Osage Co. law enforcement officials do not hesitate writing citations to out of town travelers. I've never received one because my car isn't physically capable of speeding....not that I would if it could....)
When such a great effort is made to decorate the outside of one's home with enough Santas to hand deliver gifts to every household in the county, surely the inside of the house is magnificent. These folks in Vienna are clearly chocked full of Christmas spirit, and it's contagious. I tried snagging my mom's 1960s Santa cum reindeer the last time I was in Louisiana, but we all suspect that someone in my neighborhood would steal it from my city yard if I displayed it. That's because I don't live in a German Catholic Ozark town.
Saturday, December 11, 2010
Wednesday, December 08, 2010
The Audubon Society organizes the CBC. The count takes place in designated circles, a set area that can encompass thousands of acres. Within that circle, birders fan out to count individual birds. So, after a full day of birding in Missouri, bird counts often reflect hundreds of cardinals, flickers and juncos with species counts ranging from 60 on the low end to 120 (usually those circles with significant waterfowl populations). One active count circle in Missouri was established in the 1960s, and data from each bird count is stored online. In this one area, for example, one can see how many pintail were there in 1965, how many brown creepers in 1980, and so on. Audubon uses the CBC information to track changes in North American bird populations; in recent years, for example, hooded merganser populations in New England have soared while grosbeaks have declined.
Christmas Bird Count circles are not common in the Ozarks, but go here to see if there's one around where you live. Don't be alarmed if you see a car full of birders glide past your property and staring at your feeders with binoculars.