Archive for January, 2017

Panthera atrox: the 1007 Pound Giant Lion

January 31, 2017

An extinct species of lion ( Panthera atrox ), similar but larger than the extant African lion ( P. leo ), occupied open habitat in North America from California to South Carolina and Florida for over 300,000 years.  The American lion evolved from the also extinct Eurasian cave lion ( P. spelea ) when the ice sheet that covered Canada isolated the 2 populations from each other. The 2 species never re-connected during interglacials because extensive spruce forests, an unfavorable habitat for lions, grew between them.  Fossil evidence of large carnivores is relatively uncommon because their populations are smaller than those of their prey. But there are 2 fossil sites that preserved a considerable number of carnivores due to unusual circumstances, and scientists were able to collect enough lion specimens from them to study and compare the anatomy of the species as a whole.  The 2 sites are Natural Trap Cave in Wyoming and the Rancho La Brea Tar Pits in California. Scientists estimated average body size and the results were astounding.

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Hercules is the world’s largest cat. It is a 922 pound lion x tiger hybrid that lives at the Myrtle Beach Safari Preserve in South Carolina.  It is smaller than the estimated size of the largest known fossil specimen of North American lion, an extinct species that formerly lived coast to coast.

The largest male Panthera atrox specimen came from an animal that was estimated to weigh 1007 pounds, though the average male weighed 544 pounds.  The largest female American lion was estimated to weight 577 pounds, while the average was 390 pounds.  By contrast the average extant African male lion weighs 392 pounds.  This means the average female American lion was about the size of the average male African lion.  The large difference in size between the sexes, known as sexual dimorphism, suggests American lions lived in social prides like their African cousins.  An 1000 thousand pound lion would be too large and slow to hunt successfully enough to sustain its bulk, but instead relied on the smaller more agile females to secure all the bison, horses, and camels he required.  A large pride could probably even take down a full grown mammoth.

The large size of the males helped them fend off other male lions that wished to usurp their mating rights and kill their offspring.  The enormous powerful males could also aid in protecting the pride’s kills from competing carnivores such as bears, saber-tooth cats, and dire wolves.  American lions had longer legs and bigger braincases than African lions, so they were faster runners and smarter as well.  P. atrox really was a king of the beasts.

Reference:

Wheeler, H.T; and G.T. Jefferson

Panthera atrox: Body Proportions, Size, Sexual Dimorphism, and Behavior of the Cursorial Lion of the North American Plains.”

In Papers on Geology, Vertebrate Paleontology, and Biostratigraphy in Honor of Michael O. Woodburne edited by L.B. Albright III

Museum of Northern Arizona Bulletin 65

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Mammoths and Mastodons were Year Round Residents of the Ohio River Valley during the Late Pleistocene

January 27, 2017

The bones and teeth of an extinct animal provide scientists with information about the life history of that particular individual.  Recently, 2 scientists analyzed the chemistry of 8 mammoth ( Mammuthus columbi ) and 4 mastodon ( Mammut americana ) teeth collected from Hamilton County, Ohio and Bullitt and Gallatin Counties, Kentucky–in other words, the Cincinnati area.  They determined 11 of these animals spent their entire lives in what was to become the Cincinnati area.  They also learned 7 of the mammoths ate different plant foods than the mastodons, but the diet from 1 individual mammoth did overlap with mastodon diets.

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Hamilton County, Ohio

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Mammoths and Mastodons lived year round in the Ohio River Valley.  They were 2 completely different species of proboscidean.

Scientists are able to determine where an animal lived during its lifetime by measuring the ratio of strontium and strontium isotopes in their teeth.  Strontium leaches from local bedrock into the water supply, and animals absorb the strontium into their bones when they drink.  Different geographical regions exhibit different ratios of strontium isotopes, so it’s possible to figure out where an animal spent time during its life.  A previous study of mastodon and mammoth teeth collected from Florida determined mastodons there migrated back and forth from central Florida to central Georgia, while Florida mammoths did not migrate.  But this study suggests most of the mastodons that lived in the Ohio River valley did not migrate.  However, there were exceptions.  The strontium ratio from 1 specimen indicated this individual wandered north from either north Georgia or southern Tennessee to the Ohio River valley.  The authors of this study estimated this could have been accomplished in as little as 5 days based on how fast modern elephants can travel.

The bone chemistry tells us mammoths mostly ate grass, while mastodons ate plants that grew in forested environments.  But again there was 1 exception–1 mammoth that fed upon forest vegetation.  During the Last Glacial Maximum much of this region was a cool arid steppe environment.  After the nearby ice sheet retreated, the steppe was transformed into an open spruce parkland, then eventually an oak and hardwood dominated forest.  This mammoth apparently adapted to the latter changes.

Mammoths and mastodons had no need to migrate away from the Ohio River.  The rich floodplain habitat and numerous mineral licks provided enough nutrition to support year round populations of both.

Reference:

Baumann, Eric; and Brook Crowley

“Stable Isotopes Reveal Ecological Differences among now Extinct Proboscideans from the Cincinnati Region, USA”

Boreas 2015

Donald Grayson’s Disingenous Case Against Overkill

January 23, 2017

I almost chose not to read Donald Grayson’s most recent book, Giant Sloths and Sabertooth Cats: Extinct Mammals and the Archaeology of the Ice Age Great Basin.  Grayson is a long time skeptic of the hypothesis that man overhunted Pleistocene megafauna to extinction, and he has authored and co-authored a number of papers explaining his position.  In my opinion overhunting by man is the only explanation for the extinction of Pleistocene megafauna that makes sense.  I’ve read his papers and consider his arguments highly illogical and unfair.  But I did purchase his book because I try to absorb all the knowledge I can about my favorite subject–the late Pleistocene ecology of North America.  I don’t have to agree with an author about everything to enjoy their work.  I saw his chapter on extinction was short, just a small portion of the book, and I assumed he would simply rehash his tired old case against overkill.  However, I was shocked at the way he misrepresented the results of a paleoecological study.  He implies the results of this study support climate change models of Pleistocene megafauna extinctions.  In fact this paper specifically states the opposite.

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Donald Grayson’s newest book.  His chapter on extinction is marred by gross deception.

Don Grayson, photo by Mary Levin, UW Photography, 2011

Donald Grayson is an archaeology professor at the University of Washington.  

On page 287 of the above book, Grayson wrote “…paleoecologist Jacquelyn Gill and her colleagues took a close look at tiny bits of Ice Age history extracted from 3 lakes and marshes in New York and Indiana.”    Grayson fails to mention the data from the lakes in New York was gathered in a study led by Guy Robinson (1).  (I will number the studies mentioned in this blog post and list them below.)  Guy Robinson’s team took samples of sediment from some New York lakes and marshes, radiocarbon dated different chronological layers of it, and measured and analyzed the volume of pollen, charcoal, and dung fungus spores in each layer.  The volume of dung fungus spores is used as a proxy to estimate populations of megafauna.  They determined local extinctions of megafauna were staggered throughout 2 thousand years, and they concluded this ruled out climate change as a cause of the megafauna extinctions.  If climate change caused the extinctions, they believed the extinctions at these different sites would be simultaneous.  Instead the local extinctions occurred at different times at different sites, and it appears as if nomadic humans were overhunting megafauna at 1 site, then moving on to another, though these local extinctions occurred shortly before the Clovis cultural era.  Increases in charcoal while megafauna populations were declining is additional evidence of probable human impact.  Jacquelyn Gill, the lead author of the paper (2) Grayson referred to in his book,  details a similar study of an Indiana lake.  The authors of this study also found that megafauna populations declined before the Clovis cultural era but also before climate caused changes in the local plant composition.  They believe human impacts are still a “plausible” cause of megafauna extinction, and they wrote “our data thus rule out the hypothesis that (i) climate-forced changes in vegetation drove the megafaunal decline, and (ii) no-analogue plant communities were created by megaherbivory.”  Megafauna became locally extinct here before the pollen evidence suggests changes in the plant community occurred.  They believe humans can still be implicated in megafauna extinctions at this site because increases in charcoal indicated humans were setting fire to the landscape during the period of megafauna decline, and there is evidence of human butchery of mammoths in southeastern Wisconsin during this same time period, suggesting that humans were likely hunting them at this location as well.

It is very dishonest of Grayson to imply these studies support climate-change models of extinction when the authors of these studies specifically state the opposite.  He should have at least informed his readers of their conclusions and explain why he has a different interpretation of the data.  The authors of these studies do note that megafauna decline occurred during a warm phase of climate, but they believe, if climate played a role, it had to be some other mechanism besides climate-driven changes in the environment.  The accepted logic behind climate change models of extinction is that changes in climate decreased the plant foods necessary to maintain viable populations of megaherbivores.  These studies show this is not the case.  Moreover, fossil coprolites show the plants Ice Age megafauna ate are still common on the landscape today, and isotopic studies indicate they were not picky feeders, but instead ate a wide variety of foods.  I think the warm climate phase provided a greater variety of edible plant foods for humans, thus increasing human populations which in turn was detrimental to megafauna.

There are many regions in North and South America where the environment did not change substantially during the most recent glacial-interglacial transition including the pampas of Argentina, southern California, and southeastern North America, especially Florida and the coastal plain.  Climate change models of extinction just don’t make sense in these regions.  Most species of megafauna enjoyed continent wide distributions, and they endured 30 glacial-interglacial transitions over the past 2 million years without suffering extinctions, yet they did become extinct about the same time man appears in the archaeological record.  This can’t be coincidence.

Grayson focuses his arguments against overkill on the Clovis blitzkrieg model of extinction.  This model proposes humans rapidly overhunted megafauna to extinction within the 500 year period of the Clovis cultural era.  There is another model of overkill: humans were responsible for overhunting megafauna, but it took place over several thousand years and also involved a change in fire regime and other human impacts.  This is known as the protracted overkill model and it is the one I favor.  Grayson ignores this model.  He doesn’t acknowledge the likelihood that pre-Clovis humans impacted megafauna populations.  I’m sure he would point out the lack of archaeological evidence for this.  His main objection to the blitzkrieg model is also a lack of archaeological evidence…he believes there are not enough kill sites (direct evidence that humans killed a beast) to justify the overkill hypothesis.  This objection is unreasonable.  99.999…etc% of the individuals of a species that ever lived left no fossil evidence at all.  It is ridiculous to expect to find fossil evidence of the last individuals of a species that just happened to be killed by men.  Moreover, Grayson never quantifies how many kill sites archaeologists would need to find before he would be convinced humans were responsible for the demise of the megafauna.  He needs to put an exact number on it or cease his objections.  Despite the odds against it, there are numerous kill sites and evidence of human-butchered megafauna bones.  Grayson dismisses over half of them, sometimes unfairly, though sometimes his skepticism is warranted.

Grayson falsely claims the overkill hypothesis has “little going for it” and he sounds annoyed on pages 279 and 280 of his book when he laments its acceptance in the popular media.  He might be annoyed because in recent years the  overwhelming number of paleoecological and statistical studies suggest man at least played some role in megafauna extinctions.  Grayson glosses over a statistical study led by G.W. Prescott (3) that determined both man and climate played a role in the end Pleistocene extinctions.  But 2 recent studies of worldwide extinction chronology (4) (5) determined extinctions are more closely tied to human expansion than climate change.  In the study led by C. Sandom they note extinctions have been severe in climatically stable regions.  They write: “Human arrival was a necessary factor for extinctions, whereas climate variation was a contributory one, enhancing regionally the effects of anthropogenic impacts on additive rather than synergistic ways.”

References:

(1) Robinson, G.S. ; L.P Burney and D.A. Burney

“Landscape Paleoecology and Megafaunal Extinction in Southeastern New York”

Ecological Monographs 2005

(2) Gill, J.L.; J.W. Williams, S.T. Jackson, K.B. Lininger, and G.S. Robinson

“Pleistocene Megafauna Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America

Science 2009

(3) Prescott, G.W. et. al.

“Quantitative Global Analysis of the Role of Climate and People in Explaining Late Quaternary Extinctions”

PNAS 2012

(4) Aravjo, Bernardo et. al.

“Bigger Kill than Chill: the Uneven Roles of Humans and Climate on Late Quaternary Megafaunal Extinctions”

Quaternary International 2015

(5) Sandom, C. et. al.

“Global Late Quaternary Megafauna Extinctions Linked to Humans, not Climate Change”

Proceedings of the Royal Society 2014

http://rspb.royalsocietypublishing.org/content/281/1787/20133254

 

A Recent Study of Pleistocene Armadillo DNA Yields 2 Surprising Results

January 19, 2017

An extinct species of armadillo ( Dasypus bellus ) ranged throughout southeastern North America during the Pleistocene.  (A much larger species, Holmesima septentrionalis, was restricted to Florida and the lower coastal plain.)  Scientists have described D. bellus , known by the common name of beautiful armadillo, as being remarkably similar to the extant 9-banded armadillo ( D. novemcinctus ).  The most notable difference between the 2 species is size–the beautiful armadillo was twice the size on average as the 9-banded armadillo.  The latter species began to expand its range into southeastern North America from Mexico within the last 150 years, and today is very common and on the increase in the region.  In a previous blog entry I hypothesized the 9-banded armadillo was a dwarf mutation of the beautiful armadillo, and it was currently recolonizing former parts of its range.  (See: https://markgelbart.wordpress.com/2012/08/19/is-the-9-banded-armadillo-dasypus-novemcinctus-a-dwarf-mutation-of-the-pleistocene-species-dasypus-bellus/ ) However, scientists were recently able to extract DNA from 2 Pleistocene-aged armadillo specimens, and they determined the history of the 2 Dasypus species is more complicated and even more interesting than previously thought.

An armadillo I saw at Scull Shoals State Park, Georgia.  2 species of similar armadillos occupied southeastern North America during the Pleistocene including this 1.

Scientists extracted DNA from an armadillo specimen found in Brynjulfson Cave, Missouri and from another specimen excavated from Medford Cave, Florida.  (They tried many other specimens but these were the only 2 that still yielded viable DNA.)  They determined the DNA of the Missouri specimen was distinct enough from modern 9-banded armadillo DNA to be considered a distinct species.  So much to my surprise, the beautiful armadillo is not the same species as the 9-banded armadillo.  But the Florida specimen held an even bigger surprise…it was a 9-banded armadillo and it dated to over 10,000 years ago.  This means both beautiful armadillos and 9-banded armadillos lived in southeastern North America during the Pleistocene.  The former went extinct while the latter was temporarily extirpated from the region but has just recently made a comeback.

The scientist who originally described the specimen from Florida noted its similarity to the 9-banded armadillo but chose to identify it as a beautiful armadillo because that was the species thought to occur there during the Pleistocene.  This individual was as large as a beautiful armadillo, showing that size alone is not enough to diagnose correct species identification.  Unfortunately, most subfossil specimens no longer contain DNA due to permineralization or decay.  All the specimens labeled ” D. bellus ” in the scientific literature should be re-labeled as ” D. species ” until scientists make a more detailed anatomical analysis of the genus, so that these 2 species can be better distinguished.

So why did the 2 species disappear from southeastern North America near the end of the Pleistocene?  Cold arid climate cycles probably caused range reductions and local extinctions, but armadillos likely re-expanded during warmer wetter climate phases.  Today, 9-banded armadillos may use manmade roads to facilitate their range expansion because it’s less strenuous to travel along cleared roadsides (though dangerous because highways are littered with armadillo corpses). During the Pleistocene armadillos probably followed trails trampled clear by herds of megafauna. This facilitated range expansion during favorable climate cycles.  The extinction of the megafauna may have played a role in the demise of armadillos that could no longer expand their range after climate deterioration caused extirpations. This isn’t a completely adequate explanation–Florida never got too cold and dry for armadillos.  The authors of the below referenced study suggest frequent manmade fires may have been detrimental to armadillos.  Native Americans set fire to the woods annually.  Modern day fire suppression may be another reason 9-banded armadillos have been able to recolonize former territory.

Reference:

Shapiro, Beth; Russell Graham, and Brandon Letts

“A Revised Evolutionary History of Armadillos (Dasypus) in North America Based on Ancient Mitochondrial DNA”

Boreas August 2014

 

 

 

 

Pleistocene Mammals of the Levant

January 14, 2017

Long before the stories in the bible supposedly took place, the Levant was a beautiful wilderness sparsely populated by humans.  The Levant is the region encompassing the modern day boundaries of Israel, Lebanon, Syria, Jordan, and Iraq.  For millions of years climatic fluctuations have caused a waxing and waning of 2 different types of environments here–Mediterranean evergreen oak woodlands and Irano-Turanan steppe consisting of deciduous oak trees and grassy understories.  Habitat for both forest species and grassland fauna has been available during every climatic stage.  The region is also a gateway between Eurasia and Africa, so animals from 3 continents converge here, making it rich in diversity.  African species such as elephants, giraffes, rhinos, hippos, gazelles, hartebeest, warthog, macaque, hyena, lion, leopard, cheetah, and Cape Hunting dog formerly lived side by side with Eurasian species including aurochs, bison, horse, ass, camel, deer, wild boar, ibex, wolf, and brown bear.

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Map of the Levant.

The fossil record suggests the fallow deer ( Dama dama ) was the most common large herbivore in the Levant for over 2 million years.  This species prefers fairly dense woodlands, so their abundance in the fossil record surprises me because I always think of this region as arid.  However, during Ice Ages, the climate in the Levant was cooler and rainier than it is today, though drier climate phases did occur cyclically.  The extinct giant deer ( Megaloceros giganteus ) and elk ( Cervus sp. ), known as red deer in Europe, also made the Levant their home.  The wild ibex ( Capra aegargus ), ancestor of the domestic goat ( C. hircus ), was common on rocky hillsides; gazelles, hartebeest, and an extinct species of warthog roamed the grassy plains.

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Fallow deer.

During warmer climate cycles hippos inhabited Lake Kinnaret.  Long chains of lakes often existed along the Jordan River, and during some climatic stages Lake Kinnaret joined the extinct Lake Amora and the Dead Sea to become 1 giant primeval lake known as Lake Lisan.  Oddly enough, geologists believe Lake Lisan was a freshwater lake in the part that covered the current site of Lake Kinnaret, while the rest of the lake was salty.

A primitive genera of elephants known as stegodon became extinct in Africa about 1 million years ago, but they still lived in the Levant for hundreds of thousands of years past their African extinction.  Stegodon survived until the end of the Pleistocene in southeastern Asia.  Two species of elephants roamed the Levant during the Late Pleistocene–the steppe mammoth ( Mammuthus trogontherii ) and the straight-tusked elephant ( Paleoloxodon antiquus ).  The former evolved into the woolly mammoth during a later Ice Age.  Straight-tusked elephants were a temperate species that couldn’t survive the climate deterioration of the last Ice Age in most of Eurasia.  However, the Levant probably provided a refuge for this species then.  I hypothesize humans overhunted straight-tusked elephants to extinction in their final refugia.  And I believe the same fate befell the temperate species of rhino ( Stephanorhinus hemiotoechus ) that occurred throughout Eurasia.  The Levant likely served as a refuge for these 2 species of megafauna during previous glacials, but human populations and/or hunting skills increased enough to permanently eliminate these slow breeding animals sometime within the timespan of the most recent Ice Age.

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Stegodon.

The lion ( Panthera leo ) that lived in the Levant was the same subspecies as the Asiatic lion found today in 1 small area of India–the Gir Forest.  This big cat survived in remote regions of the Levant until the 19th century.  There is still a small population of leopards in the Levant.  Two species of wolves ranged through the Levant–the timber wolf ( Canis lupus ) and the Egyptian wolf ( C. lupaster ).   Though the latter species occasionally interbreeds with golden jackals ( C. aureus ), a genetic study determined they are more closely related to C. lupusA single specimen of Cape Hunting dog ( Lycaon pictus ) was excavated from Hayonim Cave, Israel.  The paper written about this site incorrectly states this as the only fossil material of Cape Hunting dog ever found outside Africa, but fossils of closely related species have been discovered in Alaska and Texas.

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Asiatic lions in Gir Forest–the same subspecies lived in the Levant until the 19th century.

Pleistocene megafauna suffered fewer extinctions in the Levant than in the Americas.  Wildlife there co-occurred for a longer time with low populations of primitive humans and had time to evolve better avoidance strategies.  Moreover, many Levant species that did become extinct in the wild still live on as domesticated descendents.  Nevertheless, most of the megafauna species were extirpated from the Levant by the 20th century.

References:

Marder, Ofer; et. al.

“Mammal Remains of Rantis Cave, Israel and mid to late Pleistocene Paleoenvironment and Subsistence in the Levant”

Journal of Quaternary Science 2011

Stimer, Mary; and Ofer Bar-Yozef

“The Fauna of Hayonim Cave, Israel: A 200,000 Year Record of Paleolithic”

American School of Prehistoric Research 48 2009

The Continent Conquering Human Flea (Pulex irritans)

January 8, 2017

A flea can jump 160 times its own body length–the equivalent of a 6 foot tall human jumping the length of over 3 football fields.  Most of the known 2500 species of fleas are ectoparasites that use this phenomenal jumping ability to leap from the ground to an host or from one host to another.  Scientists believe the human flea was originally a parasite of wild cavies, species of rodents native to South America.  9,000 years ago, South American Indians began domesticating a species of cavy, either Cavia tschudii or C. aperearesulting in the well known household pet, the guinea pig ( C. porcellus ).  The domestication process may have been instigated by the cavies rather than humans.  Cavies likely were attracted to the shelter of human dwellings where they fed on vegetal kitchen scraps.

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The human flea expanded to many times its size. Their toes serve as a lever that helps them jump many times their body length.

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The guinea pig is thought to be the original host of the human flea.  Fur traders spread the flea from South America to North America and across the Bering Strait to Asia.

By 7,000 years ago, guinea pigs were commonly raised in many South American Indian households.  Maintaining a population of 20 individuals yielded about 12 pounds of meat per month, so they served as a valuable source of food, lessening the need to hunt wild animals.  Fleas from guinea pigs made the leap to man and from there they conquered 5 continents.  According to the lead author of the below referenced study, they advanced through a “step by step gift exchange of furs from South to North America and over the Bering Strait.”  Fur traders slept on their skins and left flea larva living in the detritus of flea feces, dried blood, and human skin flakes that accumulated on their unwashed beds.  After mature fleas feed on blood, they lay their eggs in this detritus.  Human fleas were carried along Asian trade routes and they conquered Egypt by 6000 BP.  The Roman armies carried fleas from Egypt to southern Europe, and the Vikings may have carried fleas from North America to northern Europe.

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Roman legions and Vikings carried fleas with them to Europe.  Bubonic plague carried by fleas from rats to humans and back depopulated Europe.  Fleas were responsible for far more deaths than Romans and Vikings.

Human fleas made a colossal impact on human history.  Fleas jumping back and forth between rats and humans spread bubonic plague, a disease that killed an estimated 30%-60% of the European population during the years 1347-1350.  Much of Europe reverted back to wilderness following this depopulation.  The Romans and the Vikings thought they had conquered the world, but they are long gone.  Human fleas are still here and can be found in just about every hotel, even in the finest, most expensive chains.

Reference:

Panagiotakopulo, Eva; and Paul Buckland

“A Thousand Bites–Insect Introductions and Late Holocene Environments”

Quaternary Science Reviews November 2016

The Super Squirrel

January 3, 2017

The eastern gray squirrel ( Sciurus carolinensis ) outlasted many of the magnificent extinct species of Pleistocene megafauna because they are well adapted to survive in environments modified by man.  They are just as much at home in suburbs, city parks, and 2nd growth forest of the countryside as they are in the middle of a pristine wilderness.  Unlike western gray squirrels ( S. griseus ), they are not shy around man and will nest in backyards or even attics.  They are nimble squirrels, able to jump from tree top to tree top in the young dense forests that replace abandoned agricultural lands.  And they have a unique way of spreading their populations.  Every September, juvenile eastern gray squirrels begin to expand their range and forage for acorns and nuts.  After they have spent enough time  burying acorns in a certain area, they establish an home range there.  This process is known as the “September shuffle.”  During colonial times when there were still vast tracks of timber, this September shuffle could seem like a massive migration, especially during years of poor mast production following a year of heavy mast production that increased squirrel numbers. (See: https://markgelbart.wordpress.com/2012/08/24/squirrel-migrations/ )

Eastern gray squirrels thrive everywhere they’ve been introduced–England, Ireland, Italy, South Africa, western Canada, and Australia (where they were eventually eradicated by man).  Much to the consternation of English naturalists, they have almost completely displaced native European red squirrels ( S. vulgaris ) on the British Isles.  There are several possible reasons for this displacement.  Eastern grays are carriers of a virus that may be fatal to European red squirrels.  They may also disrupt red squirrel mating and outcompete them for food, and they are simply better adapted to living adjacent to people.  But the most compelling ecological explanation involves comparing European and American Ice Ages.

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The American eastern gray squirrel in Brandon Hill Park, Bristol, England.  Gray squirrels are better adapted to living in deciduous woodlands than native red squirrels and they are displacing them.

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The Eurasian red squirrel is being displaced by introduced American gray squirrels in Great Britain and Italy.

In Europe glaciers covered a greater percentage of territory than they did in North America.  Most of the unglaciated region consisted of grassy or shrubby mammoth steppe with pockets of spruce and pine growing in moist protected areas.  Some southerly lowlands supported more extensive conifer forests.  The deciduous oak forests that dominate most of Europe today were restricted to narrow strips along the Mediterranean coast.  Because glacial stages were 5-10 times longer than interglacials, European red squirrels became better adapted to live in conifer forests.  However, in North America, even during the severest stadials, there were always extensive oak and oak/pine forests that supported large populations of gray squirrels.  Eastern grays evolved the ability to digest acorns better than red squirrels can.  Although eastern grays are not native to Europe, they are a better fit for the interglacial oak forests that exist there today.  Ecological displacement of 1 species by another has occurred thousands of times during earth’s history.  People may object to the displacement of European reds by eastern grays because man played a role in the introduction of the latter, but it is not unnatural or detrimental to the overall ecosystem in this case.

Eastern grays along with California ground squirrels, introduced fox squirrels ( S. niger ), and turkeys are displacing and outcompeting western gray squirrels on the Pacific coast of North America.  All seem to be better adapted to anthropogenic environments.  Western grays are now restricted to deep wilderness preserves.  Introduced eastern gray squirrels are also displacing American red squirrels ( Tamiasciurus hudsonicus ) in British Columbia.

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The American red squirrel is being displaced by gray squirrels in some parts of its range as well.

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Taxidermic mounts of eastern and western gray squirrels. The western is larger with a bushier tail.  Introduced Eastern gray squirrels and fox squirrels, as well as native California ground squirrels and turkeys are outcompeting western grays in suburban areas of California heavily modified by man.

Eastern gray squirrels have co-existed with fox squirrels for hundreds of thousands of years but are more common in many areas, including Richmond County, Georgia where I live.  Eastern grays quickly recolonize agricultural land replaced by dense 2nd growth forest, while fox squirrels prefer mature forests with widely spaced trees.  Because most of southeastern North America was clear cut between 1865-1945, gray squirrels have been quicker to return and spread throughout their range.  Without human introduction fox squirrels may never return to formerly clear cut land.

Eastern gray squirrels boldly live next to people and their unique September shuffle makes them a super squirrel, able to expand their populations and survive where other squirrels can’t.

Reference:

Bruemmer, Corrie; Peter Lurz, Karl Larsen, and John Gurnell

“Impact and Management of Alien Eastern Gray Squirrel in Great Britain and Italy: Lessons from British Columbia”

Proceedings of the Conference on the Biology and Management of Species and Habitats at Risk 1999