Posts Tagged ‘evolution’

The Squirrel-Conifer-Fungi Connection

June 14, 2014

The evolutionary divergence of the northern flying squirrel (Glaucomys sabrinus) from the southern flying squirrel (G. volans) is an excellent example of speciation resulting from environmental change.  Genetic studies suggest both of these American species of flying squirrels diverged from Eurasian flying squirrels between 4-6 million years ago.  Eurasian flying squirrels are much more diverse and include 44 species, most of which live in southeast Asia–evidence this part of the world is where they originally evolved.  During the late Miocene about 5 million years ago, a forested landbridge connected Asia with America, explaining how the ancestor of both American species of flying squirrels colonized this continent.  Genetic evidence suggests the 2 American species of flying squirrels diverged from each other early during the Pleistocene between 1-2 million years ago when Ice Ages began to become more severe.  Boreal spruce forests expanded during Ice Ages, growing as far south as middle Georgia and Alabama.  In the middle south spruce forests grew in higher elevations while deciduous oak forests still occurred in adjacent lower elevation.  Oak forests are rich in mast such as acorns and nuts, but spruce forests offer less food for squirrels–seeds from spruce cones are only available for 2 months of the year.  However, underground fungi, also known as truffles, are available year round in spruce forests.  For most species of squirrels, fungi is a minor component of their diet, but truffles and other fungi make up 85% of the northern flying squirrel’s diet whereas southern flying squirrels eat more acorns, nuts, berries, and animal matter.  The ancestors of the northern flying squirrel were those individuals from the parent population best able to subsist on a diet of mostly fungi.  These individuals were able to colonize spruce forests, while the rest of the parent population remained in oak forests.  Eventually, this habitat partition resulted in a divergence between the 2 American species.

Photo: Northern Flying Squirrel, Glaucomys sabrinus.

Northern flying squirrels eat mostly fungi which is a minor component in most squirrel’s diet.  The ability to subsist on a diet of mostly fungi enabled this species to colonize spruce forests.  Eventually, they evolved into a different species than southern flying squirrels because of this capability.

Elaphomyces or truffle–favorite food of the northern flying squirrel.

 

 Red Spruce (Picea rubens)

Red spruce (Picea rubens).  Red spruce, truffles, and northern flying squirrels are beneficial and interdependent to each other.

Fossils of both species of flying squirrels have been found at Ladds and Kingston Saltpeter Cave in Bartow County, Georgia.  This is evidence that patches of spruce forest grew near patches of oak forest in this region during some climatic stages of the Pleistocene.  Northern flying squirrels are confined to the former; southern flying squirrels require the latter.

There is an interesting ecological interdependence between northern flying squirrels, red spruce, and several species of fungi.  Truffles grow intertwined with the red spruce roots, and they exchange nutrients.  The squirrels eat the truffles and spread their spores throughout the forest in their droppings.  A healthy spruce forest requires an abudance of truffles.  Many red spruce forests have been logged, and without the squirrel’s help, trees such as oak, maple, beech, and cherry are replacing them.  In West Virginia the U.S. Forest Service has successfully re-established red spruce forests.  Foresters discovered that red spruce seedling grow best in ground ripped apart by bulldozers and strewn with woody debris.  Some of these young spruce forests are on land reclaimed from strip mining. 

 Report fox squirrel sightings in Florida Sherman's Fox Squirrel

Fox squirrel.  This species may play a role in distributing fungi in longleaf pine savannah. 

Rhizopogon nigrescens–a fungi common to longleaf pine savannahs and likely an item in the diet of the fox squirrel.

Virgin stand of longleaf pine (Pinus palustris) in east Texas (circa 1908).

Although fox squirrels (Scirius niger) have a much more varied diet than northern flying squirrels, they occasionally eat fungi and may play a role in the health of longleaf pine savannahs.  Certain kinds of fungi that grow in the soil of savannahs also exchange nutrients with longleaf pine trees, and fox squirrels spread these spores in their dung as well.  Fox squirrels and longleaf pine savannahs were formerly common in the south, particularly on the coastal plain, but today both are rare.  The changes man has wrought have really sickened the natural communites of the world.

Reference:

Arbogast, Brian

“A Brief History of the New World Flying Squirrel: Phylogeny, Biogeography, and Conservation Genetics”

Journal of Mammalogy 88 (4) 2008

Advertisement

Ice Age-Influenced Avian Speciation in North America

December 22, 2013

The evolution of a new species requires geographical or ecological isolation from its parent species.  In nature this can occur in any number of ways–the uplifting of a mountain chain, a rise in sea level that creates an island, climate-induced ecological change, individual differences in foraging preferences within a population., etc.  Scientists have even created new species of bacteria, fruit flies, and worms in the lab by isolating populations of these organisms from their parent populations.  After many generations of reproductive isolation, the new species will not or can not successfully mate with members of their parent population when reintroduced.  In North America there are many examples of eastern and western bird species that are so similar it’s obvious they evolved from a single common ancestor.  The geographical barrier that isolated eastern and western avian populations is well known.

During the Miocene forested environments covered most of the North American continent.  But early during the Pliocene, about 5 million years ago, Ice Ages began to occur.  The middle of the continent became desert grassland that was unsuitable habitat for forest birds, thus isolating eastern populations from western populations.  In 3 cases, this isolation resulted in subspecific differences.  The common flicker (Colaptes auratus) includes the yellow shafted eastern form and the red shafted western form.  The yellow rumped warbler (Dendroica coranata) is split into the eastern myrtle warbler and the western Audubon’s warbler.  The dark-eyed junco (Junco hyeanalis) includes the eastern slate-colored and the western Oregon.  Ornithologists formerly thought the eastern and western forms of these 3 were separate species, but it was discovered they freely interbreed in regions where their populations overlap, despite differences in physical characteristics.

The common flicker. Unlike most woodpeckers, it forages on the ground, feeding on ants and beetles, rather than pecking wood for insect borers.  There are always a few of these nesting in my neighborhood during spring and summer.  The eastern and western forms of this species were formerly thought to be different species.  Geographical isolation resulted in subspecific differences but not complete speciation.

There are at least 22 examples of eastern species of birds with a similar but distinct western counterpart including eastern and western peewees, eastern and western bluebirds, scarlet and western tanagers, eastern and western screech owls, among many others.  These birds are considered distinct species.

Eastern bluebird.  I also see a few of these in my neighborhood during spring and summer.

Eastern Bluebird Range MapWestern Bluebird Range Map

Range maps of eastern and western bluebirds.  Both species descend from 1 common ancestral species that formerly occurred across the continent before Ice Ages caused unsuitable desert grassland habitat to replace forested habitat in the middle of the continent.

During the present interglacial, forested habitat is once again becoming more widespread.  Moreover, man often plants trees in region that were once prairie, and he suppresses natural fires necessary for the development of grasslands.  As a result, similar eastern and western species of birds are expanding their ranges and occasionally, they come into contact and hybridize.  Hybridization is another mechanism that plays a role in the evolution of new species.  Similar species that were once reproductively isolated but come into contact again may backcross and evolve into yet another new species.  An estimated 9% of bird species are known to hybridize with other bird species.  (Homo sapiens may be a hybrid species.  DNA evidence suggests some Eurasian Homo sapiens have some Homo neanderthalis ancestry.)

Eastern x Western Screech-Owl hybrid

Eastern and Western Screech Owl hybrid.  These 2 species were isolated during Ice Ages by a desert grassland barrier.  Now, they are both expanding their ranges and reuniting.  Hybridization is another mechanism that can result in new species.

Hybridization can endanger a species through genetic swamping.  Barred owls (Strix varia) are expanding their range into the habitat of northern spotted owls (Strix occidentalis).  Environmentalists saved spotted owls from clear-cutting, but within the last 30 years, barred owls have successfully invaded the Pacific northwest.  Barred owls usually just eat the smaller spotted owls, but they also mate with them–47 hybrids have been reported.

Ice Age glaciers also provided a barrier that geographically isolated 7 ancestral populations of birds, resulting in 14 species.  Glacial barriers split northern shrikes from loggerhead shrikes, Bohemian waxwings from cedar waxwings, 3-toed woodpeckers from black- backed 3-toed woodpeckers, boreal owls from saw-whet owls, black billed magpies from yellow-billed magpies, northern goshawks from Cooper’s hawks, and boreal chickadees from black-capped chickadees.  During Ice Ages, northern shrikes, Bohemian waxwings, 3-toed woodpeckers, boreal owls, black-billed magpies, northern goshawks, and boreal chickadees found refuge in Beringia and Eurasia, while loggerhead shrikes, cedar waxwings, black-backed 3-toed woodpeckers, saw-whet owls, Cooper’s hawks, and black-capped chickadees lived in North America south of the glaciers.

Top: Loggerhead shrike (Larius ludovicianus).  Bottom: Northern shrike (Larius excubitor).  They both descend from 1 common species with a circumpolar distribution.  Ice Age glaciers separated this ancestral population, resulting in 2 distinct species.  Northern shrikes usually have gray over their bills, while loggerhead shrikes usually have black over their bills.  The former also have larger bills.

Since the end of the Ice Age, the Eurasian species mentioned above have recolonized much of Canada but maintain separate breeding grounds from their American sister species.

References:

Newton, Ian

Speciation and the Biogeography of Birds

Elselvier Science 2003

Pielou, E.C.

After the Ice Age

The University of Chicago Press 1991

Note: * I discovered plagiarism in the book written by Ian Newton.  He plagiarized a passage from After the Ice Age and didn’t even cite that work in his book.*  Wow! What lazy scholarship.  He didn’t even bother to put the original awkwardly written passage in his own words.

It’s Ice Cream for Deer but Poison for Humans

February 15, 2012

One of the dumbest examples of wilderness survival folklore ever espoused is the notion that to determine whether a potentially edible plant is poisonous or not, a person should observe an animal consuming the plant.  The logical fallacy is the assumption that if the animal could eat the plant and not die, than it would be safe for humans to eat.  This is a stupid assumption for 2 reasons:  First, the animal could crawl off in the bushes and die later out of sight.  Second, and more importantly, all animals have completely different physiologies than humans.  There are many plants highly poisonous to humans but perfectly edible to many species of mammals, birds, and especially insects, such as caterpillars which consume poisonous plants that make them inedible to birds when the caterpillars become butterflies.  Below are 2 species of common plants found in Georgia that are favorite foods of deer but are poisonous to humans.

Strawberry bush–Euonymous americanus.  Naturalist refer to the plant as “ice cream” for deer.  But it is poisonous to humans.  It’s in the bittersweet family.

Buffalo nut–Pyrularia pubera.  Also a favored deer edible that is poisonous to humans.  It’s in the sandalwood family.

Deer eat strawberry bush twigs, and birds eat the fruits, but both parts are deadly to humans, causing vomiting, diarrhea, irregular hearbeats, convulsions, coma, and death.   Scientists don’t know what type of poison it is.  Strawberry bush is also poisonous to livestock.  It was advantageous for deer to evolve the ability to digest a plant that was likely poisonous to competing herbivores of the Pleistocene, such as bison and horses.  I wonder if other browsing Pleistocene herbivores (mastodons, tapirs, Jefferson’s ground sloths) could also eat strawberry bush without ill effect.  Browsers tend to be more resistant to plant poisons because they eat small amounts of a great variety of foods and don’t concentrate the poison in their systems.  Grazers eat large quantities of fewer species of plants, making it more difficult to evolve the ability to eat toxic vegetation.  Deer probably evolved the capacity to survive eating toxic plants because they only nibbled on the plant, and individuals that could survive eating small quantities passed this characteristic on to the next generation, unlike bison which ate such large quantities that no individuals survived consuming the toxins.   Gradually, each generation of deer had a growing inherited capacity to digest this toxic plant with no ill effects.

Buffalo nut is toxic to humans, rabbits, and pigs, but not deer, cattle, horses, sheep, and mice.  Its poison is an amino acid similar to that found in cobra poison.  The protein stimulates growth hormone in deer and may facilitate antler growth. In addition to harboring plant toxins, buffalo nut is a parasite, living on nutrients from other tree’s roots.  The roots of a buffalo nut “kiss” the roots of other species forming a hausteum, an attachment that helps them leech nutrients absorbed by the other tree. Many species of trees serve as host species for buffalo nut, including oak, chestnut, and hemlock.

Both strawberry bush and buffalo nut grow as understory trees in disturbed moist woodlands–a habitat that expanded during interstadials and interglacials but decreased during stadials.  Grazers always became more abundant during stadials when arid cool climates fostered the growth of grasslands but decreased the abundance of toxic woodland plants.  Browsers increased when forests expanded.  Strawberry bush and buffalo nut are known as “gap phase” species, thriving in areas of the forest disturbed by fire, storm, or human activity.

Like most plants, strawberry bush and buffalo nut are invisible in the Pleistocene fossil record, but they must have been present then or they wouldn’t be here today.

Speaking of (or rather writing of) ice cream for deer, I tried growing fava beans in my garden 2 years ago.  Fava beans are a cold hardy legume.  I read they could survive temperatures as low as 15 degrees F.  Because winters in Augusta, Georgia seldom get that cold, I predicted they would do well.  I had a great stand of fava beans in my backyard by early December.  One afternoon while taking a walk in broad daylight, I saw a deer.  It stopped about 20 yards from where I stood.  It seemed unafraid and even stomped its hooves as if attempting to intimidate me.  I resumed walking up the street until I heard hooves hitting pavement behind me.  I realized it was heading straight for my fava bean patch.  I raced back to scare it away but 2 big dogs came out of nowhere and chased the fleeing deer from my garden for me.  My fava beans were safe but nor for long–a few days later the temperature dropped below 15 degrees, an unfortunate stroke of luck because temps here get that cold maybe once every 10 years.  The favas did sprout back from the roots but production was meager compared to what would have been from the lush first growth.

The Stupidity of Answers-in-Genesis

September 15, 2011

I’m sorry I’m opening this week’s blog entry with a photograph of the republican presidential candidates instead of something like a photo of a giant ground sloth fossil.  Actually, a dead ground sloth would make a better president than any of the big business puppets running for the 2012 presidential election.  Rick Perry, cowboy redneck, will probably be our next president.  Just what we need–another really bad president from Texas.  Some liberals are in panic while other are in denial.  I don’t see what the big difference is between him and Obama.  Obama has been a center right president; Perry will be an ultra-right president.  Whoopee!  That difference doesn’t inspire me to vote.  All the republican presidential candidates with the exception of John Huntsman, who polls less than 1%, professed a disbelief in the science of evolution and anthropogenic global warming, throwing red meat to their mentally-challenged base.

Roughly half of the American people prefer to believe ancient story-tellers over modern scientists.  They think the earth is 6,000 years old and God created it in 6 days and anybody who disagrees with them is an immoral fascist/socialist on the road to perdition.  Yet, if they fall ill, they don’t consult an 11th century physicians manual.  They go running to the nearest modern medical professional.  I suppose if believing in evolution was a life or death decision, there would be more believers.

Recently, all of the real presidential contenders for the republican nomination considered it necessary to profess a disbelief in the fundamental basis of all biological science.  I doubt they honestly disbelieve science.  Instead, they’re appealing to an uneducated segment of society with an unfortunate belief system.  Scientific ignorance has become politically tied to the republican’s other twisted talking points such as cutting taxes, deregulation, and hostility to the government.  Conservatives have so successfully shouted down liberals that democratic politicians also promise to cut taxes, deregulate, and carry on expensive, unnecessary wars of aggression against brown-skinned people, even though those are the policies that created our current economic doldrums.  The U.S. is such a gullible nation.

The Reverend Ken Ham is a snake oil salesman profitting from this gullibility.  He founded the Creation Museum in Kentucky.  He charges $20 admission, but most of the workers there are unpaid volunteers who must sign a vow that they believe in a literal translation of the bible.  In addition to his for profit museum he’s selling ridiculous anti-science propaganda to churches, mostly in the U.S.  He must be raking in millions annually.  When perusing his fodder for the bible-thumpers who want their ignorance reinforced with likeminded rubbish, it doesn’t take long to discover the absurdity of his claims.

Replica of a T. Rex skull fossil.  Ken Ham believes T. Rex was a plant-eater, until Eve convinced Adam to eat the apple.  The first sin is what forced some animals to become carnivores after they were all thrown out of paradise.  One look at a T. Rex’s teeth debunks the claim that it ever ate plants because they’re absolutely unsuited to a plant-based diet.  Some creationists claim the flood caused the extinction of dinosaurs and other prehistoric creatures, but not Ken Ham.  He insists on biblical accuracy, and the bible says Noah put an example of every living animal on the Ark.  It was only after the flood that dinosaurs became extinct, so he insists dinosaurs co-existed with man, at least for awhile, despite the total lack of fossil evidence for the overlap.  And a lack of archaeological evidence as well.  Surely, the natives would have collected T. Rex bones.

One quote from Reverend Ham makes it evident he’s never read a geology textbook.  He stated, “there’s no evidence whatsoever that the world and its fossil layers are millions of years old.”  No evidence?  Why do almost all, if not all, professional geologists believe the world is 4.6 billion years old?  Would they believe that with no evidence?  Here’s a brief summary of the evidence that the earth is older than 6,000 years old.

1. Dendrochronology–shows earth’s at least 10,000 years old.

2. Ice Core data–shows earth’s at least hundreds of thousands of years old.

3. Varves–show earth;s at least’ millions of years old.

4. Coral reefs–one’s 130,000 years old.

5. Astronomers measure the galaxy as 100,000 light years across.  Visible starlight is that old.

6. Rates of Continental drift–suggest earth’s at least millions of years old.

7.  Analysis of the Geological Column which is consistent with the fossil record.  For example part of the Rocky Mountains rests over a massive fossil coral reef that itself took millions of years to grow.  Why would God hide a fossil coral reef under the Rocky Mountains?  No mammal fossils are found in Coal age deposits.  No dinosaur fossils are found in Pleistocene deposits, etc.

8. The radiometric age of some minerals on earth is 4.1 billion years old.

9. The ratio of Lead isotope decay from samples of earth and meteorites is consistent with a 4.6 billion year old earth.

10. The oldest age determination of meteorites are all consistently between 4.4 and 4.6 billion years old.

Creationist arguments against these points mostly consist of either God made it look that way or that scientists base their assumptions on such things as the speed of light and the freezing point of water have always remained the same.  Yes, those are assumptions, but I think they’re pretty safe assumptions.  For the above points to be in error, it would take many drastic changes in the known laws of physics.  Creationists might dispute this evidence, but for Ken Ham to claim there is no evidence whatsoever proves he ignores real science.

One of the biggest fraudulent claims creationists often make is that there are no transitional fossils.  There are literally thousands of transitional fossils.  Because evolution is an ongoing process, all organisms can be considered transitional, but the fossil record also clearly shows a progression of speciation with transitional characteristics.  The fossil record of the horse is a good example, and creationists recognize this and attack the science with many unfounded criticisms.  I found a series of articles written for answers-in-genesis  by a Presbyterian minister who questioned evidence supporting horse evolution.  I believe Peter Hastie wrote all three of the following articles, though he only signed his name to one.  They are: “Horse find defies evolution,” “Horse nonsense,” and “What happened to the horse?”   So we have a case of Presbyterian minister going against paleontologists and vertebrate zoologists.  All three articles consist of falsehoods and gross misunderstandings of evolution.

Artist’s depiction of eohippus, or hyracotherium, also known as the dawn horse.

In “Horse nonsense” Peter Hastie makes the bizarre claim that Eohippus was actually related to the rabbit, not the horse.  As the above artist’s depiction indicates, the dawn horse greatly resembles a horse, not a rabbit.  (He didn’t use a scientific name but he wrote cony which is another common term for rabbit.  Maybe he meant hyrax.  It bares no resemblance to a hyrax either.)  He claims there is no sound evidence linking the dawn horse with the modern horse, but evidentally, professional scientists do, and any layman looking at the picture can see the great similarity.  Hastie also rejects horse evolution because horse fossils are found in different localities.  He claims it is circular reasoning to use horse fossils from different species collected from differenct localities.  He demands a fossil site that shows the entire evolutionary history of the horse in successive stages.  I don’t quite understand why he considers this circular reasoning, but I suppose, if there was one fossil locality that had every complete fossil of every horse species that ever lived in successive ages, he’d still find an excuse to reject it.   Constructing an evolutionary tree is like putting the pieces of a puzzle together when the pieces are located in different rooms of a house.  I wouldn’t call that circular reasoning.

In “Horse fossil defies evolution” Hastie demonstrates that he doesn’t really understand evolution.  He refers to an article from National Geographic Magazine about a fossil site in Nebraska.  He doesn’t even mention the name of the fossil site–an unscholarly omission–but I’m certain the article’s about the famous Ashfall fossil site.  Hastie thinks he’s disproven the evolution of the horse because extinct species of both one and three-toed horses were found at the site, showing they lived at the same time.  He thinks this is evidence that one-toed horses could not have evolved from three-toed horses.  To put it bluntly, his reasoning is just stupid.  Evolution doesn’t occur in a neat linear models.  Instead, it is more comparable to a bush upon which different branches can exist at the same time, although they all originated from the same trunk.  One species doesn’t necessarily evolve into another and then suddenly become extinct itself.  Speciation usually occurs in geographically isolated populations which can later colonize regions where their ancestors still live.  There are many extant species today that coexist with their ancestral species.  Fish crows (Corvus ossifragus) evolved from common crows (Corvus brachyrhyncos) and both coexist today, sometimes in the same habitat.

Bruce Macfadden’s chart of horse evolution.  Note it’s more like a bush than a linear line, as incorrectly depicted in old science textbooks.

In “What happened to the horse?” Hastie makes several false or unsubstantiated claims.  First, he states that a fossil of eohippus was found in the same sedimentary strata as that of a modern horse, and he rejects the scientific explanation that the older fossil was reworked by claiming there’s no evidence of geological activity that would cause reworking of an older fossil into younger strata.  I have no way of checking this claim because he doesn’t cite the scientific article he gleaned this bit of information from.  He also gives no scientific reason why he rejects the possibility of reworking.  He’s a Presbyterian minister, not a geologist, so he has no qualification or knowledge to make this kind of judgement.  Second, he claims horse evolution is contradicted by genetic evidence.  This is false.   The only genetic studies of horse evolution merely suggest the number of Pleistocene horse species is much fewer than previously thought from what scientists had gathered from fossil evidence.  Scientists already agree there was only one genus of horse in the Pleistocene.  I researched this topic and could find no genetic studies of Pliocene or Miocene horses.  Third, he states the lineage of horse evolution was debunked 40 years ago.  Again, this is false.  Scientists noted that the original model of horse evolution as depicted in textbooks was an incorrect oversimplification.  Scientists still accept the evolution of the horse beginning with the dawn horse and ending with the modern horse.  They simply corrected the original model which incorrectly showed a neat linear progression and included dead-end species no longer believed to be directly ancestral to modern horses.

This is the evolution of the horse toe bone.  There’s a reason why creationists attack this with such ferocity.  It’s good evidence of evolution.

How Unusually Cool Ice Age Summers Probably Shaped Periodical Cicada (Magicicada) Evolution

May 3, 2011

It sounds like everybody’s burglar alarm is blaring in Evans, Georgia.  But the noise doesn’t originate from annoying, malfunctioning security systems.  Instead, the 13 year periodical cicadas have emerged.  For over a decade these insects have lived a foot underground, well below the frost line, but now they’re ready to mate–a frantic affair that takes place within a timespan of 3-4 weeks.  Almost their entire lives, they’ve lived as nymphs, surviving on the xylem fluids of deciduous trees.  The urge to mate causes them to dig tunnels to the surface which they crawl through.  Sometimes they continue to crawl, making it halfway up a wall or a tree trunk before the winged adult bursts through the back of the shell of its thorax.  The holes from which they’ve emerged are visible, their molted shells scattered under foot like discarded shrimp exoskeletons at a Cajun seafood boil.

Photo from google images of a periodical cicada.

The unusually long period between emergences among the 7 species of periodical cicadas in the genus Magicicada puzzles scientists who hypothesize about its evolution.  Magicicada emergences in large numbers are obviously a defense mechanism known as predator satiation.  Like passenger pigeons, they occur in such a high population that they overwhelm the ability of predators to consume them.  Unlike other types of cicadas which are strong, fast fliers, periodical cicadas are clumsy and slow, but so many appear at once that predators are unable to consume most of them before they have a chance to mate and lay eggs.  Some scientists think their emergences every 13 or 17 years (depending on the species) is a way to keep predators from increasing their own populations after exploiting them as a food source, thus avoiding a cycle when predator numbers eventually escalate enough to decimate cicada numbers.  This seems an unlikely explanation to me for 2 reasons: cicadas are only available for a few weeks a year which is not enough time to have a significant long term impact on predator populations.  More bird nestlings may survive at first due to the abundance of cicadas, but then for the rest of the year, they must adapt to the normal supply of food.  Moreover, the average wild bird only lives 2 years–far shorter than 13 or 17 years.  Cicadas could avoid upswings in predator populations with much shorter periods between emergences.  Other scientists believe the odd high prime numbers emergences can be explained by a combination of predator cycle avoidance and interspecific competition among nymphs.  Although several entymologists have derived statistical models supporting this theory, I think the paleoclimate explanation proposed by R.T. Cox, C.E. Carlton, and independently by Yoshimura is more plausible.

Periodical cicadas depend specifically upon deciduous forests.  During the coldest stages of Ice Ages, deciduous forests north of the southern Appalachians were rare relics outnumbered by other environments such as spruce forests and prairies.  The bulk of deciduous forests then occurred south of the Appalachian mountains.  Even here, summer temperatures occasionally were too cold for cicadas in the Magicicada family.  They require temperatures above 68 degrees F for a period of 3-4 weeks for flight and mating.  Drs. Cox and Carlton assumed that during the coldest stadials (which lasted on average 1500 years) 1 in 50 summers failed to reach this temperature, and cicada reproduction failed.  Using a statistical formula, they estimated that over a 1500 year stadial, cicadas emerging every 6 years had a 4% chance of avoiding unusually cool summers; cicadas emerging every 11 years had a 51% chance of avoiding unusually cool summers; but cicadas emerging every 17 years had a 96% chance of avoiding unusually cool summers.  Cicadas emerging after shorter periods were eventually eliminated from the gene pool, while those with genes for longer cycles became dominant.

Map of Magicicada ranges from the below referenced paper.  The distribution of 13 and 17 year periodical cicadas supports the paleoclimatic explanation for their high prime number emergences.

17 year cicada species tend to live north of 13 year cicada species, even though the shorter cycle is a dominant gene.  Summers too cool for breeding would’ve occurred more frequently in the norther parts of their range, so those with 17 year cycles would’ve had a greater chance of avoiding them than those with the 13 year cycle.

Reference:

Cox, R.T. and C.E. Carlton

“Paleoclimatic influence in the evolution of periodical cicadas (Insects: Homiptra:Cicidae: Magicicada spp.)”

The American Midland Naturalist 120: 183-193 1988

Notes on my observations of periodical cicadas

–Periodical cicadas are slow.  I was able to catch one by simply picking it off the ground after if fell in flight and landed on its back.

–Birds are feasting on them.  Crows are catching the nymphs as soon as they crawl to the top of their tunnels.  I also saw a Canadian goose nab one that fell in a small lake.

–Wow! They are loud.

–They must be mole food during their nymph stage.

–Evans has become heavily developed.  Cicada habitat has been greatly reduced and covered with blacktop parking lots from which they can never emerge and escape.  I wonder if this is another creature that survived for millions of years, until the actions of Homo sapiens eventually renders them extinct.

The Extinct Pleistocene Giant Tortoise (Hesperotestudo crassicutata) Must Have Been Able To Survive Light Frosts

April 15, 2011

Illustration of the extinct giant tortoise that lived in the southern parts of North America.  It grew as large as the Galapagos Island tortoises but was more closely related to the much smaller extant gopher tortoise.

Scientists often use the presence of giant tortoise fossils as a proxy for past temperatures.  They conclude that because giant tortoises can not survive freezing temperatures than they must have lived during a time when the region was completely frost free.

Hesperotestudo crassicutata scute

Photo of part of a tortoise shell or scute from a specimen found in Texas.

Three species of closely related land tortoises lived in southeastern North America: a giant species (Hesperotestudo crassicutata) that grew as big as modern day Galapagos Island tortoises, an intermediate-sized species (Hesperotestudo incisa), and the gopher tortoise (Gopherus polyphemus) which is still extant.  It has occurred to me that the two larger species must have been able to survive light frosts, otherwise they would have become extinct when Ice Ages began.  Here are 5 reasons why I have come to this conclusion and disagree with the scientific consensus that the presence of tortoise fossils indicates warmer winters in this region than those of today.

1. The giant Pleistocene tortoise existed for at least 2 million years.  Within this vast time span, there must have been climatic phases, or at least events of crazy weather, that led to frosts in the deep south.  Today, frosts occur as far south as

Look at how much average temperatures fluctuated before the Holocene (~11,000 BP) when it’s assumed once a decade frosts began occurring in south Florida.  Notice also how much lower average temperatures were previous to the Holocene.  It doesn’t make sense the frosts in the deep south just began occuring 11,000 years ago.  They must have occurred before then.

south Florida at least once a decade.  It doesn’t make sense that these once a decade frosts just began to occur ~11,000 years ago and were absent for the previous 2 million years.  It just seems improbable that frosts began to occur in the deep south during the Holocene, a time of relative climatic stability, but didn’t occur during the Ice Ages which were times of dramatic climatic fluctuations (as the above chart shows) and generally of cooler climates.  If it’s true that giant tortoises couldn’t survive in an environment of light frosts, than that means they were extirpated in the southeast every time there was a frost.  They could only recolonize the south from enclaves in central America or what’s now Mexico, but that would mean a geographical corridor in the deep south must have remained frost free for thousands of years at a time–an unlikely climatic scenario, even during warm interglacials.

2. Scientists believe giant tortoises couldn’t escape the cold because they didn’t dig burrows.  This is a shaky assumption.  The only surviving species of giant tortoise lives on islands near the equator where there are no frosts.  As I discussed with my first point, Hesperotestudo did evolve in a region that must have had occasional light frosts, and therefore to survive, it must have evolved adapatations to escape the cold.  Moreover, Hesperotestudo is not the same species as extant giant tortoises, and we have no knowledge of its behavior patterns.  It’s closest living relative, the gopher tortoise, has a deeply innate instinct to dig burrows, and I see no reason for the assumption that giant tortoises didn’t also dig burrows.  Sea turtles dig deep pits to lay their eggs, proving that size is no obstacle to digging deep holes.

Gopher tortoises dig extensive burrow systems. The giant Pleistocene tortoise was closely related to the gopher tortoise.  There is no reason for the assumption that they did not also dig burrows which would have helped them survive frosts.

3. There is no evidence of tropical plants or pollen in the Pleistocene fossil record of the deep south.  If winters were warmer than those of today, and frost free, there should be fossils of tropical species of plants.  Instead, for example, a study of fossil plants from a site in the Aucilla River in north Florida, dating to the Pleistocene, found almost the exact same species that exist in the region today.  No tropical species were found.  Only 3 species outside their present day region were discovered here–osage orange, wild squash, and hazlenut. All three are temperate species, and the latter prefers cooler temperatures than exist today here.

4. Fossils of extant mammal species tend to be on average of individuals larger than those of the same species found in the region today.  According to Bergmann’s Rule, this indicates cooler climates and precludes warmer winters.

5. The prolonged freeze of 2009/2010 in south Florida caused a high mortality rate of the invasive Burmese python but did not cause their complete extirpation.  It seems reasonable to suppose that eventually, large reptiles that are maladapted to occasional frosts, would through selective pressure evolve to have an adapatation that enables them to seek thermal refuges.  And in fact, there are 2 clades of Burmese pythons with differing behavior patterns in their responses to frosts: the majority of the ones imported for the pet trade come from southeast Asia, and they’re naive to frost; but another population of this species occurs in temperate regions, and they’ve learned to seek refuge and hibernate during colder times of the year.

Like the northern population of Burmese pythons, and the American alligator, the giant Pleistocene tortoise was likely an animal of the subtropics that extended its range into southern temperate regions during warmer climatic stages.  And like pythons and alligators, selective pressures chose those individuals that took action to escape frost.  Alligators know to escape frost by moving into deep water, while caimans and crocodiles and southern Burmese pythons continue basking in subfreezing temperatures which leads to their deaths.  Like the alligator, Pleistocene giant tortoises must have survived frosts by moving to thermal enclaves such as burrows they dug themselves, the dens of other species, caves, hot springs, or under upturned tree roots.  How they survived frost is a subject for conjecture, but I have no doubt that somehow they must have.

Cougars vs. Jaguars

July 8, 2010

Cougars and jaguars co-existed for at least 500,000 years throughout North America, and today still co-exist in many areas of South America and Mexico.  Both species are adaptable enough to occupy a wide variety of environments, including deserts, lightly wooded savannah, flooded swamps, and tropical rain forests.  They also feed upon many of the same prey species.  This spawns two questions: what ecological differentiation allows two big cat species to co-occur on the same range, and what factors allowed cougars to remain in much of North America where jaguars were extirpated?  A number of scientific studies help solve these ecological mysteries.

Comparison of cougar and jaguar diets

Studies of jaguar and cougar diets consistently show significant differentiation.  Although cougars and jaguars tackle many of the same species, the latter selects for larger sized individuals.  One study of co-occurring jaguar and cougar populations in Venezuala–a region consisting of woodland, savannah, and swamp–found the following differences in prey size selection between the two species.

…………………………………….Cougars……………………………Jaguars………………

Small size prey…………………17%……………………………………1%……………….

Medium size prey……………..31%……………………………………14%……………..

Large prey……………………….52%……………………………………85%…………….

For example in this region collared peccaries are an important diet item for both species, but cougars exclusively take small juveniles, while jaguars take mostly adults and sub-adults.  Both big cats took a wide range of prey species with cougars taking 12 different kinds of animals and jaguars taking 10.  Jaguars preyed more heavily upon capybaras here than cougars did.  Jaguars also preyed upon white-lipped peccaries–an aggressive species that cougars completely avoided.  White-lipped peccaries live in large groups and frequently come to the aid of their comrades and attack predators.  They’ve been known to kill jaguars and even humans.

Illustration by John James Audubon

Another study of jaguar diet, this one in southern Brazil where flooded plains are the predominant habitat, found that the jaguar diet there included 31% cattle, 24% caiman, 21% peccary, 4% feral hog, 3.0% marsh deer, 3.2% giant anteater, 2% capybara, 1.6% brocket deer, and about 10% other.  438 prey items were recorded, showing that jaguars will take what’s generally available.  Incidentally, both jaguars and cougars are capable of killing the alligator-like caiman, but take them less than would be expected based on their abundance.

Illustration by John James Audubon

A third study, this one in Mexico where both jaguars and cougars mostly prey on deer, peccary, and armadillo, also found that jaguars select for larger prey items.  This study concludes that the “cougar’s ability to exploit smaller prey gives them an advantage over jaguars when faced with human-induced habitat changes.”  This conclusion brings to obvious light one of the reasons why cougars survived throughout much of North America where jaguars didn’t.  After Indians overhunted much of North America’s megafauna, jaguars had difficulty finding the larger prey they preferred.  The extinction of two Pleistocene species of peccary in North America was probably devastating.  Indians even overhunted white tail deer into scarcity as John Lawson, an early European explorer (circa 1704) noted when he pointed out that deer were rare around large Indian settlements in South Carolina.  But cougars could survive in these areas on rabbits, possums, raccoons, and turkeys.

I agree that the preference for larger game that no longer exists is one factor that’s limited the jaguar’s range in North America, but I think there are other factors.

Evolution of size, coat color, adaptability to cold, and personality traits

The fossil record suggest jaguars, along with dire wolves, were the most common large carnivores (excluding omnivorous bears) in southeastern North America during the Pleistocene.  Yet, cougars found their niche here too.  During the Pleistocene both species were somewhat larger than the present day versions of these species.  Rancho La Brean specimens of cougars show that on average they were 5% larger than those of today, while Pleistocene jaguars approached modern day tigers in size.  I think this is due to the larger size and quality of prey available, particularly horses and the larger sized species of peccaries, and it’s clear these two big cats not only had a better diet, but further impetus to evolve to a greater size, so they could successfully exploit this larger prey.  One study reported that modern jaguars living in areas where cattle were introduced tend to approach the size of the larger Pleistocene jaguars, and it’s believed that jaguar populations increased following the introduction of European livestock to South America.

I theorize the spotted coat of the jaguar is another factor in its range reduction.  Indians valued the beauty of its fur and hunted them unmercifully.  There’s a possibility that Pleistocene cougars had spotted coats.  Scientists believe that cougars evolved from a kind of spotted cheetah.  Cougar kittens retain these cheetah-like spots–evidence of this evolution.  But I think many adult cougars may have been spotted until very late in the Pleistocene when man colonized the continent and hunted the spotted cougars for their coats, leaving only the dull tawny and gray coated individuals to breed, which in turn genetically swamped the spotted ones.

It has been suggested that spotted cats are more vulnerable to cold climate–another factor which may limit the jaguar’s range, but I disagree with this hypothesis.  The snow leopard of the Himalayas is an example of a spotted cat that lives in a cold region.  Moreover, jaguar fossils have been excavated from as far north as Oregon and Pennsylvania when even during the warmest interglacials, subfreezing temperatures occurred during winter. 

Jaguar fossils in Georgia have been excavated from Ladds Quarry and Kingston Saltpeter Cave.  A nearly complete skull was recovered from the former location along with giant tortoise and armadillo bones that have jaguar gnaw marks on them.  Fossils from this period probably date to a warm climate phase, but the jaguar remains from KSC are associated with the kinds of animals that live in cold and temperate climates, indicating jaguars survived colder conditions than any endured by extant populations.  Cougar fossils also were found at Ladds and in Yarbrough Cave which dates to the last glacial maximum.

One more factor in the cougar’s survival where jaguars didn’t may be evolutionary selection towards more timid individuals.  Those members of the cougar population that learned to avoid man were more likely to survive.  Timidity possibly occurred less frequently in prehistoric jaguar populations.

Cougars vs. Jaguars, wolves, and bears

So which would win in a battle between a jaguar and a cougar?  According to scientific studies, cougar and jaguar ranges frequently overlap, but they tend to avoid each other.  Certainly, a jaguar wouldn’t think it worth the effort to battle a raging mother cougar defending her kittens.  Conversely, a cougar would be out of its mind to engage in a battle with a larger, more powerful cat that bites harder than any other kind of cat in the world.  However, in one paper, international big cat expert, Howard Quigley, did cite a case of a jaguar attacking and killing a cougar.

Packs of wolves also dominate cougars in the Rocky Mountains.  Wolves occasionally kill cougar kittens, sub-adults, and even adults.  The average biomass of wolves in packs that attack a cougar outweighs the cat by a 13:1 ratio.  Rarely, cougars have been reported to kill wolves (sub-adults and adults, but not pups), but in these cases it was one-on-one and the biomass was a 1:1 ratio.  A certain percentage of cougar kills are lost to wolves and bears in areas where their ranges overlap.

References

Carvolcanti, Sandra; and Eric Gese

“Kill rates and predation patterns of jaguars (Panthera onca) in the southern pantanal of Brazil”

Journal of Mammalogy 91 (3) 722-736 2010

Hoogesteyn, Rafael; and Edgardo Mondolfi

“Body mass and skull measurements in four jaguar populations and observations on their prey base”

Bulletin of the Florida Museum of Natural History V. 39 (6) pg. 195-219 1996

Hornocker, Maurice; Sharon Negri, and Alan Rabinowitz

Cougar: Ecology and Conservation

University of Chicago Press 2002

Nunez, Rodrigo; Brian Miller, and Fred Ludjey

“Food habits of jaguars and cougars in Jalisco, Mexico”

Journal of Zoology 252 (3) 373-379

Scognamillo, Daniel; et. al.

“Co-existence of jaguar (Panthera onca) and puma (Puma concolor) in a mosaic landscape in the Venezualan llanos”

J. Zoological Society of London 259 269-277 2003