Posts Tagged ‘Gopherus polyphemus’

Fire Suppression = A Decline in Biodiversity (Part 2–The Animals of Longleaf Pine Savannahs)

June 29, 2011

Fox Squirrels come in several color phases–orange, black, and gray.  Some have white or gray masks as well.

Fox Squirrel–Sciurus niger

I love these big colorful squirrels.  I lived in Niles, Ohio until 1975, and our home was bordered by oak woods on 2 sides.  Big orange fox squirrels were the playful denizens there.  But since I’ve lived in Georgia, I’ve only seen one–a black masked fox squirrel foraging with a group of gray squirrels (Sciurus carolinensis) in a pecan orchard in Burke County.

This range map is bullshit.  No statewide survey of fox squirrels has been done in at least 50 years, if ever.  It’s likely an accurate range map would show a much patchier distribution.

Southern fox squirrels differ in their habitat requirements from northern fox squirrels, despite being the same species.  The former prefer mature longleaf pine savannahs with fingers of oak forests, while the latter thrive in oak/hickory woods.  Fox squirrels are declining in Georgia because longleaf pine savannahs were largely replaced with shorter rotation loblolly pine tree farms.  Lumber companies harvest loblolly pines every 50 years which is not enough time for trees to develop snags.  The Trees are also planted closely and fire is suppressed.  Gray squirrels are more abundant today in state because they’re well adapted to the dense young forests that have sprouted on abandoned agricultural lands.  Gray squirrels escape predation by jumping from tree top to tree top, while fox squirrels prefer to dash on the ground as far as they can before retreating to a tree.  Though clumsy in trees compared to their smaller cousins, their larger size allows them to put up more of a fight, if a predator catches up to them.  This difference in behavior explains why gray squirrels occur in closed canopy forests, and fox squirrels prefer open parkland forests.  For this reason I think fox squirrels were more abundant in this region during the Pleistocene when open environments were common.  Areas managed for red-cockaded woodpeckers should benefit fox squirrels.  Forest managers used longer rotations and fire to maintain the bird’s required habitat.

Red Cockaded Woodpecker–(Picoides borealis)

Photo of a red cockaded woodpecker from google images.  All the photos in this entry are borrowed from there.

Thirty years ago, this bird was on the verge of extinction, despite having formerly been common throughout the south.  Fire suppression and short forest management rotation nearly caused the death of this species.  Young pine trees never develop the soft rot that red cockaded woodpeckers need for boring nesting cavities.  As a defense mechanism, red cockaded woodpeckers constantly peck wells below their nesting cavities from which pine sap continously flows.  The pine resin repels rat snakes–their number one predator.  For this defense mechanism to work, live trees are a must.  And without fire hardwood understory reaches the level of the nesting cavity allowing flying squirrels, and other predators easy access.  Flying squirrels will decimate red cockaded woodpecker nests.

In a successful effort to save the birds, scientists identified habitat requirements and some suitable land was set aside and managed using prescribed burns and longer tree harvest rotations.  Birds were relocated to the best habitat, artificial nesting boxes were installed to supplement the shortage of good nesting trees, and flying squirrel exclusion devices were used.  In many protected areas red cockaded woodpecker family groups (family groups consist of 2-10 individuals) have increased dramatically to the point where it’s no longer necessary to provide artificial nests or to protect them from flying squirrels.  At SRS for example the population grew from 1 family group in 1987 to 30 by 2003.

Sandhill Crane–(Grus canadensis)

These impressive birds grow to 5 feet tall.  They prefer to nest in grassy marshes adjacent to prairies or savannahs.  The real life version of Sesame Street’s Big Bird used to be common, but since grasslands and wetlands have declined so have the birds.  Georgia’s population includes a permanent one consisting of small family groups, and large congregations of winter migrants.  They’re omnivorous feeding on insects, crayfish, mice, snakes, frogs, worms, acorns, fruit, roots, and farmer’s crops.

Bachman’s Sparrow–(Peucaea aestivalis)

Another inhabitant of open pine savannahs that is declining in abundance.  I heard this bird’s song on a youtube video and recognized it as one I’ve heard.  Evidentally, the sparrow still occurs in Augusta.

Indigo Snake–(Drymarchon corais)

This snake grows to 9 feet long, making it the longest serpent in North America.  They’re rare because their habitat has been fragmented, and they need large ranges.  They hunt during the day and retreat into gopher tortoise burrows at night.  A wide variety of prey is taken–other snakes including venemous ones, small mammals, birds, frogs, and fish.  Indigo snakes don’t kill by constriction or envenomation, but instead bite the head of their prey and thrash, breaking the spines of the small creatures.  Their metabolism is faster then that of most other snakes.

Gopher Tortoise–(Gopherus polyphenus)

 

Gopher tortoises depend on a frequent fire regime to spark the growth of the kinds of plant they eat.  They also like sandy soil that makes it easy for them to dig their elaborate tunnel systems.  They’re a keystone species–over 60 vertebrates and invertebrates depend on their burrows for shelter.  (See also my article–“The Giant Extinct Tortoise, Hesperotestudo crassicutata, must have been able to survive light frosts” from my April or March archives)

Popular game animals such as white tail deer, turkey, and quail thrive in longleaf pine savannahs.  Savannahs were a favored habitat of many extinct Pleistocene species as well including mammoth, long horned bison, horses, llamas, Harlan’s ground sloth, hog nosed skunks, giant tortoises, and others.

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.