Pleistocene Manatees (Trichechus manatus)

Mammoths and mastodons no longer roam North America, but a relative of the elephants can still be found in Florida.  The manatee belongs to the superorder paenugulata which includes the proboscidea (elephants), the hyracoidea (hyraxes), and the sirenia (manatees and dugongs).  Strange as it may seem, these quite different looking animals are somewhat closely related.  Manatees share many anatomical characteristics with elephants.  Their incisors resemble elephant tusks, and the toenails on their flippers exactly match those found on elephant toes.  Manatees use their lips to feed on vegetation, much like elephants use their trunks when foraging for food.  And manatee teeth are replaced by horizontal forward movement– the same process of dental development that occurs in elephant mouths.  A scientist first recognized the anatomical similarities between manatees and elephants in 1945.  Recent genetic studies confirm this early cladistic analysis.

The proboscidea, hyracoidea, and sirenia orders belong to the same clade–the paenugulata.

All of these species of manatees are still extant except for Steller’s Sea Cow which was overhunted  to extinction in 1768.

The species of manatee still extant in Florida today ecologically replaced an extinct species of dugong during the late Pliocene or early Pleistocene.  This species is known as the West Indian manatee because it occurs along the Caribbean island coasts–also known as the West Indies.  Manatees occasionally swim as far north as Massachusetts during summer but return to waters off the coast of south Georgia and Florida before winter.  West Indian manatees can’t survive cold water temperature.  Fossil evidence shows manatees have long straggled north of their winter range–remains of manatees dating to the Pleistocene have been found near the coasts of South Carolina, Virginia, and New Jersey.  There is some evidence that manatees were extirpated from Florida during the coldest stage of the last Ice Age.  Fossils of manatees dating to before the Last Glacial Maximum in Florida resemble a subspecies no longer found in the state.  Manatees from the Caribbean recolonized Florida following the end of the last Ice Age.  Pleistocene-age manatee bones have been excavated from over 24 sites in Florida, and men hunted them as soon as Indians arrived in the region.

Manatees in the St. Mary’s River, Georgia.  I saw manatees when I visited Wakulla Springs, Florida.

West Indian manatees feed upon over 60 kinds of aquatic plants such as eel grass and turtle grass, and they incidentally ingest snails and small fish while munching on vegetation.  The extinct Stellar’s sea cow ( Hydromalis gigas ) ate kelp.  Stellar’s sea cow was the largest species of manatee, formerly reaching lengths of 30 feet.  It was the only species of manatee adapted to live in cold water.  They evolved a layer of blubber to help them cope with the frigid temperatures of the north Pacific.  Sea cows were widespread during the Pleistocene, ranging as far south as Monterey Bay, California, but by 1747 when they were first discovered by Europeans, they were already relegated to a small relic population off Commander Island located in the remote Bering Sea.  They were overhunted to extinction by 1768.

Some archaeologists speculate Paleo-Indians first reached North America by following a route along the Pacific coast, but they have no concrete evidence.  The reduction in the population and range of Stellar’s sea cow may be indirect evidence supporting this hypothesis.  Prehistoric seafaring people likely overhunted Stellar’s sea cow and extirpated them over most of their former range.  Sea cows reproduced slowly and were easier to hunt than whales.  Kelp beds, the habitat they preferred, have remained abundant throughout their decline and extinction, so ecological change can’t be the reason they became extinct.

All extant species of manatees are in danger of extinction today precisely because of the slow reproductive rate that doomed Stellar’s sea cow.  Manatees reproduce fast enough to replace populations lost to cold snaps, red tides, and other causes of natural mortality, but the addition of deadly boat propellers to their environment may be pushing them over the edge.

Pleistocene Pecans (Carya illinoinensis)

The pecan tree is 1 of 17 species of hickory trees.  Hickories are native to North America and Asia and formerly occurred in Europe, but Ice Ages, beginning about 2.5 million years ago, wiped them out there.  European mountains have an east to west orientation, while American mountains are oriented north to south.  Hickories prefer temperate climates, and the east-west mountains blocked their retreat in Europe during glacial expansions.  This explains why hickories and so many other tree species survived Ice Ages in North America but not in Europe.

Evidence of fossil pollen grains suggests hickory trees grew alongside dinosaurs during the late Cretaceous, though the oldest fossil hickory nut dates to about 34 million years ago.  Most early hickory species had thin shells, but they evolved thicker shells about 38 million years ago in response to the evolution of tree squirrels.  Squirrels love the nutrient rich nuts, so hickories evolved nuts with thicker shells, and the squirrels in turn evolved greater gnawing power.  Evolution is a constant struggle.  However, pecans retained the thinner shells of their early ancestors.  This puzzled me because it seems as if squirrels would have eliminated all hickory species with thinner shells because they were easier to exploit.  I wondered if pecans were a recent species, cultivated and spread by Native Americans.  I’ve concluded however, based on certain lines of evidence, that pecans are an ancient species of hickory, not a recently evolved species manipulated by man.

Wild pecan tree.

Native range of wild pecan trees.  Man has greatly expanded this range by planting pecan orchards.  Georgia is now the leading producer of pecans, though they are not native to this state.  Pecans need longer growing seasons than other species of hickory because their nuts mature later.

Genetic studies determined pecans have a large genetic diversity within populations.  If pecans descended from human cultivation, they would have low genetic diversity because they would descend from a small population initially cultivated by man.  I was also mistaken in considering squirrels the only major predator of hickory nuts.  The pecan weevil ( Curculio caryae ) infests all species of hickories, and pecan trees growing in mixed stands with other hickory species have an advantage over their cousins.  Pecans mature later in the season than other species of hickory.  The pecan weevil hatches and emerges in August and will infest whichever hickories have developed kernels.  Because thick shelled hickories mature before thin-shelled pecans, the pecan weevil will infest them first and go through their life cycle without ever infesting the thin-shelled pecan.  Weevils will wait for pecans to mature, if no other hickory trees are available.  So though thin shelled pecans may suffer heavier squirrel predation, they are less likely to have their nuts destroyed by weevils, if they grow near other species of hickory.

Pecan weevil larva.  Pecans mature later than hickories.  Though squirrels favor pecans over hickories, the later maturing pecans are less likely to be attacked by pecan weevils in mixed forests, giving pecans an advantage over other hickory species.

Pecans are native to river bottomland terraces where they grow in forests dominated by sycamore, sweetgum, and elm.  Other subdominants in these terrace forests include water oak, box elder, silver maple, cottonwood, green ash, hackberry, and other hickory trees. Pawpaw, bamboo cane, pokeweed, grape vine, poison ivy, and green brier make up the thick undergrowth of bottomland forests.

Pecans hybridize with 5 other species of hickory.  The nuts produced by wild pecans and hybrids vary in quality.  Most are smaller and have somewhat thicker shells than cultivated varieties of pecans, and some even have high amounts of bitter tannins–all part of their ongoing evolutionary war with squirrels and weevils.  Human cultivation of pecans on a large scale began circa 1900.  Though Georgia isn’t part of the pecan’s native range, the state is the leading producer, and there is a large demand in China and India, resulting in high prices at the grocery store for the nuts.

Most cultivated varieties of pecans don’t mature before the first killing frost occurs in Midwestern states.  A few small early maturing varieties can produce in the Midwest as can the hican–an hybrid cross between pecan and shellbark hickory.

 

 

 

 

 

 

 

 

 

 

 

Hican nuts–an hybrid cross between a pecan and a hickory.  They produce earlier maturing nuts  for northern locations that have frosts before pecans can fully develop.

The southern Mississippi River Valley has long served as a refuge for pecans and other hickory trees during glacial expansion cycles.  Here, they grew in mixed Ice Age forests with spruce, beech, walnut, and oak.  Pecans expanded their range north up the Mississippi River Valley following the end of the last Ice Age.

The oldest written recipe for pecan pie dates to 1886.  It was a custard pie made with sugar, eggs, and butter.  (Sugar/custard pies originated during the Middle Ages.)  Pecan pies became more popular in the 1930s when some unnamed employee of Karo syrup invented a recipe for a pecan pie using syrup as well as sugar.  I prefer my pecan pie made with maple-flavored corn syrup.

Pecan pie with whiskey maple cream sauce.  I like my pecan pies made with maple flavored corn syrup.

 

Forest Succession and Changing Song Bird Species Composition in Central Georgia

Cotton and corn cultivation were important in central Georgia until the boll weevil struck in the 1920’s.  Then the depression bankrupted many farmers who tried to persevere, despite this agricultural pest.  This economic calamity gave ecologists the opportunity to study forest succession as fallow fields eventually were transformed into climax forests.  In less than a year bare soil becomes covered in grass and weeds 2 feet tall.  Ragweed, asters, and broomsedge (a type of bunch grass) take over in the 2nd year, and by the 3rd year broomsedge and pine saplings up to 3 feet tall predominate.  These 1st three years are known as the “grassland stage.”

If left unmodified, years 3-10 are known as the “grass and shrub stage.”  Broomsedge and pine saplings are joined by blackberry, blueberry, sumac, greenbrier, and persimmon often covered by grape vines, Virginia creeper, Carolina jessamine, and honeysuckle–all plants that thrive in the sun.  Eventually, pine trees emerge above this tangled mess.  During years 11-30 the landscape is known as a “young pine forest.”  An “old pine forest,” years 31-60, hosts tall pine trees but with a dense oak understory.  This mixed pine/oak forest is habitat for more species of birds than any other stage.  Lightning strikes, red heart disease, and pine beetles kill many pine trees during this stage, opening up the forest canopy and creating uneven-aged stands of trees beneficial for many different species of birds.  After 60 years left fallow the land becomes a climax oak/hickory forest.

Below is a chart interspersed with photos showing the association of bird species with each stage of forest succession.

Years 1-3 (Grassland Stage)–grasshopper sparrow, field sparrow, song sparrow, meadowlark, killdeer plover, quail, junco, horned lark.

Grasshopper sparrows (Ammodramus summurum) are abundant in old fields.

Years 3-10 (Grass and Shrub Stage)–Add white-throated sparrow, rufus-sided towhee, cardinal, catbird, mockingbird, mourning dove, Carolina wren, and brown thrasher.

 

 

 

 

 

 

 

 

 

 

 

Covey of quail.  This species becomes most abundant 3-5 years after cleared land is left fallow.

Years 11-30 (Young Pine Forest)–Subtract most of the grassland species but add flicker, blue jay, chickadee, titmice, pine warbler, and white-eyed vireo.

 

 

 

 

 

 

 

 

 

 

 

 

 

Rufus sided towhees move into young pine forests.

Years 31-60 (Old Pine Forest Stage)–Subtract mourning dove, catbird, mockingbird, brown thrasher, and white-eyed vireo, but add summer tanager, woodpeckers, yellow-throated warbler, black and white warbler, wood thrush, flycatchers, red-eyed vireo, and kinglets.

Carolina wrens are abundant in old pine forests with an hardwood understory.

> 60 years (Climax Oak/Hickory Forest) Subtract towhee, pine warbler, and tanager, but add white breasted nuthatch.

White breasted nuthatches won’t move into a forest until it is at least 50 years old.  Last time I saw this species was when I visited Marshall Forest in Rome, Georgia which is a virgin forest.

Forest succession from bare soil to climax forest has occurred in Georgia ever since Indians began cultivating the land here over 1000 years ago.  However, habitat including each successional stage is much older than this because our present day species of song birds, especially habitat specialists, have existed for over 1 million years.  Before man impacted the environment, changes in the landscape depended upon natural disturbances.  Heavy acorn consumption by megafauna along with trampling and bark-stripping suppressed tree recruitment and growth.  Lightning-ignited fires thinned forest into open woodlands.  Tornadoes and downbursts flattened wide swaths of trees.  Drought, ice storms, floods, and fluctuating climate cycles also changed forest structure and tree species composition.  Landscapes are never eternally permanent.

References:

Johnson and Odum

“Breeding Bird Populations in Relation to Plant Succession on the Piedmont of Georgia”

Ecology 37 1956

Meyers, J.M. and A.S. Johnson

“Bird Communities Associated with Succession and Management of Loblolly-Shortleaf Pine Forests”

U.S. Forest Service General Technical Report

 

Native Fish Species Composition of Piedmont Tributary Creeks of the Chattahoochee River

The many present day creeks and small rivers that flow through the piedmont region of central Georgia originated between 15,000 years BP-8,000 years BP when water tables rose as a result of melting glaciers far to the north of the state.  Before this, during the Glacial Maximum, the regional landscape was much more arid and only the largest of rivers and creeks still flowed…and those were often low flowing and clogged with sandbars.  Intermittent springs probably occurred in the lowest areas of topography along the present day courses of smaller streams.  Climatic phases with increased precipitation raised the water table enough to cause water flow between springs, and these creeks eventually emptied into the nearest river.  So much atmospheric moisture was released at the end of the last Ice Age that rivers and creeks had a larger flow than they do today.  This occurred between ~10,000 years BP-~5,000 years BP when rivers were classified as “supermeandering.”  Fish found their way from rivers into newly formed creeks during the late Pleistocene/early Holocene, though a few species may had persisted in relic Ice Age springs before water tables rose.  About 40 years ago the noted naturalist, Charles Wharton, electro-fished a small unnamed creek located 1.4 miles south of Sopa Creek, a tributary of the Chattahoochee River, and he determined the “near original” composition of fish species typical of piedmont streams that flow into this river.  These creeks flow through steep terrain often between high bluffs and where protected are still very beautiful natural areas.

Cobb County, Georgia.  Charles Wharton electro-fished a small stream here over 40 years ago and determined the original fish species composition of piedmont Chattahoochee feeder creeks.

This is where Sopa Creek flows into the Chattahoochee River.  Sherman ordered his troops to cross over the rocks here during the Civil War.

The fish species Wharton found in his survey included band fin shiner ( Notropis zonistius ), central stoneroller ( Campostoma anomalum ), creek chubsucker ( Erimyzon oblongus ), Alabama hog sucker ( Hypentelium etowanum ), yellow bullhead catfish ( Ictalurus natalis ), bluegill ( Lepomis machrochorus ), and banded sculpin ( Collus carolinae ).  The band fin shiner is a small minnow native to the Chattahoochee River drainage, though it has been introduced to other river systems wherever fishermen dump their bait buckets.  The stoneroller is a widespread species in the Midwest.  It eats algae and may school in the hundreds.  They grow up to 8 inches long.  The creek chubsucker can grow twice as long as the stoneroller, and it eats small crustaceans and insect larva in addition to algae.

Alabama hog sucker.

The yellow bullhead catfish is omnivorous and can grow up to 6 pounds, though it normally reaches a weight of about 2 pounds.  Bluegills also grow large enough to make a good meal.  Early settlers placed fish traps in the nearest streams and caught supper, while they were busy clearing and cultivating their land.  Bluegills and catfish living in clear moving streams with rocky  bottoms probably taste better than those taken from muddy ponds.

Yellow bullhead catfish.

Bluegill sunfish or bream.

The banded sculpin is a freshwater relative of a large family of saltwater species.  Banded sculpins are nocturnal ambush predators that live under stones.  They compete with crayfish for the same type of habitat.

Banded sculpin.

The origin of the name Sopa Creek has a disputed origin.  This stream flows for 11.6 miles through Marietta until it empties into the Chattahoochee River.  Today, the headwaters emerge from a spring under a manmade culvert, but I’m sure the original landscape was picturesque.  Now, it is surrounded by suburban sprawl.  Some say this creek gets its name from the foam caused by water rushing through rocks.  The foam resembles soap spuds, and supposedly an early mapmaker misspelled soap.  Others claim the creek is named after an old Cherokee Indian (Old Sopa) who lived nearby.  He reportedly refused to be removed when is compatriots were force marched to Oklahoma on the Trail of Tears.

Reference:

Wharton, Charles

The Natural Environments of Georgia

Georgia Department of Natural Resources 1978

 

Pleistocene Ungulates of Interstadial Oak Woodlands and Forests in Southeastern North America

I have long been curious about the wildlife I would encounter, if I could travel in a time machine to a wilderness cabin located in central Georgia 36,000 years ago.  This climatic stage was an interstadial–a relatively warm wet phase of the Ice Age.  It was likely well before people entered the region, so I could experience an ecosystem completely uninfluenced by man.  Pollen evidence from deep ocean cores suggests an expansion of oak woodlands and forests during interstadials, while pine and spruce declined.  (Botanists distinguish the difference between woodland and forest.  A woodland has 50%-80% canopy coverage; a forest has >80% canopy coverage.)  Oak woodlands were probably the most common natural community in the Georgia piedmont during interstadials.  They had an open structure with centuries-old, large diameter trees in the overstory and herbaceous and grassy understories.  Megafauna trampling and foraging along with low intensity fires and occasional windstorms maintained the open structure of the woodlands.  Areas less frequented by megafauna and protected from fire fostered thicker forests.  Oaks dominated the landscape but co-occurred with hickory, chestnut, and pine.  The warmer the climate phase, the greater the variety of trees.

Oak woodlands provided ample food for a large population of animals.  Acorns and plants growing in the understory fed herds of ungulates as well as bears, small game, and birds.  Bison, horses, and mammoths prefer(ed) prairies and meadows, and mastodons foraged alongside streams.  Although these species occasionally wandered into woodlands, they were probably less common than other species of ungulates in this environment.  Instead, ungulates that fed mostly on forest vegetation prevailed in oak woods.  Studies of bone chemistry that determined dietary preference suggest forest denizens included white-tail deer, long-nosed peccary, tapir, and paleollama.  These are the ungulates I would expect to see from a window in my imaginary wilderness cabin.  Fossil remains of paleollama ( Palaeolama mirifica) have not been found north of the coastal plain, but they may have ranged into the piedmont.  Its cousin, the large headed llama ( Hemiauchenia macrocephela ), was more widespread and isotopic studies indicate it could subsist on either prairie or forest vegetation.  The presence of at least 1 species of llama in central Georgia seems likely.  And of course herds of ungulates attracted a whole array of predators.  The woods of today seem so destitute by comparison.

 

 

 

 

 

10 white-tail deer and a turkey.  This species of deer and its immediate ancestor have populated southeastern North America for millions of years.

Long-nosed peccary.  The success of invasive wild hogs shows that forest environments in the south can support a large population of pig-like animals.

Mountain tapir with a baby.  Tapirs that lived in the upper south during the Pleistocene likely were adapted to temperate climates like this species.  Isotopic studies of tapir bones indicate they preferred the thickest part of the forest.

Paleollamas.  They occurred in Florida and the coastal plain and may have ranged into the piedmont.  This species of llama also preferred deep forest, but its cousin, the large-headed llama, was more adaptable.