Florida Sand Scrub Habitat Hosts Pliocene-Age Relicts

About 2 million years ago, an exceptionally dry climate phase occurred over most of North America.  Grasslands and scrub habitat stretched in a continuous belt from southern California to Florida.  Most of the large vertebrates that thrived in such an environment such as llamas, camels, flat-headed peccaries, pronghorns, horses, and donkeys have been rendered extinct or extirpated from the southeast, but the sandhill habitats of north and central Florida still host scores of relict invertebrates in addition to the Florida scrub jay.  Specimens found at the Inglis fossil site in Citrus County, Florida provide a glimpse of the fauna formerly inhabiting the once extensive arid grassland and scrub habitat that existed across the southeast during the late Pliocene.  In addition to the above mentioned species, the antelope jack rabbit (Lepus alleni), now confined to the American southwest, was a common component of the ecosystem when the climate was drier.

Antelope jack rabbits and an extinct species of jack rabbit lived in southeastern North America during the late Pliocene when the climate was much drier than it is today.

Pleistocene glacial cycles also fostered drier climates and an increase in scrubland and grassland habitat, but these environments never again formed an unbroken corridor from west Texas to Florida.  I hypothesize that pine and oak forest species evolved a greater drought tolerance and were able to grow in some areas with favorable conditions, thus forming interdicting fingers of habitat that prevented some scrubland species, such as jack rabbits, from recolonizing the southeast.

The shaded black areas indicate sand scrub habitat–an environment that once stretched from southern California to Florida.  A continous sand scrub belt hasn’t existed for at least 1 million years.  Many small species have become isolated in these relict habitats.

Most of Florida is so low lying in elevation that numerous high sea stands have inundated much of the state.  High sea stands have occurred on many occasions dating as far back as the Miocene and as recently as the Sangamonian Interglacial of the late Pleistocene.  High hilltops, however, remained above sea level as islands surrounded by sandy beaches.  The sand scrub areas of today are simply remnants of these sandy beaches.

The Florida scrub jay (Aphelocoma coerulescens) used to be considered the same species as the Western scrub jay (A. californicus).  About 20 years ago scientists declared they were a separate species because they have a shorter broader bill and are less able to disperse following an acorn crop failure.  Fossil evidence shows that Florida scrub jays were a distinct species as long as 2 million years ago.

The Florida scrub jay is an example of a scrubland species now isolated from populations of its ancestral species–the Western scrub jay.  The fossil evidence from Inglis shows that by 2 million years ago, the Florida scrub jay was already a distinct species from the Western scrub jay.  Florida scrub jays are habitat specialists that will not even travel through unsuitable habitat.  They are endangered today because much of their habitat has been transformed into subdivisions and citrus orchards.  Families of scrub jays living on 1 patch of remnant scrubland will not fly through an orange orchard to reach another patch of scrubland.  Studies show that for the bird to survive, they will need corridors of protected scrubland habitat to prevent extinction through inbreeding.

Scrub jays are tame birds, known for taking food from people’s hands.  Offspring help care for young, a habit that makes them semi-communal birds.  Scrubland habitat in Florida provides a reliable crop of acorns which along with seeds, insects, and small lizards makes up the bulk of their diet.  Despite growing stunted, sand live oaks (Quercus germinata). myrtle oaks (Q. myrtlefolia), and scrub oaks (Q. iopina) provide plenty of mast, unlike Rocky Mountain oaks which may fail to produce acorns in the harsher climate there.  This accounts for the behavioral difference between Florida scrub jays and Western scrub jays. The former never evolved the habit of dispersing when the acorn crop fails because in Florida’s climate that seldom happens, but the latter did of necessity and is therefore more widespread and not endangered.

Over 70 species of invertebrates are also unique to the Florida scrublands.  Because it’s such a harsh environment, most plants growing there are high in toxins and have evolved thorny structures to discourage herbivores.  But these defenses don’t deter many of the insects that have co-evolved with them.  Scrub rosemary is a toxic plant that unwillingly hosts species of a grasshopper, moths, and beetles. 

Florida sand scrub wolf spider killing an insect.  Note the spider is the same color as the sand.

Florida sand hair ant (Componotus floridanus).  The hair enables them to travel through sand without sinking.

Other unusual invertebrates are specially adapted to living in sand.  They have waxy armor that protects them from being shredded by sharp grains of sand, and they have stiff hairs that help them locomote through sand without slipping backward.  One species of harvester ant has hair under its mandible in the shape of a basket to carry sand when they excavate their 3 foot deep nests.  Hunting wasps are common, and they actively defend their paralyzed prey because in the thinly vegetated habitat, it’s more likely to be discovered by other carnivores such as tiny yellow predatory ants, wireworms, and robber fly larvae which abound under the sand. 

 Each isolated sand scrub community has its own species of short-horned scrub grasshopper…an ideal case study for biologists interested in evolution.  The wealth of unique arthropod species found in the Florida scrub attracts entomologists and evolutionary biologists who consder the scrublands a mecca of potential new discoveries.  And just think–these invertebrate species once shared a wider range with now extinct megafauna.

Reference:

Deyrup, Mark and Thomas Eisner

“Last Stand in the Sand”

Natural History Magazine (102) 12 December 1993

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Rabbits will Inherit the Earth

Matthew 5:5 (“Blessed are the meek for they shall inherit the earth”) always reminds me of rabbits for these meek creatures surely could outlast man.  Imagine if humans destroyed each other with nuclear, chemical, or biological weapons.  With a penchant for rapid breeding, rabbits could rapidly recolonize the world after the warlike species, Homo sapiens, annihilated itself.

Georgia is home to 4 species of rabbits, and during the Pleistocene the southeast also harbored at least 2 kinds of hares.  At various times the lagomorphs (hares and rabbits) may have been more abundant (as a biological mass) than any single species of megafauna.  Scientists interpeted a fossil site near Gainesville, Florida to have been a dire wolf den because they found a skull belonging to Canis dirus in association with hundreds of rabbit bones.  Rabbits must have been an easy and abundant food source, more reliable than any single species of megafauna.  Rabbits easily survived the Pleistocene extinction event that wiped out many of the larger, fiercer animals.  The meek really did inherit the earth.

Here’s a review of rabbit and hare species found or formerly found in Georgia.

Rabbits

Eastern Cottontail–Sylvilagus floridanus

Photo of an eastern cottontail from google images.

While this species is by no means endangered, there are likely far fewer than there were as recently as 50 years ago.  Suburbs and shopping centers are replacing the early successional forests they prefer.  And the natural areas we let remain are maturing into older stands of timberland which is not as favorable a habitat for rabbits.  Rabbits like young forests with saplings, shrubs, and grassy open areas.  This type of habitat was abundant during the Pleistocene, thanks to rapid climate fluctuations, unchecked fires, and megafauna foraging.

New England Cottontail–Sylvilagus transitionalis

In a blog entry from a few weeks ago I listed the species found at the Ladds fossil site and mistakenly noted, about the New England cottontail, that I thought it was doubtful a subspecies could be determined based on a bone.  I didn’t realize the New England cottontail was a distinct species, not just a subspecies.  Today, the New England cottontail is being considered a candidate for the endangered species list.  Hunters introduced the eastern cottontail to New England, and it is doing well, but the New England cottontail is not adapting to suburbanization and is restricted to a small number of locations.  It looks much like an eastern cottontail.  They can hybridize with eastern cottontails in captivity but won’t do so in the wild.  Before advances in DNA research, scientists had to compare skulls to determine whether a cottontail was an eastern or a New England.  But now scientists can analyze the DNA of rabbit scat to identify species.  However, the fossil specimen from Ladds that Clayton Ray identified as a New England cottontail was probably an Appalachian cottontail.

Appalachian cottontail–Sylvilagus obscura

Photo of an Appalachian cottontail.  They look exactly like New England cottontails.  Only DNA analysis can determine the difference.  For that matter, visual inspection can’t differentiate between this and the eastern cottontail.  A skull comparison or a DNA anlysis is necessary for species determination between those species as well.

This species wasn’t identified or recognized until 1992.  Before then, it was considered the same species as the New England cottontail.  Scientists noted enough genetic differences to mark it as a distinct species, though there is academic debate about this.  Again, visual determination of live speciments can’t distinguish the difference between this and the eastern cottontail.  Instead, DNA tests or skull measurements are necessary.  The Appalachian cottontail inhabits heath balds in the north Georgia mountains.

Swamp rabbit–Sylvilagus aquatica

As this photo from google images shows, swamp rabbits readily take to water.  This is the rabbit that attacked President Carter.

Many readers of this blog may be too young to know about an event that occurred involving this species during the presidency of Jimmy Carter.  On vacation from the presidency Jimmy Carter sat in a canoe and fished a  Georgia swamp.  A swamp rabbit attacked his boat–probably the only instance when a sitting president was attacked by an animal.  I guess the rabbit was swimming in the swamp and felt threatened by the canoe.

Swamp rabbits occur alongside rivers and streams in the Georgia piedmont.  They’re known as canecutters because they eat bamboo cane which used to grow in thick stands many miles long in low areas of central Georgia.  Though canebrakes are rare today, swamp rabbits still can reside near the existing and numerous beaver ponds, another favored habitat.

Marsh rabbit–Sylvilagus palustris

Photo of a marsh rabbit from google images.

The range of this species takes up where the swamp rabbit’s leaves.  Whereas swamp rabbits occur in low areas of the piedmont, marsh rabbits inhabit coastal plain wetlands.

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Antelope Jackrabbit–Lepus alleni

 

 

Photo of an antelope jackrabbit from google images.

Fossil hunters occasionally find jackrabbit bones in florida.  Antelope jackrabbits inhabited the southeast until, at least, the middle Pleistocene (~300,000 BP).  Dry climate phases created large scale grassland and even desert-like chapparel habitats where antelope jackrabbits shared the range with pronghorns, cheetahs, and camels.  As I speculated in my blog entry “The disjunct range of the burrowing owl,” a corridor between western grasslands and eastern grasslands must have existed until the Stagell Interglacial.  Forested habitats increased during this lengthy interglacial, and this probably ended the occurrence of many western species (though not all) in the east.  The skeleton of a large unnamed extinct species of jackrabbit, estimated to be about 2 million years old, has also been discovered in Florda.  Both species undoubtedly occurred in what’s now Georgia.  Today, antelope jackrabbits must be considered a relic species, restricted to southwestern deserts.

Snowshoe hare–Lepus americanus

 

 

Lynx attacking a snowshoe hare.  Photo from google images.

Fossil evidence proves Arkansas was home to snowshoe hares during the last Ice Age.  It’s quite possible snowshoe hares occured in north Georgia during the Pleistocene, and they probably lived in what’s now Tennessee.  Arkansas is well south of the present day range of this species.

Red Stewed Rabbit

In my irregular series on this blog, “If I could live in the Pleistocene,” I imagine living 41,000 years ago in what’s now east central Georgia but with modern conveniences such as a nice adobe brick home with solar-powered electricity, woodstoves,  running water from a well, and fresh produce grown in a well protected garden. (See my September and December archives) Though I raise poultry and milk cows in this imaginary utopia, I try to utilize as much game and fish as I can.  Rabbit would likely have to be an item in my diet, though I’m not too keen on killing them–their alarm call sounds like a human baby crying.  In real life I’ve experimented with rabbit and have learned that it is a good stewing meat.  Rabbit is all white meat with a flavor slightly superior to chicken.  If you’ve never had it, and someone served it to you, and you didn’t notice the different bone structure, you would think you were eating chicken. There’s not much fat on a rabbit but that’s the only part that might taste a little unusual in my opinion.

Many people fry rabbit like chicken.  It’s ok this way but I think a little dry.  Other cooking methods are apt to make the rabbit have a rubbery texture.  That’s why I recommend stewing rabbit in a crockpot.  Here’s the best recipe for rabbit I know.

Marinate a disjointed rabbit in 1 cup of soy sauce, 2 tbls of vegetable oil, 2 tbls of honey, 1 bunch of chopped green onions, and 5 spice powder and ginger powder to taste.  Place the rabbit pieces and the marinade in the crockpot and cook for 6 hours.  The meat falls of the bone.  A little bit of the sauce goes a long way–it’s a marinade, not a gravy, but a couple of sp0onfuls will season a side of egg noodles well.

Rabbit meat stewed in a crockpot with just onions, water, and salt also makes a good base for a Brunswick stew.  Just shred the meat, remove the bones, and add crushed tomatoes, cooked potatoes, canned limas, canned corn, and red and black pepper.