THE EVERGLADE MAGAZINE
Naturalist's Niche


by Steve Woodmansee

Introduction

We South Floridians are blessed with a subtropical climate hosting a great variety of organisms. In fact, Florida contains more species of reptiles, amphibians and plants than any state in the continental United States. In the Everglades, unusual and sometimes endangered critters and flora make their homes in numerous types of ecosystems, or communities. I'll discuss what I believe are some of the more interesting ones. Since my column will only be around this year, I will inevitably leave out some things. My objective is to cover not only animals, but all types of organisms, including plants and their relatives, along with their habitats. I hope that my articles will inform the reader, portraying the Everglades in both an interesting and educational light.





Geology



Geologically speaking, South Florida and the Everglades are new. During the Pleistocene or Ice Age 100,000 thousand years ago (which was warm at times, causing the ice to melt), the sea was 25 feet higher, totally submerging the Everglades region. Live coral reefs were located where the upper Keys are today, and the Atlantic coastal ridge was made up of oolitic sand mounds. Both areas hardened into rock during the Wisconsin Glacial Period about 80,000 years ago, when the Earth's temperature decreased and much of the ocean froze into huge glaciers. Roughly 5,000 years ago, mangroves slowly took over the freshwater marsh of Biscayne Bay as the sea level rose. Barrier islands formed into today's Cape Florida and Cape Sable. By 3,000 B.C.E. the Everglades had formed. The sea level continues to rise, more quickly than the three-inches-per-century rate of 100 years ago. Next time, I will explain how human interference with South Florida's hydrology caused this change.





Wetlands



Compared with the mostly desert lands on the same lati-tude, Florida stands out for its many wetlands. Swamps border the state; their water flows into Florida both below and above ground, seeping into porous rock aquifers. The deepest aquifers contain a lens of fresh water floating on saltier water. Heavy rain forces the fresh water up to form springs. Before drainage lowered the water table, these springs even erupted in Biscayne Bay! Much of Florida's fresh water is constantly recycled, evaporating into clouds and raining back down during the wet season. Drainage canals have altered South Florida's hydrology, reducing the surface evaporation area of wetlands so that rain has become rarer and less predictable. Channelization has also allowed more salt water to creep into the aquifer. But winter is still the dry season, when water levels go down and living things must adapt -- like the well-suited alligator, which I will discuss next time.





Alligator



Alligator mississippiensis, or the American Alligator, is the largest predator, reptile and four-legged animal in the Glades, averaging eight feet long (some reach 17 feet). Found throughout the southeastern U.S., alligators are most common in Florida's fresh and brackish waters. Though fearsome-looking, gators generally pose no threat toward people unless they are fed and begin to associate humans with food. Strangely enough, in South Florida, alligators mainly eat apple snails, whose shells may help them digest. One reason for the gator's nasty reputation: Mothers can be very protective of their young. Gators build nests and lay eggs, shielding them from such predators as raccoons. They even bite the eggs gently to help the babies hatch, protecting them for several years until they are about 12 inches long and have almost no predators except other gators. During the dry season, alligators dig precious watering holes where fish, wading birds and other hungry and thirsty Everglades inhabitants congregate.





Sawgrass



When Marjory Stoneman Douglas coined the term "river of grass," she was referring to sawgrass, the principal plant of the Everglades. Growing within a freshwater marsh and savannah-type ecosystem inundated by water most of the year, sawgrass is an important source of food for many organisms, like insects and deer -- especially after fires. Like most graminoids, sawgrass has adapted to fire, using its rhizome, or underground stem, to survive. "Sawgrass" is actually a misnomer. Cladium jamaicense is a sedge, not a grass. Grasses belong to the family Poaceae, whereas sawgrass is a member of the family Cyperceae. Sawgrass is so named because of the tooth-like serrations along the leaf. If you were to grab a leaf and run it along the edge downward, you would probably get cut. Remember, sedges have edges, and this sedge has three of them -- the third running along the midrib. A cross-section of this

graminoid looks like a V. We could change the common name to "sawsedge," but it wouldn't sound quite right!





Mosquito Fish



Walking along the Anhinga Trail in Everglades National Park, one can witness a plethora of fishes, including numerous game fish such as largemouth bass, freshwater catfish, mudfish, pickerel, and numerous sunfish or bream. However, the species of fish most representative of the park is the mosquitofish. This little guy can be seen everywhere there is fresh or brackish water. Although it measures only several centimeters in length, Gambusia holbrooki serves a very important role: It eats mosquito larvae. Another prominent fish is the Florida gar, a fascinatingly prehistoric-looking fish that sits and lurks while waiting for unsuspecting prey (like the mosquitofish) to swim close to its mouth so it can snatch it. Found further north is its close cousin the alligator gar, which can grow quite massive and is one of the largest freshwater fish in Florida. Although fishing is permitted within

the park, due to the water's high mercury content, freshwater fish are considered unsafe to eat.





Mangroves



In southern Florida, the most dominant coastal community is the mangrove swamp. Mangroves benefit us in numerous ways: Among other things, they provide nutrients to coral reefs and are a nursery for developing fish and shrimp, which find sanctuary from predators among the intricate root systems; they are an important habitat for nesting birds; they prevent soil erosion and act as a buffer to storms' tidal surges, protecting us from the infliction of even further damage; and they remove pollutants from the surrounding water. Without them, our tourism industry would be in jeopardy: Recreational fishing would be severely affected, and our oceans would not be as clean. South Florida, put simply, would not be as nice a place to visit or live. While Florida has lost much of its mangrove community to development, a great number remain in conservation areas like ENP. Though not endangered, mangroves are a "species of special concern" and it is illegal to cut them without permission.





Wading Birds



Certainly one of the most aesthetic reasons to visit the park, wading birds provide tranquil beauty to the Everglades. These long-legged, usually carnivorous fowl hunt mainly aquatic or marine life with a variety of methods. Herons and egrets tend to stalk and ambush their prey. Ibises probe the muck with their curved bills in a sewing machine motion, often in groups. Wood storks insert their open beaks into the water, waiting for prey to pass through their bills. Then, with lightning-fast reflexes, they clamp onto their unsuspecting dinner. In the early 19th century, many wading birds were hunted almost to extinction for their feathers to adorn ladies' hats. Later, when the Everglades' water flow was altered, bird populations took another severe blow. Some winter oases, which the birds depended on for food during the dry season, dried up; many birds starved to death. Today, their numbers have mostly stabilized, thanks to laws and adaptation to artificial winter refuges such as canals.





Spiders



Aside from snakes, spiders have the undeserved distinction of being some of the most feared animals on the planet. Scientists have even suggested a human genetic predisposition to account this for phobia, since it seems to be a constant worldwide. Although all spiders carry venom, only a few are deadly to most humans. Spiders' most obvious trait is their ability to spin silk, which they have adapted to a variety of uses. Silver, Southern and Golden Orb-weavers spin stationary orb-webs in areas frequented by insects. The deadly Black Widow builds less geometric cobwebs in habitats such as decomposing logs. Not all spiders wait for their prey to entangle themselves. The nocturnal ogre-faced spider fashions a net to actively snare an unsuspecting moth or mosquito. Fishing spiders build a web below the water surface and fill it with a dome of breathable oxygen, resting there between periods of hunting small

fish. Wolf and jumping spiders capture their prey on foot as their names suggest, without using a web at all.





Sea Grass



Not unlike mangroves, sea grasses are vital to the health of South Florida, performing many of the same functions. They act as a sanctuary to developing marine life, and provide food and nutrients to other outlying communities such as intertidal zones and coral reefs. They also indicate severe pollution and other environmental fluctuations since they are sensitive to subtle changes. Sea grasses seem to do best around estuarine environments, where fresh and salt water mix. Sea grass beds house diverse organisms such as mermaid's tea cups, chicken liver sponges, arrow crabs, sea hares and bone fish. Interestingly, sea grasses are actually flowering vascular plants. Like porpoises, their ancestors were once terrestrial, and over time adapted to marine life. Three species are most common in south Florida: Turtle, shoal and manatee. Turtle grass is the most common here, with a relatively wide leaf blade compared to the other two species. Shoal grass has a thin blade but is flattened like turtle grass. Manatee grass is thin, but cord-shaped.





Hurricanes



Florida has a long history of being plagued by hurricanes. However, these destructive storms also provide a natural function, dispersing seeds (some from as far away as Africa) and increasing the ranges of plants. Hurricanes help "flush" and renew natural systems, such as making additional sunlight in closed canopy systems available to many new species. Only when humans alter their environment do hurricanes become an undue burden. For example, exotic pest species such as Burma reed and Melaleuca may unfortunately benefit from storms by spreading their range even further. During Hurricane Andrew in 1992, many pines were knocked down or damaged by strong winds. Due to the artificial lowering of the water table through drainage, pines outside the Park could not produce enough sap to discourage predators like pine-bark beetles and were unable to heal their wounds.





Fire



Smoky Bear is wrong. Fire is an essential force in nature to which animals and plants have been adapting ever since terrestrial ecosystems have existed. In fact, some of Florida's rarer habitats, such as pine rocklands, marshes and coastal strands, are dependent upon fire for their survival. Some adaptations to fire are thick, insulating bark, underground stems, quickly-burning leaves, and underground burrows. Burns open the canopy, permitting light-dependent plants such as pines and saw palmettos to grow and reproduce. Fire also encourages new growth important for deer and insects, and releases nutrients into the soil, causing plants to flower. Naturally, most fire climax communities burn every five to ten years; these fires are slow and rarely spread to the crowns of trees. However, the policy of fire suppression has made fuel loads very high, creating danger-ously hot blazes. Today, deliberately-set "controlled burns" are neccessary to remove flammable plant material and make full-scale fires less destructive.





Coral Reefs



Coral reefs are the most energy-efficient of all ecosystems. Corals provide nutrients and a home for cyanobacteria, which in turn give food through photosynthesis to the corals. Like their close relatives, the sea anemones, adult corals are sessile, or immobile. Coral comes in two types: soft and hard. Soft corals, such as sea fans, are common in both tropical and temperate climates, and often inhabit deeper water. Hard corals require shallower as well as cleaner water due to their close relationship with cyanobacteria, which require sunlight. Hard corals are the primary contributors to coral reef construction, excreting calcium carbonate as a byproduct to form "homelike" surroundings that are often quite intricate, such as those of elk and staghorn corals. Over time this limestone builds up, forming reefs. Coral reefs feed a large variety of species, including hundreds of different fish, crustaceans, sponges and algae. Although protected, reefs face an uncertain fate due to recreational overuse and pollution.



Cypress Swamps



Cypress swamps, often depicted as mysterious and dangerous with dark-as-molasses water full of gators and cottonmouths, are actually beautiful and tranquil. These forested wetlands are dominated by trees, bromeliads and other canopy species. South Florida cypress swamps come in two types: strands and domes. Unique to Florida, strands are formed when acids etch away limestone, forming slight, irregular depressions. They are fairly continuous strips of swamp with fluctuating water levels depending on peat build-up and encompassing many square miles, as in the Fakahatchee Strand in southwestern Florida. Because strands are so large, they contain a greater variety of plants and animals than the smaller cypress domes -- doughnut-shaped tree islands that dot the marshy sawgrass prairies and have a less regular flow of water. Smaller trees fringe the edges, with larger ones toward the middle. The center of the doughnut is a dugout depression created by alligators, forming a wet haven during the dry season.





Raptors



One of the most popular activities within Everglades National Park is bird watching. Especially fun to watch are the spectacular flyers known as birds of prey, such as owls, hawks, kites, eagles, falcons and vultures. These raptors are all carnivores; most have strong talons for grasping prey, along with curved, razor-sharp beaks for tearing prey apart. Owls are nocturnal, silent flyers with excellent hearing that helps them locate prey in the dark. Diurnal hawks, eagles and kites are "model" raptors and are some of the larger and stronger representatives, except for kites, which specialize in eating smaller prey. Falcons are the fastest and most capable flyers, able to catch birds on the wing. Vultures have a keen sense of smell for finding the carrion on which they feed. Raptors benefit humans in many ways, such as feeding on rats and other pests. Sitting atop the food web, raptors are "indicator"

species whose presence helps determine the health of rare communities. It is illegal to hunt or harm raptors.



Pine Rockland



Of all communities in ENP, perhaps most rare is pine rockland, named for the predominance of surface limestone (Miami oolite) and its main canopy emergent, Southern slash pine (Pinus elliotii var.densa). A basic soil averaging a pH of near 8 distinguishes this unique ecosystem from other pine communities. Pine rocklands occur on an eastern ridge of limestone, usually three to six meters above sea level, that runs southwestward through Dade County. Though it contains few trees, the pine rockland's lower shrub and herb layers boast over 350 native plant species, including the endangered Deltoid spurge, Small's polygala, Crenulate lead plant and flax. During floods, deer seek refuge in these uplands. Historically, people have also favored this high ground; development has decimated over 90 percent of the original pine rocklands. The largest chunk left is in the Park. Pine rockland exists only in the U.S., the Bahamas and Cuba; therefore, the preservation of what little remains is paramount.





Apple Snail



Anyone who has hiked, paddled, or slogged through the Everglades has perhaps wondered at the peculiar, small white balls clinging to sawgrass or floating aquatic plants. These are the eggs of one of the most important animal species in the Everglades food web, the freshwater apple snail (Pomacea paludosa). Adult snails average the size of a lime, or up to two inches across. They feed mostly on periphyton and decayed plant matter and are not just the predominant, but sometimes the only prey eaten. Oddly, adult alligators consume so many apple snails that some biologists once believed the snail to be their major food source. Current thought, however, is that alligators, which normally swallow rocks to aid in digestion, eat apple snails for this purpose because South Florida limestone dissolves too quickly in their stomach acids. Even more dependent upon apple snails are limpkins, which also eat frogs and lizards, and snail kites, which depend solely on apple snails for food.





Reptiles



South Florida has the distinction of having more reptiles than anywhere in the U.S. Its warm, moist climate is conducive to their proliferation. Turtles, crocodilians, lizards and snakes can all be seen in the Everglades. Traits common to all reptiles are dermal scales and a body temperature which cannot be internally regulated, i.e. "cold blood." Some reptiles are typical to only a few habitats, while others are pandemic. Alligators can be seen wherever there is a freshwater source, while endangered crocodiles are much rarer, being localized to remote areas of the southern coastline in brackish water and mangrove/spartinea marsh habitat. Sliders are turtles restricted to deeper water such as rivers, canals and gator holes. Sea turtles nest only on coastal beaches such as Cape Sable. Skinks, box turtles, diamondback rattlesnakes and indigo snakes favor the drier terrain of pine rocklands and hammocks, although not exclusively. Carolina anoles, everglade racers and rat snakes are found in most habitats.





Air Plants



Literally meaning "upon plant," epiphytes are plants that grow on other plants. While some are parasitic, such as mistletoe and love vine, which feed on their hosts, most Florida epiphytes are commensals: One species benefits (the epiphyte) while the other (the host) is unaffected. Commensals are also known as "air" plants because they were thought to derive nutrients from their namesake. In reality, they absorb water from rainfall and humidity, and nutrients from fallen leaves. Many bromeliads have leaves which conduct water toward their centers, forming a reservoir. Typical adaptations are waxy surfaces, which reduce the evaporation of water, and hairy leaves, which capture airborne water. Some epiphytic orchids have bulbs for storing water and food. Being subtropical, South Florida is fortunate to have the most epiphytic orchids in the continental U.S. The common resurrection

fern actually curls up, turning brown during drier times of the day or year; soon after a rain, it opens and turns green again.





Hardwood Hammocks



Hardwood hammocks are dominated by flowering subtropical hardwood trees and have a humid climate. In Everglades National Park, hardwood hammocks exist on elevated areas, such as shell mounds built by native peoples over thousands of years, and within pine rockland and sawgrass prairie. Trees often found in hardwood hammocks include lysiloma, mastic, gumbo limbo, pigeon plum, live oak, paradise tree and Jamaican dogwood. In fact, some of the larger hammocks boast over 40 species of trees. Hammock soil is rich in limestone and organic material. However, because they are geologically recent, hardwood hammocks contain very little soil; like sunlight, there is much competition for it. Therefore, if trees get too tall, they can fall over during high winds. The resulting gaps in the canopy create a rich subcommunity where several light-loving species do well, such as Florida trema, Firebush and vines. Eventually, though, these openings are refilled by the more aggressive hardwood trees.





Mammals



At first glance, Everglades National Park would not appear to be very good habitat for terrestrial mammals. And, unfortunately, few large land-loving mammals exist in the Park today. However, one can still happen upon a great deal of variety. Rare sightings of otter, deer, marsh rabbit, cotton rat and gray squirrel are possible during the day. During twilight, bobcats, foxes, opossums and raccoons can all be seen. Periods of high water are difficult for terrestrial mammals, especially larger species such as panther and deer. Deer overpopulate and overgraze the few remaining upland habitats; many starve to death. Their overabundance is also due to extirpations or reductions of predators such as wolves and panthers. Marine mammals such as the West Indian manatee and bottle-nosed dolphin can be seen in the salt and brackish coastal waters where there is an abundance of food. Manatees feed primarily on sea grasses, whereas dolphinseat the many fish that congregate in these rich estuarine environments.




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