Evolution of Cervidae
The emergence of ungulate type mammals is thought to have occurred during the mid-Tertiary period based upon the fossil record for the “Old World” tropics. However, Key Deer (Odocoileus Virginianus Clavium) emerging from “New World” (more advanced) types of deer may have evolved due to temperature extremes at northern latitudes from a Eurasian species. The deer present in the tropical to subtropical environment played a modest ecological role at best. (Geist, V.) Consistent with the tropics were areas of nutrient lacking or leached soils. Due to the climate and weather patterns associated with the lower latitudes, some species of deer adapted to a fertile land surfaces that have been inundated with nutrient rich silt and loess from glacial actions, floods, wild fires, and avalanches. Constructive and destructive happenings have been the driving forces behind the evolution of the deer. Fossil evidence also suggests that deer overall did not flourish in a mature, species rich environment, but rather in a younger type of new growth area. Therefore, Artiodactyla of North America evolved as an opportunistic species by taking advantage of high nutrient food surpluses that existed. The deer’s big appetite for highly digestible nutrient rich forage apparently drove its evolution. (Geist, V.) The “New World” (Odocoilnae) represents a very successful and highly independent group of deer as compared to other Eurasian species. Throughout the evolution of these highly advanced deer there has been a trend with increases in body size, size and complexity of antlers, and establishment of a social habitat. However, the Florida Key Deer do not represent a species that follows these trends. Florida Key Deer are one of sixteen subspecies of deer in North America. As referenced from V. Geist and R. Putnam, the “New World” types of deer probably emerged from a northern species trying to escape the cold temperatures of the time. It’s speculated that white-tailed deer immigrated into Southern Florida during the most recent ice age about 15,000 to 20,000 y.b.p. During this global transition period the Keys were not islands, but merely a continuous ridge of land. Accompanying the receding glaciers (about 10,000 y.b.p.) global water levels began to rise and the whitetails found themselves isolated. Isolation was a driving force for individual species evolution. Typically species of large mammals that become isolated on small tracts of land become smaller and adapt to environments with limited resources.
Even toed vs. odd toes ungulates
The even toed ungulate (Artiodactyla) is named for having two or four digits. The Key deer may be referred to as having a cloven hoof (ungulate) with two toes. Observed on the “New World” deer the third and fourth digits are well developed but the second and fifth are present only as distal ends. The first digit is entirely absent. V. Geist presents the evolution of the two subfamilies. Old World Cervidae vs. New World. Perissodactyla, the odd toed ungulates, consist of a small order of herbivores that are distinguished from Artiodactlya by the presence of a prominent third digit. The horse family (Equida) has only one functional toe whereas the rhinoceros bears the majority of body mass on three digits. The lighter faster mammals run on only one (horse) or two (deer) toes. Of the two orders, Artiodactyla is the most successful based upon the diversity of species. Through time the diversity of Perissodactyla has diminished.
Taxonomy of Key Deer
Kingdom- Aniamalia
Phylum- Chordata
Class- Mammalia
Order- Artiodactyla
Family- Cervidae
Genus- Ordocoileus
Species- Virginianus
Subspecies- Clavium
Description of Key Deer
The Florida Key deer is the smallest species of Virginia White-Tailed deer in the United States. Colors vary from reddish brown to a grizzly gray/ blue-gray color. The molting between different colored hair depends primarily on altitude and latitude. Throughout one year all N. American deer will have two complete hair molts, where southern deer shed their coats earlier than northern species and later during the summer. Mature male Key deer range in weight from 55 lbs. to 75 lbs. (24.9 kg- 34 kg) and measure 25 in. to 30 in. (63.5 cm-76.2 cm) at the shoulder. Female weight ranges from 45 lbs. to 65 lbs (20 kg – 29.5 kg). As compared to the white-tailed deer (Ordocoileus Virginianus) Key deer have characteristics of a stockier body, shorter legs, and a wider skull. The fact that Key deer are proportionally smaller than the neighboring white-tail relative found at greater latitudes clearly resembles Bergmann’s Rule. (Northern White-tails typically stand 40 in. (101.6 cm) at the shoulder and weigh less than 160 lbs. (72.6 kg)). Bergmann’s Rule states that body mass of a geographic race is in direct relation to the North/South distance form the equator. (Rue, L.) Therefore, isolation on an island is a prime ingredient for evolving mechanisms that produce adaptations to limited resources and less annular fluctuations in climate .The rule does vary according to the opportunistic feeding behavior of deer. A preferred, abundant food source must be present to meet the nutritional needs. If not, body mass and volume decrease. To ensure that the forage is properly digested Key deer are equipped with specific teeth to increase mechanical digestion. Premolars and molars are permanently fixed to the mandible and maxilla. Canines are absent and incisors are located on the anterior end of the mandible only.
Digestive System/Diet
The digestive system is adapted for the fibrous diet of plant material. The ruminant four-chambered stomach must meet the energy requirements of a grazing (grasses and herbaceous vegetation) ungulate by absorbing the maximum of nutrients while leaving little to waste. Mechanical digestion in the mouth is vital to the diet of all deer. Key deer along with other orders of Artiodactyla are known for their cud chewing based upon a symbiotic relationship that exists with deer and the bacteria and protozoa found in the first chamber (rumen) because of the inability to digest cellulose. Animals unable to digest this part only obtain 20% of nutritional energy from plants. Therefore, the Key deer, and other highly evolved species, rely on bacteria to break down the cellulose to release its energy content. From this an increased energy content of 50%-60% is available for absorption. (Putnam, R) The bacteria also aid in the in the continual process of forming a cud that can be regurgitated at a later time for post-mastication. Post-mastication usually occurs in a “safe place.” Since most ungulates cannot digest cellulose as mentioned earlier, their attention becomes divided during grazing from predation. A survival strategy of fast eating and minimal chewing allows a deer to be more receptive since 50% of their time is spent grazing. The re-chewed cud (now referred to as pulp) enters the reticulum, omasum, and finally the abomasum (true stomach for chemical digestion by gastric processes). Ultimately, Key deer are making the most of low quality but high intake of foodstuffs. The Florida Key deer’s primary food source, following an herbivorous diet is the red mangrove, black mangrove, Indian Mulberry, Silver and Brittle Thatch Palm fruits, Blackbead, grasses, Pencil Flower, Acacia, and Wild Dilly fruits. Precipitation influences what plants are grazed upon and during a drought plants typically left alone become a staple food source. As quoted by Portman, “the single most significant factor affecting the pattern of habitat use expressed is the quality and availability of forage.” The grazing behavior occurs mostly in the late evening, night, and early morning. In addition to forage, freshwater is important to the survival of Key deer because of its limited availability. Specifically with the Key deer problems have occurred from humans feeding the deer on the lower keys even though regulations exist that make it illegal.
Nervous System
Two special senses have evolved through selective pressures in nature for the majority of all deer distributed globally. From studies, deer sight (vision) is not limited to black and white. Within close range there is some resemblance of color vision. At greater distances deer rely heavily on vague movement. Combined with a significant sense of smell, and selective pressures present, deer can be very elusive. However, the minimal accounts of predation on Key deer and their close capacities with humans makes for a detrimental life style in an insular environment.
Habitat/Range
Historically there are no records documenting the precise origin of the Florida Key Deer. However, in the writings of Spanish explorers during the 1500’s observations of Key deer are briefly mentioned. Key deer are restricted to Monroe County, Florida and reside predominantly on the Lower Keys of; Big Pine (5,997 acres), Big Torch, Cudjoe, Howe, Little Pine, Little Torch, Middle Torch, No Name (998 acres), Sugarloaf, and Summerland. The underlying resource that enables these particular islands to be populated is the availability of fresh water. Two thirds of the population can be observed on Big Pine and No Name Key because of the abundance of freshwater during the wet and dry seasons. Areas typically used for grazing are the pinelands, hardwood hammocks, recent clearings, roadsides, and grassy areas. (The Red Book, FWS) The habitat may be used year-round or seasonally within a given range. Also, they may be found foraging in residential areas feeding on ornamental plants and grasses where they can seek refuge from biting insects. (USFWS)
Status and Conservation
Presently the biggest impact on the mortality of the Key deer is the loss of habitat to development. Future human population growth only increases these situations. Loss of habitat increases mortality of Key deer from road kills, predation from dogs, mosquito ditches, over-hunting during the 1940’s and 1950’s, and a fragmented habitat due to development. The Key deer has been designated as an endangered species under the Endangered Species Act of 1973, and protected under the Lacey Act. Due to efforts from local, state, and national agencies the population of Key deer is approximately 800. Other resources give a more conservative population of 600-700. With increases in population the probability of motor accidents also increase. Some resources list highway deaths as the number one mortality factor for the Key deer. With expanding development the Key deer have found their range limited while their population grows at a rate of 1% - 3% each year. A result of this is an increase in disease transmission of stomach worms and brain abscesses. Efforts in the future may experiment with expanding the Key deer habitat by relocating them to other non or less populated islands with similar habitats. Currently, the National Key Deer Refuge (estab. 1957) has been established to manage the population of deer found on Big Pine. Acquiring more land is the single most important factor to protect the Key deer along with efforts of habitat management and restoration. Examples of habitat restoration include prescribed burning, mowing of clearings and fire breaks, filling of mosquito ditches, limiting the influx of saline water, removing exotic vegetation and planting native species, and development and protection of habitat corridors.
References:
Conservation Management Institute Website, March 28, 2001.
Florida Environment Website, March 6, 2000.
Geist, V., and F. Walther, eds. 1974. The behavior of ungulates and its relation to management. Internat. Union Conserv. Nature and Natural Resources Publ., n.s., no. 24, 2 vols.
Geist, V., Deer of the World, Their Evolution, Behavior, and Ecology: Stackpole Books; 1st Edition: l998.
Hickman, Roberts, Larson. 1997. Integrated Principles of Zoology; pgs. 602, 607, 616, 623, 702, 705.
Prescott, Harley, Klein. 1993. Microbiology, 2nd ed. pgs. 568-571.
Putnam, R. 1988. The natural history of the deer. Comstock Publ. Assoc., Cornell Univ. Pr., Ithaca. 191 pp. QL737.U55P87 1989.
Rue III, L.L.; The Deer of North America; Outdoor Life Books, Danbury, CT. , 1989.
Smith, Robert L. 1996. Ecology and Field Biology, 5th ed. pgs. 109-112, 125-127, 179, 472.
Texas A & M Website, Key Deer Research Project.
The Ultimate Ungulate Website, April 13, 2001.
U.S. Fish and Wildlife Service 1990. Endangered and Threatened Species of the Southeastern United States (The Red Book)
U.S. Fish and Wildlife Service Website, National Key Deer Wildlife Refuge
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