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Diversity of Living Deer
The artiodactyl family Cervidae (deer) has a rich fossil record going back to the early Miocene, around 20 million years ago, and includes several species of very large deer that persisted through the Pleistocene. The cervids still with us today include a number of well known and widespread species, as well as some very poorly known and endangered species. Mattioli (2011) recognized 53 cervid living species placed in 18 genera. He noted, however, that cervid taxonomy is still evolving and that a list of living cervid species 30 years earlier would likely have included only around 34 species. This change is due to the availability of new taxonomic data (notably, DNA sequence data) and approaches, as well as the discovery of entirely new forms. Many taxonomic discoveries likely still lie ahead.
There are two distinct subfamilies within the Cervidae:
1) Subfamily Cervinae (8 genera with 30 species). This subfamily includes two tribes, Muntiacini and Cervini.
a) Tribe Muntiacini. This tribe includes two genera, Elaphodus (with just the single species E. cephalophus, the Tufted Deer) and Muntiacus (muntjacs, 11 spp.), both of which are composed of deer that are relatively small and stocky with males whose antlers are fairly short and simple. Muntiacini are well known for having karyotypes with very few chromosomes.
b) Tribe Cervini. This tribe includes six genera: Axis (4 spp.), Dama (2 spp.), Rusa (4 spp.), Cervus (5 spp.), Elaphurus (1 spp.) and Rucervus (2 spp.). Axis and Rusa deer have three-pointed antlers. Dama (fallow deer) have palmate antlers. Cervus have more complex, four-to-six-pointed antlers. Elaphurus has unusual antlers with a foreshaft and hindshaft. Rucervus is composed of graminivorous deer with specialized molars.
2) Subfamily Capreolinae (or Odocoileinae) (10 genera with 23 species). Nearly all deer in the Capreolinae exhibit a precocious development of the first set of antlers and their permanent dentition is in place by 18 months. This subfamily includes three tribes: Capreolini, Alceini, and Odocoileini.
a) Tribe Capreolini. This tribe includes the Chinese Water Deer (1 species, Hydropotes inermis), which are unusual antlerless deer in which males have long upper canines, and roe deer (Capreolus, 2 spp.).
b) Tribe Alceini. This tribe includes only the Moose (Alces alces).
c) Tribe Odocoileini. This tribe includes the Caribou or Reindeer (Rangifer tarandus) and all the New World deer (known as the neocervines). There are six genera of New World deer: Odocoileus (2 species), Blastocerus (only Marsh Deer, B. dichotomus), Ozotoceros (only Pampas Deer, O. bezoarticus), Hippocamelus (2 species), Pudu (2 species), Mazama (brocket deer, 10 species; some genetic evidence suggests that Mazama should be split into two genera). In many species in this tribe, there is a time lag of a month or two between the shedding of antlers and their regrowth. Some species are multiparous, i.e., females can give birth to more than one offspring per litter. In White-tailed Deer, first-time breeders, as well as does in the tropics, usually produce singletons, whereas adults in temperate regions typically have twins. With the exception of the Caribou, deer fawns are "hiders" rather than "followers", remaining concealed in vegetation for the first few days, or even weeks, of life (in contrast, newborn Caribou can stand an hour after birth and follow their mothers after 5 to 7 hours). Newborn deer of most species have a spotted coat, which may help them remain unnoticed in vegetation.
Some species formerly considered to belong in the Cervidae are now recognized not to fall within this group based on new genetic and other data, e.g., the musk-deer (now placed in their own family, Moschidae). Some deer once thought to have retained various traits from ancient lineages, such as the antlerless Chinese Water Deer, are now recognized as members of recent lineages in which these apparently "retained" traits, such as lack of antlers, were actually secondarily derived.
Ecology and Behavior
The extant cervids vary considerably in body size, ranging from the 5.5 kg Northern Pudu (Pudu mephistophiles) to the 770 kg Moose. In some species, males and females are the same size (e.g., Red Muntjac, Muntiacus muntjac), but most cervids show some degree of sexual size dimorphism. In Chinese Water Deer and Fea's Munjac (Muntiacus feae), females are slightly heavier than males, but in most cases males are larger. In some Caribou populations, the mean body weight of males can be twice that of females. In addition to size dimorphism, other sex-specific characteristics seen in some cervid species include differences in antlers, neck manes, dewlaps, and nuptial coats. Sexual dimorphism tends to be more pronounced in more strongly polygynous species, in which a male tends to monopolize a group of females. In Chital (Axis axis), Western Red Deer (Cervus elaphus), Common Fallow Deer (Dama dama), and Barasingha (Rucervus duvaucelii), males are on average 70-90% heavier than females. In Wapiti (Cervus canadensis) of Siberia and North America, males weigh 30-40% more than females. Some cervid species exhibit a high degree of geographic variation in body size. In White-tailed Deer, for example, body size ranges from 100-130 kg in Canada to 30-35 kg on some islands in the Florida Keys (U.S.A.) and in South America. In Western Red Deer, there are ecotypes adapted to different regional habitats with adult stags ranging in size from 110 kg to 300 kg. Other types of geographic variation occur as well. For example, during the last glacial maximum, 18,000 years ago, Mule Deer populations in western North America were separated and diverged, with those now in the Pacific Northwest, known as "Black-tailed Deer", having a tail that is black above, whereas other Mule Deer have a conspicuous white rump patch and a white tail with a black tip. Mule Deer run with a four-footed bounding gait known as "stotting" and can briefly reach a speed of 40km/h. Their large ears are around two thirds the length of the face.
Among the most distinctive characteristics seen in cervids is the presence of antlers. These paired cranial appendages are outgrowths of the frontal bone that grow and are shed each year (these are quite distinct from the horns of Bovidae, which are permanent appendages consisting of a bony core covered by a hollow keratinized sheath). In most deer species, only males grow antlers and the annual antler cycle is closely tied to the testosterone cycle. The only known exception is the Caribou, in which a large fraction of females develop antlers each year (although males shed their antlers from November to January whereas female antlers are retained through the winter and shed from March to May, during the calving period). Chinese Water Deer never grow antlers, although phylogenetic evidence suggests that their ancestors did.
Deer occur in a wide range of habitats, including forests, woodlands, and wood edges. The broad habitat use of some species can result in very large geographic ranges. For example, White-tailed Deer are found from the tropical forests of South America to the boreal forests of Canada. Other deer species showing broad geographic and habitat ranges include Western Red Deer, Hog Deer (Axis porcinus), and Chital. Some species (muntjacs, brockets) spend most of their time in dense vegetation; a few species are found only in open habitats; Barasingha, Brow-antlered Deer (Rucervus eldii), Pere David's Deer (Elaphurus davidianus), and Chinese Water Deer live in the tall grassy vegetation around marshes. Caribou are found in circumpolar barren tundras and high Arctic deserts. Several high-elevation species (White-lipped Deer [Cervus albirostris]; huemuls [Hippocamelus]; Central Asian Red Deer [Cervus wallichii]; pudus [Pudu]; and the three South American dwarf deer, the Little Red Brocket [Mazama rufina], Common Dwarf Brocket [Mazama chuny], and Merida Brocket [Mazama bricenii) spend most of their time above the treeline on summit meadows and scrublands, sometimes up to 5100 m above sea level. Living at high elevations requires special adaptations to cope with limited oxygen availability, intense solar radiation, and low temperatures.
Deer first reached South America via the Panamanian Land Bridge around 2.5 million years ago. Some of the deer that evolved in South America are quite specialized. For example, Marsh Deer (the largest deer in South America) are found in swamps and other wetlands, usually with water around a half meter deep. Their legs are long for wading and, like most deer, they swim well. Pampas Deer are the only deer specialized to live in savannas and prairies. As is the case for most deer species living in open habitats, the size dimorphism between males and females is not very great.
Many cervids, especially medium- and large-sized species, have a well developed vocal repertoire. Olfactory communication is also very important. Every species has at least three different kinds of scent glands. Glands between the pads of Pampas Deer hooves produce a substance with an onion-like smell which can be detected over long distances.
Deer must fill their rumens every few hours, so feeding dominates their time budget. Many deer are browsers and some species (such as many brockets) are largely frugivorous (fruit-eating). Some deer are predominantly grazers (e.g., Pere David's Deer, Barasingha, and Brow-antlered Deer, all characteristic of wet grasslands). Wapiti of Siberia and North America and White-lipped Deer, which have colonized dry grasslands, are mainly grazers but include leaves and twigs in their diet. Common Fallow Deer and Sika Deer (Cervus nippon) have a relatively large rumen and are able to feed on coarse plants, but may switch to a browsing diet when necessary.
In all deer, parental care is provided exclusively by the female.
Deer and Humans
Humans have always hunted deer in Europe, Asia, and the Americas. Subsistence hunting of deer is still still significant in Southeast Asia and South America. Deer are hunted for meat as well as for their skins (for clothing ) and antlers (for tools).
Around the globe, deer species have often been translocated by humans. For example, Persian Fallow Deer (Dama mesopotamica) were brought from Lebanon to Cyprus in the 9th millenium BC, the Portugese are believed to have introduced Hog Deer to Sri Lanka in the 16th century, and Dutch sailors and traders likely brought Javan Deer (Rusa timorensis) to Mauritius in the 17th century. In the 1920s and 1930s, Caribou were released on the sub-Antarctic islands of South Georgia and Kerguelen to provide meat for the crews of whaling vessels. Australia now has six established species of non-native deer and New Zealand has nine. The Western Red Deer was transported to Sardinia around 8000 years ago, probably from the Italian Peninsula. Some species, such as Common Fallow Deer and Javan Deer, have been moved around so much by humans that it is now difficult to identify the native range. In addition to being moved to new regions to establish populations for hunting, live deer have been collected as novelties and these deer have sometimes escaped and established populations. Thus, for example, there are now feral populations in Great Britain of Sika Deer, Reeve's Muntjac (Muntiacus reevesi), and Chinese Water Deer. Since the late 1970s, deer farming has become common in China, Korea, Taiwan, Europe (especially Great Britain), Australia, and New Zealand, with the meat going mainly to European markets and velvet to Asia.
The only deer species that has been successfully domesticated is the Reindeer (domesticated Caribou), with Reindeer husbandry dating back several thousand years. Attempts were made to tame Moose in the former Soviet Union during the 20th century.
Although some deer species have been very well studied (e.g., Western Red Deer, Wapiti, Western Roe Deer, Moose, Caribou, White-tailed Deer, Mule Deer), others are very poorly known (e.g., some Southeast Asian muntjacs, South American brockets, pudus, and Philippine Brown Deer [Rusa marianna]).
Conservation Status of Deer
Although populations of several deer species in some western countries are excessive given the available habitat, on a global scale many deer species are threatened by habitat loss and hunting (for food, traditional medicine, and other uses), conflicts with domestic livestock, and other causes. Only one deer species is known to have gone extinct since 1600, Schomburgk's Deer (Rucervus schomburgki), which was known only from seasonally flooded swampy plains in central Thailand. This species went extinct as a result of habitat destruction (following the extensive conversion to rice production in the late 19th century) and persecution in the early 20th century). A number of deer are listed as Endangered or Vulnerable by IUCN. The only species listed as Critically Endangered (as of 2011) is Bawean Deer (Axis kuhlii), found only on Bawean Island between Java and Borneo. However, two other island species are listed as Endangered: Calamian Deer (Axis calamienensis, found on three main islands of the Calamian Islands in the Philippines) and the Philippine Spotted Deer (Rusa alfredi, restricted to two islands of the Western Visayas). Persian Fallow Deer, Giant Muntjac (Muntiacus vuquangensis), Hog deer, Brow-antlered Deer, and South Andean Huemul (Hippocamelus bisulcus) are also Endangered. Another 16 species are listed as Vulnerable (many of these are island species or species with very fragmented distributions). Tufted Deer (from China) and Pampas Deer (from South America) are listed as Near Threatened. Even some species listed as Least Concern are rapidly decreasing due to overhunting and deforestation (e.g., Common Brown Brocket [Mazama gouazoubira] and Amazonian Brown Brocket [Mazama nemorivaga] in the tropics and Eastern Roe Deer [Capreolus pygargus] in temperate and boreal regions). Many large populations of Caribou may be exhibiting long-term declines (apparently as a consequence of ecological changes resulting from a warming climate). Recovery efforts for some species, such as Pere David's Deer and Persian Fallow Deer, have achieved significant success through captive breeding, although populations remain vulnerable and Persian Fallow Deer is still listed by IUCN as Endangered. Hybridization with introduced species poses a threat to some species (e.g., introduced Sika breeding with native Western Red Deer in the British Isles).
(Mattioli 2011 and referenes therein)