Mammalian Populations and Evolution PDF

Rapid evolution of secondary sexual characteristics, including size, can take place in a species with such a social structure. A complex behaviour termed 'play' frequently occurs between siblings, between members of an age, class, or between parent and offspring. Play extends the period of maternal...

Rapid evolution of secondary sexual characteristics, including size, can take place in a species with such a social structure. A complex behaviour termed 'play' frequently occurs between siblings, between members of an age, class, or between parent and offspring. Play extends the period of maternal training and is especially important in social species, providing an opportunity to learn behaviour appropriate to the maintenance of dominance. Territory Many mammals have territories, areas from which members of the same species are excluded. Many wild animals compete for food and mates with members of their own species, particularly during the breeding season, or times of low food supplies. If the mammal has a fixed residence, (e.g. burrow or hole) this usually forms the centre of the area. Territory boundaries are usually marked by scent, from various species-specific scent glands or through urine or dung marking. Thus, an invading animal is at an immediate psychological advantage. Should a challenge follow, the intruder usually breaks off the encounter in a submissive display characteristic of the species. Territories may be sex specific; a male cat (tigers and other solitary cats) holds a large territory, within which there may be several individual females' territories. The map shows the territories of wolf packs in a national park in North America. Territorial and aggressive displays are described later in the course. An exception to the strong territorial drive of most species is the prairie dog, which lives in large friendly communities ('towns'). When a next litter is reared, adults relinquish the old burrow to the young and move to the 'edge of town' to establish a new home burrow. The vast majority of mammalian species drive off young when they are old enough to fend for themselves. A home range of a mammal is a much larger area than a defended territory. It is usually the areas within which an animal will forage for food. Home ranges may overlap between animals, and some communal areas may be mutually agreed. Mammalian populations A population of animals includes all members of a species that share a particular area and could potentially interbreed. All mammals (like other organisms) live in ecological communities, each composed of different animal and plant species. Each species is affected by the activities and populations of the other species inhabiting their environment; in addition, all can be affected by climatic conditions, both in the long and in the short term. Because of these various influences, most populations vary in size from time to time. Populations of small mammals are always lowest before the breeding season, and greatest just after the addition of new members, beyond these expected changes in mammalian populations, fluctuations can occur for other reasons. Irregular populations are commonly produced by variations in climate, such as unusually cold, hot, dry, and wet seasons or by natural disasters such as floods, fires or severe storms. These are density independent factors, because they affect a population whether it is crowded or dispersed. The most dramatic population fluctuations are density dependent, that is, they correlate with population overcrowding. Cycles of abundance are common amongst many rodent species, one of the better known being the mass migrations of lemmings resulting from population peaks. This species breeds throughout the year, although more are born in the warmer months. Gestation lasts only 21 days, with spring born babies being weaned in 14 days and capable of reproducing by the end of the summer. At their highest population density, the local environment is devastated by grazing and tunnel building. Overcrowding produces long mass migrations to find new sources of food and space. They will swim across small lakes and streams, but as they cannot distinguish the size of bodies of water, attempts are still made to cross large bodies of water resulting in drowning. As lemmings are the main prey for many carnivores, birds, and mammals, their populations are also affected. More information on ecological systems is provided in a later module. Mammalian classification There are 19 mammalian orders, unfortunately, only brief details can be provided, although students may wish to use the following information as a starting point for further research. Order Ornithodelphia -- monotremes (duck-billed platypus, echidnas). Egg laying species limited to Australasia and New Guinea. Order Marsupiaria -- viviparous pouched mammals (opossums, kangaroos, koalas, Tasmanian wolves, wombats, bandicoots, etc.) have an abdominal pouch. There are 260 species in Australia, 80 in South America and one (Virginia opossum) in North America. Infraclass Eutheria -- all remaining groups are placental mammals. Order Insectovora -- insect eating mammals. There are 419 species including shrews, hedgehogs and moles. Worldwide distribution (except in Australia) Order Macroscelidea -- elephant shrews, long legged, large eyed, insect eaters. 15 species widespread in Africa. © OXL/CN/AN 2022 127 Student No: PD24-51917-ZOCIE15 Email: walkergrace116\@gmail.com Name: Grace Walker Order Dermoptera -- flying lemurs, which are thought to be related to true bats, and have recently been proposed as being close to an ancestral primate form. Order Chiroptera -- bats, the only true flying mammal (925 species). Wings are modified forelimbs in which the second to fifth digits are elongated to support a thin skin membrane for flying. The first digit (thumb) is short with a claw. Order Scandentia - tree shrews. Small squirrel-like animals of the tropical rain forests of southern and Southeast Asia. There are 16 species. Order Xenarthra -- anteater, armadillo, sloth. Species are either toothless (Anteaters) or have simple peg like teeth. Most are found in South and Central America. 29 species. Order Pholidota -- pangolins. An odd group of mammals whose bodies are covered with overlapping horny scales formed from fused bundles of hair. Seven species found in tropical Asia and Africa. Order Lagomorpha -- rabbits, hares and picas. Lagomorphs have long, constant growing incisors like rodents, but unlike rodents, they have an additional pair of peg-like incisors growing behind the first pair. All lagomorphs are herbivores with worldwide distribution (except Australia) and there are 80 species. Order Rodentia -- gnawing mammals, including squirrels, Rats, capybara, and beaver. There are 2277 species. Rodents comprise nearly 40% of all mammalian species, they are characterised by two pairs of sharp incisors used for cutting tough plant material. Their success is probably due to their small size, short breeding cycle, and ability to gnaw and eat a wide variety of foods. Rodents are found in vast numbers on all continents except Antarctica, most islands, and in all habitats except oceans. They are the only placental order, other than bats (Chiroptera) and Pinnipeds, to reach Australia without human introduction. Order Carnivora -- flesh eating mammals with 280 species. dogs, cats, bears, weasels, seals, sea lions and walruses. All carnivores (except the giant panda) have predatory habits, with teeth adapted for tearing flesh. They have worldwide distribution except for Australia. Even Antarctic is the occasional home to seals. Among familiar families are canidae (dog family consisting of dogs, wolves, foxes and coyotes), felidae (cat family, ranging from tigers to domestic cats), Ursidae (bear family), Procyonidae (racoons), Mustelidae (Fur bearing family, martens, skunks, weasels, otters, badgers, mink and wolverine) Otariidae (fur seals and sea lions). Order Tubulidentata -- aardvark. One species in Africa. Order Proboscidea -- proboscis mammals: Elephants. Largest living land animals, which have two elongated incisors as tusks and well-developed molar teeth. Asiatic (Indian) Elephants have long been domesticated, but the taming of African elephants is more problematic. However, the ancient Carthaginians and Romans used them extensively for war. Order Hyracoidea - coneys are herbivores restricted to Africa and Syria. They are a curious group, with superficial resemblances to short-eared Rabbits, but their teeth resemble those of Rhinoceroses, with hooves on their toes and pads on their feet. There are 11 species. Order Sirenia - sea Cows and Manatees are large aquatic mammals with large heads, no hind limbs, and forelimbs modified into flippers. There are four living species, the Dugong (Seacow) of coastal East Africa, Asia and Australia and three Manatees (Caribbean, Florida and Amazon areas). A fifth species, Steller's Sea Cow, was hunted to extinction in the mid 18th century. Order Perissodactyla -- odd-toed hoofed animals, Horses, Asses, Zebra, Tapirs, and Rhinoceros. There are 18 species. Odd- toed hoofed animals have an odd number of toes (one or three), each with a cornifed hoof. Both Perissodactyla and Artiodactyla are often referred to as ungulates (hoofed mammals), with teeth adapted for grinding plants. The horse family (equidae), which includes donkeys, asses, and zebra, has only one functional toe. Tapirs have a small functional proboscis formed from the upper lip and nose. The Rhinoceros includes several species found in Africa and South East Asia, which are hunted extensively for the proposed medicinal properties of their horns. All species are herbivorous. Order Artiodactyla -- even-toed hoofed mammals, Pigs, Camels, Deer, Hippopotamuses, Antelopes, Cattle, Sheep and Goats. There are 217 species. Most of this group have two toes, although the hippopotamus and a few others have four. Many, such as cattle, deer, and sheep, have antlers or horns. The group is divided into nine living families, and many extinct ones, and includes the most valuable domestic animals. Artiodactyla is usually divided into three suborders, the Suina, (pigs, peccaries and hippopotamuses) Tylopoda, (camels) and the Ruminantia (deer, giraffe, sheep, cattle). Order Cetacea -- whales, dolphins, and porpoises. There are 78 species. Their anterior limbs are modified into broad flippers, but posterior limbs are absent. Some have a fleshy dorsal fin, and the tail is divided into transverse fleshy flukes. Their nostrils are represented by a single or double blowhole on top of the head. They have no hair except for a few on the muzzle, and no skin glands, except mammary and those of the eye. There are no external ears and eyes are small. The order is divided into two sub orders, the Odontoceti (toothed whales, including dolphins, porpoises and sperm whales) and the Mysticeti (baleen whales, right whales, grey whales and blue whales amongst others). Baleen whales are generally larger than toothed whales. Rather than teeth, baleen whales have a straining device of whalebone (baleen) attached to the palate, used to filter plankton. The blue whale is the largest animal ever to have lived. Order Primates - this order is first amongst all animals in terms of brain development, with particularly large cerebral hemispheres. Most species are arboreal. Primates represent a line that branched early from other mammalian groups, and they have retained many primitive characteristics. They generally have five digits (with flat nails) on their fore and hind limbs. Forelimbs are usually adapted for grasping, as are often the hind limbs. There are two suborders, and 223 species. Suborder Strepsirhini - lemurs, aye-aye, lorises, pottos, and bush babies. There are seven families of arboreal primates, referred to as prosimians, concentrated in Madagascar, but also found in Africa, Southeast Asia and the Malay Peninsula. All have a wet naked region (rhinarium) surrounding comma shaped nostrils, and a long prehensile tail. Food is both animal and plant in origin, and there are 47 species. Suborder Haplorhini - tarsiers, marmosets, New and Old World monkeys, gibbons, gorillas, chimpanzees, orang-utans and humans. This group has characteristically dry noses, ringed nostrils and differences in uterine anatomy, placental development, and skull morphology, which distinguish it as a suborder. Family Tarsiidae contains the Tarsiers, Nocturnal Primates with large forward-facing eyes and reduced snouts. New World monkeys (sometimes called Platyrrhine, because of their widely spaced nostrils) make up two families. Callitichidae contains the marmosets and tamarins (26 species), which have a quadrupedal mode of locomotion and are small in size, and the Cebidae, which are capuchin-like monkeys, larger than the Callitchidae, and are represented by species such as spider monkeys and howler monkeys. They have prehensile tails, which are used as a fifth hand. Old World Monkeys, termed catarrhine, because their nostrils are set close together and open to the front, are in family Ceropithecidae (81 species), including mandrills, baboons, macaques and langurs. The thumb and large toe are opposable, and some have internal cheek pouches. Family Hylobatidae contains gibbons and siamangs (11 species). All have arms longer than legs, and locomote by true branchaition (swinging). Family Hominidae contains four living genera and five species. gorilla (one species), pan (two species of chimpanzee) pongo (one species, orang-utan), and homo (one species, humans). Humans Biologically, Homo sapiens are a product of the same processes that have directed the evolution of every organism from the beginning of life. Mutation, isolation, genetic drift, and natural selection have operated for us as they have for all other species. Yet, we are unique within the species on Earth in having a non-genetic cultural evolution that provides a constant relationship between past and future experiences. Our symbolic language, capacities for conceptual thought, knowledge of our history, and ability to manipulate our environment, all emerge from this non-genetic cultural endowment. However, we owe much of what we are to our arboreal ancestry, which gave us binocular vision, superb visual-tactile discrimination and manipulation skills, which allow us to perform fine manipulations. Human evolution Humans are primates; a fact scientists even before Linnaeus recognised. All primates share distinguishing characteristics: grasping fingers on all four limbs, flat finger nails, (not claws) and forward pointing eyes with binocular vision, giving excellent depth perception. The earliest primate was previously thought to be a small nocturnal animal similar in appearance to tree shrews, although molecular genetic tests have now determined that the flying lemurs of South East Asia are more likely to be similar to the first primates. This ancestral primate stock split into two major lineages, one gave rise to the Prosimians (true lemurs and tarsiers), and the other to Simians (monkeys and apes). These animals all have an arboreal lifestyle, which is probably the lifestyle of the ancestors of both groups. Flexible limbs are essential for active animals moving through trees. Grasping hands and feet (in contrast to rodents and squirrels who have clawed feet) enabled primates to grasp limbs, hang from branches, seize and manipulate food and, were significantly pre-adapted to manipulate tools. Primates have highly developed sense organs, especially binocular vision. The cerebral cortex is also highly developed in order to process the information needed to produce the precise timing, muscle co ordination, distance judgements, and alertness needed to live an omnivorous arboreal lifestyle. The earliest simian fossils appeared in Africa from the late Eocene, about 40 million years ago. Many of these primates had changed to diurnal activity rather than being nocturnal, making vision the dominant sense, which was now enhanced by excellent colour vision. Three major simian groups are recognised; New World Monkeys of central and southern America (Ceboids) including howler monkeys, spider monkeys and tamarins; Old World monkeys (Ceropithecoids) including mandrills and colobus monkeys, and, lastly, anthropoid apes. Old World monkeys and apes are sister taxa compared to New World monkeys. They share several attributes such as lacking a non-grasping tail; having close-set nostrils, better opposable grasping thumbs, and more advanced teeth. Apes differ from Old World monkeys by having a larger cerebrum, a more dorsally placed scapula, and loss of the tail. The earliest ape fossils appear in 25 million year old deposits. At this time, the area consisted of woodland and savannah, perhaps motivated by the greater abundance of food on the ground. These forms left the trees and became largely terrestrial, much like modern baboons. The first hominids gradually evolved a more upright stance due to the advantages of better views of predators, leaving hands free for manipulation and carrying objects, whilst on the open savannah lands. This vitally important transition was an enormous leap, because it required extensive restructuring of the skeleton and muscle attachments. Evidence of the earliest hominids is extremely rare; however, 2001 saw the discovery of a chimp-like hominid skull, (see left) Sahelanthropus tchadensis in Chad, dated at about seven million years old. Although its brain is no larger than that of a chimp, its relatively small canine teeth, massive brow ridges on a short face, and a mouth and jaw that protrude less than in most apes, confirm that this is a hominid rather than an ape. Until this skull was found, the earliest known fossil was Ardipithecus ramidus, dated at 4.4 million years old. It had a mixture of primitive ape-like features, and derived hominid traits, with some contested evidence that it was bipedal. Additional Ardipithecus ramidus fossils, found between 1997 and 2001, extend its existence back to 5.5 million years ago. Until the discovery of Sahelanthropus tchadensis, the most celebrated fossil was a 40% complete skeleton of a female Austalopthiecus afarensis, named 'Lucy', which was discovered in 1974. She is thought to have been a short, bipedal hominid with a face and brain size similar to modern chimpanzees. In 1995, Australopithecus anamensis, believed to be an intermediary form between A. ramidus and A. afarens, had extremely human-like lower leg bones providing strong evidence that this species was bipedal. In the last decade, there have been many australopithecine fossil discoveries, with eight species being proposed, including, Australopithecus africanus (similar to 'Lucy', but having a more human-like face, larger body, and a brain about 1/3 the size of a modern human). Paranthropus robustus is thought to have been about the same size as a Gorilla, heavily jawed with skull crests and large back molars; they are thought to be a side branch in hominid evolution, not directly related to humans. There is disagreement over when the first true members of Homo appeared, and even about what constitutes a member of the genus Homo. The earliest currently known species was Homo habilis, a fully upright hominid, thought to have been about 130cm tall, with a larger brain and more human-like in shape than the australopithecines. Examinations of skulls have shown a bulge in the area occupied by the speech area in humans, suggesting they may have been capable of at least rudimentary speech. Homo erectus is a later species, larger and having a low but distinct forehead, and strong brow ridges. Its brain capacity was intermediate in size between H. habilis and humans. It was a social animal, living in groups of 20--50 individuals, with a successful and complex culture; it was widespread throughout the tropical and temperate old world. Recent molecular genetic studies indicate that human populations have formed a single evolutionary line for the previous 1.7 million years. During this time, several major expansions of populations out of Africa occurred. Anthropologists have named fossil species to denote spatial and temporal variation in phenotypic characteristics within this lineage. However, according to most biological criteria, they were assumed to be a single species. The earliest fossils, classified as Homo sapiens (wise man), from 500,000 to 300,000 are now identified as H. heidelbergensis. The well-known human group of Neanderthals was previously classified as a sub species of Homo sapiens, but has now been re-classified as a separate species, H. neandertalensis. They had a brain size within the range of modern humans and were proficient hunters and tool users. They were not a homogenous group, but varied geographically in response to local conditions and population isolation. SPECIES TIME PERIOD Sahelanthropus tchadensis Ardipithicus ramidus 7 million years ago 5 to 4 million years ago Australopithecus anamensis Australopithecus afarensis (oldest ancestor) 4.2 to 3.9 million years ago 4 to 2.7 million years ago Australopithecus africanus Paranthropus robustus 3 to 2 million years ago 2.2 to 1.6 million years ago Homo habilis Homo erectus 2.2 to 1.6 million years ago 2.0 to 0.4 million years ago Homo sapiens archaic Homo sapiens neandertalensis 400,000 to 200,000 years ago 200,000 to 30,000 years ago Homo sapiens sapiens 200,000 years ago to present About 30,000 Neanderthals and Homo erectus disappeared around 10,000 years after the first appearance of H. sapiens in Europe and Eastern Asia. Modern humans were, in comparison, tall, with a © very different culture to Neanderthals. Implement crafting developed rapidly and artistry and sophisticated language emerged. It should be noted that species differentiation is based purely on morphology. Recognition of three or more distinct species of Homo does not necessarily mean that the lineage branched. It is possible that we are observing phyletic change within a single species through time; the species names only denote different grades of evolution. Using tools has been interpreted as a sign of intelligence, and it has been theorised that tool use may have stimulated certain aspects of human evolution such as the continued expansion of the human brain. Palaeontology has yet to explain the evolutionary expansion of this organ, despite being extremely demanding in terms of energy consumption. The brain of a modern human consumes about 400 kilocalories per day, which is one fifth of the energy consumption of a human body. Increased tool use would allow for hunting and consuming meat, which is more energy-rich than plants, in order to supply this energy. Precisely when early humans started to use tools is difficult to determine, because the more primitive these tools are the more problematic it is to determine origins, natural objects or human artefacts. There is debated evidence that the australopithecines (4 million years ago) used broken bones as tools. Stone tools have been found from around 2.6 million years ago, when H. habilis in Eastern Africa used choppers made from round pebbles split by simple strikes. This event marks the beginning of the Palaeolithic, or Old Stone Age; its end is taken to be the end of the last Ice Age, 10,000 ago. H. erectus (700,000--300,000 years ago) made large stone hand-axes out of flint and quartzite, at first quite roughly, later 'retouched' by additional, more subtle strikes at the sides of the flakes. After 350,000 BP, (Before Present) the more refined so-called Levallois technique was developed. It consisted of a series of consecutive strikes, by which scrapers, slicers, needles, and flattened needles were made. Finally, after about 50,000 BP, ever more refined and specialised flint tools were made by the Neanderthals and the immigrant Cro-Magnons (knives, blades, skimmers). During this period, bone tools were also made. Until about 50,000-40,000 years ago, the use of stone tools seems to have progressed stepwise: each phase (habilis, erectus, Neanderthal) started at a higher level than the previous one, but once that phase had started, further development was slow, showing these earlier Homo species to be culturally conservative. After 50,000 BP, human culture apparently started to change at much greater speed: 'modern' humans started to bury their dead carefully, made clothing out of hides, developed sophisticated hunting techniques (such as pitfall traps, or driving animals to fall off cliffs), and made cave paintings. This speed-up of cultural change occurred at the same time as the emergence of Homo sapiens. Artefacts such as fish hooks, buttons and bone needles began to show signs of variation among different populations of humans, something that had not been seen in human cultures prior to 50,000 BP. How Homo sapiens replaced the coexisting homo 'species' has been much debated. Different schools of thought include a multi- regional model where populations gradually evolved at the same time to a more violent 'out of Africa' theory involving Homo sapien groups out-competing and replacing individual Neanderthal groups within territories. This model has gained support by recent research using mitochondrial DNA (mtDNA). After analysing genealogy trees constructed using 133 types of mtDNA, the research concluded that all humans are descended from a woman from Africa, dubbed 'Mitochondrial Eve'.