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154 Cards in this Set
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Subungulates orders (Superorder Paenungulata) |
Oder Hyracoidea, Proboscidea, Sirenia * Subungulates and true ungulates are not closely related groups. * Part of the Afrotherian mammalian radiation |
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Oder Hyracoidea (Hyraxes) |
Family: Procaviidae * Hyraxes are found in central and southern Africa, Algeria, Libya, Egypt, and parts of the MiddleEast. * Hyraxes have a rodent‐like diastema and well developed incisors. Like rodents, their incisors are evergrowing with enamel on the front only so they remain large and sharp throughout the animal’s life. They are all herbivorous and have lophodont molars with horizontal ridges. * hyraxes are the closest living relatives of the elephants. * Hyraxes are very small compared to the other extant subungulates. * Poor thermoregulators * Long gestation (8 months) young are born precocial. |
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Order Proboscidea (Elephants) |
Family: Elephantidae * The two extant genera are found in Africa and Asia, respectively, and are not closely related. * The wooly mammoth, a member of the family Elephantidae, went extinct a mere 4000 years ago. Scientists have been able sequence DNAfrom frozen specimens and are attempting to clone wooly mammoths. * The mastodon was a member of the extinct family Mammutidae. It was contemporary with humans in North America up until about 8000 years ago. Some evidence suggests humans played a role in their extinction while others claim climate change was the major factor. * Characterized by having their nose and upper lip modified into a trunk and their second upper incisors modified into tusks. Tusks are open rooted and grow throughout the elephant’s life. * Horizontal tooth replacement * cheekteeth are hypsodont * Elephants are long-lived and have a 20 month gestation period. Extended parental care due to slow juvenile growth. * very sparse body hair and highly vascularized ears help to dissipate heat. * Elephants are the largest terrestrial vertebrates making them efficient hindgut fermenters. * Elephants have a strong matriarchal social structure. * Males fight among themselves for access to females * The matriarch in a group is an important source of “knowledge” remembering location of resources. |
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Order Sirenia (Dugongs and manatees) |
Family: Dugongidae (Dugongs) Family: Trichechidae (Manatees) * Sirenians are the only herbivorous marine mammals. * Dugongs and manatees require 1) relatively shallow waters where sunlight can penetrateenough to support growth of their preferred plant foods and 2) water temperatures around20°C because of their low metabolism and thermoregulatory capability. As a result they are restricted to coastal areas of tropical and subtropical regions. * Like other marine mammals, they have massive, dense bones that help overcome buoyancy. They have no hind limbs and only vestigial pelvic bones, similar to cetaceans.Their forelimbs are modified into paddle‐like flippers and their tails are enlarged and horizontally flattened. They have thick, flexible lips and snouts with tactile vibrissae. *The major morphological difference between dugongs and manatees is the shape of the tail. Dugongs have a slight fork in their tails while manatees have a rounded, spoon‐shapedtail. * All four species of sirenians are considered threatened. Boat propellers, loss of habitat to development, reduced water quality, commercial fishing, seismic surveys, and oil and gas drilling negatively affect populations. |
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Order Cetartiodactyla |
Formerly two orders: Order: Cetacea (whales and dolphins) Order: Artiodactyla (even-toed hoofed animals) * The order Cetartiodactlya contains cetaceans and the even-toed hoofed mammals formerly known as orders Cetacea and Artiodactlya, respectively. These two groups were previously separated based on morphological evidence. Molecular evidence shows that the order Artiodactlya is paraphyletic without the inclusion of cetaceans. |
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Cetaceans (whales, porpoises, and dolphins) |
* They form a monophyletic group, but Artiodactlya would not be a monophyletic group without including cetaceans. * They are highly derived (the result of rapid evolutionary change) and evolved from a terrestrial ancestor to an obligatory aquatic lifestyle. * The blue whale is the largest animal known to have inhabited the Earth, ever! * Buoyant environment allows for large body size. * Two major groups (formally suborders): * Mysticeti: baleen whales * Odontoceti: toothed whales * Cetaceans are highly intelligent, many are migratory, have well developed communication, of conservation concern. |
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Morphology of Cetaceans |
* Cetaceans are secondarily aquatic, meaning that all their morphological characteristics are derived from those of ancestral terrestrial mammals through a gradual transition from land to sea. * They have extreme morphologies including a streamlined, fusiform body shape that reduces drag; complete absence of hind limbs; forelimbs modified into flippers; tail flukes; and fins. * They have well developed ears, but no external ear (pinnae). Their skulls are telescoped with nostril located on top of the head. * Their thick layer of blubber provides insulation, helps with buoyancy, and is an important energy store. *They have three-chambered stomachs; however, they are all carnivorous and do not ruminate. |
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Distinguishing between Mysticeti and Odontoceti |
* Mysticetes have more robust-looking heads and plates of baleen instead of teeth. * Odontocetes have a beak-like appearance to their rostrum and a concave head. In general, odontocetes are smaller than mysticetes. * A closer look at the skeletal morphology reveals a vestigial pelvis, but complete lack of hind limbs in this whale. Seals and sea lions have fully developed hind limbs. |
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Environmental adaptations Cetaceans |
* Cetaceans have many adaptations both to conserve heat and to dump heat. One adaptation is having a low surface area to volume ratio. * Cetaceans have a thick layer of blubber that acts as insulation. * They also have a counter-current heat exchange system that includes a rete mirabile (Latin for wonderful net)- a close network of veins that surround major arteries. The venous blood absorbs heat from arterial blood as blood returns to the body core. * Tremendous pressure and lack of oxygen experienced while diving. To do so they have dense, non-compressible bones to maintain support for their bodies. They also have fairly rigid upper airways, but their lungs collapse at depth. Fully collapsing lungs are also important for avoiding decompression sickness. * A typical terrestrial mammal will use 4% of the oxygen that enters its lungs, while whales use 12% (more efficient). Whales also have twice the number of red blood cells (erythrocytes) per volume of blood and two to nine times the amount of oxygen-binding protein in their muscles (myoglobin) as terrestrial mammals. * They maintain a constant blood pressure to the vital organs while diving by decreasing blood pressure through slowing the heart beat (brachycardia) and increasing blood pressure in extremities through vasoconstriction (decreasing the diameter of blood vessels). |
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Mysticeti: baleen whales |
* Baleen is composed of keratin. * These baleen plates act as combs to strain zooplankton and phytoplankton from the water. The zooplankton is scraped from the baleen with the tongue and then swallowed. * Mysticete whales are generally larger than odontocete whales, and unlike odontocetes, they do not echolocate. They do produce various sounds including moans, grunts, chirps, whistles, and clicks. These sounds are important for communication. * Unlike odontocete whales, mysticetes have a symmetrical, convex skull. Family: Balaenopteridae * The family Balaenopteridae includes the rorquals, also known as tube-throated whales. * They were overexploited for oil, meat, and “whalebone”, or baleen. |
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Odontoceti: Toothed whales |
* The toothed whales, in contrast to baleen whales, have asymmetrical skulls and are all active predators of fish and squid for which they need teeth. They have well developed echolocation capabilities which they use for locating and immobilizing prey. Family: Delphinidae and Physeteridae * The family Delphinidae includes 34 species of dolphins. They are the most varied family of cetaceans and include the smallest cetacean (Heaviside’s dolphin) and the orca, or killer whale. Most prey on fish, but orcas may take marine mammals, other cetaceans, and sharks. * The family Physeteridae includes the sperm whale, dwarf sperm whale, and pygmy sperm whale. They have a huge spermaceti organ that may account for up to 10% of their total mass. This organ functions in focusing echolocation signals and was highly sought after for the oil contained in it. |
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Echolocation in Cetaceans |
* whales produce sounds with nasal sacs located in their forehead region. * toothed whales use much lower frequency sounds. The size of prey detected by whales is much larger; larger than most bats even so whales do not need to produce such high frequency sound. Whales are able to discern direction of their echoes with specialized tympanic bones that are not fused to the skull as in other mammals. * Sound is produced with the nasal air sacs and “monkey lips” (an organ within the head). It then bounces off the concave skull and passes through the melon. Returning sound hits the jaw bone and travels through the dentary to the middle ear. * Like bats, toothed whales use different calls for different function. This figure shows a feeding buzz similar what we saw in bats! |
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Order Cetartiodactyla (Artiodactyla) |
Notice the former order Cetacea isthe sister taxon to Hippopotamidae. |
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Order Cetartiodactyla (Artiodactyla) |
* The artiodactyls are also referred to as “even‐toed ungulates". * Artiodactyla cannot be considered an order (according to the cladist view)because it is paraphyletic without the inclusion of cetaceans. * Artiodactyls exhibit diverse digestive anatomies, from simple, nonruminating stomachs insuids and tayassuids (more omnivorous), to complex, four‐chambered ruminating stomachsin “more derived” families. * In most species of artiodactyls the 3rd and 4th digits are fused together into a cannon bone.This is an adaptation to lengthen the leg and increase efficiency and speed. Additionally, artiodactyls have reduced or absent 2ndand 5th digits. They walk on the tips of their toes on their “nails”, or hooves, and are veryfast runners. * Their teeth are either bunodont (rounded‐ e.g., pigs) for crushing, or selenodont(sharp, cresent‐shaped enamel ridges) for grinding vegetation. * Antlers are bony structures usuallyrestricted to males and are found in many families. They are shed and regrown each year.True horns are found only in the family Bovidae and are composed of a bony core with akeratinized sheath. Horns are usually found in both sexes and are not shed. |
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Family Camelidae (camels, llamas, vicunas, alpaca, and guanacos) |
* Camelids are highly adapted to extreme environments, especially arid environment. Theycan eat vegetation with a high salt content that most mammals find unpalatable and theycan go long periods of time without access to freestanding water. The camel’s hump is a fatreservoir that swells and shrinks when they are water stressed. * They are currentlyfound in Africa, Asia, and South America. The family arose in North America in the early tomid Eocene and expanded thereafter, but all members went extinct in North America. |
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Family Suidae (pigs, wild boars, and warthogs) |
* They are native toEurope, Africa, and Asia, but have been introduced worldwide. * Suids are very fecund; they can have multiple litters per year with many piglets per litter. * They are gregarious (social) and feral pigs oftendig up the ground like a rototiller leaving a path of destruction in their wake (omnivorous). Their tusks(ever‐growing upper canines that curve upward) serve multiple function includinguprooting food and sexual selection. |
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Family Tayassuidae (peccaries/javelina) |
* Members of the family Tayassuidae are sometimes referred to as pigs, but they are notpigs! * Theyare smaller than suids (~20 kg) and have smaller, sharp‐edged canines that pointdownwards. They are much more herbivorous than suids, but still somewhat omnivorous. * Their large canines keep their jaws in strict alignment to avoid shattering their teeth. Theyhave a pouched stomach that is more complex than in pigs. |
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Family Hippopotamidae (hippopotamus) |
* Two species (hippo, and pygmy hippo) * They both lack hair except for a few bristles around the snout. Hippos donot have sweat glands. They do however have glandular skin that exudes a pigmented fluidthat some claim resembles blood. * They are found in freshwater habitats in Africa and spend most of their lives in rivers andlakes, but venture out at night to graze. Hippos are important ecologically as they transportlarge quantities of nutrients from terrestrial to aquatic ecosystems via their feces. |
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Family Tragulidae (chrevotains/mouse deer) |
* restricted to Africaand India. Their common name, mouse deer, reflects their very small size. The Java mousedeer is the smallest artiodactyl in the world. They lack facial glands, body glands, andantlers, but males possess large, curved incisors, or tusks. |
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Family Moschidae (musk deer) |
* There are seven species, all restricted to Asia. Like tragulids, they lack antlers and maleshave long, curved canines. Males have a musk gland anterior to their genitals that is heavilysought after for fine perfumes and in Asian traditional medicine. |
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Family Cervidae (elk, moose, caribou, and deer) |
* Cervids are highly sexually dimorphic. Males of all but one species (Chinese water deer)have antlers and both sexes of caribou have antlers. * Cervids are highly specialized ruminants and have selenodont dentition for grindingvegetation. Olfaction is also important for communication. Cervids have several glands located on theirface (prelacrimal), between their toes (interdigital), or on their lower hind limbs (tarsal ormetatarsal). |
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Family Bovidae (cows, sheep, goats, African antelope) |
* The family Bovidae is the largest family of artiodactyls. * They have hypsodont and selenodont cheeckteeth and lack upper incisors and canines.Males have horns, as do most females. Bovids are highly advanced herbivores and havecomplex, four‐chambered ruminating stomachs. * Bisonare often considered functionally extinct since remaining populations are descendants ofextremely small populations and the great migratory herds no longer exist. Migratoryanimals are particularly vulnerable to human disturbance. |
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Family Giraffidae (giraffe and okapi) |
* The giraffe is found in savannas, grassland, and open woodlands throughout sub‐Saharan Africa. The okapi is restricted to densely forested areas of the Democratic Republicof Congo. * Both species have long legs and necks; much more dramatically so in giraffes. Both speciesalso have unusual pelage color patterns. They have small rooted cheekteeth and short,bony horns comprised of “ossicones”, which are permanent bony projections over thefrontal and parietal bones. Giraffes use their necks to feed high up in the trees as well as inaggressive male‐male neck wrestling to establish dominance hierarchies. |
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Family Antilocapridae (antelope) |
* The family Antilocapridae is monotypic and endemic to North America. The pronghorn, or“pronghorn antelope”, is the fastest mammal in North America. It is hypothesized that theirgreat speed is the result of predation pressure from the now extinct North Americancheetah as there are no longer predators capable of running down a pronghorn. * Pronghorn are sexually dimorphic in size, pelage color, and horn morphology. Pronghornhorns, like bovid horns, are composed of a bony core with a keratinized sheath. Unlikebovids, however, the keratinized sheath is shed each year. |
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Order Perissodactyla (odd toed ungulates) |
* The order Perissodactyla contains three families: horses, rhinoceroses, and tapirs. * Like artiodactyls, they are adapted for a highly cursorial lifestyle andhave highly reduced foot morphology. The third digit is enlarged and is the major weightbearing axis of the limb. This condition is referred to as mesaxonic and is characteristic ofperissodactyls. * All are large, terrestrial herbivores. Perissodactyls do not ruminate like artiodactyls. Theyare hindgut fermenters and instead of complex stomachs they have a large cecum andcolon to provide more storage volume and surface area for nutrient absorption. * They have highcrownedteeth with no discernable roots (hypsodont). |
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Family Equidae (horses, donkey, and zebra) |
* Feral horses and asses are widespread in North America and have led to some highlycontroversial management issues. Horses have been released more recently and continue to bereleased into areas where they cause environmental damage. * In places where equids are native, most are threatened or endangered. |
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Family Tapiridae (tapirs) |
* They all have short legs, small eyes, small ears, and a flexible proboscis formed bythe nose and upper lip. All species are hunted for meat and suffer from loss of habitat dueto forest clearing. They are nocturnal and eat shoots, twigs, grass, fruits, aquaticvegetation, and occasionally cultivated crops. |
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Family Rhinocerotidae (rhinos) |
* There are four genera and five extant species of rhinos in Asia and Africa. Fossil evidencesuggests that the largest terrestrial mammal ever was a rhinoceros 25-30 MYA. All fivespecies are highly endangered because of hunting for their horns (that recently were valuedat tens of thousands of dollars a kilo). |
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Zoogeography (biogeography) |
* Biogeography is the study of the distribution of organisms, both extant and extinct. * Zoogeography is likewise the study of the distribution of animals. * Zoogeography seeks to uncover the processes that leadto those patterns. Zoogeography can be studied at many spatial, temporal, and taxonomicscales: from a single mountain range or smaller to the entire globe, historical, “deep time”versus present day features. * The fundamental question in zoogeography is: What factors determine the range of aspecies? Furthermore, why does a particular region contain the species we observer there? |
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Zoogeographical scales |
* Historical zoogeography is concerned with long term geological and evolutionary history. Major patterns of diversification and extinction over large geographic and deep time scalesare examined to describe past and present patterns of distribution. * Endemism and disjunct distributions are particularly interesting and important clues tounraveling history. Endemic species are those restricted to a particular geographic area. * The term “disjunct” describes a distribution pattern that is characterized by a gap. * Ecological zoogeography, in contrast, is concerned with present‐day features that restrictorganisms to their current environments. This is typically studied on a much smaller spatialand temporal scale such as ecological communities and islands. Important topics includefactors that drive patterns of species richness and community‐level interactions. |
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Historical Zoogeography |
* One of the fundamental principles in historical zoogeography is vicariance. Vicariance refersto the splitting of a species’ range into two or more smaller ranges by a dispersal barrier. The barrier results in interrupted gene flow followed by genetic diversification, andpotentially allopatric speciation. Sympatric speciation, on the other hand, describesspeciation through genetic diversification without geographic separation. |
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Other important processes that affect species distribution |
* The dispersal hypothesis states that a barrier existed and a subset of individuals crossed thebarrier to found a new breeding population. The geographic separation of the new andoriginal populations subsequently led to allopatric speciation. * Extinction is another important process to consider. Extinctions can be local and may only include aportion of a species’ range. There are many factors affecting local extinction includingcompetition for resources or environmental changes. |
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Faunal regions of the world as defined by Wallace (1876) |
* In his travels, Wallace recognizeddistinct differences among the distribution of taxa worldwide, which he referred to as“provincialism”. * One particularly interesting transition is “Wallace’s Line”. Itdelineates the transition between Oriental and Australian faunal assemblages. We now knowthat a deep channel separated these two regions during the last glacial maximum whileother land masses were connected due to lower sea level. |
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What causes these different patterns of diversity and endemism? |
* Extinction, dispersal, and diversification all shape the patterns of species diversity.Background extinction is always occurring, however extinction rates are higher in smallerareas (island biogeography theory), if there are dramatic shifts in climate, or if newcompetitors or predators enter the system. * Areas gain species through dispersal and diversification. |
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Palearctic (Eurasia, including North Africa and all of Europe and Asia) |
* The Palearctic is the largest faunal region in terms of area, but familial diversity is moderateand there are no endemic families. Half of the families found in the Palearctic are alsofound in the Nearctic. The Palearctic region is fairly well connected to multiple other regions. A large amount of faunal exchange occurred between the Nearctic and Palearctic across theBering land bridge. A period of low sea level! * # families = 42; endemic = 0 |
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Neararctic (North America north of Mexico and Greenland) |
* The Nearctic faunal region is the second largest and likewise has moderate familialdiversity. Similar to the Palearctic, it has few endemic families. However, the connectionwith Central and South America is fairly recent and narrow. The Nearctic region is thereforenot as well connected as the Palearctic to other regions and this may explain the greaternumber of endemic families than in the Palearctic. * # families = 37; endemic = 2 The two endemic families, both monotypic, include the pronghorn “antelope” andmountain beaver. * The Nearctic shares about half of its diversity with the Neotropical region. The faunalexchange between these two continents has occurred in the last three million years sincethe formation of the Panamanian land bridge. |
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Neotropical (Central Mexico throughout South America including the Caribbean Islands) |
* The Neotropical region has high familial diversity and the greatest number of endemicfamilies. South America has been relatively isolated and climatically stable over time. The Neotropicscontain an enormous species diversity as well. * # families = 50; endemics = 19 * Colombia has the highest species diversity of any country in the world for birds and issecond for amphibians. There are two major mountain ranges that separate the country into distinct regions. In addition to the variation inecosystems within the country, faunal interchange between the Nearctic and Palearcticfaunal regions occurred through the narrow Panamanian land bridge. |
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Oriental (Tropical Southeast Asia, India, and southeast Asian Islands) |
* It represents a crossroads between Palearctic, Ethiopian, and Australianfaunal regions. As a result, there is high familial diversity, but few endemic families. * # families = 50; endemics = 4 |
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Australian (Australia and New Guinea) |
* The Australian faunal region has been very isolated for a relatively long time. This isolationaccounts for the low familial diversity and high endemism. * # families = 28; endemics = 17 |
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Oceanic (Islands of the Pacific Ocean) |
* Mammalian diversity is very low and consists mainly of bats and marine mammals. |
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Disjunction |
* Another explanation for disjunct distributions isextinction. Maybe they were distributed throughout the intervening areas, but went extinctthere. A third explanation is continental drift; maybe the land masses themselves moved! * It was not until the1960’s, after plate tectonics was put forward as a mechanisms for continental drift, that itwas actually widely accepted. Continental drift explains a lot of the distributions we seetoday. * Plate tectonics is the study of the movement of crustal plates, upon which the continents ride. * Continental drift is the movement of the continents over geologic time. |
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Continental Drift |
* Approximately 225 million years ago the continents were all joined together. Rememberthat mammals first appeared approximately 240 million years ago, so the continents werestill joined. * Approximately 200 million years ago Pangaea broke up into two land masses. This roughlycorresponds to the therian‐prototherian split. * Major radiations occurred during the Cretaceous after the mass extinction of dinosaurlineages. * Recall that marsupials originated in North America and moved through South America andAntarctica into Australia. Australia has been isolated since the Cretaceous thereforemarsupials were able to diversify with virtually no eutherians to compete with. South America was also isolated for a long time. |
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Origins of mammals now found in South America |
* There is evidence that the orders Cingulata (armadillos) and Pilosa (anteaters and sloths)arose in South America. Marsupials entered South America via “sweepstakes dispersal”(random and rare events such as rafting). Monkeys, porcupines, guinea pigs, etc. arrivedfrom Africa and raccoons and their allies arrived from North America via sweepstakes(remember they were not as far apart as they are now). Ocean currents play an importantrole in sweepstakes dispersal, and the position of the continents affects ocean currents.The Great American Faunal Interchange (GAFI) occurred after the formation of the isthmusof Panama approximately 3 MYA. As the continents drew nearer, interchange became easier, particularly after the land bridgearose. |
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The theory of island biogeography |
* The theory of island biogeography states that the number of species on islands is a functionof colonization rate and extinction rate and these factors in turn are related to the size ofthe island and distance to the mainland: * Closer islands will have a higher colonization rate than further islands because animalscan get there more easily. * Larger islands will have a lower extinction rate than smaller islands because they cansupport more animals and therefore are not as affected by stochasticity. |
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Pleistocene zoogeography of N. American mammals |
* A great number of species went extinct in North America toward the end of thePleistocene. The two main theories are climate changeand overhunting by humans. |
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Glacial cycles of the Pleistocene |
* The ratio of oxygen isotopes present in diatoms (phytoplankton) varies depending on howmuch water is contained in ice versus oceans. We can see large fluctuations of heating and cooling over the last 2million years. * Ice sheets thousands of feet thick covered much of North America 20,000 years ago. Concordance: multiple unrelated species showing the same distribution/structure. * From these current and historical species ranges (there are more that tell a similar story),we see little evidence of extinctions as the glaciers advanced. We do see evidence fordistributional shifts. * Again, when we look at genetic variation, we see different clades in the Pacific Northwest,again indicating concordance among many species of boreal specialists. A lengthy isolation during the last ice age allowed for genetic divergence. * So, there is evidence for distributional shifts and speciation as a result of the Pleistoceneglaciations. |
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Pleistocene glaciation evidence for extinctions? |
* 70% of the large mammals, also known as Pleistocene megafauna, went extinct in NorthAmerica roughly 10,000 years ago. * There was a rapid die‐off of large mammals approximately ten thousand years ago. Whydidn’t small mammals go extinct? * One hypothesis is the “Pleistocene overkill” theory. It proposes that the rapid die off oflarge mammals is a direct result of contact with humans. * The Pleistocene overkill hypotheses suggests that the arrival of humans and subsequentquick spread across landscape led to the decline and extinction of Pleistocene megafauna. |
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Locomotion involves tradeoffs |
* Becoming more specialized for one type of locomotion often makes you less efficient at the other types. |
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Requirements for and components of movement |
* Support/stability: As you will recall from earlier discussions on mammalian evolution,our reptile‐like ancestors had a splayed stance compared to the more upright stance inmodern mammals. Mammals exhibit trade‐offs between support/stability and maneuverability. Posture is a key component of support and stability. * Propulsion: Different movements and amounts of power lead to different gaits. * Maneuverability: Different lifestyles require different levels of maneuverability, or abilityto change direction from side to side. * Endurance: A rabbit is very fast for short bursts, but cannot sustain high speeds. |
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Modes of locomotion (walking and running) |
* Walking and running involve similar motions. Species that move predominantly by walkingare referred to as “ambulatory” and those adapted for running are “cursorial”. Scurrying, orscampering, is a sort of fast walking often seen in small mammals such as rodents. |
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Stance for walkers and runners |
* Plantigrade: all or most of the foot is in contact with the substrate. This posture isassociated with the primitive, walking gait. (Humans) * Digitigrade: metacarpals and metatarsals are elevated to an acute angle with respect tothe substrate and only the phalanges make contact. Most digitigrade species have somereduction in digits. * Unguligrade: in addition to elevated metacarpals and metatarsals, unguligrade specieshave elevated phalanges as well so that only the very tips of fingers and toes contact thesubstrate. They exhibit reductions in the number of digits; increased length of theremaining metacarpals, metatarsals, and phalanges; and developed of hooves. |
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Postures associated with walking and running |
* In plantigrade species thecalcaneous (heel) bone is in contact with the substrate. In digitigrade species the calcaneous is elevatedabove the substrate. In unguligrade species the calcaneous is elevated and the metatarsalsare elongated such that the joint between the phalanges and metatarsals is where wemight otherwise expect to find the calcaneous. In other words, unguligrade species have anextremely elongated foot that acts like an extension of the leg itself. * The elephant has a “graviportal”stance with the legs positioned directly vertically below the body. The skeleton bears mostof the weight and is less energetically expensive than having to support the massive weightmuscularly. However, the elephant is not very flexible or maneuverable. The impala’s legsare splayed slightly out to the side. This arrangement allows for a swinging motion of thelegs supported by muscles. |
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Modes of locomotion (jumping and ricocheting saltatorial) |
* Saltatorial locomotion includes leaping, jumping, and ricocheting. Jumping involves the useof all four feet while ricocheting involves the hind limbs predominantly. Ricochetingmammals tend to have short front limbs and well developed hind limbs (kangaroo andkangaroo rat). |
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Saltatorial specialization |
* Lengthened hind limbs and long, elastic tendons that store energy like a spring arespecializations associated with advanced saltatorial locomotion. * shift their center of mass backwards * An elongatedtail also helps with balance * Enlarged muscles and tendons in the hip region |
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Modes of locomotion (swimming) |
* Amphibious mammals have other, not so obvious adaptations for swimming. Water shrewshave a fusiform body shape to reduce drag and a fringe of hairs on its feet that increasessurface area. Muskrats have laterally flattened tails that are used forpropulsion and as a rudder for directional control. * Tradeoffs - efficiency in water vs. efficiency on land |
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Modes of locomotion (flying and gliding) |
* Gliding has evolved multiple times in mammals (e.g., flying squirrels, colugos, and somegliding possums). However, true flight has only evolved once in bats. In gliding mammals,the patagium acts like an airfoil that is manipulated by moving the hands and feet tocontrol direction. * Tradeoffs - reduced efficiency on the ground, limited to light loads. |
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Modes of locomotion (scansorial/arboreal) |
* Themore specialized species are for arboreal locomotion, the less agile they tend to be on theground. Generalist species that climb usually do so with claws and footpads. Many morespecialized species have prehensile tails (e.g., opossum, bottom right). Arboreal primatesthat swing from branch to branch (brachiate) have: long arms; prehensile hands, feet, andsometimes tails; and opposable thumbs and big toes. |
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Modes of locomotion (digging and burrowing, fossorial) |
* They spend much of theirlives underground so they need to be strong, but they do not need to be very agile or fast.They tend to have a fusiform body shape, strong forelimbs, large front feet with claws,small eyes, and lack pinnae. Some species such as true moles have a short, sculptedhumerus with projections for increased muscle attachment surfaces. * Pocket gophers, African mole rats (naked mole rat pictured above), and blind mole‐rats digwith their large incisors. These species have lips that close behind their incisors to preventdirt from getting in their mouths, robust zygomatic arches for powerful masseter muscleattachment, and strong neck muscles. |
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Pectoral girdles |
* The pectoral girdles of most mammals consist of shoulder blade (scapula) and often a clavicle. * Diggers: Fossorial species, such as this armadillo, have extensions and spines on the scapula forlarge muscle attachment. Bony projections where the scapula contacts the humerusstrengthen the joint but reduce rotation. They have short, robust bones, short hands, andlarge claws. * Swimmers: This seal also has short, robust, “misshapen” bones providing more surface area for muscleattachment associated with strong forearms. Most of the movement required forswimming is in the shoulder, therefore the wrist is not very flexible. * Climbers: This arm of an arboreal primate is like that of humans. The bones are relatively long andnot very robust. There is a wide range of motion in the shoulder allowing the arm to moveupward and outward. The space between the radius and ulna allows 180 degree rotation of the hand and aflexible wrist joint allows even further hand motions. Long, prehensile fingers allow forgrasping. The elbow joint is a locking joint and only allows movement in one plane. The trade off in having such a wide range of motion is a reduction is stability. * Runners: forearm moves forward and backward, but not outward. There is noclavicle, the ulna has been reduced, and the wrist joint is constrained. |
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Runners |
* Runners achieve high speeds by increasing stride length, stride rate, or both. The unguligrade posture increases stride length and therefore increases speed without anincrease in stride rate. This strategy requires less energy. Digitigrade posture increasesstride length, but to a lesser degree. * The loss of the clavicle allows the forearms to swing back and forth more freely becausethe scapula moves as part of the limb, thus lengthening the stride and increasing potentialfor speed. Reduction in number of digits, limb elements lengthened and often fused. * stride length can be increased by flexing the spine. * Muscles inserted close to joints move the joint through a wider angle increase stride length. * More muscles working on single joint increase force, but not velocity. More musclesworking on multiple joints increase force and velocity. |
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Feeding (adductor muscles of the mandible) |
* The temporalis muscle originates on the skull and inserts on the coronoid process. It isassociated with vertical motion of the lower jaw. It is particularly large in carnivores thatneed to clamp down on prey and have strong chewing force for slicing meat and bone.
* The masseter muscle originates on the zygomatic arch and inserts on the angular process.It serves as an outer sling for the lower jaw. * The pterygoideus muscle likewise acts like aninner swing for the jaw. The masseter and pterygoideus are much more welldeveloped in herbivores than carnivores. * The beaver has ever‐growing incisors for gnawing and cheekteeth adapted forgrinding plant material. The saber‐toothed cat has enlarged canines for grasping preyand sharp carnassial teeth for slicing meat and bone. |
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Gut Morphology (Insectivores and Carnivores) |
* Stomach is large and simple * % of gut volume = 65% * Post gastric tract is short (4-6x body length) * Intestinal differentiation is slight to non existent * Cecum is vestigial or absent * Large intestine is short and 15% of gut volume * Animal material is relatively easy to digest. Insectivores and carnivores therefore haverelatively simple stomachs with short, simple post‐gastric digestive tracts. |
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Regions of the simple stomach |
* When food enters the stomach muscular actionbreaks down food mechanically as chemicals, particularly hydrochloric acid (HCl), furtherdigest food. Then the highly acidic mixture is buffered to increase pH before absorption canoccur in the intestines. * Stratified squamous epitheliumdescribes multiple layers of cells stacked on top of each other. In some cases this region iscornified (keratinized) to aid in mechanical breakdown, particularly of course food. Thecardiac glands secrete mucous and the pyloric glands secrete mucous and gastrin toregulate pH. |
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Fermentation |
* The mammalian digestive system is incapable of digesting plant cell walls without help frommicroorganisms. Humans are omnivorous and not particularly specialized to digest plantmaterial. We have approximately 5600 species of microbes in our colon! * Microbes live in the digestive tracts of mammals and break down the polysaccharides inplant cell walls into volatile fatty acids (VFAs). VFAs can be digested by mammals anddepending on the location of the microbes in the digestive tract, the microbes themselvesmay also provide a significant source of nutrients. In a way, some mammals are farmingmicrobes by feeding them plants! Therefore manyspecialized herbivores have “fermentation chambers” |
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Hindgut vs foregut fermentation |
* There are two main categories of fermenters. Hindgut fermenters (e.g., horse, elephant)have small, simple stomachs but complex folds (sacculation) in their large intestines thatserve as a fermentation chamber. Foregut fermenters (e.g., deer, sheep) have a large, multichamberedstomach that is highly compartmentalized to provide the right conditions at theright time. |
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Herbivores hindgut |
* Stomach is small and simple * % of gut volume = 9% * Post gastric tract is long (10-15x body length) * Intestinal differentiation strong * Cecum is huge * Large intestine is very large sacculated (45%) |
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Herbivores foregut |
* Stomach is large and compartmentalized * % of gut volume = 67% * Post gastric tract is very long (20-27x body length) * Intestinal differentiation present * Cecum is small or absent * Large intestine is short (10%) |
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Foregut fermenters |
* Mammals that eat a particularly low‐quality diet consisting mainly of leaves tend to beforegut fermenters. Koalas, kangaroos, sloths, and some leaf‐eating monkeys are not veryspecialized foregut fermenters. * Hippos, camelids, pronghorn, bovids, and cervids (members of the now defunct orderArtiodactyla), on the other hand, have highly specialized stomachs. These are the onlyfamilies with true separation of the stomach chambers. The first chamber of the stomach,the rumen, acts as a fermentation chamber. Members of these families are referred to asruminants. |
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Stomach of a ruminant (foregut fermenters) |
* Have one stomach withfour main chambers. Ruminants chew their food then swallow it as any other herbivorewould. The food then enters the rumen where microbes start to digest it. Larger particlesare regurgitated, chewed and swallowed again. * The reticulum acts as a pump, flushing fluid into the rumen and washing small particles andmetabolic byproducts on to the omasum. Fermentation occurs inboth the rumen and the reticulum. * The muscular omasum further kneads the mixture and removes most of the water. Fromthe omasum the food then moves on to the abomasum which is the true stomach. Hereacids further digest the metabolic byproducts of the microorganisms and microorganismsthemselves. Then the material moves on to the small intestine for absorption. * The ratio of the rumen volume to body volume is correlated with diet quality. A largerumen indicates a low quality diet. |
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Drawbacks to a rumen |
* A rapid change in diet isdifficult for the microbes to adjust to and can lead to acidosis. If the diet shifts toward morestarches and sugars too quickly, certain bacteria will produce lactic acid too quickly for thebacteria that normally use lactic acid and pH in the rumen will drop. If severe enough, theanimal will die. * This process also requires a lot of water. * food must still be of higher quality than hindgut fermenters because theprocess is so slow and plant tannins slow down the microbial process even further. * Need a constant food supply for microbes to survive. |
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Hindgut fermentation |
* Hindgut fermentation takes place post‐stomach in the cecum or colon. This process isfaster than foregut fermentation and can handle poorer quality food, however individualsmust consume a greater proportion of food to obtain the same amount of nutrition.Foregut fermenters can recycle the nitrogenous byproducts of microbial action through therumen and saliva whereas hindgut fermenters cannot. This process takes place poststomach and as a result hindgut fermenters cannot take advantage of the microbesthemselves as a food source unless they are coprophagic‐ i.e., they eat their own feces. |
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Hindgut (cecal) fermenter |
* They have a greatly enlarged cecum that acts as afermentation chamber rather than a large colon. |
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Omnivores |
* Omnivores have simple stomachs but exhibit a mixture of other characteristics. Most havesome capacity for fermentation but do not rely heavily on it. The degree of fermentation and size ofassociated structures can vary within a species depending on diet. |
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Energy demands and body size |
* Larger animals require more energy to function simply because they are larger. However,large animals need PROPORTIONALLY less energy than small animals. * Small animals must process food more quickly, therefore, hindgut fermentation is morecommon in small animals than foregut fermentation. |
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Diet specific patterns |
* Large herbivores such as elephants are not likely to be foregutfermenters because they would have to eat such a large quantity of higher quality food(compared to what a hindgut fermenter can eat). Also, the slow passage rate of foregutfermentation may be too long for such a large quantity of food. * 1) eat high quality food in small amounts andprocess it rapidly (small‐bodied HF); 2) eat medium‐quality food and process it very slowlybut thoroughly (FF); or 3) eat poor quality food in very large amounts and process it veryfast to skim off the digestible portions (large‐bodied HF). |
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Influence of these patterns on life history |
* Large animals that need large quantities of food but can handle poor quality food are oftenseasonally migratory and gregarious. Animals that require less food of higher quality aremore likely to be solitary and territorial because good forage may be hard to come by. * For example, squirrels feed on high quality foodsuch as seeds and nuts. Squirrels are solitary and often cache or hide their food. Rabbits, incontrast, eat very poor quality food and are often seen in large numbers. |
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Seasonal variation in food availability and quality |
* The quality of food available to carnivores does not change very much as long as preyspecies are around (although the amount of fat on the prey does matter‐ you can starve todeath on lean meat). Some carnivores/insectivores (e.g., bats) hibernate when food is lessavailable. Other carnivores, such as wolverines, cache food (store it for later consumption). * Herbivores are more affected by seasonality when it comes to food quality. |
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Nutritional strategies of large herbivores |
* Most large herbivores must deal with poor quality food at certain times of the year. * Rapidly‐growingvegetation is more nutritious because the cell walls are thinner and easier to digest. * Seasonality also affects production of secondary defense chemicals in plants such astannins and toxins that make them less palatable. * One strategy to maximize nutrition is to follow the food (migrate). * Many species timereproduction so that food availability coincides with their period of highest energyrequirements. |
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Environmental adaptations (cold) |
* Mammals regulate their temperatures using physiological mechanisms - endothermy * Regulation also occurs through behavioral adjustments * Mammals maintain a relatively constant body temperature (are homeothermic) * Eutherians are better thermoregulators than either prototherians or metatherians. Internalbody temperature does not vary very much in eutherians. |
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Thermal neutral zone |
* The thermoneutral zone is the range in temperatures at which basal metabolic rate (BMR)is sufficient to balance heat loss and heat gain. When temperatures exceed thethermoneutral zone, the body must expend energy or modify behavior to increase heatloss. Likewise when temperatures drop below the thermoneutral zone, the body mustexpend energy to increase metabolic heat production and reduce heat loss. * Ifcore body temperature drops below the lower critical temperature for too long it will leadto hypothermia and death. * If the core body temperature exceeds the uppercritical temperature for too long it will lead to hyperthermia and death. * Mammals deal with the cold by either avoiding it or resisting it. Avoiding cold conservesenergy while resisting cold requires expending energy. |
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Body size |
* Total energy use increases with increased body size because it takes more energy to powermore mass. However, when you compare the amount of energy expended per kilogram ofbody mass, there is an inverse relationship between size and energy use. Larger animals use more energy, but proportionally lessenergy than smaller animals. * The surface area to volume ratio is very important for the efficiency of regulating internalbody temperature. Large animals lose heat less quickly than small animals because of lower surface:volume ratio. |
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Bergman's rule |
* According to Bergman’s rule, body size of individuals within a given species increases asabsolute latitude increases (distance from equator). The empirical data to support Bergman’s rule are mixed,however general trends are visible. * Body shape is an important determinant of the surface area to volume ratio. Moresurface area leads to greater heat loss. |
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Allen's rule |
* According to Allen’s rule, animals in colder climates have shorter appendages than inwarmer climates. Like Bergman’s rule, this is generally debated‐ but it appears to hold truefor some features and groups. * Caribou appear to an exception to Allen’s rule because they have very long legs. |
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Countercurrent heat exchange |
* Caribou use a countercurrent heat exchange system to help maintain a warm internal coretemperature. Their long legs are very cold compared to their core, but the cold venousblood returning to the core from the legs is heated by the warm arterial blood runningdown to the legs. This countercurrent system maintains a stable warm core and coldextremities. |
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Insulation |
* Insulation is another common strategy for conserving heat. The lynx has thickfur. The seal has thick blubber. Polar bears have both. * Insulation is particularly important in aquatic mammals because water holds heat betterthan air. Hair is an important insulation, however it loses much of its insulating propertieswhen wet. Aquatic mammals with fur (as opposed to cetaceans) have thick, specializedhairs that trap air and keep the skin dry. * Most marine mammals have a thick layer of blubberthat helps insulate them. Too much insulation can cause them to overheat during periodsof high activity, however, so they must have means of dumping heat quickly. Seals andother marine mammals have blubber “windows”, or areas where their blubber is less thick.They can increase blood flow to these windows to dump heat. |
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Nests |
* One behavioral strategy to maintain heat is to construct nests, dens, lodges, or burrows. |
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Foraging zones |
* The subnivean zone is a space between the relatively warm ground and the cold snow thatforms when water vapor condenses and freezes again. The pocket of air in the subniveanzone is much warmer than the ambient temperature above the snow because the groundretains heat better than air and the snow act as insulation. Many small mammals use thisspace for foraging and movement and pikas may even disperse through the subniveanzone. |
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Food hoarding |
* Food hoarding is an important strategy both to ensure food during the winter and reducethe time spent outside in the cold. Scatterhoardersscatter food around, usually burying it, and use scent or memory to find it again. Larder‐hoarders such as wolverines and Douglas squirrels make one or a few large cachesthat they then must protect. |
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Torpor |
* Torpor is a form of dormancy that is not as severe in degree or duration as hibernation. |
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Hibernation |
* Hibernation is much more extreme than torpor and may last multiple months. An animalwith a normal body temperature of 38°C can have a hibernating temperature of nearfreezing. Periodic arousals from torpor to raise body temperature are necessary to avoid shuttingdown completely. |
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Environmental adaptations to (Heat) |
* There are many means to regulate body temperature and conserve water, includinganatomical, physiological, and behavioral mechanisms. |
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Kidneys |
* One way of conserving water is having highly efficient kidneys. The medulla and papilla arevery prominent in the kidneys of desert dwelling mammals and result in more concentrated urine than non‐desert‐dwelling species. Having more concentrated urine reduces the amount of water lost. * Merriam’s kangaroo rat is a desert dwelling rodent that has highly concentrated urine, fecesand milk. The young, however, do not produce as highly concentrated waste products andthe mother is able to consume the urine and feces of her young to recover much of thewater. |
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Diet |
* One strategy for obtaining water is to eat foods with a high water content such assucculents or live prey. * Other species eat foods high in carbohydrates, such as seeds, that yield metabolic waterwhen oxidized within the body. Storing seeds in moist burrows allows seeds to gain moisture. * This chisel‐toothed kangaroo rat uses its teeth to scrape the salty layer off the outside ofthe leaves of the saltbush and consumes the inner, less saline portion. * Oryx maximize their water intake by feeding on plants with the highest water content atdifferent times of the day. They will feed on succulents during the day and then shift toDiasperma at night when the water content of the leaves is higher. |
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Temperature regulation |
* Evaporative cooling is an effective means of cooling the body, however it requires bothwater and convection (air movement/wind). Water absorbs heat as it evaporates into vaporand thus is a major mechanism of heat dissipation through sweating and or panting. * Panting involves evaporative cooling on the tongue and palate. Rapid, shallow breathingprovides airflow over the upper respiratory surfaces and promotes heat loss. Heat andwater are both lost during panting, but some water is conserved through condensation. * Panting is an active means of regulating temperature, while sweating is a passive meansthat relies on wind or movement to create air convection. |
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Panting and sweating |
* Loss of water with both * Sweat contains electrolytesthat must be replenished to maintain proper body function. * panting uses muscular activity and thus generates some heat * both promote evaporative heat loss * panting can help keep the brain cool |
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Brain |
* It is very important to keep the brain cool because if overheated the brain does notfunction properly and affects other body functions. The carotid rete (rete = Latin for net) isa special counter‐current system that cools the brain. * In thissystem, cool venous blood from the nasals runs along warm arterial blood to cool it beforeit reaches the brain. |
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Saliva spreading |
* Saliva spreading is another means of cooling through evaporation. Saliva spreading isvoluntary, unlike sweating, and is most effective in dealing with short‐term heat stress.However, it requires a lot of water because hair must be completely saturated. |
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Escape the heat |
* A common behavioral mechanism for avoiding heat exposure is to use shelters such asburrows or dens during the hottest times of the day. |
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Estivation |
* Estivation is a period of dormancy in reaction to excessive heat that is similar to torpor butless extreme. Physical activity generates heat so it is common for small mammals tobecome inactive, or lethargic, during the hottest times of the day. |
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Reproduction |
* Monotremes lay eggs, metatherians usually have an external pouch where extremely altricial young develop, and eutherians have a well developed placenta that provides for extended development of the fetus within the mother. * Recall also the general trend for fewer large litters at higher latitudes and more small litters near the tropics. This trend is related to the reliability of available food. |
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Monotremes |
* Monotremes have a single opening for reproduction and waste removal called a cloaca. * Females produce milk through mammary glands, but do not have nipples so young must lap the milk off of their mother’s body. Monotremes lack a placenta and instead lay eggs. |
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Marsupials |
* Most marsupials have a choriovitilline placenta that is characterized by a large yolk sac, less developed membranes than the eutherian placenta, and no villi. * Offspring are born extremely altricial and in most cases complete their development within a pouch. * Marsupial females invest much more energy in lactation than they do in gestation. Have a cloaca, less extreme than in monotremes. |
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Eutherians |
* No cloaca * Eutherians have a chorioallantoic placenta that provides a much more intimate connection between mother and offspring. The placenta anchors the fetus within the mother’s uterus, transports nutrients from the mother to the offspring, removes waste products from the fetus, and produces hormones that regulate organs of both the mother and the fetus. The placenta, specifically the trophoblast, also suppresses the immune system of the mother to prevent rejection of the embryo as an alien object to the mother. Together, these characteristics provide for much more developed, precocial young. |
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Estrous cycle |
* Estrus refers to the period of reproductive receptability. Species that only have one period of fertility each year are called monestrous and those that have multiple cycles per year are polyestrous. * The estrous cycle is controlled by hormones produced in the anterior pituitary gland of the brain (FSH and LH) and hormones produced in the ovaries (estrogen and progesterone). |
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Hormones in the estrous cycle |
* Follicle stimulating hormone (FSH) from the anterior pituitary gland in the brain stimulates development of the follicular cells which then release estrogen (estradiol). Estrogen then stimulates the release of leuteinizing hormone (LH) which leads to ovulation (bursting of the follicle and release of the egg). Ovulation suppresses FSH production. * The ruptured follicle forms the corpora luteum (lutea = plural; so named because of the yellow follicular cells that fill it) which begins to produce progesterone. Progesterone promotes the growth of the uterine lining (endometrium) and stimulates development of the mammary glands. * In marsupials, the production of progesterone does not inhibit production of FSH so the estrous cycle does not stop when the female becomes pregnant. |
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Tyranny of the estrous cycle |
* As a result, gestation must be short (less than a single estrous cycle), leading to altricial young and greater emphasis on lactation in marsupials. The phrase “tyranny of the estrous cycle” implies that in marsupials, the cycle continues no matter what, unlike in eutherians where the cycle is cut short if pregnancy occurs. |
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Other variations in reproductive sequence |
* Most common sequence * Ovulation - gametogenesis (usually spontaneous) * Copulation - insemination * Fertilization - formation of diploid zygote * Implantation - attachment of the endometrium * Gestation - intrauterine development * Partuition - birth * Lactation |
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Induced ovulation |
* In mammals that experience induced ovulation, eggs are released within a few hours AFTER copulation. (Copulation then ovulation) * Cats, some mustelids, rabbits and rodents |
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Delayed fertilization |
* Many bats delay fertilization by mating in the fall while swarming before hibernation. The female stores sperm in either her uterus or upper vagina, then when she rouses in the spring she ovulates and fertilizes the eggs with the stored sperm. The ability to time reproduction is advantageous. |
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Delayed implantation |
* Still another variant: Delayed implantation occurs when the egg is fertilized and a blastocyst forms, but it remains in a state of suspended animation until conditions are ideal for implantation and development. * Ursids, mustelids, armadillos * Delayed implantation can either be obligate (always occurs, e.g.: armadillos) or facultative (dependent on environmental conditions). |
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Embryonic diapause |
* Embryonic diapause is similar to delayed implantation in that the blastocyst enters a stage of dormancy in the uterus. Many marsupials exhibit this pattern. * In red kangaroos, the female can have 3 offspring in different stages of development: a “weaned” joey outside the pouch that returns to its mother to suckle relatively low protein milk from its mother’s teat; a pouch young attached to its mother’s teat feeding on high fat milk; and an embryo in diapause within the uterus. The presence of the suckling pouch joey prevents further development of the embryo until it is almost weaned. The birth of the developing fetus usually coincides with the joey leaving the pouch. |
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Spontaneous ovulation is the norm |
* Spontaneous ovulation (independent of copulation) is the norm in mammals. The strategies above are deviations from the “norm” and in many cases are means of dealing with environmental stress and variability. |
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Mating systems |
* Monogamy - 1 male, 1 female (Rare 5-10%)
* Polygyny - 1 male > 1 female (~ 90%) * Polyandry - 1 female > 1 male (Extremely rare < 1%) * Nearly all mammal mating systems involve one male mating with multiple females(polygyny). |
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Asymmetry in parental investment |
* Anisogamy refers to the difference in size and number ofmale and female gametes. The energy investment in producing gametes is significantly greater in females. * Females (eggs) - large in size, relatively few, energetically expensive. * Males (sperm) - small in size, millions, and energetically cheap. * After fertilization, the female gestates the fetus, then must feed and care for the offspringonce born. Reproduction is very energetically costly for females. * Female reproductive potential is limited by the number of eggs and young she cansuccessfully produce. * The limiting factor in reproductive potential for males is access tocopulations with females. Therefore, females are often a scarce resource for males. |
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Reproductive success (RS) |
* Reproductive success (RS) - the number of offspring surviving to reproductive age. * Females are limited primarily by access to food and theirown physical condition. Male reproductive success is limited by access to females. |
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Bateman gradient |
* The Bateman gradient states that the variance in male reproductive success is greater thanin females. Variance is a measure of how much a group of values deviates from theexpected value (mean of those values). * most females mate and they only need to mate once a reproductive cycle to produce theirmaximum number of offspring that cycle. As a result there is a lot less variation in thenumber of offspring produced among females. Males on the other hand can increase theirreproductive success by mating multiple times. Some males mate a lot more than others. * Afemale’s reproductive success is dependent on the number of offspring she can successfullyraise to maturity while a male’s reproductive success is primarily dependent on the numberof females he is able to fertilize. As a result, females put most of their effort into parentalcare while males put theirs into mating. Additionally, females tend to be more choosyabout who they mate with. |
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Types of polygyny
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* Female‐defense polygyny involves females that aggregate naturally for reasons unrelated toreproduction, such as availability of food resources or nesting sites. The male excludesother males from access to the females and claims the females as his harem. The male thathold the harem typically fathers the majority of the offspring.
* Resource‐defense polygyny is similar to female‐defense polygyny. In this system the maledefends a territory that contains resources essential for females to reproduce (food ornesting sites). This is common in situations where resources are clumped or patchilydistributed. * When females are widespread it is much more difficult to monopolizemultiple females, so males exhibit other strategies. * Lek polygyny occurs when movement or distribution of females is predictable and malesestablish temporary aggregations to advertise themselves to females. In these systems the lekking ground does not necessarily contain resources and insteadserves primarily as a display site for the female to choose her mate. * In scramble competition polygyny, the most successful males are those that can cover moreground and thus find more females to mate with. Females are generally widely dispersed inthese systems. |
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Intrasexual selection |
* In these systemsmales compete among themselves for access to females and the winner ends up siring themost offspring. Male‐male competition is common in bovids and cervids where highlyritualized battles occur using antlers or horns. These structures may be selected for throughmale‐male competition (the male with the largest horns/antlers wins the battles and gainsaccess to more females), through female‐choice (intersexual selection: females areattracted to males with large horns/antlers). |
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Intersexual selection |
* Even in cases where there is obvious male‐male combat for access to females, femalechoice may still be important. * Intersexual selection where the female is attracted to a particular trait in males may lead torunaway selection, or extremely exaggerated traits that appear to serve no function. These traits do not increase survival, only reproductive potential. * Other models of intersexual selection suggest that sexually‐selected traits are honestindicators of male quality and thus good genes. These traits are energetically costly toproduce and carry, therefore the male must be of superior quality if he can produce them. |
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Fluctuating asymmetry |
* In addition to size and color, symmetry of sexually selected traits may also be indicative offitness. Fluctuating asymmetry refers to the random deviations from symmetry of pairedtraits and is often more pronounced in sexually selected traits such as antlers. Sexuallyselected traits may be particularly prone to fluctuating asymmetry because they are signalsof male quality. |
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Sexual dimorphism |
* In cases where both sexes play a role in courtship, both intra‐ and inter‐sexual selection canoccur simultaneously. These processes promote sexual size dimorphism. In elephant seals, the male is huge in size as compared with the female. There is selectivepressure for extremely large males because social rank and thus copulatory success ispositively correlated with body size. * Mean harem size and male to female size ratio are positively correlated in pinniped species.As the average number of females in a male’s harem increases, so does the differencebetween male and female body sizes. |
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Polyandry |
* Some species of canids such as the African wild dog sometimes exhibit polyandry whereone female mates with multiple males. * Most cases in mammals where a female mates with multiple males falls into the categoryof promiscuity because males also mate with multiple females. Promiscuity is common inmany mammals, including rodents. |
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Monogamy |
* Monogamy occurs when neither sex can monopolize more than one member of theopposite sex. Monogamy can be either facultative if female densities are low and a malecannot find multiple females, or obligate if parental care from both parents is required tosuccessfully raise offspring. (Canids) |
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Sperm competition |
* Sperm competition is common in promiscuous systems where females mate with multiplemales during a single estrous period. There are two sets of strategies: first‐male advantageinvolves strategies that reduce the chance that subsequent copulations will fertilize thefemale’s eggs; and second‐male advantage strategies reduce the chance that previouscopulations will be successful. |
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Asociality |
* Systems are considered asocial when individuals only come together for temporaryassociations to mate or during mother‐neonate relationships. (Solitary) |
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Eusociality |
* In mammals, eusociality is extremely rare. In order to be considered trueeusociality there must be division of labor (the presence of castes). A “caste” is a groupresponsible only for a specific job (e.g., food gathering). * Specifically, eusociality is characterized by:1) Cooperative care of young2) Reproductive castes with non‐reproductive members caring for reproductive nestmates3) Overlapping generations such that offspring care for their siblings |
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Sociality |
* When individuals of the same species associate with each other beyond mating and parental behavior. * There are costs and benefits associated with sociality. Benefits include: - Defense from physical factors (e.g. cold temperatures), predators, or aggressiveconspecifics - Increased foraging efficiency - Group defense of resources - Easier identification of potential mates - Division of labor - Rich learning environment for young of highly‐intelligent species |
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Advantages of sociality |
* Defense - improved detection of threats, repulsion of predators, and improved defense of limited resources * Improved foraging efficiency (A single wolf cannot take down a large elk, but a pack easily can). * Overall increase in resource use efficiency (Taking advantage of other groups members’ knowledge or following previously made trailsis more efficient than wandering off on your own to forage). * Improved care of offspring |
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Costs of sociality |
* Socialitymay lead to increased competition. In many social systems a dominancehierarchy is established to maintain stability within the group. * High densities of individuals increases risk of infection from diseases and parasites. * Competition for dominance within the group sometimes leads to injury or death, especiallyof juveniles that may inadvertently get in the way. (Increased agonistic behavior) |
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Evolution of sociality |
* From an evolutionary perspective, costs and benefits are measured in reproductive success(or reproductive fitness), which is the number of offspring that survive to reproductive age,or the number of genes that get passed on to the next generation. In order for sociality toevolve, the benefits to the individual must outweigh the costs to the individual. * In true altruism, there is a cost to the actor and a benefit to the recipient. * Incooperative behavior, on the other hand, both the actor and recipient benefit. |
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Evolution of altruism and eusociality |
* The answer lies in kin selection and the idea of maximizing “inclusive fitness” rather thanindividual fitness. In other words, it is not how many offspring you have, but rather howmany copies of your genes get passed on to the next generation through your offspringAND your relatives’ offspring. You and your “kin” share some of your genes in common,therefore the offspring of your kin also have some of your genes. |
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Hamilton's rule |
* Hamilton’s rule states that genes for altruistic behavior can spread if the product of thebenefit to the recipient (B) and the coefficient of relatedness between the actor andrecipient (r) is greater than the cost to the actor (C): Br > C |
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Coefficient of relatedness (r) |
* For DIPLOID organisms, half of the genetic material is inherited maternally and halfpaternally. For any particular allele there is a 50:50 change that it came from either parent.Therefore on average offspring share half of all their genes with each parent: r = 0.5. * For the parent offspring example there is only one step and one path: parent to offspring.For half‐siblings there are two steps, but still only one pathway: one half‐sibling to sharedparent, and shared parent to the other half‐sibling. As we saw from the previous slide aparent and offspring have an r=0.5, therefore half‐siblings have an r = 0.5*0.5 = 0.25.* Half‐siblings are common in polygynous and promiscuous mating systems. * For full‐siblings there are two paths of two steps each resulting in an r = 0.25 + 0.25 = 0.5.This is twice the value of r for half siblings. * For first cousins, relatedness is even more diluted. We know from the previous examplesthat r for parent‐offspring = 0.5 and r for full‐siblings = 0.5, therefore first cousins =0.5*0.5*0.5 = 0.125 = 1/8 |
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Inclusive fitness |
* Inclusive fitness = direct fitness + indirect fitness = your offspring + sum[(each of yourrelatives’ offspring)*(r between you and that relative)] * When a behavior increases indirect fitness there is a potential for kin selection as long asthe increase in indirect fitness exceeds any resulting decrease in direct fitness. |
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Kin selection |
* Kin selection requires a relatively high degree of relatedness AND the ability to recognizeindividuals. * Naked mole rats (Eusocial) They feed on large tubers that are few and far between, but when they are found they mayfeeds the whole colony. Many individuals are more successful at locating tubers than asingle or a few individuals. Naked mole rats are not haplodiploid, but they are highly inbredand therefore have a high degree of relatedness among individuals in a colony. |
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Reciprocal altruism |
* “Reciprocal altruism” can be a stable explanation. In order for reciprocal altruism to evolvethere must be some form of control of cheaters, otherwise everyone would cheat and thesystem would collapse. Certain conditions must be met: - Coalitions must be stable. The group must stay together longer than a single event. - Individuals must have good memory capacity. - There must be some form of punishment for cheaters. (primates) * You would expect to see more reciprocal altruism in a small town because people are morelikely to know each other and run into each other on a regular basis. People are more likelyto help people they know than people they will never see again. Also, people are highlymotivated by consequence. |
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Conservation |
* Historically, most conservation efforts focused on game species. Restrictions on hunting have existed for centuries and game reserves date back multiple millennia. Most historical reserves were established to protect the resources for the wealthy and land owners from the rest of the people. * In order for conservation efforts to be successful, there must first be a comprehensive understanding of the biology of the species and species interactions. (interdisciplinary science) |
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IUCN red list |
* The IUCN is an international body that assess the conservation of species on a yearly basis. The IUCN Red List is comparable to the US Endangered Species List, but it does not carry the same legal repercussions. The list includes all species, not just threatened or endangered ones. |
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Factors explaining extinction risk in mammals |
* Size of geographic range is negatively correlated with extinction risk: the larger the geographic range, the smaller the risk. * Adult body mass is positively correlated with extinction risk. Larger mammals are at greater risk for a number of reasons. They generally have larger home ranges and smaller population sizes. They also tend to have a later age of sexual maturity and fewer number of offspring resulting in slow population growth. * Species that live in areas with high human population density are at higher risk from habitat loss, harvesting, and other factors. * There is a general trend for higher extinction risk at higher latitudes. This may be related to higher human population densities at higher latitudes, larger body size at higher latitudes (remember Bergmann’s rule), or likely both. |
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Categories of threat |
* Habitat loss is arguably the single greatest threat to species diversity. * Habitat fragmentation is often related to habitat loss, although loss of connectivity can occur without significant loss of habitat. Barriers to dispersal such as roads can have significant effects on animal movement. * Humans exploit mammals for many uses such as food, fur, clothing, ornamentation, medicinal uses, and the pet trade. * Human-wildlife conflict is an important issue particularly with predators and “pest” species. * Disease, particularly those transmitted by domestic animals, can be a great threat, as can introduced species that outcompete or predate native species. * Hybridization is also an important conservation issue. |
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Habitat loss |
* Tallgrass prairie, Atlantic rainforest, bottomland hardwood, old-growth forest, and tropical forest. * Habitat specialist tend to be at highest risk |
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Habitat fragmentation |
* In recent years more emphasis has been placed on protecting habitat AND connectivity of habitat. In many places there is much interest in mitigating the effects of highways on wildlife movement. Wildlife crossings not only increase connectivity for the animals that use them, but also reduce vehicle-wildlife collisions and improve driver safety in areas of high animal density. |
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Conflict with humans |
* Mammals are often perceived as disease reservoirs; sometimes justifiably and sometimes not. * Crop raiding is another serious source of human-wildlife conflict. |
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Disease |
* Diseases may spread more quickly among domesticated animals because they are kept in close contact with each other, however they can build up immunity over generations of exposure. When they are moved around the world by people, the native wildlife have never been exposed to the disease and are therefore highly susceptible. |
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Introduced species |
* Mammals are often introduced by humans either on purpose or accidentally. Introduced predators, mammalian and otherwise, affect small mammals and other prey species. Introduced herbivores can potentially affect whole communities through cascading effects. |
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Hybridization |
* Hybridization between closely related species or subspecies/populations that would not normally interbreed can have genetic implications resulting from introgression (mixing of the gene pools). |
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Problems inherent to small populations |
* Fewer individuals means increased probability of inbreeding. Inbreeding leads to loss of genetic diversity, fixation of alleles, and an increase in deleterious (harmful) alleles. * Demographic stochasticity refers to fluctuations in demographic parameters (i.e., birth and death rates) due to random chance. In small populations, demographic stochasticity can lead to extinction because such fluctuations have a proportionately greater effect on small populations than large populations. |
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Management of harvested populations |
* For harvested populations such as game species, in general there has been a shift from “killing as many as possible” to a “sustainable harvest” model. This is achieved through controlling the number and timing of take of harvested species. * only effective in areas with stable governments and sufficient alternative resources for humans. |
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Protection and enforcement |
* There is a lot of debate as to the effectiveness of the “carrot” versus the “stick” models as conservation strategies. The incentive, or carrot model says that if given enough incentive people will want to protect wildlife and conserve resources. The punishment, or stick model says that enforcement through fines, jail time, or other form of punishment is necessary. * Most countries have laws against poaching, but infrastructure, money, and political stability are necessary to enforce the laws. There must be viable alternatives to poaching and there must be efforts to help improve the livelihoods of the people doing the poaching before laws can be effective. |
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Reserves and parks |
* Reserves and parks are common in many countries, but how they are managed varies widely. In many cases parks and reserves exist on paper, but there is no actual enforcement or management on these “paper parks”. In the United States many of the National Parks were established to preserve “landscapes” that are pretty to look at rather than to conserve ecosystems and biodiversity (although parks still play a critical role in conservation and do protect a lot of biodiversity anyway!) |
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Community Conservation Areas |
* A community conservation area (CCA) provides incentive to the local people by returning profits from tourism and other activities back to the community. * In game reserves local hunting and settling is outlawed, but expensive safaris are allowed. The hunters are usually foreigners who pay a lot of money to hunt big game. Much of the profits may go to the safari companies (usually run by foreigners), and sometimes the local communities receive only small benefits. |
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Mammals are wide-ranging/may be migratory |
* Migratory species and species with large home ranges are particularly difficult to protect in traditional protected areas. Migratory or other vagile species may frequently move between areas that have different protections and restrictions to take. Migratory species can also be difficult to protect because they may have different habitat requirements in different places and different times of the year. |
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Reserve design |
* Single Large Or Several Small reserves? * Everyone agrees that the best model is many large reserves, however that is not realistic given limitations on available land and money. * Some would argue that the single large reserve is better because it is a larger, more continuous area. The four small reserves are fragmented in comparison, more vulnerable to negative edge effects, and can support fewer individuals and species. However, others would argue that it is better to have several small reserves so as to not “put all your eggs in one basket” so to speak. Additionally, it may be the case that the single large reserves only represents a single habitat type and the four small ones represent multiple habitat types among them. |
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Translocation and reintroduction |
* Translocation - moving animals to unoccupied habitat * Reintroduction - releasing individuals to a region where they have been extirpated. * Augmentation - adding new individuals to increase population size or increase diversity. |
