Mammals

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Mammals
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Class Mammalia

• Small number of species 4500
• But probably more successful than most animal
  groups (except insects) at exploiting all
  available environments

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Class Mammalia

• Very diverse group not constrained by particular
  lifestyle (like flight in birds)
• Diversity makes it difficult for layperson to
  identify various mammals as being closely related

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Class Mammalia

• Descended from therapsid reptiles with
  mammal-like characteristics
• Important structural changes from reptiles to
  mammals

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Class Mammalia

• Limbs from lateral to ventral
• Higher center of gravity - less stability
• Required greater development of cerebellum -
  muscular coordination center in brain

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Class Mammalia

• Separation of air and food passageways in head
• Can breathe with mouth full of food
• Allows prolonged chewing some early digestion

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Subclass Theria

• Most mammals belong to Subclass Theria
• Descended from some common ancestor 150 million
  years ago

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Subclass Theria

• Infraclass Metatheria - marsupials - pouched
  mammals
• Infraclass Eutheria - placental mammals

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Subclass Prototheria

• Monotremes
• Small group of egg-laying mammals
• So different from other groups of mammals
• Entirely different origin?

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All mammals

• Characteristics unique and diagnostic for mammals
• Hair - greatly reduced in aquatic mammals
• Mammary glands - milk secreting glands for
  nourishing young

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Integument Derivatives

• Skin generally thicker than in other vertebrates
• Dermis thicker than epidermis
• Epidermis very thin where covered with hair,
  thicker on palms, soles

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Integument Derivatives

• Hair derived from epidermis
• Probably evolved from reptilian scales
• Scales still present in some (tail of rat, beaver)

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Integument Derivatives

• Grows from follicle
• Epidermal structure sunk deep into dermal layer
  and beyond
• Grows by addition of new cells at base of follicle

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Integument Derivatives

• Cells pushed upward die from lack of nourishment
• Dead cells mostly keratin - same material in
  nails, claws, feathers

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Integument Derivatives

• Hair consists of 3 layers
• Medulla - core
• Cortex - contains pigment
• Cuticle - composed of imbricated scales
• Different types of hair result from differential
  development of the 3 layers

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Integument Derivatives

• Each follicle has muscle attached to it - erector
  muscle
• Contraction causes hair to stand up straight
• Increase insulation thickness, serve as warning

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Fur or Pelage

• Most mammals have two kinds of hair
• Thick, soft underhair - provides insulation
• Coarse, long guard hair - protects and provides
  coloration

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Fur or Pelage

• Hair stops growing when it reaches certain length
• Remains in follicle until new growth starts, then
  falls out

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Fur or Pelage

• Mammals lose hair in periodic molts
• Most have 2 annual molts - entire pelage shed
  (humans shed and replace continually)
• Spring - thin summer
• Fall - heavy winter

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Fur or Pelage

• Pigmentation and molts allow mammals to be
  different colors in different seasons
• Brown in summer
• White in winter - leukemism

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Fur or Pelage

• Lack of pigment results in albinism - recessive
  gene - blocks pigment formation (dont confuse
  with leukemism)
• Excess of black pigment is melanism

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Derivatives of Hair

• Vibrissae - sensory hairs on snouts, other parts
  of head
• Incorrectly called whiskers

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Derivatives of Hair

• Quills - defensive structures in porcupines,
  hedgehogs, echidnas
• Break off after barbed tip embeds in flesh of
  other animal
• Work in deeper with time

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Glands

• Mammals also have variety of epidermal glands
• Greatest variety among vertebrates
• 4 basic types

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Glands

• Sweat glands - simple, tubular, highly coiled
• Cover most of body
• Not found in other vertebrates
• Open directly to skin surface
• Two types

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Glands

• Sweat glands - eccrine glands
• Secrete watery sweat for temperature regulation
• Hairless regions in most mammals (especially foot
  pads)

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Glands

• Some mammals dont have eccrine glands - rodents,
  rabbits, whales
• Some have them all over body - humans, horses,
  dogs
• Racial differences in abundance in humans

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Glands

• Sweat glands - apocrine glands
• Found in all mammals
• Longer, more winding than eccrine glands
• Open into follicle at surface
• Secretion not involved with heat regulation

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Glands

• Apocrine gland activity correlated with some
  aspects of sexual cycles
• Human females have twice as many as males

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Glands

• Scent glands - location and function vary
• Communication, warning, defense, attraction
• E.g., skunk
• Humans have many, but taught to dislike their
  scent

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Glands

• Sebaceous glands - associated with hair follicle
• Secrete fat (sebum) to keep hair and skin soft
• Polite fat - does not turn rancid
• Generally all over body - most numerous on human
  scalp, face

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Glands

• Mammary glands - modification of apocrine,
  sebaceous glands?
• Present in both genders, functional only in
  female
• Secrete milk to nourish young

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Glands

• Contain varying quantities of fat (3-5),
  protein, carbohydrate, salts
• Higher fat content (30-40) in marine and arctic
  mammals, where development is rapid

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Horns Antlers

• 3 kinds of horns or horn-like structures found in
  mammals
• 1) true horns
• 2) antlers
• 3) rhino horns

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Horns Antlers

• True horns
• Found in ruminants like cows, goats, antelope
• Hollow sheaths of keratinized epidermis
  surrounding core of bone arising from skull

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Horns Antlers

• Not normally shed
• Not branched (but may be greatly curved, twisted)
• Found in both sexes

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Horns Antlers

• Antlers
• Deer family (Cervidae)
• Generally males only (except caribou - females
  smaller)
• Entirely bone when mature

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Horns Antlers

• Annual growth
• Develop beneath cover of highly vascularized soft
  skin - velvet
• Growth complete, blood vessels constrict, velvet
  dies and is rubbed off

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Horns Antlers

• Antlers dropped after breeding season
• New buds appear within few months
• New pair larger, more elaborate
• Strain on mineral metabolism - moose, elk must
  accumulate 50 lbs of calcium salts from
  vegetable diet

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Horns Antlers

• Rhinoceros horn
• Hairlike horny fibers arise from dermal papillae
• Cemented together to form single horn
• Dagger handles and medicinal uses

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Teeth

• Teeth are a less obvious characteristic of
  mammals
• Reveal more about lifestyle than any other
  characteristic
• Not in monotremes, some whales, anteaters

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Teeth

• Diphyodont teeth - two sets of teeth
• Set of deciduous milk teeth replaced by set of
  permanent teeth
• Reptiles have polyphyodont teeth - many sets -
  all are homodont - uniform, unspecialized

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Teeth

• Mammals have heterodont teeth - specialized for
  various functions

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Teeth
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Teeth

• Incisors - snip, bite - simple crowns, slightly
  sharp edges

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Teeth

• Canines - piercing - pointed, long conical crowns

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Teeth

• Premolars - shear, slice - flat compressed crowns
  with 1 or 2 cusps

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Teeth

• Molars - crushing, grinding - broad with variable
  cusp arrangement
• Always belong to the permanent set

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Teeth

• Different diets necessitate differing development
  of different teeth
• Carnivores - large canines, some small and/or
  modified molars and premolars

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Teeth

• Rodents and herbivores - large incisors, reduced
  canines, large molars
• Incisors grow continually, must be worn away to
  keep pace with growth

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Teeth
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Digestive Systems

• Different diets also necessitate differing
  digestive systems
• Herbivores face special problem - indigestibility
  of cellulose, chief carbohydrate in plants

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Digestive Systems

• No digestive enzyme to break down cellulose
• Depend on anaerobic bacteria to do it
• Developed various digestive structures where
  microbes can do their thing

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Digestive Systems

• Two basic approaches
• 1) hind-gut approach
• 2) fore-gut approach

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Digestive Systems

• Hind-gut approach
• Horses and rabbits and others
• Large sidepocket - cecum - at junction of small,
  large intestines
• Houses microbes

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Digestive Systems

• Sometimes all isnt digested first time through
• Rabbits, hares, some rodents eat fecal pellets -
  coprophagy
• More bacterial fermentation, chance to absorb
  vitamins manufactured by bacteria

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Digestive Systems

• Humans have vestigial cecum - appendix

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Digestive Systems

• Fore-gut approach
• Cattle, deer, sheep, antelope are ruminants
• Have huge, 4-chambered stomach where digestion
  occurs

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Digestive Systems

• Grass passed down esophagus to rumen
• Broken down by bacteria and formed into small
  balls of cud in reticulum
• Regurgitated to mouth and chewed to crush fibers

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Digestive Systems

• Swallowed to rumen again for further digestion by
  bacteria
• Finally passed through reticulum and churned in
  omasum

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Digestive Systems

• Passed into abomasum - true stomach
• Proteolytic enzymes secreted, normal digestion
  occurs

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Digestive Systems

• Small intestine very long, coiled
• Much longer in herbivores than in carnivores,
  insectivores
• Cow small intestine - 50 m (165 feet)

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Size vs. Food Consumption

• The smaller the mammal, the greater its metabolic
  rate, and the more it must eat relative to its
  size
• Small mammals spend more time hunting, eating
  than large mammals

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Size vs. Food Consumption

• 2 g shrew eats gt its body weight in food each day
• Will starve to death in few hours if deprived of
  food

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Size vs. Food Consumption

• Large carnivore may only need one meal every few
  days to remain healthy

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Migration

• Few mammals make seasonal migrations
• Much more difficult than for birds
• Most that do live in, near North America

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Migration

• Barren-ground caribou - seasonal movements gt1000
  km
• North for calving, south for winter

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Migration

• Longest mammal migrants are whales, seals
• Fur seal females migrate 2800 km to give birth,
  winter
• Males stay north

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Migration

• Few bats with power of flight use it to migrate
• Most hibernate during winter
• 4 spp. of American bats migrate - red bat
• Winter in Mexico, summer north, west

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Flight

• Flight, gliding evolved independently in several
  different groups marsupials, rodents, lemurs,
  bats
• Bats are only true fliers - nocturnal insectivore
  niche left open by most birds

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Flight

• Success of bats
• 1) flight
• 2) ability to navigate via echolocation

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Echolocation

• Fly and avoid obstacles in complete darkness
• Locate catch insects with precision and speed
• Find way deep into caves - new habitat

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Echolocation

• Emit short pulses (5-10 msec) from mouth
• Ultrasonic to human ear
• 10-200 pulses/sec
• Echo received with great ears - form image of
  surroundings as good as eyes of other mammals

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Echolocation

• May be used by other insectivorous mammals
  shrews, tenrecs
• Crudely developed compared to bats

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Echolocation

• Echolocation highly developed in toothed whales,
  e.g., sperm whale
• Varying frequency clicks produced in sinus
  passages

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Echolocation

• Focused by lens-shaped melon in forehead
• Returning echoes channeled through oil-filled
  cavity in lower jaw to inner ear

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Echolocation

• Allows whales to determine size, shape, speed,
  distance, directions, density of everything in
  water
• Keep track of members of pod

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Hibernation

• True hibernators ground squirrels, woodchucks
• Body temperature falls within few degrees of
  freezing
• Breathing, heart rates drop extremely low

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Hibernation

• Not true hibernation bears
• Breathing, heart rates fall, but body temperature
  remains similar

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Reproduction

• Most mammals have definite mating seasons
• Usually winter or spring
• Timed to coincide with most favorable time for
  rearing young after birth

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Reproduction

• Female mating function restricted to time during
  periodic cycle - estrous cycle
• Female receptive during brief period of cycle -
  estrus or heat
• Several other stages

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Reproduction

• Proestrus - period of preparation
• New ovarian follicles grow

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Reproduction

• Estrus - mating, ovulation, fertilization,
  implantation, pregnancy

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Reproduction

• Metestrus - if no mating or fertilization, a
  period of repair

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Reproduction

• Diestrus - uterus becomes small, anemic

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Reproduction

• Monestrous - single estrus during breeding season
• Dogs, foxes, bats
• Polyestrous - recurrence of estrus during
  breeding season
• Mice squirrels, tropical animals

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Reproduction

• Humans and Old World monkeys have slightly
  different cycle
• Post-ovulation period terminated by menstration -
  menstrual cycle

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Reproduction

• 3 different patterns of reproduction among
  mammals
• 1) monotremes
• 2) marsupials
• 3) placentals

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Reproduction

• Monotremes - egg-laying mammals
• One breeding season each year
• Ovulated eggs (2) fertilized in oviduct
• Shell added in oviduct
• Eggs laid in burrow nest
• Incubated for 12 days

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Reproduction

• Hatch, fed milk (licking, not suckling)
• No gestation - period of pregnancy
• Developing embryo uses nutrients in egg
• Young reared on milk

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Reproduction

• Marsupials - pouched mammals
• Brief gestation period, but physiology and
  lactation complicated
• E.g., red kangaroo

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Reproduction

• 1st pregnancy of season followed by 33-day
  gestation, joey born underdeveloped
• Crawls into pouch, attaches to nipple
• Mother immediately becomes pregnant again

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Reproduction

• Presence of young in pouch arrests development at
  100-cell stage - diapause
• Lasts 235 days until joey leaves pouch
• 2nd joey develops, born in month, enters pouch

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Reproduction

• Becomes pregnant again
• Arrested development
• Oldest joey returns to nurse from time to time
• 3 young at once

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Reproduction

• Some marsupial variations
• Development delays
• Common features
• Born at underdeveloped stage
• Prolonged development attached to mammary gland

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Reproduction

• Placentals - most successful mammals
• Reproductive investment is in gestation
• Embryo nourished by food via placenta

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Reproduction

• Gestation variable
• Mice - 21 days
• Rabbits - 30-36 days
• Cats, dogs - 60 days
• Cattle - 280 days
• Elephants - 22 months
• Baleen whales - 12 months
• Bats - 4-5 months

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Reproduction

• Variable condition at birth - well-furred and
  mobile to naked, blind, helpless
• Human growth slower than any other mammal

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of Young

• Smaller animals, larger litters
• Larger animals, smaller litters
• Status in food web important
• Carnivores - 1 litter of 3-5 young
• Mice - 17 litters of 4-9 young per year

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of Young

• Large mammals - single young with each pregnancy
• Elephant - 4 young per 50-year reproductive life

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Territory

• Defended area for exclusive use
• Marked using scent glands
• Varies in size from huge (grizzly bear) to small
  (squirrel)

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Territory

• Owner comfortable within territory, intruder at
  psychological disadvantage

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Territory

• Owner comfortable within territory, intruder at
  psychological disadvantage

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Territory

• Some territories established for use by family
  unit
• Male beaver defends territory, female and young
  use it

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Territory

• Some live in friendly towns - prairie dog
• Parents give old home to young and move out

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Home Range

• Larger foraging area surrounding defended
  territory
• Neutral zone used for foraging by owners of
  several territories

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Us Them

• Biggest impact - domestication
• Dogs, cats 10,000 years ago
• Food animals much later

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Us Them

• Beasts of burden
• Some no longer exist in wild - llama, alpaca,
  1-humped Arabian camel

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Us Them

• Some not truly domesticated - do not breed in
  captivity
• Reindeer, Asian elephant

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Us Them

• Problem mammals - rodents, rabbits
• Damage crops, foods, carry diseases

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Us Them

• Problems with us
• 300 species endangered
• Includes all cetaceans, cats, otters, primates
• Hunting, collecting, habitat destruction, species
  introductions