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Overview

Brief Summary

Mammals are vertebrate animals which feed their young on milk produced by mammary glands. All have hair at some point in their lives, even if they have only a few (like most whales).

They are generally endothermic ("warm-blooded"), producing body heat internally. Some species, such as seals regularly also use the sun or other environmental heat sources in addition to the metabolic heat they produce.

Most species give birth to living young - with the notable exception of the monotremes (the platypus and the echidnas) of Australia and the southern Pacific region, which lay leathery shelled eggs.

The approximately 5000 species of mammals range in size from the 100 foot long (30m) blue whale to the 3/4 inch (30-40mm) long Old World hognosed bat.

Various species of mammal can swim, climb, run and fly.

Mammals are distributed worldwide, occurring on all continents and most islands. Even islands that are said to be without mammals will have whales in the nearby waters. One species has even begun to colonize local space off earth.

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Comprehensive Description

Diversity

The Class Mammalia includes about 5000 species placed in 26 orders. Systematists do not yet agree on the exact number or on how some orders and families are related to others. The Animal Diversity Web generally follows the arrangement used by Wilson and Reeder (2005). Exciting new information, however, coming from phylogenies based on molecular evidence and from new fossils, is changing our understanding of many groups. For example, skunks have been placed in the new family Mephitidae, separate from their traditional place within the Mustelidae (Dragoo and Honeycutt 1997, Flynn et al., 2005). The Animal Diversity Web follows this revised classification. Whales almost certainly arose from within the Artiodactyla (Matthee et al. 2001; Gingerich et al. 2001). The traditional subdivision of the Chiroptera into megabats and microbats may not accurately reflect evolutionary history (Teeling et al. 2002). Even more fundamentally, molecular evidence suggests that monotremes (Prototheria, egg-laying mammals) and marsupials (Metatheria) may be more closely related to each other than to placental mammals (Eutheria) (Janke et al. 1997), and placental mammals may be organized into larger groups (Afrotheria, Laurasiatheria, Boreoeutheria, etc.) that are quite different from traditional ones (Murphy et al. 2001).

All mammals share at least three characteristics not found in other animals:   3 middle ear bones,   hair, and the production of milk by modified sweat glands called   mammary glands.  The three middle ear bones, the malleus, incus, and stapes (more commonly referred to as the hammer, anvil, and stirrup) function in the transmission of vibrations from the tympanic membrane (eardrum) to the inner ear. The malleus and incus are derived from bones present in the lower jaw of mammalian ancestors. Mammalian hair is present in all mammals at some point in their development. Hair has several functions, including insulation, color patterning, and aiding in the sense of touch. All female mammals produce milk from their mammary glands in order to nourish newborn offspring. Thus, female mammals invest a great deal of energy caring for each of their offspring, a situation which has important ramifications in many aspects of mammalian evolution, ecology, and behavior.

Although mammals share several features in common (see Physical Description and Systematics and Taxonomic History), Mammalia contains a vast diversity of forms. The smallest mammals are found among the shrews and bats, and can weigh as little as 3 grams. The largest mammal, and indeed the largest animal to ever inhabit the planet, is the blue whale, which can weigh 160 metric tons (160,000 kg). Thus, there is a 53 million-fold difference in mass between the largest and smallest mammals! Mammals have evolved to exploit a large variety of ecological niches and life history strategies and, in concert, have evolved numerous adaptations to take advantage of different lifestyles. For example, mammals that fly, glide, swim, run, burrow, or jump have evolved morphologies that allow them to locomote efficiently; mammals have evolved a wide variety of forms to perform a wide variety of functions.

  • Nowak, R. 1991. Walker's Mammals of the World. Baltimore: Johns Hopkins University Press.
  • Vaughan, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, 4th Edition. Toronto: Brooks Cole.
  • Gingerich, P., M. ul Haq, I. Zalmout, I. Khan, M. Malkani. 2001. Origin of whales from early artiodactyls: Hands and feet of Eocene Protocetidae from Pakistan. Science, 293: 2239-2242.
  • Dragoo, J., R. Honeycutt. 1997. Systematics of mustelid-like carnivores. Journal of Mammalogy, 78: 426-443.
  • Janke, A., X. Xu, U. Arnason. 1997. The complete mitochondrial genome of the wallaroo (Macropus robustus) and the phylogenetic relationship among Monotremata, marsupialia, and Eutheria. Proc. National Academy of Sciences, 94: 1276-1281.
  • Matthee, C., J. Burzlaff, J. Taylor, S. Davis. 2001. Mining the mammalian genome for artiodactyl systematics. Systematic Biology, 50: 367-390.
  • Murphy, W., E. Eizirik, S. O'Brien, O. Madsen, M. Scally, C. Douady, E. Teeling, O. Ryder, M. Stanhope, W. de Jong, M. Springer. 2001. Resolution of the early placental mammal radiation using Bayesian phylogenetics. Science, 294: 2348-2351.
  • Teeling, E., O. Madsen, R. Van Den Bussche, W. de Jong, M. Stanhope, M. Springer. 2002. Microbat paraphyly and the convergent evolution of a key innovation in Old World rhinolophoid microbats. Proc. National Academy of Sciences, 99: 1431-1436.
  • Wilson, D., D. Reeder. 1993. Mammal Species of the World. Washington D.C.: Smithsonian Institution Press.
  • Flynn, J., J. Finarelli, S. Zehr, J. Hsu, M. Nedbal. 2005. Molecular phylogeny of the Carnivora (Mammalia): assessing the impact of increased sampling on resolving enigmatic relationships. Systematic Biology, 54/2: 317-337.
  • Klima, M., W. Maier. 1990. Body Structure. Pp. 58-84 in B Grzimek, ed. Grzimek's Encyclopedia of Mammals, Vol. 1, 1 Edition. New York: Mcgraw-Hill.
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Distribution

Geographic Range

Mammals can be found on all continents, in all oceans, and on many oceanic islands of the world.

Biogeographic Regions: nearctic (Introduced , Native ); palearctic (Introduced , Native ); oriental (Introduced , Native ); ethiopian (Introduced , Native ); neotropical (Introduced , Native ); australian (Introduced , Native ); antarctica (Native ); oceanic islands (Introduced , Native ); arctic ocean (Native ); indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )

Other Geographic Terms: cosmopolitan

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Physical Description

Morphology

Sexual Dimorphism

Males larger than females in 45% of species, and average 18% heavier than females overall; females slightly larger in only 3 orders; Sexual Dimorphism in shape, color, pelage, tooth size, horns and antlers; females have mammary glands; intromittent organs and scrotal sacks often externally obvious in males.
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Physical Description

All mammals have   hair at some point during their development, and most mammals have hair their entire lives. Adults of some species lose most or all of their hair but, even in mammals like whales and dolphins, hair is present at least during some phase of ontogeny. Mammalian hair, made of a protein called keratin, serves at least four functions. First, it slows the exchange of heat with the environment (insulation). Second, specialized hairs (whiskers or "vibrissae") have a sensory function, letting an animal know when it is in contact with an object in its environment. Vibrissae are often richly innervated and well-supplied with muscles that control their position. Third, hair affects appearance through its color and pattern. It may serve to camouflage predators or prey, to warn predators of a defensive mechanism (for example, the conspicuous color pattern of a skunk is a warning to predators), or to communicate social information (for example, threats, such as the erect hair on the back of a wolf; sex, such as the different colors of male and female capuchin monkeys; or the presence of danger, such as the white underside of the tail of a white-tailed deer). Fourth, hair provides some protection, either simply by providing an additional protective layer (against abrasion or sunburn, for example) or by taking on the form of dangerous spines that deter predators (porcupines, spiny rats, others).

Mammals are typically characterized by their highly differentiated   teeth. Teeth are replaced just once during an individual's life (a condition called   diphyodonty). Other characteristics found in most mammals include: a   lower jaw made up of a single bone, the dentary; four-chambered hearts; a secondary palate separating air and food passages in the mouth; a muscular diaphragm separating thoracic and abdominal cavities; a highly developed brain; endothermy and homeothermy; separate sexes with the sex of an embryo being determined by the presence of a Y or 2 X chromosomes; and internal fertilization.

Often, characteristics of skulls and dentition are used to define and differentiate mammalian groups. To make these easier to comprehend within the accounts of lower mammalian taxa, we provide links to   dorsal,   ventral, and   lateral views of the skull of a dog on which the major bones, foramina, and processes have been labelled. Closeups of the   basicranial region,   orbital region, and   lingual and   labial views of a mandible are also available. A partially labeled   full skeleton of a raccoon has also been prepared.

Other Physical Features: endothermic ; heterothermic ; homoiothermic; bilateral symmetry ; polymorphic ; venomous

Sexual Dimorphism: sexes alike; female larger; male larger; sexes colored or patterned differently; female more colorful; male more colorful; sexes shaped differently; ornamentation

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Ecology

Habitat

Different species of mammals have evolved to live in nearly all terrestrial and aquatic habitats on the planet. Mammals inhabit every terrestrial biome, from deserts to tropical rainforests to polar icecaps. Many species are arboreal, spending most or all of their time in the forest canopy. One group (bats) have even evolved powered flight, which represents only the third time that this ability has evolved in vertebrates (the other two groups being birds and extinct Pterosaurs).

Many mammals are partially aquatic, living near lakes, streams, or the coastlines of oceans (e.g., seals, sea lions, walruses, otters, muskrats, and many others). Whales and dolphins (Cetacea) are fully aquatic, and can be found in all oceans of the world, and some rivers. Whales can be found in polar, temperate, and tropical waters, both near shore and in the open ocean, and from the water's surface to depths of over 1 kilometer.

Habitat Regions: temperate ; tropical ; polar ; terrestrial ; saltwater or marine ; freshwater

Terrestrial Biomes: tundra ; taiga ; desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains ; icecap

Aquatic Biomes: pelagic ; reef ; lakes and ponds; rivers and streams; coastal ; brackish water

Wetlands: marsh ; swamp ; bog

Other Habitat Features: urban ; suburban ; agricultural ; riparian ; estuarine ; intertidal or littoral

  • Reichholf, J. 1990. Mammals in the Balance of Nature. Pp. 120-159 in B Grzimek, ed. Grzimek's Encyclopedia of Mammals, Vol. 1, 1 Edition. New York: Mcgraw-Hill.
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Migration

Introduction

Regarding the four indigenous marine mammals of the Belgian Continental Shelf, the harbour porpoise is the most common species. It is, however, difficult to estimate the total population size which harbours our shelf during winter. But it is sure that our population is of minor importance on the international level. At the Belgian coast, the harbour porpoise seems not to prefer a certain area above another, although clearly avoids the shallower parts along the West coast and the heavily navigated lanes around the port of Zeebrugge.
White-beaked dolphins are quite common in the Southern North Sea, but are rarely seen at the Belgian Continental Shelf. This also accounts for the harbour and the grey seals, which are real coastal inhabitants and rarely occur in open sea. Every winter, few harbour seals stay at the mouth of the Yzer in Nieuwpoort, occasionally some specimens are reported at other places on the Belgian coast.
  • Stienen, E.W.M.; Van Waeyenberge, J.; Kuijken, E. (2003). Zeezoogdieren in Belgisch mariene wateren [Marine mammals in Belgian marine waters]. Rapport Instituut voor Natuurbehoud, A.2003.152. Instituut voor Natuurbehoud: Brussel, Belgium. 15 pp.
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Trophic Strategy

Food Habits

As a group, mammals eat an enormous variety of organisms. Many mammals can be carnivores (e.g., most species within Carnivora), herbivores (e.g., Perissodactyla, Artiodactyla), or omnivores (e.g., many primates). Mammals eat both invertebrates and vertebrates (including other mammals), plants (including fruit, nectar, foliage, wood, roots, seeds, etc.) and fungi. Being endotherms, mammals require much more food than ectotherms of similar proportions. Thus, relatively few mammals can have a large impact on the populations of their food items.

Foraging Behavior: stores or caches food ; filter-feeding

Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore , Eats eggs, Sanguivore , Eats body fluids, Insectivore , Eats non-insect arthropods, Molluscivore , Scavenger ); herbivore (Folivore , Frugivore , Granivore , Lignivore, Nectarivore ); omnivore ; planktivore ; mycophage ; coprophage

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Associations

Plant / resting place / within
imago of Aphodius ater may be found in dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius borealis feeds on dung/debris dung of Mammalia

Plant / resting place / within
imago of Aphodius brevis may be found in dung of Mammalia

Plant / resting place / within
imago of Aphodius coenosus may be found in dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius conspurcatus feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius consputus feeds on dung/debris dung of Mammalia

Plant / resting place / within
imago of Aphodius constans may be found in dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius contaminatus feeds on dung/debris dung of Mammalia

Plant / resting place / within
imago of Aphodius depressus may be found in dung of Mammalia
Other: sole host/prey

Animal / dung/debris feeder
larva of Aphodius distinctus feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius equestris feeds on dung/debris dung of Mammalia

Plant / resting place / within
imago of Aphodius erraticus may be found in dung of Mammalia

Plant / resting place / within
imago of Aphodius fasciatus may be found in dung of Mammalia

Plant / resting place / within
imago of Aphodius fimetarius may be found in dung of Mammalia

Plant / resting place / within
imago of Aphodius foetens may be found in dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius foetidus feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius fossor feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius granarius feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius haemorrhoidalis feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius ictericus feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius lapponum feeds on dung/debris dung of Mammalia

Plant / resting place / within
imago of Aphodius lividus may be found in dung of Mammalia

Plant / resting place / within
imago of Aphodius merdarius may be found in fresh or older dung of Mammalia

Plant / resting place / within
imago of Aphodius nemoralis may be found in dung of Mammalia

Plant / resting place / within
imago of Aphodius paykulli may be found in dung of Mammalia

Plant / resting place / within
imago of Aphodius porcus may be found in dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius prodromus feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius pusillus feeds on dung/debris dung of Mammalia

Plant / resting place / within
imago of Aphodius rufipes may be found in dung of Mammalia

Plant / resting place / within
imago of Aphodius rufus may be found in dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius scrofa feeds on dung/debris dung of Mammalia

Animal / dung/debris feeder
larva of Aphodius sordidus feeds on dung/debris dung of Mammalia

Plant / resting place / within
imago of Aphodius sphacelatus may be found in dung of Mammalia

Animal / carrion / dead animal feeder
larva of Aphodius subterraneus feeds on dead Mammalia

Plant / resting place / within
imago of Aphodius zenkeri may be found in dung of Mammalia

Animal / pathogen
Aspergillus flavus infects Mammalia

Animal / pathogen
Aspergillus fumigatus infects Mammalia

Animal / pathogen
Aspergillus niger infects Mammalia

Animal / dung/debris feeder
larva of Bellardia feeds on dung/debris decaying matter of Mammalia

Animal / dung saprobe
fruitbody of Calocybe constricta is saprobic in/on dung or excretions of urine of Mammalia

In Great Britain and/or Ireland:
Animal / parasite / ectoparasite / blood sucker
adult of Cimex lectularius sucks the blood of Mammalia

Animal / pathogen
cells of Cryptococcus (bot.) infects Mammalia

Animal / parasite / ectoparasite / sweat sucker
imago (female) of Drymeia vicana sucks the sweat of Mammalia

Animal / rests in
Entamoeba muris rests inside large intestine of Mammalia

Animal / dung/debris feeder
larva of Eristalis feeds on dung/debris wet manure of Mammalia

Plant / resting place / within
imago of Euheptaulacus sus may be found in dung of Mammalia

Plant / resting place / within
imago of Euheptaulacus villosus may be found in dung of Mammalia

Animal / associate
larva of Fannia canicularis is associated with nest of Mammalia

Animal / carrion / dead animal feeder
larva of Fannia scalaris feeds on dead rotting meat of Mammalia

Animal / pathogen
Cryptococcus yeast anamorph of Filobasidiella neoformans infects Mammalia

Animal / dung/debris feeder
larva of Geotrupes mutator feeds on dung/debris buried dung of Mammalia

Animal / dung/debris feeder
larva of Geotrupes pyrenaeus feeds on dung/debris buried dung of Mammalia
Other: sole host/prey

Animal / dung/debris feeder
larva of Geotrupes spiniger feeds on dung/debris buried dung of Mammalia

Animal / dung/debris feeder
larva of Geotrupes stercorarius feeds on dung/debris buried dung of Mammalia

Animal / dung/debris feeder
larva of Geotrupes stercorosus feeds on dung/debris buried dung of Mammalia

Animal / dung saprobe
fruitbody of Hebeloma radicosum is saprobic in/on dung or excretions of nest of Mammalia

Animal / dung saprobe
sporangiophore of Helicostylum piriforme is saprobic in/on dung or excretions of dung of Mammalia

Animal / dung/debris feeder
larva of Helophilus pendulus feeds on dung/debris wet manure of Mammalia

Plant / resting place / within
imago of Heptaulacus testudinarius may be found in dry dung of Mammalia

Animal / associate
larva of Hydrotaea capensis is associated with cadaver of Mammalia

Animal / parasite / ectoparasite / sweat sucker
imago (female) of Hydrotaea irritans sucks the sweat of Mammalia

Animal / parasite / ectoparasite
larva of Lucilia sericata ectoparasitises wound of Mammalia
Other: minor host/prey

Animal / dung associate
larva of Musca domestica inhabits dung of Mammalia

Animal / associate
larva of Neoascia is associated with wet manure of Mammalia

Animal / dung/debris feeder
larva of Neoascia podagrica feeds on dung/debris wet manure of Mammalia

Animal / carrion / dead animal feeder
larva of Onthophagus coenobita feeds on dead buried corpse of Mammalia

Animal / dung saprobe
ascoma of Onygena corvina is saprobic in/on dung or excretions of hair of Mammalia
Other: major host/prey

Plant / resting place / within
imago of Oxyomus sylvestris may be found in dung in fields of Mammalia
Other: minor host/prey

Animal / dung associate
larva of Sarcophaga incisilobata inhabits dung of Mammalia

Animal / parasite
larva of Sarcophaga melanura parasitises Mammalia
Other: minor host/prey

Plant / resting place / on
larva of Sarcophila latifrons may be found on carrion of Mammalia

Animal / carrion / dead animal feeder
fruitbody of Schizophyllum commune feeds on dead dead horn of Mammalia
Other: unusual host/prey

Animal / parasite / ectoparasite / blood sucker
imago of Stomoxys calcitrans sucks the blood of Mammalia
Other: sole host/prey

Animal / dung saprobe
gregarious, semi-immersed perithecium of Subbaromyces splendens is saprobic in/on dung or excretions of Mammalia

Animal / dung/debris feeder
larva of Syritta pipiens feeds on dung/debris wet manure of Mammalia

Animal / carrion / dead animal feeder
Trox sabulosus feeds on dead dead horn of Mammalia

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Ecosystem Roles

The ecological roles, or niches, filled by the nearly 5000 mammal species are quite diverse. There are predators and prey, carnivores, omnivores, and herbivores, species that create or greatly modify their habitat and thus the habitat and structure of their communities [e.g., beavers damming streams, large populations of ungulates (Artiodactyla and Perissodactyla) grazing in grasslands, moles digging in the earth]. In part because of their high metabolic rates, mammals often play an ecological role that is disproportionately large compared to their numerical abundance. Thus, many mammals may be keystone predators in their communities or play important roles in seed dispersal or pollination. The ecosystem roles that mammals play are so diverse that it is difficult to generalize across the group. Despite their low species diversity, compared to other animal groups, mammals have a substantial impact on global biodiversity.

Ecosystem Impact: disperses seeds; pollinates; creates habitat; biodegradation ; soil aeration ; keystone species

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Predation

Predation is a significant source of mortality for many mammals. Except for those few species that are top predators, mammals are preyed upon by many other organisms, including other mammals. Other groups that typically eat mammals are predatory birds and reptiles. Many species cope with predation through avoidance strategies such as cryptic coloration, by restricting foraging to times when predators may not be abundant, or through their sociality. Some mammals also have defensive chemicals (e.g., skunks) or bear some type of protective armor or physical defense (e.g., armadillos, pangolins, New World porcupines and Old World porcupines).

Known Predators:

Anti-predator Adaptations: aposematic ; cryptic

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Known predators

Mammalia is prey of:
Aquila chrysaetos
Buteo regalis
Buteo swainsoni
Camponotus
Noctuidae
Pyralidae
Blattaria
Vespidae
Silphidae
Dermestes carnivorus
Scarabaeidae
Drosophilidae
Prochyliza azteca
Trigona
Phaenicia eximia
Hemilucilia segmentaria
Cochliomyia macellaria
Serpentes
Aves
Thamnophis sirtalis
Lampropeltis triangulum
Butorides virescens
Anas fulvigula
Buteo lineatus
Pandion haliaetus
Falco biarmicus
Herpetotheres cachinnans
Grus japonensis
Larus californicus
Larus canus
Tyto alba
Otus asio
Otus trichopsis
Surnia ulula
Micrathene whitneyi
Strix varia
Asio flammeus
Corvus corax
Corvus caurinus
Spermophilus lateralis
Sciurus niger
Sciurus carolinensis
Onychomys arenicola
Ursus maritimus
Ursus arctos
Lontra canadensis
Mustela vison
Bassariscus astutus
Nasua nasua
Panthera onca
Canis rufus
Panthera pardus
Cerdocyon thous
Lycaon pictus
Otocyon megalotis
Alligator mississippiensis
Paleosuchus trigonatus
Puma concolor
Didelphis marsupialis
Antechinus swainsonii
Dasycercus cristicauda
Dasyurus maculatus
Oncifelis geoffroyi
Oncifelis colocolo
Prionailurus viverrinus
Ardea alba
Asturina nitida
Ictinia mississippiensis
Otus kennicottii
Ciccaba nigrolineata
Pulsatrix perspicillata
Galago alleni
Cebus olivaceus
Papio hamadryas
Hylobates klossii
Eliomys quercinus
Hydromys chrysogaster
Heloderma horridum
Ailuropoda melanoleuca
Helarctos malayanus
Tremarctos ornatus
Pseudalopex griseus
Pseudalopex gymnocercus
Pseudalopex vetulus
Vulpes cana
Vulpes chama
Leopardus tigrinus
Lynx pardinus
Oreailurus jacobita
Prionailurus planiceps
Galidia elegans
Mungotictis decemlineata
Bdeogale nigripes
Herpestes edwardsii
Herpestes ichneumon
Suricata suricatta
Crocuta crocuta
Lutrogale perspicillata
Arctonyx collaris
Melogale everetti
Melogale moschata
Melogale personata
Conepatus chinga
Conepatus semistriatus
Galictis cuja
Ictonyx striatus
Martes melampus
Martes zibellina
Mustela altaica
Mustela kathiah
Mustela putorius
Mustela sibirica
Bassaricyon gabbii
Prionodon pardicolor
Sus verrucosus
Tatera indica
Chaetophractus villosus
Crocidura leucodon
Cardioderma cor
Macroderma gigas
Megaderma lyra
Vampyrum spectrum
Prionailurus iriomotensis
Canis lupus dingo
Canis lupus familiaris
Papio anubis
Papio cynocephalus
Papio papio
Papio ursinus

Based on studies in:
USA: California, Cabrillo Point (Grassland)
USA: California, Coachella Valley (Desert or dune)
Costa Rica (Carrion substrate)

This list may not be complete but is based on published studies.
  • L. D. Harris and L. Paur, A quantitative food web analysis of a shortgrass community, Technical Report No. 154, Grassland Biome. U.S. International Biological Program (1972), from p. 17.
  • L. F. Jiron and V. M. Cartin, 1981. Insect succession in the decomposition of a mammal in Costa Rica. J. New York Entomol. Soc. 89:158-165, from p. 163.
  • Polis GA (1991) Complex desert food webs: an empirical critique of food web theory. Am Nat 138:123–155
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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Known prey organisms

Mammalia preys on:
fruit
canopy--leaves
flowers
Insecta
leaves and trunks
roots
trunk
fungi
macrocrustacea
Aythya affinis
Actinopterygii
Mytilus
Littorina
Acmaea
Carcinus
Tautogolabrus
Arthropoda
Plantae
detritus
hyperparisitoids
Orchelimum vulgare
Crossoptilon mantchuricum
Gallicolumba luzonica
Sorex dispar
Didelphis marsupialis
Akodon cursor

Based on studies in:
Malaysia (Rainforest)
USA: Iowa, Mississippi River (River)
USA: Maine, Gulf of Maine (Littoral, Rocky shore)
USA: California, Coachella Valley (Desert or dune)

This list may not be complete but is based on published studies.
  • C. A. Carlson, Summer bottom fauna of the Mississippi River, above Dam 19, Keokuk, Iowa, Ecology 49(1):162-168, from p. 167 (1968).
  • D. C. Edwards, D. O. Conover, F. Sutter, Mobile predators and the structure of marine intertidal communities, Ecology 63(4):1175-1180, from p. 1178 (1982).
  • J. L. Harrison, The distribution of feeding habits among animals in a tropical rain forest, J. Anim. Ecol. 31:53-63, from p. 61 (1962).
  • Polis GA (1991) Complex desert food webs: an empirical critique of food web theory. Am Nat 138:123–155
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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Diseases and Parasites

Neutrophils

Neutrophils are a type of granulocyte that all mammals posses. Neutrophils are crucial to protecting mammals against infections. Because of this, 50 - 80% of white cells circulating in the blood are neutrophils. Neutrophils are produced in the bone marrow of mammals. The average adult Homo Sapiens manufactures 100 billion neutrophils per day.

Neutrophils take 1 week to manufacture, yet once they are released into the bloodstream of mammals, they only survive for 12 hourse at longest. Because of this, the bones of most mammals have vast reserves of neutrophils in the case of an infection.

Neutrophils are 12 - 15 micrometers long. As they are granulocytes, their nucleus is divided into 2 - 5 lobes.

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Life History and Behavior

Behavior

Communication and Perception

Generally, olfaction, hearing, tactile perception, and vision are all important sensory modalities in mammals. Olfaction plays a key role in many aspects of mammalian ecology, including foraging, mating and social communication. Many mammals use pheromones and other olfactory cues to communicate information about their reproductive status, territory, or individual or group identity. Scent-marking is commonly used to communicate among mammals. They are often transmitted through urine, feces, or the secretions of specific glands. Some mammals even use odors as defense against mammalian predators (e.g. skunks), which are especially sensitive to foul-smelling chemical defenses.

Typically, mammalian hearing is well-developed. In some species, it is the primary form of perception. Echolocation, the ability to perceive objects in the external environment by listening to echoes from sounds generated by an animal, has evolved in several groups. Echolocation is the main perception channel used in foraging and navigation in microchiropteran bats (Chiroptera) and many toothed whales and dolphins (Odontoceti), and has also evolved to a lesser degree in other species (e.g., some shrews).

Many mammals are vocal, and communicate with one another or with heterospecifics using sound. Vocalizations are used in communication between mother and offspring, between potential mates, and in a variety of other social contexts. Vocalizations can communicate individual or group identity, alarm at the presence of a predator, aggression in dominance interactions, territorial defense, and reproductive state. Communication using vocalizations is quite complex in some groups, most notably in humans.

Mammals also perceive their environment through tactile input to the hair and skin. Specialized hairs (whiskers or "vibrissae") have a sensory function, letting an animal know when it is in contact with an object in its external environment. Vibrissae are often richly innervated and well-supplied with muscles that control their position. The skin is also an important sensory organ. Often, certain portions of the skin are especially sensitive to tactile stimuli, aiding in specific functions like foraging (e.g., the fingers of primates and the nasal tentacles of star-nosed moles). Touch also serves many communication functions, and is often associated with social behavior (e.g., social grooming).

Vision is well-developed in a large number of mammals, although it is less important in many species that live underground or use echolocation. Many nocturnal animals have relatively large, well-developed eyes. Vision can be important in foraging, navigation, entraining biological rhythms to day length or season, communication, and nearly all aspects of mammalian behavior and ecology.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: mimicry ; duets ; choruses ; pheromones ; scent marks ; vibrations

Perception Channels: visual ; tactile ; acoustic ; ultrasound ; echolocation ; vibrations ; chemical

  • Apfelbach, R., U. Ganslosser. 1990. Behavior. Pp. 160-177 in B Grzimek, ed. Grzimek's Encyclopedia of Mammals, Vol. 1, 1st Edition. New York: Mcgraw-Hill.
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Life Cycle

Development

There are three major groups of mammals, each is united by a major feature of embryonic development. Monotremes (Prototheria) lay eggs, which is the most primitive reproductive condition in mammals. Marsupials (Metatheria) give birth to highly altricial young after a very short gestation period (8 to 43 days). The young are born at a relatively early stage of morphological development. They attach to the mother's nipple and spend a proportionally greater amount of time nursing as they develop. Gestation lasts much longer in placental mammals (Eutheria). During gestation, eutherian young interact with their mother through a placenta, a complex organ that connects the embryo with the uterus. Once born, all mammals are dependent upon their mothers for milk. Aside from these few generalities, mammals exhibit a diversity of developmental and life history patterns that vary among species and larger taxonomic groups.

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Life Expectancy

Lifespan/Longevity

Just as mammals vary greatly in size, they also vary greatly in lifespan. Generally, smaller mammals live short lives and larger mammals live longer lives. Bats (Chiroptera) are an exception to this pattern, they are relatively small mammals that can live for one or more decades in natural conditions, considerably longer than natural lifespans of significantly larger mammals. Mammalian lifespans range from one year or less to 70 or more years in the wild. Bowhead whales may live more than 200 years.

  • Grzimek, B. 1990. General Introduction. Pp. 4-5 in B Grzimek, ed. Grzimek's Encyclopedia of Mammals, Vol. 1, 1st Edition. New York: Mcgraw-Hill.
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Reproduction

Generally, most mammalian species are either polygynous (one male mates with multiple females) or promiscuous (both males and females have multiple mates in a given reproductive season). Because females incur such high costs during gestation and lactation, it is often the case that male mammals can produce many more offspring in a mating season than can females. As a consequence, the most common mating system in mammals is polygyny, with relatively few males fertilizing multiple females and many males fertilizing none. This scenario sets the stage for intense male-male competition in many species, and also the potential for females to be choosy when it comes to which males will sire her offspring. As a consequence of the choices females make and the effort males put into acquiring matings, many mammals have complex behaviors and morphologies associated with reproduction. Many mammal groups are marked by sexual dimorphism as a result of selection for males that can better compete for access to females.

About 3 percent of mammalian species are monogamous, with males only mating with a single female each season. In these cases, males provide at least some care to their offspring. Often, mating systems may vary within species depending upon local environmental conditions. For example, when resources are low, males may mate with only a single female and provide care for the young. When resources are abundant, the mother may be able to care for young on her own and males will attempt to sire offspring with multiple females.

Other mating systems such as polyandry can also be found among mammals. Some species (e.g. common marmosets and African lions) display cooperative breeding, in which groups of females, and sometimes males, share the care of young from one or more females. Naked mole rats have a unique mating system among mammals. Like social insects (Hymenoptera and Isoptera), naked mole rats are eusocial, with a queen female mating with several males and bearing all of the young in the colony. Other colony members assist in the care of her offspring and do not reproduce themselves.

Mating System: monogamous ; polyandrous ; polygynous ; polygynandrous (promiscuous) ; cooperative breeder ; eusocial

Many mammals are seasonal breeders, with environmental stimuli such as day length, resource intake and temperature dictating when mating occurs. Females of some species store sperm until conditions are favorable, after which their eggs are fertilized. In other mammals, eggs may be fertilized shortly after copulation, but implantation of the embryo into the uterine lining may be delayed (“delayed implantation”). A third form of delayed gestation is "delayed development", in which development of the embryo may be arrested for some time. Seasonal breeding and delays in fertilzation, implantation, or development are all reproductive strategies that help mammals coordinate the birth of offspring with favorable environmental conditions to increase the chances of offspring survival.

Some mammals give birth to many altricial young in each bout of reproduction. Despite being born in a relatively underdeveloped state, young of this type tend to reach maturity relatively quickly, soon producing many altricial young of their own. Mortality in these species tends to be high and average lifespans are generally short. Many species that exemplify this type of life history strategy can be found among the rodents and insectivores. At the other end of the life history spectrum, many mammals give birth to one or a few precocial young in each bout of reproduction. These species tend to live in stable environments where competition for resources is a key to survival and reproductive success. The strategy for these species is to invest energy and resources in a few, highly developed offspring that will grow to be good competitors. Cetaceans, primates and artiodactyls are examples of orders that follow this general pattern.

Among mammals, many reproductive strategies can be observed, and the patterns listed above are the extremes of a continuum encompassing this variation. Environmental factors, as well as physiological and historical constraints all contribute to the pattern of reproduction found in any population or species. Differences in these factors among species have led to the diversity of life history traits among mammals.

Key Reproductive Features: semelparous ; iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; induced ovulation ; fertilization (Internal ); viviparous ; oviparous ; sperm-storing ; delayed fertilization ; delayed implantation ; embryonic diapause ; post-partum estrous

A fundamental component of mammalian evolution, behavior, and life history is the extended care females must give to their offspring. Investment begins even before a female's eggs become fertilized. All female mammals undergo some form of estrus cycle in which eggs develop and become ready for potential fertilization. Hormones regulate changes in various aspects of female physiology throughout the cycle (e.g., the thickening of the uterine lining) and prepare the female for possible fertilization and gestation. Once fertilization occurs, females nurture their embryos in one of three ways--either by attending eggs that are laid externally (Prototheria), nursing highly altricial young (often within a pouch, or "marsupium"; Metatheria), or by nourishing the developing embryos with a placenta that is attached directly to the uterine wall for a long gestation period (Eutheria). Gestation in eutherians is metabolically expensive. The costs incurred during gestation depend upon the number of offspring in a litter and the degree of development each embryo undergoes.

Once the young are born (or hatch, in the case of monotremes) females feed their newborn young with milk, a substance rich in fats and protein. Because females must produce this high-energy substance, lactation is far more energetically expensive than gestation. Once mammals are born they must maintain their own body temperatures, no longer being able to depend on their mother for thermoregulation, as was the case during pregnancy. Lactating females must provide enough milk for their offspring to maintain their body temperatures as well as to grow and develop. In addition to feeding their young, females must protect them from predators. In some species, young remain with their mothers even beyond lactation for an extended period of behavioral development and learning.

Depending upon the species and environmental conditions, male mammals may either provide no care, or may invest some or a great deal of care to their offspring. Care by males often involves defending a territory, resources, or the offspring themselves. Males may also provision females and young with food.

Mammalian young are often born in an altricial state, needing extensive care and protection for a period after birth. Most mammals make use of a den or nest for the protection of their young. Some mammals, however, are born well-developed and are able to locomote on their own soon after birth. Most notable in this regard are artiodactyls such as wildebeest or giraffes. Cetacean young must also swim on their own shortly after birth.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female); post-independence association with parents; extended period of juvenile learning; inherits maternal/paternal territory; maternal position in the dominance hierarchy affects status of young

  • Nowak, R. 1991. Walker's Mammals of the World. Baltimore: Johns Hopkins University Press.
  • Vaughan, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, 4th Edition. Toronto: Brooks Cole.
  • Wilson, D., D. Reeder. 1993. Mammal Species of the World. Washington D.C.: Smithsonian Institution Press.
  • Lazaro-Perea, C., C. Castro, R. Harrison, A. Araujo, M. Arruda, C. Snowdon. 2000. Behavioral and demographic changes following the loss of the breeding female in cooperatively breeding marmosets. Behavioral Ecology and Sociobiology, 48: 137-146.
  • Stockley, P. 2003. Female multiple mating behaviour, early reproductive failure and litter size variation in mammals. Proceedings of the Royal Society of London, Series B., 270: 271-278.
  • Keil, A., N. Sachser. 1998. Reproductive benefits from female promiscuous mating in a small mammal. Ethology, 104: 897-903.
  • Apfelbach, R. 1990. Body Functions. Pp. 85-106 in B Grzimek, ed. Grzimek's Encyclopedia of Mammals, Vol. 1, 1st Edition. New York: Mcgraw-Hill.
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Evolution and Systematics

Functional Adaptations

Functional adaptation

Cell metabolism produces heat: mammals
 

Cells within brown adipose tissues of mammals and birds produce heat by uncoupling of mitochondrial respiration.

   
  "Mammals and birds are endotherms and respond to cold exposure by the means of regulatory thermogenesis, either shivering or non-shivering. In this latter case, waste of cell energy as heat can be achieved by uncoupling of mitochondrial respiration. Uncoupling proteins [UCPs], which belong to the mitochondrial carrier family, are able to transport protons and thus may assume a thermogenic function. The mammalian UCP1 physiological function is now well understood and gives to the brown adipose tissue the capacity for heat generation. But is it really the case for its more recently discovered isoforms UCP2 and UCP3? Additionally, whereas more and more evidence suggests that non-shivering also exists in birds, is the avian UCP also involved in response to cold exposure? In this review, we consider the latest advances in the field of UCP biology and present putative functions for UCP1 homologues." (Mozo et al. 2005:227)
  Learn more about this functional adaptation.
  • Mozo, J.; Emre, Y.; Bouillaud, F.; Ricquier, D.; Criscuolo, F. 2005. Thermoregulation: What role for UCPs in mammals and birds?. Bioscience Reports. 25(3-4): 227-249.
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Functional adaptation

Skin properties derive from arrangement of components: mammals
 

The skin of mammals may derive its unique mechanical properties and other characteristics from the arrangement of its stratum corneum keratin intermediate filaments into cubic rod-packing symmetry.

         
  "A new model for stratum corneum keratin structure, function, and formation is presented. The structural and functional part of the model, which hereafter is referred to as 'the cubic rod-packing model', postulates that stratum corneum keratin intermediate filaments are arranged according to a cubic-like rod-packing symmetry with or without the presence of an intracellular lipid membrane with cubic-like symmetry enveloping each individual filament. The new model could account for (i) the cryo-electron density pattern of the native corneocyte keratin matrix, (ii) the X-ray diffraction patterns, (iii) the swelling behavior, and (iv) the mechanical properties of mammalian stratum corneum. The morphogenetic part of the model, which hereafter is referred to as 'the membrane templating model', postulates the presence in cellular space of a highly dynamic small lattice parameter (<30 nm) membrane structure with cubic-like symmetry, to which keratin is associated. It further proposes that membrane templating, rather than spontaneous self-assembly, is responsible for keratin intermediate filament formation and dynamics. The new model could account for (i) the cryo-electron density patterns of the native keratinocyte cytoplasmic space, (ii) the characteristic features of the keratin network formation process, (iii) the dynamic properties of keratin intermediate filaments, (iv) the close lipid association of keratin, (v) the insolubility in non-denaturating buffers and pronounced polymorphism of keratin assembled in vitro, and (vi) the measured reduction in cell volume and hydration level between the stratum granulosum and stratum corneum. Further, using cryo-transmission electron microscopy on native, fully hydrated, vitreous epidermis we show that the subfilametous [sic] keratin electron density pattern consists, both in corneocytes and in viable keratinocytes, of one axial subfilament surrounded by an undetermined number of peripheral subfilaments forming filaments with a diameter of ~8 nm." (Norlén and Al-Amoudi 2004:715)
  Learn more about this functional adaptation.
  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
  • Norlen, L.; Al-Amoudi, A. 2004. Stratum Corneum Keratin Structure, Function, and Formation: The Cubic Rod-Packing and Membrane Templating Model. Journal of Investigative Dermatology. 123(4): 715-732.
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Functional adaptation

Bones' supporting beams provide strength: birds and mammals
 

Thigh bones of birds and mammals withstand strain as size increases by reorganizing internal structure of trabeculae ("little beams").

       
  "Many bones are supported internally by a latticework of trabeculae [Latin: "little beams"; they provide structural support, especially near joints]...We analysed trabecular geometry in the femora of 90 terrestrial mammalian and avian species with body masses ranging from 3 g to 3400 kg. We found that bone volume fraction does not scale substantially with animal size, while trabeculae in larger animals’ femora are thicker, further apart and fewer per unit volume than in smaller animals...[T]rabecular scaling does not alter the bulk stiffness of trabecular bone, but does alter strain within trabeculae under equal applied loads. Allometry of bone’s trabecular tissue may contribute to the skeleton’s ability to withstand load, without incurring the physiological or mechanical costs of increasing bone mass." (Doube et al. 2011:3067)

"Trabecular bone scales allometrically, within physiological limits to trabecular size. Reorganization of bones’ internal structure might protect trabeculae from increased strains owing to large body size, representing a mass-efficient strategy for maintaining bone strain in a safe range at the trabecular scale. This may represent a new approach to designing cellular solids for engineered structures of differing scale." (Doube et al. 2011:3072)
  Learn more about this functional adaptation.
  • Doube M; Kłosowski MM; Wiktorowicz-Conroy AM; Hutchinson JR; Shefelbine SJ. 2011. Trabecular bone scales allometrically in mammals and birds. Proceedings of the Royal Society. B, Biological sciences. 278: 3067–3073.
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Functional adaptation

Ears convert energy: mammals
 

The hairs in mammalian ears convert motion into electrical energy and back in order to amplify sound via the prestin protein.

       
  "A new Cambridge-based venture called IntAct Labs is investigating how to harness the power generating capabilities of life for space applications. It would involve the use of a protein called prestin found in human ear-hair as a means of powering space suits. The protein converts motion into electrical energy -- and if it's augmented with an electricity-conducting microbe, it could form self-healing, semi-living 'skins' that convert Martian wind and even the jogging and walking of astronauts into electricity. Prestin is found in the outer hair cells of the human ear. In the cell membranes of these cells, prestin also converts electrical voltage into motion, elongating and contracting the cell. This movement amplifies sound in the ear." (Courtesy of the Biomimicry Guild)
  Learn more about this functional adaptation.
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Functional adaptation

T cells fight infections: mammals
 

The immune system of our body fights infections by creating T cells.

   
  New infections stimulate the creation of T cells, or T lymphocytes, specific to the  organism that set off the infection. If that organism appears again, the  immune system is ready to attack. One problem with this method in the  immune system is that the offending organism can avoid attack by  changing its identity. Biological  control relies on  diversity. The more species there are, the more stable any ecological  system is and the more resistant it is to attack from outside organisms.  Response to parasites, viruses, bacteria, and other invaders lies in  creating and maintaining diversity, and  accepting some degree of damage. (summarized from Stevens 1998:64)
  Learn more about this functional adaptation.
  • Stevens, M. 1998. Pest control. New Scientist. 159(2144): 64.
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Functional adaptation

Optimal branching of vascular vessels minimizes work: mammals
 

Vascular and respiratory vessels in mammals minimize the amount of biological work required to operate by being arranged hierarchically.

     
   "The vessels found in mammalian cardiovascular and respiratory systems are usually arranged in hierarchical structures and a distinctive feature of this arrangement is their multi-stage division or bifurcation. At each generation, the characteristic dimension of the vascular segments will generally become smaller, both in length and diameter." (Barber and Emerson 2008: 179)
 
"The branching structures found in mammalian cardiovascular and respiratory systems have evolved, through natural selection, to an optimum arrangement that minimizes the amount of biological work required to operate and maintain the system. The relationship between the diameter of the parent vessel and the optimum diameters of the daughter vessels was first derived by Murray (1926) using the principle of minimum work. This relationship is now known as Murray’s law and states that the cube of the diameter of a parent vessel equals the sum of the cubes of the diameters of the daughter vessels." (Barber and Emerson 2008: 180)

[This mathematical structure is also found in trees and other organisms that exhibit branching]
  Learn more about this functional adaptation.
  • Barber RW; Emerson DR. 2008. Optimal design of microfluidic networks using biologically inspired principles. Microfluidics and Nanofluidics. 4: 179-191.
  • Murray CD. 1926. The physiological principle of minimum work. I. the vascular system and the cost of blood volume. PNAS. 12: 207-214.
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Functional adaptation

Sweating aids thermoregulation: mammals
 

The sweat glands of many mammals aid thermoregulation through evaporative cooling.

     
  "Sweat glands play an extremely important part in temperature control. Shaped like a tube, knotted at the bottom and opening out of the epidermis at a 'pore', sweat glands secrete a colourless liquid which evaporates on the surface of the skin removing excess heat…There are two kinds of sweat glands: apocrine, associated with hairy skin, and eccrine, associated with smooth. Apocrine glands seem to be concerned mainly with producing scented secretions, and are progressively replaced in the more advanced mammals - gorillas, chimpanzees, and especially man - with eccrine glands, whose secretion dilutes and spreads that of the apocrine glands." (Foy and Oxford Scientific Films 1982:79)

"From the evidence of comparative mammalian physiology, we suggest that the very common apocrine sweat gland is not primitive but is both specialized and efficient as a cooling organ in an animal with a heavy fur coat and relatively slow movement. The remarkable thermal eccrine sweating system of humans probably evolved in concert with bipedalism, a smooth hairless skin, and adaptation to open country by the ancestors of H. sapiens." (Folk and Semken 1991:185)
  Learn more about this functional adaptation.
  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
  • Folk GE; Semken A. 1991. The evolution of sweat glands. International Journal of Biometeorology. 35(3): 180-186.
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Functional adaptation

Filaments adopt geometric symmetry: mammals
 

The formation and dynamics of the keratin intermediate filaments in mammalian stratum corneum may be the result of membrane templating.

   
  "Keratin is tough, adaptable, flexible, resistant to water, and provides a good protective covering for the rest of the body. These qualities also make it an ideal material for the moulding of claws, nails and hooves…" (Foy and Oxford Scientific Films 1982)

"A new model for stratum corneum keratin structure, function, and formation is presented. The structural and functional part of the model, which hereafter is referred to as 'the cubic rod-packing model', postulates that stratum corneum keratin intermediate filaments are arranged according to a cubic-like rod-packing symmetry with or without the presence of an intracellular lipid membrane with cubic-like symmetry enveloping each individual filament. The new model could account for (i) the cryo-electron density pattern of the native corneocyte keratin matrix, (ii) the X-ray diffraction patterns, (iii) the swelling behavior, and (iv) the mechanical properties of mammalian stratum corneum. The morphogenetic part of the model, which hereafter is referred to as 'the membrane templating model', postulates the presence in cellular space of a highly dynamic small lattice parameter (<30 nm) membrane structure with cubic-like symmetry, to which keratin is associated. It further proposes that membrane templating, rather than spontaneous self-assembly, is responsible for keratin intermediate filament formation and dynamics. The new model could account for (i) the cryo-electron density patterns of the native keratinocyte cytoplasmic space, (ii) the characteristic features of the keratin network formation process, (iii) the dynamic properties of keratin intermediate filaments, (iv) the close lipid association of keratin, (v) the insolubility in non-denaturating buffers and pronounced polymorphism of keratin assembled in vitro, and (vi) the measured reduction in cell volume and hydration level between the stratum granulosum and stratum corneum. Further, using cryo-transmission electron microscopy on native, fully hydrated, vitreous epidermis we show that the subfilametous [sic] keratin electron density pattern consists, both in corneocytes and in viable keratinocytes, of one axial subfilament surrounded by an undetermined number of peripheral subfilaments forming filaments with a diameter of ~8 nm." (Norlén and Al-Amoudi 2004:715)
  Learn more about this functional adaptation.
  • Norlen, L.; Al-Amoudi, A. 2004. Stratum Corneum Keratin Structure, Function, and Formation: The Cubic Rod-Packing and Membrane Templating Model. Journal of Investigative Dermatology. 123(4): 715-732.
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Functional adaptation

Muscles produce energy and heat: mammals
 

Muscles are contractile tissues that produce force and cause motion through a process involving electrical impulses and metabolization of glucose, producing ATP and lactic acid.

   
  "The muscle consumes oxygen and fuel that can be transported via a circulation system; the muscle itself supports the chemical reaction that leads to mechanical work; electrochemical circuits can act as nerves, controlling actuation; some energy is stored locally in the muscle itself; and, like natural muscle, the materials studied…contract linearly." (Madden 2006:1559)
  Learn more about this functional adaptation.
  • Madden, J. D. 2006. Artificial muscle begins to breathe. Science. 311(5767): 1559-1560.
  • Ebron VH; Yang Z; Seyer DJ; Kozlov ME; Oh J; Xie H; Razal J; Hall LJ; Ferraris JP; MacDiarmid AG; Baughman, RH. 2006. Fuel-powered artificial muscles. Science. 311(5767): 1580-1583.
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Functional adaptation

Herbivores digest toxic plant compounds: mammals
 

Many herbivorous mammals are capable of safely ingesting various toxic plant compounds in part thanks to biotransformation enzymes.

   
  "Many mammalian herbivores continually face the possibility of being poisoned by the natural toxins in the plants they consume. A recent key discovery in this area is that mammalian herbivores are capable of regulating the dose of plant secondary compounds (PSCs) ingested

"The majority of wild mammalian herbivores confront food items which contain a myriad of chemical compounds that are potentially poisonous. Plant secondary compounds (PSCs) are arguably some of the most abundant and diverse naturally occurring toxins on earth. Although some herbivores behaviourally circumvent ingestion of marked quantities of PSCs either through food manipulation or avoidance (Dearing 1997), many herbivorous mammals regularly ingest foods with PSCs that if over-ingested could have serious consequences including deathThus, herbivores have evolved physiological mechanisms for processing PSCs as well as behavioural feedback mechanisms to permit feeding on plants with toxins while avoiding ill effects

"The specialist's constraint: Few mammalian herbivores have evolved the ability to forage nearly exclusively from a single species of plant (Freeland & Janzen 1974). Surprisingly, the plant species consumed by specialists tend to be low in nutrients and well-defended by PSCs (Shipley et al. 2006). Specialist herbivores are extraordinary because they are capable of taking in large doses of plant toxins with no obvious ill effects. The biotransformation enzymes permitting a diet rich in PSCs are just being discovered (Ngo et al. 2000; Ngo et al. 2006; Haley et al. 2007a,b). Not surprisingly many of these enzymes are in the diverse superfamily of the cytochrome P450 enzymes." (Torregrossa & Dearing 2009:48-9)
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  • Torregrossa AM; Dearing MD. 2009. Nutritional toxicology of mammals: regulated intake of plant secondary compounds. Functional Ecology. 23(1): 48-56.
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Functional adaptation

Whiskers detect details: mammals
 

The whiskers of some mammals help detect detailed surface textures via tapered ends.

   
  "The role of facial vibrissae (whiskers) in the behavior of terrestrial  mammals is principally as a supplement or substitute for short-distance  vision. Each whisker in the array functions as a mechanical transducer,  conveying forces applied along the shaft to mechanoreceptors in the  follicle at the whisker base. Subsequent processing of mechanoreceptor  outputallows high  accuracy discriminations of object distance, direction, and surface  texture. The whiskers of terrestrial mammals are tapered and  approximately circular in cross sectionWe argue that a tapered  whisker provides some advantages for tactile perception (as compared to a  hypothetical untapered whisker), and that this may explain why the  taper has been preserved during the evolution of terrestrial mammals

"We suggest that one of the main advantages of whisker taper, at least  for active whiskers, is to provide a small diameter at the whisker tip,  to allow for a finer probe of small surface features." (Williams & Kramer 2010:e8806)
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  • Williams CM; Kramer EM. 2010. The advantages of a tapered whisker. PLoS One. 5(1): e8806.
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Functional adaptation

Footpads manage increasing body mass: mammals
 

The footpads of mammals maintain functional integrity as body mass increases through changes in geometry and material properties.

     
  "In most mammals, footpads are what first strike ground with each stride.  Their mechanical properties therefore inevitably  affect functioning of the legs; yet interspecific  studies of the scaling of locomotor mechanics have all but neglected the  feet and their soft tissues. Here we determine how  contact area and stiffness of footpads in digitigrade carnivorans scale  with body mass in order to show how footpads’  mechanical properties and size covary to maintain their functional  integrity.  As body mass increases across several orders of  magnitude, we find the following: (i) foot contact area does not keep  pace  with increasing body mass; therefore pressure  increases, placing footpad tissue of larger animals potentially at  greater risk  of damage; (ii) but stiffness of the pads also  increases, so the tissues of larger animals must experience less strain;  and  (iii) total energy stored in hindpads increases  slightly more than that in the forepads, allowing additional elastic  energy  to be returned for greater propulsive efficiency.  Moreover, pad stiffness appears to be tuned across the size range to  maintain  loading regimes in the limbs that are favourable  for long-bone remodelling. Thus, the structural properties of footpads,  unlike  other biological support-structures, scale  interspecifically through changes in both geometry and material  properties, rather  than geometric proportions alone, and do so with  consequences for both maintenance and operation of other components of  the  locomotor system" (Chi & Roth 2010)
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  • Chi KJ; Roth VL. 2010. Scaling and mechanics of carnivoran footpads reveal the principles of footpad design. J R Soc Interface.
  • Bates KL. 2010. The bigger the animal, the stiffer the 'shoes'. Duke University Office of News & Communications [Internet],
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Functional adaptation

Pads cushion feet: mammals
 

The foot pads of many mammals provide cushioning using hydrostatic structures, essentially working as fluid-filled cushions.

     
  "Human heel pads and other mammalian foot pads make use of hydroskeletal support; our pads, which provide impact damping, some energy storage, and protection for bones, work as fluid-filled cushions--see, for instance, Ker (1999). They're complexly viscoelastic--if you want a stable reading of your height, you should stand for almost two minutes to allow your pads to creep into stability (Foreman and Linge 1989)." (Vogel 2003:417)
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  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
  • Ker, RF. 1999. The design of soft collagenous load-bearing tissues. Journal of Experimental Biology. 202: 3315-3324.
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Functional adaptation

Elastic blood vessels accommodate pumping: mammals
 

The cylindrical veins and arteries of mammals play a crucial role in the smooth pumping of blood due to their elastic walls.

   
  "In a typical mammal body, the cylindrical arteries and veins which carry the blood have walls, containing the elastic fibre elastin, which expand to accommodate the spurts of blood pumped by the heart and then shrink again, pushing the blood onwards. The heart alone could never propel the blood all the way round the body if the blood vessels had rigid walls -- the blood would be stopping and starting all the time, instead of flowing. Strokes occur when the elasticity is lost." (Foy and Oxford Scientific Films 1982:23)

"The aortic wall of all vertebrates except agnathans contains a rubbery protein called elastin that allows the vessel to expand under the high pressures associated with cardiac contraction. In expanding, energy from the blood is temporarily stored in the elastin as elastic energy, but is promptly returned to the blood when the elastin recoils in diastole. This recoil acts as a second pump, forcing the blood on downstream and smoothing out pressure fluctuations. The total work of the heart is reduced as long as the transfer of energy into and out of the elastin is efficient. Elastin achieves both efficiency and long-range deformation with a high molecular mobility, although it is not clear how this mobility is achieved. Covalent crosslinks that unite individual molecules in an insoluble extracellular network ultimately limit this mobility and so allow the network to return to its original dimensions without permanent strain. Both high molecular mobility and insolubility are unusual for a protein, but they are understood to be necessary for elastomeric performance." (Chalmers et al. 1999:301)
  Learn more about this functional adaptation.
  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
  • Chalmers, G. W. G.; Gosline, J. M.; Lillie, M. A. 1999. The hydrophobicity of vertebrate elastins. Journal of Experimental Biology. 202(3): 301-314.
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Functional adaptation

Sticky proteins serve as glue: mammals
 

The bioadhesive glues used by mammals, plants, and mussels for adherance to mucosal surfaces (mucoadhesion) are made up of sticky proteins.

   
  "Bioadhesion may be defined as the state in which two materials, at least one of which is biological in nature, are held together for extended periods of time by interfacial forces. In the pharmaceutical sciences, when the adhesive attachment is to mucus or a mucous membrane, the phenomenon is referred to as mucoadhesion." (Smart 2005:1557)
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  • Smart, J. D. 2005. The basics and underlying mechanisms of mucoadhesion. Advanced Drug Delivery Reviews. 57(11): 1556-1568.
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Functional adaptation

Uterus expands/contracts: mammals
 

The uterus of female mammals can expand and contract to accommodate its contents thanks to spiral muscle fibers in its central myometrial layer.

     
  "Similarly, the uterus of female mammals must expand and contract with gestation and birth, often an order of magnitude (ten-fold). The hooped fibers of chitin in the locust are paralleled in the interior circular muscle fibers of the uterus. Of the three layers of the uterus, the central myometrial layer is responsible for the expansion and contraction of the uterus. It is composed of connective tissue, mainly smooth muscle fibers with an external layer laid longitudinally and an internal layer laid circularly at the base which then spirals in both directions around the uterine body (which might even be a logarithmic spiral…).

The lessons from these 'hooped' chitin fibers and spiral muscle fibers could be incorporated into a polymer packaging material, thereby allowing for expansion and contraction of the packaging depending on the size of its contents. The result of packing multiple items into a shipping case would be the absolute minimization of air space between objects created by the packaging alone. Additionally, the same packaging product could be specified for a large variety of object sizes, i.e. the bag holding the baby shoe would be the same SKU as the one holding the basketball shoe or the soccer ball." (Biomimicry Guild unpublished report)
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Functional adaptation

Eyelids cleanse eyes: mammals
 

The eyelids of mammals provide lubrication for the eye using teardrops that are applied during blinking.

   
  "Being a particularly delicate instrument, the eye needs protection -- usually, an eyelid. Most mammals have two eyelids, one above and one below, but some - such as horses and deer - have a third, inner eyelid, the nictitating membrane, which may move upwards or sideways across the eyeball. Both types of eyelid can be closed to protect the eye from a blow, or from dirt; in closing - blinking - they wipe the eyeball clean and lubricate it with teardrops." (Foy and Oxford Scientific Films 1982:124)
  Learn more about this functional adaptation.
  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Functional adaptation

White blood cells roll and stick: mammals
 

White blood cells of mammals roll along blood vessel walls, and anchor when they find an infection or cell damage via cell-adhesion molecules (CAMs) with variable affinity.

     
  "Dan Hammer of the Univ. of Pennsylvania in Philadelphia is studying how white blood cells roll their way through the bloodstream, yet are able to anchor themselves where they are needed. He hopes that if he can devise materials that mimic the cells' roll-and-stick ability, he'll be able to devise a new targeted drug-delivery system. White blood cells have surface proteins called selectins that stick out of the cell surface. Fluid pushes the cell along--bonds form in front and are broken in the back, resulting in the cartwheeling motion." (Courtesy of the Biomimicry Guild)

Watch video
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  • Pennisi, E. 2002. Biology reveals new ways to hold on tight. Science. 296(5566): 250-251.
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Functional adaptation

Ear-flaps concentrate sound waves: mammals
 

The external ear-flaps of many mammals aid hearing by concentrating sound waves.

   
  "It is only among mammals that ears become noticeable, even striking, because of the visible external ear-flaps behind the narrow opening of the outer ear tube…The most obvious use of the ear-flap, though not necessarily the most important, is to gather and concentrate sound waves." (Foy and Oxford Scientific Films 1982:167)
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  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Functional adaptation

Mast cells reduce inflammation: mammals
 

Mast cells of mammals reduce long-term inflammation by secreting a protein known as interleukin-10.

   
  "Allergic contact dermatitis, such as in response to poison ivy or poison oak, and chronic low-dose ultraviolet B irradiation can damage the skin. Mast cells produce proinflammatory mediators that are thought to exacerbate these prevalent acquired immune or innate responses. Here we found that, unexpectedly, mast cells substantially limited the pathology associated with these responses, including infiltrates of leukocytes, epidermal hyperplasia and epidermal necrosis. Production of interleukin 10 by mast cells contributed to the anti-inflammatory or immunosuppressive effects of mast cells in these conditions. Our findings identify a previously unrecognized function for mast cells and mast cell–derived interleukin 10 in limiting leukocyte infiltration, inflammation and tissue damage associated with immunological or innate responses that can injure the skin." (Grimbaldeston et al. 2007:1095)
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  • Grimbaldeston, Michele A.; Nakae, Susumu; Kalesnikoff, Janet; Tsai, Mindy; Galli, Stephen J. 2007. Mast cell-derived interleukin 10 limits skin pathology in contact dermatitis and chronic irradiation with ultraviolet B. Nat Immunol. advanced online publication:
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Functional adaptation

Temporary covering protects from dirt and impact: mammals
 

The eyes of mammals are protected from dirt and impacts by eyelids.

   
  "Being a particularly delicate instrument, the eye needs protection -- usually, an eyelid. Most mammals have two eyelids, one above and one below, but some - such as horses and deer - have a third, inner eyelid, the nictitating membrane, which may move upwards or sideways across the eyeball. Both types of eyelid can be closed to protect the eye from a blow, or from dirt; in closing - blinking - they wipe the eyeball clean and lubricate it with teardrops." (Foy and Oxford Scientific Films 1982:124)
  Learn more about this functional adaptation.
  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Functional adaptation

Wetting agent reduces surface tension: mammals
 

Alveoli in mammalian lungs manage surface tension through use of a wetting agent whose concentration varies with alveolar expansion.

   
  "The individual alveoli have somewhat the same problem as the pair of lungs--why doesn't one alveolus expand to the point of explosion…before the others begin to inflate?…Lungs filled with air take more force to inflate than do lungs deliberately filled with a salt solution. With air inside, the outward pressure difference across the alveolar walls must work against tissue and the surface tension of the layer of water inside the alveoli. The latter opposes the formation of additional air-water interface as the alveoli expand. The surface tension, though, is drastically reduced by a wetting agent secreted by cells in the alveolar walls. But, and here's the trick, the effectiveness of the wetting agent depends on its concentration, which falls as the alveoli expand. Thus the force of surface tension rises sharply as an alveolus inflates, opposing further inflation. As a result of this wetting agent (or surfactant or detergent), the alveolar wall has a functionally curved stress-strain plot…and the requisite nonlinear elasticity." (Vogel 2003:53)
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  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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Functional adaptation

White blood cells adhere closely: mammals
 

White blood cells of mammals adhere tightly to target cells by increasing their surface area using arm-like projections and shape deformation.

   
  "Dr. Shasha Klibanov, Dr. Jonathan Lindner, and graduate student Jack Rychack of the University of Virginia are studying how leukocytes bind at high speeds to areas of infection. Physicians want to use microbubbles in combination with ultrasound to locate tumors or inflammation in the body. The microbubbles appear as a highlighted signal within the tissues or organ, enhancing the image. However, the microbubbles have low binding ability, so pass the target site and don't adhere efficiently. The researchers found that leukocytes have 'arms' that help bind them to the surface of an infection, and the blood cells deform to increase the surface contact area, increasing their adhesion to the infection. The researchers have modified the microbubbles to increase their surface area and adding micron projections to mimic leukocyte arms." (Courtesy of the Biomimicry Guild)
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Functional adaptation

Specialized teeth wear down but remain effective: grazing animals
 

The teeth of grazing mammals wear down but not smooth because of a side-by-side layered arrangement of enamel, dentine, and cementum.

           
  "Grazing has perhaps elicited the most dramatic dental specializations in mammals. About twenty million years ago, grasses and grasslands appeared on earth. Grass (and, incidentally, wood) provides poor fodder. It yields little energy relative to its mass, so a grazer has to process huge volumes. Much of that energy comes as chemically inert cellulose, which mammals hydrolyze only by enlisting symbiotic microorganisms in rumen or intestine. It's full of abrasive stuff like silicon dioxide and has lengthwise fibers that demand cross-wise chewing rather than rapid tearing. Long-lived grazers, concomitantly, have especially special teeth, with their components typically layered side by side, as in figure 16.5b. This odd-looking arrangement ensures that, while teeth may wear downthey won't wear smooth. The harder material (enamel, most particularly) will continue to protrude as the softer materials (cementum and dentine) wear down between them." (Vogel 2003:333)
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  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records: 80874
Specimens with Sequences: 87508
Specimens with Barcodes: 65561
Species: 2890
Species With Barcodes: 2560
Public Records: 60210
Public Species: 1851
Public BINs: 3156
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Barcode data

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Conservation

Conservation Status

Overexploitation, habitat destruction and fragmentation, the introduction of exotic species, and other anthropogenic pressures threaten mammals worldwide. In the past five centuries at least 82 mammal species have gone extinct. Currently, the International Union for Conservation of Nature and Natural Resources (IUCN) has listed about 1000 species (roughly 25% of all known mammals), as being at some risk of extinction. Several factors contribute to a species' vulnerability to human-induced extinction. Species that are naturally rare or require large home ranges are often at risk due to habitat loss and fragmentation. Species that are seen to threaten humans, livestock, or crops may be directly targeted for extirpation. Those species that are exploited by humans as a resource (e.g., for their meat or fur) but are not domesticated are often depleted to critically low levels. Finally, global climate change is adversely affecting many mammals. The geographic ranges of many mammals are shifting, and these shifts often correlate with changes in local temperatures and climate. As temperatures rise, which is especially pronounced in polar regions, some mammals are unable to adjust and are consequently at risk of losing their environment.

  • Reichholf, J. 1990. Endangerment and Conservation. Pp. 178-191 in B Grzimek, ed. Grzimek's Encyclopedia of Mammals, Vol. 1, 1st Edition. New York: Mcgraw-Hill.
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Some mammal species are considered to have a detrimental impact on human interests. Many mammals that eat fruit, seeds, and other types of vegetation are crop pests. Carnivores are often considered to be a threat to livestock or even to human lives. Mammals that are common in urban or suburban areas can become a problem if they cause damage to automobiles when they are struck on the road, or can become household pests. A few species coexist exceptionally well with people, including some feral domesticated mammals (e.g., rats, house mice, pigs, cats, and dogs). As a result of either intentional or unintentional introductions near human habitation, these animals have had considerable negative impacts on the local biota of many regions of the world, especially the endemic biota of oceanic islands.

Many mammals can transmit diseases to humans or livestock. The bubonic plague is perhaps the most well-known example. Plague is spread via fleas that are carried by rodents. Rabies, which can be transmitted among mammalian species, is also a significant threat to livestock and can kill humans as well.

Negative Impacts: injures humans (bites or stings, causes disease in humans , carries human disease); crop pest; causes or carries domestic animal disease ; household pest

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Economic Importance for Humans: Positive

Mammals are a vital economic resource for humans. Many mammals have been domesticated to provide products such as meat and milk (e.g., cows and goats) or fiber (sheep and alpacas). Many mammals are kept as service animals or pets (e.g., dogs, cats, ferrets). Mammals are important for the ecotourism industry as well. Consider the many people who travel to zoos or to all corners of the world to see animals like elephants, lions, or whales. Mammals (e.g., bats) often help control populations of crop pests. Some species like Norway rats and domestic mice are vitally important in medical and other scientific research; because humans are mammals, other mammals can serve as models in human medicine and research.

Positive Impacts: pet trade ; food ; body parts are source of valuable material; ecotourism ; research and education; produces fertilizer; controls pest population

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