Packrat
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A pack rat or packrat, also called a woodrat or trade rat, are any
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
in the North and Central American rodent genus ''Neotoma''. Pack rats have a rat-like appearance, with long tails, large ears, and large, black eyes. Pack rats are noticeably larger than
deer mice Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reindee ...
, harvest mice, and
grasshopper mice Grasshopper mice are rodents of the genus ''Onychomys'', occurring in North America. They feed on insects and other arthropods. Biology The three species in this genus of New World mouse, New World mice are only distantly related to the common h ...
, and are usually somewhat larger than
cotton rat A cotton rat is any member of the rodent genus ''Sigmodon''. Their name derives from their damaging effects on cotton as well as other plantation crops, such as sugarcane, corn, peanut and rice. Cotton rats have small ears and dark coats, and a ...
s.


Species

''Neotoma'' includes three subgenera: * Subgenus ''Neotoma'' ** '' Neotoma albigula'' - white-throated woodrat *** ''
Neotoma albigula varia The Turner Island woodrat (''Neotoma albigula varia'') is a subspecies of rodent in the family Cricetidae. It is found only in Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of ...
'' - Turner Island woodrat ** '' Neotoma angustapalata'' - Tamaulipan woodrat ** '' Neotoma bryanti'' - Bryant's woodrat *** '' Neotoma bryanti anthonyi'' - Anthony's woodrat † *** '' Neotoma bryanti bunkeri'' - Bunker's woodrat † *** '' Neotoma bryanti martinensis'' - San Martín Island woodrat † ** '' Neotoma chrysomelas'' - Nicaraguan woodrat ** '' Neotoma devia'' - Arizona woodrat ** '' Neotoma findleyi'' - Findley's woodrat † ** '' Neotoma floridana'' - eastern woodrat (Florida woodrat) *** '' Neotoma floridana smalli'' - Key Largo woodrat ** ''
Neotoma fuscipes The dusky-footed woodrat (''Neotoma fuscipes'') is a species of nocturnal rodent in the family Cricetidae. They are commonly called "packrats" or "trade rats" and build large, domed dens that can reach several feet in height. Coyotes and oth ...
'' - dusky-footed woodrat ** '' Neotoma goldmani'' - Goldman's woodrat ** '' Neotoma insularis'' ** '' Neotoma lepida'' - desert woodrat ** '' Neotoma leucodon'' - white-toothed woodrat ** '' Neotoma macrotis'' - big-eared woodrat ** ''
Neotoma magister The Allegheny woodrat (''Neotoma magister''), is a species of " pack rat" in the genus ''Neotoma''. Once believed to be a subspecies of the eastern woodrat (''Neotoma floridana''), extensive DNA analysis has proven it to be a distinct species. ...
'' - Allegheny woodrat ** '' Neotoma melanura'' ** '' Neotoma mexicana'' - Mexican woodrat ** '' Neotoma micropus'' - Southern Plains woodrat ** ''
Neotoma nelsoni Nelson's woodrat (''Neotoma nelsoni'') is a species of rodent in the family Cricetidae. It is endemic to Mexico, where it is known only from the eastern slopes of the volcanoes Orizaba and Cofre de Perote. Due to the small geographic range, isola ...
'' - Nelson's woodrat ** ''
Neotoma palatina A pack rat or packrat, also called a woodrat or trade rat, are any species in the North and Central American rodent genus ''Neotoma''. Pack rats have a rat-like appearance, with long tails, large ears, and large, black eyes. Pack rats are notice ...
'' - Bolaños woodrat ** ''
Neotoma stephensi Stephen's woodrat (''Neotoma stephensi'') is a species of rodent in the family Cricetidae found in Arizona, New Mexico and Utah in the United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. ...
'' - Stephens' woodrat * Subgenus ''Teanopus'' ** ''
Neotoma phenax The Sonoran woodrat (''Neotoma phenax'') is a species of rodent in the family Cricetidae found only in Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bo ...
'' - Sonoran woodrat * Subgenus ''Teonoma'' ** '' Neotoma cinerea'' - bushy-tailed woodrat Daggers mark extinct species.


Range and distribution

Woodrats reach their greatest diversity in the deserts of the western United States and northern Mexico. Several species are also found in the deciduous forest of the east coast, juniper woodlands in the southwest, oak woodlands along the coastal western United States and in the Sonoran Desert, and in the forest and rocky habitats of the western United States and western Canada.


Habitat

Each species of pack rat is generally restricted to a given type of habitat within its range. Pack rats live anywhere from low, hot, dry deserts to cold, rocky slopes above timberline. Pack rats build complex houses or dens made of twigs, cactus joints, and other materials. These contain several nest chambers, food caches, and debris piles. Dens are often built in small caves or rocky crevices, but when close by human habitations, woodrats will opportunistically move into the attics and walls of houses. Some ''Neotoma'' species, such as the white-throated woodrat (''N. albigula''), use the bases of prickly pear or cholla cactus as the sites for their homes, using the cactus' spines for protection from predators. Others, like the desert woodrat (''N. lepida'') will build dens around the base of a yucca or cactus, such as
jumping Jumping or leaping is a form of locomotion or movement in which an organism or non-living (e.g., robotics, robotic) mechanical system propels itself through the air along a ballistic trajectory. Jumping can be distinguished from running, gallo ...
and teddy-bear chollas. The largest species, ''Neotoma cinerea,'' has a bushy, almost squirrel-like tail. Bushy-tailed woodrats '' Neotoma cinerea'' occupy a range of habitats from boreal woodlands to deserts. They are cliff-dwellers and are often found on isolated, high-elevation exposed boulder areas under a variety of temperature and moisture conditions. They require adequate shelter among the rocks, though they are occasionally found inhabiting abandoned buildings as well.


Characteristics


Behavior

Pack rats are nest builders. They use plant material such as twigs, sticks, and other available debris. They are particularly fond of shiny objects. A peculiar characteristic is that if they find something they want, they will drop what they are currently carrying—for example, a piece of cactus—and "trade" it for the new item. They can also be quite vocal and boisterous. Getting into everything from attics to car engines, stealing their treasures from humans, damaging electrical wiring, and creating general noisy havoc can easily cause them to become a nuisance.


Diet

Bushy-tailed woodrats feed primarily on green vegetation, twigs, and shoots. Mexican woodrats eat seeds, fruits, acorns, and cactus. The pack rat microbiome has symbiotic roles in
digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...
, recycling endogenous
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, and the
detoxification Detoxification or detoxication (detox for short) is the physiological or medicinal removal of toxic substances from a living organism, including the human body, which is mainly carried out by the liver. Additionally, it can refer to the period of ...
of dietary toxins. The bacterial composition of the pack rat’s gut
microbiome A microbiome () is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupying a reasonably wel ...
is affected by what it eats, and by association, the geography of where the animal is from. However, while the bacterial composition of the pack rat microbiome is influenced by diet and geography, it is the animals’
genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...
that has the most influential role on bacterial composition.


Size

Adult bushy-tailed woodrat males usually weigh , with an average of , and adult females usually weigh , with an average of . These ranges are relatively large because this species occupies a large geographic range, and its body size is closely correlated with climate. Average males range in size from , with the average being , and average females range from , with the average being .


Reproduction and life history

Reproductive habits of rodents are variable in the wild. Offspring are born naked and helpless and must be cared for in nests called middens. Some female pack rats have been known to deliver up to five litters per year with each litter having as many as five young. The offspring may open their eyes between 10 and 12 days after being born and are usually weaned between 14 and 42 days. After around 60 days, most become sexually mature. Populations may cycle approximately every 8 years due to variation in reproduction and juvenile survival. Female annual survival rates vary by age from 0.42 for juveniles to 0.71 for 1–2 year olds, and very few females (less than 5%) live beyond 3 years of age.


Midden

A pack rat midden is a debris pile constructed by a woodrat. A midden may preserve the materials incorporated into it for up to 50,000 years, thus may be analyzed to reconstruct their original environment, and comparisons between middens allow a record of vegetative and
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
to be built. Examinations and comparisons of pack rat middens have largely supplanted pollen records as a method of study in the regions where they are available. In the absence of rock crevices or caves, the dens are often built under trees or bushes. The pack rats will also use plant fragments, animal dung, and small rocks in building the den. The vast majority of the materials will be from a radius of several dozen yards of the nest. Woodrats often urinate on the debris piles; sugar and other substances in the
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellular ...
crystallize Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...
as it dries out, creating a material known as amberat, which under some conditions can cement the midden together, and can encase plant fragments, pellets and other debris in an
amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In ...
-like matrix. The resilience of the middens is aided by three factors. The crystallized urine dramatically slows the decay of the materials in the midden; the dry climate of the American Southwest further slows the decay; and middens protected from the elements under rock overhangs or in caves survive longer.


Climate indicators

Zoologists examine the remains of
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s in middens to get a sense of the fauna in the neighborhood of the midden, while
paleobotanists Paleobotany, which is also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleogeogr ...
can reconstruct the vegetation that grew nearby. Middens are considered reliable "time capsules" of natural life, centuries and millennia after they occurred. Woodrat middens are composed of many things, including plants, macrofossils, and fecal pellets. Paleo-ecologists have used a variety of techniques to analyze the plant and animal material in pack rat middens describe paleo-communities and infer paleo-climate. For example, the plant species present in middens, and the carbon isotope ratios on material in middens have been widely studied. The analysis of middens was key in understanding the biota around
Pueblo Bonito Pueblo Bonito (Spanish for ''beautiful town'') is the largest and best-known great house in Chaco Culture National Historical Park, northern New Mexico. It was built by the Ancestral Puebloans who occupied the structure between AD 828 and 1126 ...
, thus helping to explain its history. One form of midden analysis examined the size of fecal pellets in pack rat middens. The size of woodrat pellet is proportional to the size of the woodrat. By measuring the pellets, the approximate size of the woodrat was determined based on data from a study of field-trapped woodrats. From Bergmann’s rule, differences in climate then can be determined. According to Bergmann’s rule, the body size of vertebrates is closely related to the average ambient air temperature in the region in which the vertebrate lives, so organisms in warmer regions are typically smaller than members of the same species in colder regions.


References


Further reading

* Betancourt, Julio L., Thomas R. Van Devender, and Paul S. Martin, eds. ''Packrat Middens: The Last 40,000 Years of Biotic Change'', University of Arizona Press, 1990, . * Duff, A. and A. Lawson. 2004. ''Mammals of the World A Checklist''. New Haven, Yale University Press. * Kays, R. W., and D. E. Wilson. 2002. ''Mammals of North America''. Princeton University Press, Princeton, 240 pp. * Musser, G. G. and M. D. Carleton. 2005. ''Superfamily Muroidea.'' pp. 894–1531 in ''Mammal Species of the World a Taxonomic and Geographic Reference'' D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore. * Ord, G., 1815. ''Zoology of North America'', in ''Guthrie's Geography'', 2nd American edition, pp. 291–361. eprint Rhoads, S.N. Philadelphia, 1894 p. 292. * * Ulev, Elena 2007. ''Neotoma cinerea''. In: ''Fire Effects Information System'', nline U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ 011, February 25 * * Linsdale, J. M., and L. P. Tevis. 1951. ''The dusky-footed wood rat''. Records made on Hastings Natural History Reservation. Berkeley, California. pp 675 . * Burt, W. H., and R. P. Grossenheider. 1976. ''A field guide to the mammals'', 3d ed. Houghton Mifflin Co., Boston. pp 289. * Schwartz, C. W., and E. R. Schwartz. 1981. ''The wild mammals of Missouri'', rev. ed. Univ. Missouri Press, Columbia. pp 356. * *


External links


"Desert Woodrats"
at DesertUSA.com
"Packrat Piles: Rodent rubbish provides ice age thermometer"
''Science News'', 24 September 2005 {{DEFAULTSORT:Pack Rat Mammals of the United States Neotoma Rats Taxa named by Thomas Say Taxa named by George Ord