Merriam Pocket Rat

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Merriam Pocket Rat
Systematics
Superordinate : Euarchontoglires
Order : Rodents (Rodentia)
Superfamily : Pocket rodents (Geomyoidea)
Family : Pocket rats (Geomyidae)
Genre : Cratogeomys
Type : Merriam Pocket Rat
Scientific name
Cratogeomys merriami
( Thomas , 1893)

The Merriam pocket rat ( Cratogeomys merriami , Syn .: Pappogeomys merriami ) is a species from the pocket rats family that occurs in central Mexico . It lives in open and wooded high areas in the southern part of the valley of Mexico and lives mostly underground. The name of the species goes back to 1893, the specific epithet merriami honors the American zoologist and ethnographer Clinton Hart Merriam . Research in 2005 revealed that the original definition of the Merriam's cup rat was a flock of species . The stock is not considered to be threatened.

features

The Merriam pocket rat is a relatively large representative of the pocket rats . An examination of 91 individuals in Morelos found an average total length of 34.6 cm for females and 36 cm for males. The average weight of the females was 676 g, that of the males 757 g. A single individual had a head-to-trunk length of 29.5 cm and a tail length of 9.5 cm. The coat is short and soft overall. The coat color of the Merriam pocket rat is very variable. At the back, it ranges from matte chestnut brown to slate black. The underside is similarly colored, but lighter. A dark spot of color appears around the ears, while the light spot of color on the base of the tail that occurs in other closely related species is not developed. The tail has only a sparse coat of fur. The hind foot length without claw is 41 mm, the longest claw measures 15 mm.

The skull becomes 64 mm long and 48 mm wide at the zygomatic arches . In general, it is characterized by its broad, strong structure. The zygomatic arches are very broad at the front, but taper slightly towards the rear. From closely related species, the Merriam pocket rat can be distinguished by a wedge-shaped lower section of the occiput (pars basilaris) that is relatively wide at over 4 mm. The Mexican pocket rat ( Cratogeomys castanops ) has a narrow, parallel-sided bone here. In addition, in the Merriam pocket rat, the zygomatic process of the temporal bone at the point of contact with the temporal bone process of the zygomatic bone is very thick with over 2.5 mm. The front incisors are very long and massive and thicker than they are wide.

distribution and habitat

Distribution area of ​​the Merriam pocket rat

The Merriam pocket rat is widespread in central Mexico . Mainly it occurs in the southern part of the valley of Mexico and the adjacent regions, so in the Sierra de Las Cruces and the Sierra de Ajusco , in the area around the twin volcanoes Popocatépetl and Iztaccíhuatl and from the Río Lerma in the valley of Toluca eastwards to the west Puebla . The total populated area is given as less than 20,000 km². The habitat extends at an altitude of 1800 to 4000 meters. The species is native to grasslands and forests consisting of pines and oaks of moderate climates, but can also be found on agricultural areas such as pastureland . In general, the Merriam pocket rat is considered to be relatively common.

Way of life

The Merriam Pocket Rat is a solitary animal, and its activities and frequencies vary throughout the year. The animals are particularly active in December and January, with the lowest activity recorded in May June. They dig underground structures whose entrances in the form of ejected earth material reach a diameter of 25 to 45 cm. The thinner the vegetation cover, the larger the hills; the largest mounds of earth were observed in spring. Due to the excavation activities, the Merriam pocket rat is often considered a "pest" on farmland and pasture because it contributes to erosion by digging up the soil and influences the composition of the vegetation. However, loosening up the earth also has a positive effect, especially on firm soils. Overall, their negative impact is overrated. The penetration of agriculturally used areas begins from undisturbed forest areas, during a nine-month study in 1993 and 1994, the animals covered 6.7% of a 1.3 hectare pasture area, whereby their activities decreased with increasing vegetation and during the rainy season.

Reproduction takes place year round, but there is an increased birth rate during the dry season from October to March. As a result, after the increased rainfall during the rainy season, the vegetation cover is thicker and therefore enough food is available to raise the young, and the burrows are less threatened by flooding. A female carries an average of three embryos .

The external parasites of the Merriam pocket rat include hair lumps of the genus Geomydoecus .

Systematics

The Merriam pocket rat is a species of the genus Cratogeomys within the family of pocket rats (Geomyidae). In addition to the Merriam pocket rat, the genus Cratogeomys includes around half a dozen other species that can be divided morphologically and genetically into two groups of species. The fumosus group contains C. fumosus and C. planiceps (originally called the gymnurus group), the castanops group includes, in addition to the Merriam pocket rat, C. castanops , C. goldmani , C. fulvescens and C. perotensis . The division into two groups of species goes back to RJ Russell, who separated the gymnurus group from the castanops group in 1968 ; the former contained five, the latter two species. However, genetic studies published in 2004 by Mark S. Hafner and research colleagues showed that only two species could be identified within the gymnurus group. Since the type species C. gymnurus could not be endured as an independent species, the species complex was renamed the fumosus group. A genetic study of the castanops group published by the same group of experts the following year came to the conclusion that the Merriam pocket rat contained two cryptic species , named C. fulvescens and C. perotensis . Morphologically, the two groups of species could be distinguished on the basis of the structure of the mastoid process, which in the fumosus group is expansively large, but in the castanops group is rather small.

The first scientific description of the Merriam pocket rat was presented by Oldfield Thomas in 1893 under the name Geomys merriami , with which he introduced the species to the lowland pocket rats . For the description, Thomas had a copy that he claims came from southern Mexico. He honored the American zoologist Clinton Hart Merriam with the species name merriami . Merriam himself laid down the generic name Cratogeomys two years later and narrowed the habitat of the pocket rat named after him to the southern part of the valley of Mexico. In part, the Merriam pocket rat was led together with the other representatives of the genus within Pappogeomys , which caused Russell to revise the pocket rats in 1968. However, the genus status of Cratogeomys was recognized again in 1982, and some scientists still led this as a subgenus of Pappogeomys until the 1990s .

Threat and protection

There are no known major threats to the Merriam pocket rat population. In parts of the distribution area, habitat is shrinking due to the expansion of agricultural land, but the species is very adaptable. Despite the only limited distribution area, the IUCN classifies the Merriam pocket rat as "not endangered" ( least concern ). Their occurrence overlaps with individual protected areas.

supporting documents

literature

  • Mark S. Hafner, Jessica E. Light, David J. Hafner, Sara V. Brant, Theresa A. Spradling and James W. Demastes: Cryptic species in the Mexican pocket gopher Cratogeomys merriami. 2005 In: Journal of Mammalogy 86 (6), 2005, pp. 1095–1108 ( online )

Individual evidence

  1. ↑ a b Beatriz Villa-C. and Richard M. Engeman: Reproductive Characteristics of Merriam's Pocket Gopher (Pappogeomys merriami merriami) from Huitzilac, Morelos, Mexico (Rodentia: Geomyidae). The Southwestern Naturalist 39 (2), 1994, pp. 156-159
  2. ↑ a b c d Oldfield Thomas: On the larger species of Geomys. Annals and Magazine of Natural History 12, 1893, pp. 269-273
  3. ↑ a b c d e Mark S. Hafner, Jessica E. Light, David J. Hafner, Sara V. Brant, Theresa A. Spradling and James W. Demastes: Cryptic species in the Mexican pocket gopher Cratogeomys merriami. Journal of Mammalogy 86 (6), 2005, pp. 1095-1108
  4. ^ A b Clinton Hart Merriam: Monographic revision of the pocket gophers, family Geomyidae (exclusive of the species of Thomomys). North American Fauna 8, 1895, pp. 1–220 (pp. 152–154) ( [1] )
  5. ↑ a b S. T. Álvarez-Castañeda, I. Castro-Arellano, T. Lacher and E. Vázquez: Cratogeomys merriami. The IUCN Red List of Threatened Species. Version 2014.3. ( [2] ); last accessed on May 16, 2015
  6. ↑ Desley Whisson and Beatriz Villa-C .: Activity Patterns of the Pocket Gopher Pappogeomys merriami merriami in a Mexican Rangeland. In: Wendy S. Halverson, A. Charles Crabb (Eds.): Proceedings of the Sixteenth Vertebrate Pest Conference. Westin Hotel, Santa Clara, California, February 28, March 1–3, 1994. University of California, Davis CA 1994, pp. 87–91, full text (PDF; 1.32 MB)
  7. ↑ Jessica E. Light and Mark S. Hafner: Cophylogeny and disparate rates of evolution in sympatric lineages of chewing lice on pocket gophers. Molecular Phylogenetics and Evolution 45, 2007, pp. 997-1013
  8. ^ Mark S. Hafner, Theresa A. Spradling, Jessica E. Light, David J. Hafner, and John R. Demboski: Systematic revision of pocket gophers of the Cratogeomys gymnurus species group. Journal of Mammalogy 85, 2004, pp. 1170-1183
  9. ↑ David J. Hafner, Mark S. Hafner, Gerald L. Hasty, Theresa A. Spradling, and James W. Demastes: Evolutionary Relationships of Pocket Gophers (Cratogeomys castanops Species Group) of the Mexican Altiplano. Journal of Mammalogy 89 (1), 2008, pp. 190-208
  10. ↑ Bo Beolens, Michael Watkins and Michael Grayson: The Eponym Dictionary of Mammals. Johns Hopkins University Press, 2009, ISBN 978-0801893049 , p. 272.
  11. ↑ Cratogeomys. In: Don E. Wilson , DeeAnn M. Reeder (Eds.): Mammal Species of the World. A taxonomic and geographic Reference. 2 volumes. 3. Edition. Johns Hopkins University Press, Baltimore MD 2005, ISBN 0-8018-8221-4 . Retrieved March 14, 2010

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