The smooth-toothed pocket gophers, genus Thomomys, are so called because they are among the only pocket gophers without grooves on their incisors. They are also called the Western pocket gophers because they are distributed in western North America. They are considered distinct enough from other pocket gophers to be recognized as a separate subfamily or tribe.

Natural history

Thomomys is highly fossorial. They rely on their incisors for digging more than most other gophers. They feed on plants, largely from beneath the surface, but they do come above ground at night. Roots, stems, leaves, and bulbs are eaten. When not directly in an agricultural field they are a benefit to humans by enriching soil and preventing runoff.

Species

Over a hundred subspecies have been described, but not all are currently recognized by modern authorities. Like many fossorial rodents, Thomomys shows a great deal of allopatric variation.

• Thomomys
  • Subgenus Megascapheus
    • Thomomys clusius - Wyoming pocket gopher
    • Thomomys idahoensis - Idaho pocket gopher
    • Thomomys mazama - western pocket gopher (including the extinct subspecies Thomomys mazama tacomensis - Tacoma pocket gopher)
    • Thomomys monticola - mountain pocket gopher
    • Thomomys talpoides - northern pocket gopher
  • Subgenus Thomomys
    • Thomomys bottae - Botta's pocket gopher
    • Thomomys bulbivorus - Camas pocket gopher
    • Thomomys townsendii - Townsend's pocket gopher
    • Thomomys umbrinus - southern pocket gopher

General Characteristics

Thomomys, commonly referred to as pocket gophers, are a group of rodents belonging to the Family Geomydae. Thomomys are unique from other gophers in that they have smooth upper incisors, free of the grooves that are common throughout other species. All species and genera share the trait of fur-lined, external cheek pockets that allow them to move food material to and from their underground dwellings. The size varies among species, but commonly ranges from the size of a smaller mole to a larger rat. Coloration can range from yellow, to grey, to brown, and even black. They are all full-bodied with squat legs, short hair, and small eyes and ears. ^[1]

Pocket gophers has special visual adaptations to match their extreme and unique subterranean lifestyle. Though the size of their eyes are typical for rodents, the lens is able to transmit light rays that fall into the ultraviolet category. They possess three different photopigments: two cone pigments specific to 367nm and 505nm, and a rod pigment at 495nm. Overall, the pocket gophers have less rod density than nocturnal rodents. ^[2]

Habitat

Thomomys inhabit Southwestern Canada, the Western United States, and a large percentage of Mexico. They thrive in fertile land often used for agriculture, but can be found in many different localities. They prefer areas with high primary productivity and nitrogen soil concentrations. ^[3]

Diet

They are fossorial herbivores that consume an extensive amount of food for their body size. This could be due to the fact that they expend copious amounts of energy excavating and maintaining their elaborate tunnel systems. It is estimated that their subterranean lifestyle requires them to use 360-3400 times the amount of energy required for above ground living. They selectively consume underground parts of perennial and annual grasses, forbs, and woody plants. They are also known to forage above ground, usually close to their burrow entrances. They are choosy and prefer certain species and parts of plants, perhaps due to their high daily energy expenditure. ^[4]

Behavior and Environmental Effects

• Tunneling and mounds

Thomomys Pocket gophers live underground and create extensive systems of tunnels through which they traverse. They move earth from below ground, and deposit it above ground in piles known as mounds. In snowy regions, they create tunnels through the snow known as earthcores. Earthcores and mounds together can cover up to 30% of the surface in highly excavated areas. The most prominent ecological effect would be that of their tunneling and mounds. The mounds are thought to increase ecological diversity of plants by providing a space for fugitive species that would otherwise have been eliminated due to competition over time. The flora of mounds differs noticeably from the surrounding areas, often with increased numbers of forbs and annuals. The actual mound soil differs in composition from that of the surrounding area as well, creating a different texture and water-holding potential. The ecological impact of this is still relatively unexplored. ^[5]

• Effects on Agriculture and Development

Thomomys Pocket gophers are able to alter the mineral availability, organic molecule concentration, texture, and moisture content of soil. This can be either a benefit or a nuisance depending on the soil condition and usage. In arid or semi-arid environments, these changes enhance vegetation growth and soil quality. They are thought to be able to help generate and regenerate prairie lands that have degraded. ^[6]

Yet they are commonly known as pests in areas of agriculture and development. They have and can cause a heavy loss to farmers by consuming the roots or underground crops themselves. Farmers try to control and limit their population in crop areas using a variety of means. In the wild however, their presence is encouraged and advantageous. . ^[7]

There are many different methods that have been used to try and eliminate overpopulation of pocket gophers in certain areas. These include, but are not limited to chemicals, propane blasting, and trapping. A park in Penn Valley CA installed owl boxes to encourage the habitation of barn owls, a natural pocket gopher predator. ^[8]

UC Davis suggests the first step to be use of a gopher probe to locate the main burrow. Then a shovel can be used to widen the opening to the main burrow and traps can be set at opposite directions within the burrow. There are a wide array of different traps that can be used, including the choker-style box trap and the pincher trap. Baiting the trap is not always necessary, though it may afford you quicker or better results. If desired, lettuce and other vegetables can be used as the bait. It is then best to cover the traps with canvas or dirt to conceal the light. If there has been no success within two days, it is advised to move and reset the traps. Toxic bates can also be used, however the strategy for placement is different than that of the non-toxic traps. ^[9]

Fumigation is usually unsuccessful because gophers can quickly seal off their burrows at the first sign of fumes. The exception to this is fumigation with aluminum phosphide, however this can only be done by a professional. ^[10]

Gas explosives and flooding have commonly been utilized to force gophers from their burrows, and while sometimes successful, it is no guarantee that you will be able to eradicate them fully. ^[11]

References

1. ^ Bayley V. 1915 Revision of the pocket gophers of the genus Thomomys. http://books.google.com/books?hl=en&lr=&id=uLTPAAAAMAAJ&oi=fnd&pg=PA7&dq=thomomys&ots=5tOty2ubS5&sig=wYZX3TOROZDKfThTsFk6oZhZCQY#v=onepage&q=thomomys&f=false
2. ^ Williams G, Calderone J, Jacobs G. Photoreceptors and photopigments in a subterranean rodent, the pocket gopher (Thomomys bottae). Journal Of Comparative Physiology A: Neuroethology, Sensory, Neural & Behavioral Physiology [serial online]. February 2005;191(2):125-134. Available from: Academic Search Premier, Ipswich, MA. Accessed December 15, 2012
3. ^ Huntly, N., & Inouye, R. (1988). Pocket gophers in ecosystems: Patterns and mechanisms. Bioscience, 38(11), 786-793.http://cedarcreek.umn.edu/biblio/fulltext/t1072.pdf
4. ^ Huntly, N., & Inouye, R. (1988). Pocket gophers in ecosystems: Patterns and mechanisms. Bioscience, 38(11), 786-793. http://cedarcreek.umn.edu/biblio/fulltext/t1072.pdf
5. ^ Huntly, N., & Inouye, R. (1988). Pocket gophers in ecosystems: Patterns and mechanisms. Bioscience, 38(11), 786-793. Retrieved from http://cedarcreek.umn.edu/biblio/fulltext/t1072.pdf
6. ^ Mielke HW 1977 Mound Building by Pocket Gophers (Geomyidae): Their Impact on Soils and Vegetation in North America Journal of Biogeography, Vol. 4, No. 2 171-180
7. ^ Bayley V. 1915 Revision of the pocket gophers of the genus Thomomys. http://books.google.com/books?hl=en&lr=&id=uLTPAAAAMAAJ&oi=fnd&pg=PA7&dq=thomomys&ots=5tOty2ubS5&sig=wYZX3TOROZDKfThTsFk6oZhZCQY#v=onepage&q=thomomys&f=false
8. ^ GOPHERS BEWARE. By: McKnight, Marianne Wilson, E: The Environmental Magazine, 10468021, Jul/Aug2010, Vol. 21, Issue 4
9. ^ http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7433.html
10. ^ http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7433.html
11. ^ http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7433.html

References

• Nowak, R. M. 1999. Walker's Mammals of the World, Vol. 2. Johns Hopkins University Press, London.