Class Mammalia Order Rodentia Suborder Sciurognathi Family Geomyidae
Small- to medium-sized herbivores, characterized by a tube-shaped body, small eyes and ears, short tail, short but stout forelimbs, and small hindlimbs
Number of genera, species
6 genera; 36 species
Meadows, prairies, woodlands, and deserts Conservation status
Critically Endangered: 2 species; Endangered: 1 species; Vulnerable: 2 species; Lower Risk/Near Threatened: 10 species
North, central, and northwestern North America
North, central, and northwestern North America
Pocket gophers have an extensive fossil record that dates back to the late Oligocene or early Miocene of North America, approximately 25 million years ago. The closest living relatives to pocket gophers are members of the rodent family Heteromyidae, which includes kangaroo rats (Dipodomys) and pocket mice (Chaetodipus and Perognathus).
Living pocket gophers comprise two major lineages, one of which contains only a single living genus, Thomomys, the other containing the living genera Geomys, Cratogeomys, Or-thogeomys, Pappogeomys, and Zygogeomys. Molecular analyses of DNA sequences support this basic subdivision within the family Geomyidae. Pocket gophers are most diverse in Mexico, where representatives of all six genera (and 22 of the 36 species) can be found.
Evolutionary relationships among species of pocket gophers have been compared to the relationships among species of chewing lice that live in the pocket gopher's fur. Surprisingly, the louse relationships almost exactly mirror the relationships among their hosts (a phenomenon known as "cospeciation"), which suggests that lice and pocket gophers have been living together for many millions of years.
Pocket gophers are extraordinarily well adapted for life in subterranean tunnels. Their body is tubular in shape, which permits them to travel rapidly both forwards and backwards in tunnels. Their eyes and external ears (pinnae) are reduced in size, and numerous hairs around the eyes and ears prevent the entry of soil. Pocket gophers have relatively short limbs and a short, almost hairless tail. Most digging is accomplished using the claws of the powerful forefeet, but the large, procumbent, and blade-like incisor teeth also are used on occasion for digging. While digging, the pocket gopher's lips can be closed behind the incisors to prevent soil from entering the mouth. Although short, the forelegs are stout, with
broad hands and long, curved claws. These powerful digging appendages can also be used to push large quantities of earth within the burrow.
Pocket gophers have cheek pouches that open external to the mouth and extend from the mouth region to the animal's shoulders (hence the common name "pocket" gopher). These commodious pouches are lined with fur and are used to transport food and nest material (but not soil) within the burrow system. When full, the pouches make the pocket gopher's head appear almost twice its natural size. The fur of pocket gophers is generally short and may be very sparse in species living in hot, tropical environments. Fur color varies widely, even within a species, and tends to match the color of freshly excavated soil (generally light brown to almost black). This camouflage appears to be an adaptation to hide the animal from aerial predators such as hawks when the pocket gopher is pushing excavated soil onto the surface.
Pocket gophers are found only in the Western Hemisphere, where their range extends from southern Canada through western North America, southward to northwestern Colombia in South America. One isolated species, Geomys
A valley pocket gopher (Thomomys bottae) in its burrow with a nest chamber. (Photo by Tom McHugh/Photo Researchers, Inc. Reproduced by permission.)
pinetis, occurs in the southeastern United States (Alabama, Georgia, and Florida).
Pocket gophers live in almost any habitat that contains friable soil and does not flood. They are known from meadows, prairies, woodlands, alpine forests, valleys, deserts, rainforests, and agricultural fields. Neither elevation nor temperature seem to limit pocket gopher distibution—they are known from hot desert habitats at sea level and also from cold, high-elevation habitats near timberline. Pocket gophers live in a wide variety of plant communities where they feed on the roots and tubers of many species of plants. They are especially abundant in agricultural fields and seem to prefer alfalfa, potato, banana, and sugar cane crops.
Pocket gophers are extremely asocial mammals that generally live alone in their burrow systems. The population density of pocket gophers tends to vary widely among habitats, depending on the availability of food resources. Numbers of individuals may be fewer than 50 to as many as several hundred individuals per acre (0.4 ha). Their burrow systems are easily recognized by the characteristic mounds of earth (generally five to 20 per burrow system) that have rounded rather
than conical tops. Burrow entrances are usually plugged with soil when not in use. Where gophers occur in high numbers, the spacing of individual burrow systems is highly uniform, producing a buffer zone between burrows. This pattern is evident even in areas that differ widely in food availability, which suggests that the buffer zones are related to social interactions among pocket gophers, rather than food availability. Although pocket gophers live in almost continual darkness, they are generally crepuscular (active mainly at dawn and dusk), and some species are nocturnal. Pocket gophers are active all year and do not hibernate.
Pocket gophers display a remarkable amount of burrowing activity, and they, like beavers, have caused numerous changes in the landscape. Estimates of the amount of soil moved by pocket gophers in a single year range from 4.4-74.5 cubic yd (3.4-57 cubic m) per acre (0.4 ha). The disturbance resulting from this burrowing activity alters both physical and biotic processes in the local environment. Although pocket gophers eat voraciously, the net long-term effect of their presence is an increase in plant biomass, probably because of the effect of their excavations on soil nutrients. Pocket gophers also spread roots,
tubers, and other plant parts as a result of their burrowing activities, and thus they contribute to the distribution of plant life in their communities. The energetic cost of the subterranean lifestyle is extraordinarily high. Thus, the advantages of living in a subterranean burrow system—including protection from predators and extreme climatic fluctuations—must be very important to pocket gopher survival.
Most mammals that burrow into the earth do so simply for shelter or dens. Pocket gophers, however, actually forage through the earth in search of food, and they leave behind them a complex network of tunnels, which they also use for shelter and nesting. Pocket gophers are strict herbivores that feed on the underground parts of plants, especially the succulent parts such as bulbs and tubers. Occasionally, pocket gophers will eat the aboveground stems and leaves of forbs located near their burrow entrances. The horizontal feeding tunnels produced by pocket gophers are usually dug at the depth of greatest root density, approximately 2-8 in (6-20 cm) below the surface. In contrast, their nest and food storage chambers may be as deep as 4.9-6.5 ft (1.5-2 m).
Pocket gophers generally breed only once per year (usually in spring), although some species are capable of producing two litters per year (spring and fall) if conditions permit. During the breeding season, reproductively mature females will allow males to enter their burrow systems for brief mating encounters. The gestation period ranges from 18 days in smaller species to more than a month in the larger species. Litter size varies widely among pocket gopher species, ranging from one to 10 young per litter, with an average of three to five young. Young pocket gophers remain in their mother's burrow for one to two months, at which time they disperse in search of a place to dig their own burrow system. Some species reach reproductive maturity at only three months of age, whereas others do not breed until they are nine to 12 months of age. Adult body size is usually attained at an age of five to nine months.
Fifteen species of pocket gophers are listed on the World Conservation Union (IUCN) Red List. These include two species listed as Critically Endangered (Cratogeomys neglectus and Orthogeomys cuniculus), one species listed as Endangered (Zygogeomys trichopus), two listed as Vulnerable (Geomys trop-
icalis and Pappogeomys alcorni), and 10 additional species listed as Lower Risk/Near Threatened.
Most of the threatened species of pocket gophers occur naturally in low abundance within restricted habitats. Current threats to these pocket gophers include competition from other gopher species and, in the case of Geomys tropicalis, loss of habitat caused by urban expansion of humans.
Pocket gophers are widely considered to be agricultural pests. In tropical areas, a single pocket gopher can destroy a family's garden in less than a month. Commercial agriculturalists regularly trap or poison pocket gophers to limit loss of crops. Early Native Americans are known to have consumed pocket gophers, and it is reported that in some areas of Latin America local people regard the meat of pocket gophers as a delicacy.
1. Querétaro pocket gopher (Cratogeomys neglectus); 2. Valley pocket gopher (Thomomys bottae); 3. Plains pocket gopher (Geomys bursarius); 4. Yellow-faced pocket gopher (Cratogeomys castanops); 5. Michoacân pocket gopher (Zygogeomys trichopus); 6. Buller's pocket gopher (Pappogeomys bulleri); 7. Large pocket gopher (Orthogeomys grandis). (Illustration by Marguette Dongvillo)
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