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Habitat utilization by Sigmodon hispidus, Reithrodontomys fulvescens, and Oryzomys palustris was compared to habitat availability, by determining if capture locations were random samples of the trapping grid with respect to mean cover of 10 plant species. A methodology, designed for this purpose and detailed in a companion paper (Kincaid and Bryant 1983), was used in which the Euclidean distance between mean vectors representing habitat utilization and availability was compared to that for random draws from the available resource spectrum. This distance (the habitat differential) was partitioned into separate components representing differential composition and dif- ferential productivity in the occupied habitats. Interspecies differences in habitat utilization were also considered relative to habitat availability. Each species utilized a habitat subset that differed significantly from the average available habitat. Sigmodon and Reithrodontomys were the most similar species, differing only in the pattern of their associations with grasses and cover. Oryzomys usually occurred in habitats dominated by dicots. Deviations for all species were usually attributable to differential composition, except for Sigmodon and Reithrodlontomvs in winter, when both exhibited significant productivity components. Habitats occupied by these rodents were significantly less heterogeneous than random subsets, but only Ory- zomys habitat always had reduced dimensionality of variation relative to that of the available habitat. Differential responsiveness to patterns of statistical variation in a patchy environment can be sufficient to produce habitat separation and is offered as a neutral model for the examination of higher-order processes.

Oxygen consumption and body temperature were monitored for two subspecies of western harvest mouse, Reithrodontomys megalotis, under standard conditions for resting (basal) metabolism and during shallow daily torpor. Reithrodontomys m. longicaudus (7.77 g), from southern California, had a resting metabolic rate 127%, and a heat loss coefficient 126%, that expected from body mass. Reithrodontomys m. ravus (9.81 g), from near the Great Salt Lake in Utah, had both a significantly lower resting metabolic rate (114%) and a significantly lower heat loss coefficient (91%) than longicaudus. Reithrodontomys m. longicaudus was readily induced to enter shallow daily torpor when held at temperatures below thermoneutrality and starved for 10-12 h. Despite its lower rate of metabolism, R. m. ravus rarely entered torpor under any combination of cold- or starvation-induced stress. This differential use of torpor between two closely related subspecies may be partially attributed to differences in body mass and heat loss. ...

(1907). XXVI.—On neotropical mammals of the genera Callicebus, Reithrodontomys, Ctenomys, Dasypus, and Marmosa. Annals and Magazine of Natural History: Vol. 20, No. 116, pp. 161-168.

Populations of Microtus, Reithrodontomys and Mus reached a peak in Tilden Park, California, in June 1961, and reproduction almost ceased until the following spring. The impact of carnivores (feral cats, gray foxes, raccoons and skunks) on this standing crop of mice was measured by analysis of carnivore droppings systematically recovered from a 35-acre study area. Eighty-eight per cent of the 4,400 Microtus , 33% of the 1,200 Reithrodontomys and 7% of the 7,000 Mus were eaten by the carnivores before the next spring. As Microtus became scarce, the carnivore diet included more Reithrodontomys, Mus , gophers and finally wood rats. Numerous carnivores continued to hunt mice on the area even after the mice had been practically exterminated. At the beginning of the study the standing crop per acre, in kilocalories, of various components of the food chain was: roots, 7.3 million; hay (excluding seeds), 8.1 million; seeds, 1.9 million; Microtus , 6,402; Mus , 4,543; Reithrodontomys , 434; and carnivores, 650. The annual caloric requirements of the peak populations (per acre) would have been: Microtus , 1.4 million; Mus , 876,000; Reithrodontomys , 82,000; and carnivores, 11,700. The peak population of mice could not have survived for one year on the available seed crop. The carnivores ate 55% of the calories available as mice and could have survived a full year if all mice had remained available to them, but by the end of December so many mice had been lost to other agents of mortality and by emigration that only a 12-day supply remained. In spite of the initial high density of mice, 7% of the seed crop escaped destruction and grew to form a rich vegetation in the following season.

U. S. Public Health Service quarantine personnel inspected 100 trucks carrying Mexican bananas as they were unloaded in Brownsville, Texas, in 1964-65. Of the animals recovered of possible public health interest, 5 species of vertebrates and 31 species of invertebrates have been identified. Included are several species not established in the United States. Rice rats, Oryzomys couesi (Alston), and harvest mice, Reithrodontomys fulvescens J. A. Allen. were the commonest rodents taken. An average of a rat or a mouse was captured for approximately each 2 trucks examined. This study suggests that present quarantine regulations should be strengthened to prevent more effectively the entrance of potential reservoirs and vectors of zoonotic infections in bananas and other fruit or vegetables imported by land vehicles.

The distribution of subadults and adults of Dermacentor variabilis (Say) in an old-field habitat on a farm near Montpelier, Virginia, was studied. The distribution of the common old-field rodent hosts of this species, Microtus pensylvanicus (Ord) and Reithrodontomys humulis (Audubon & Bachman) also was studied. The rodent hosts were found to be most abundant near the center of their habitat area, and commonest in grass-dominant localities. However, subadult ticks were taken most frequently on hosts trapped at or near the old-field: forest edge. The low woody-deciduous forest had a consistently higher atmospheric moisture content than the old-field habitat during daylight. The possible influence of this difference in atmospheric moisture content between habitat types on tick survival and distribution is discussed. It was concluded that the old-field habitat is a highly unsatisfactory environment for subadult ticks of this species, with the exception of the zone near the deciduous forest edge. Adult ticks were also most numerous near the forest border. However, in contrast to the subadults, adults were abundant also in areas far from the forest edge, perhaps as a result of dispersal.

1. 1. Among cricetids there appears to be a direct relationship between the percentage medullary thickness and the ability to concentrate urine, at least congenerically. 2. 2. A correlation was established between a renal index and the rainfall within the geographic range of each taxon. 3. 3. A pattern was found relating renal structure to the speculated relative moisture availability among environmental associates within specific geographic areas.

We investigated the relative densities of granivorous, nocturnal desert rodents in small plots within two arid regions of Arizona to study how sympatric species avoid competitive extinction. The most common rodents were kangaroo rats, Dipodomys spp., and pocket mice, Perognathus spp. We attempted correlating the density of each species with several environmental measurements, derived from the soil's i) depth; ii) texture or iii) resistance to sheer stress; or from the plant's i) species diversity; ii) growth forms or iii) foliage density. Successful variables were derived from plant growth form and foliage density. The soil's resistance to sheer stress also seemed important for a few species. In general, kangaroo rats were associated with sparseness of vegetation; pocket mice with denseness. One group of mice, which we term bush mice, seemed to require bushes and included two Perognathus spp., three Peromyscus spp., and probably a harvest mouse (Reithrodontomys fulvescens). Two other Perognathus spp. were taken in grassy habitats. Some suitable habitats tended to be complementary to others, suggesting that species associated with them are competitors. Comparisons of the density and distribution of D. merriami, present in both regions but under different biotic circumstances, reinforces the opinion that competition is responsible for the complementariness of habitats. In some cases the evidence suggests that competitive coexistence is accounted for by the fact that different specializations are needed to escape predation in different environments. We use variables which correlate with the relative density of various species to construct a model of habitat complexity. The rodent species diversities obtained in our plots can be approximately accounted for by this model. The model is based on the premises that the rodents collectively discriminate four qualities of soil surface, and three heights and two densities of vegetation. In general, specializations based on biotic variables appear most important.

Three abundant rodents, the cotton rat (Sigmodon hispidus), the harvest mouse (Reithrodontomys fulvescens), and the rice rat (Oryzomys palustris) are sympatric in southeast Texas. From January 1970 to May 1970, six presumably homogeneous areas, three control, were live—trapped. Mark—release—recapture and selective removal techniques were used to monitor species composition within the areas. Estimates of the number of individuals per species, body weights, and sex ratios were obtained at 2—week intervals. When cotton rats were experimentally removed, no change in the mean weights of harvest mice or rice rats were revealed by linear regression analysis. When harvest mice and rice rats were removed, cotton rat females exhibited a significant increase in mean weight. A significant change in sex ratio of cotton rats, from a greater proportion of males to a greater proportion of females, was recorded in the areas where harvest mice and rice rats were removed. Although the number of captures per species declined...

Summary As a result of a plague epizootic in the San Bruno Mountains, a mammalectoparasite survey was undertaken in the vicinity in spring, 1954. Trapping was conducted in 25 designated areas, using lines of 25 or 50 Museum Special snap traps. The principal vegetation types represented were chaparral, coastal scrub, woodland and grassland. Small mammals were most abundant in chaparral and coastal scrub, very few in dense woodland or grazed grassland. There were often high populations in ungrazed grassland with shrub clumps or tall forbs. Peromyscus maniculatus was the most abundant and widespread species. Reithrodontomys megalotis occurred infrequently but was negatively correlated with the abundance of P. maniculatus. The overall population of Microtus californicus was low and colonies were scattered; greatest abundance was in ungrazed grassland with forbs or shrub clumps. Other species taken were Peromyscus californicus, Mus musculus, Thomomys bottae, Rattus norvegicus, Sorex trowbridgei, and Sorex vagrans. There were many Rattus norvegicus on hog farms adjoining the U. S. P. H. S. study area. Fifteen species of fleas were obtained in the survey. Opisodasys keeni was predominant on P. maniculatus. Malareus telchinum was predominant on Microtus californicus but was also abundant on P. maniculatus and was generally the most ubiquitous flea species. Catallagia wymani occurred frequently on P. maniculatus and M. californicus. Hystrichopsylla sp. and Atyphloceras multidentatus were important primarily as nest fleas of M. californicus and probably of Peromyscus. Rattus norvegicus trapped from hog farms bore almost entirely Nosopsyllus fasciatus. No effect of habitat differences was apparent for fleas on P. maniculatus. Differences in the degree of non-randomness of flea distribution on various host species are discussed. Frequency indexes for the presence of flea species on different host species are calculated as a measure of host specificity. The specificity of most of the prominent fleas was low. Microtus californicus is considered a key species in promoting flea exchange. Two positive pools were obtained by us, one in Rivera Canyon about ¾ mile from the study area, and one following control operations on the ridge above the study area. It is suggested that the epizootic must have been essentially limited to this vicinity. After the initial survey, poison grain was distributed by air over about 500 acres. The results were evaluated by the use of repeated traplines. Apparent reductions of from 25 to 80 per cent were registered in four different areas. Microtus was most severely affected. Trapping about two months later showed that populations had generally regained their previous levels. Reithrodontomys displayed a striking and unexplained increase. The density of fleas on hosts increased sharply immediately after poisoning. The poisoning operation was apparently ineffective in reducing the plague transmission potential among wild rodents. Rats were successfully controlled on the hog farms. The role of habitat distribution is emphasized in governing interspecific host and flea contacts, continuity of distribution of host populations and potential for the contact of native mammals with humans and domestic rats.

Reithrodontomys brevirostris Goodwin, 1943. Am. Mus. Novit., 1231:1. TYPE LOCALITY: Costa Rica, Alajuela, canyons above Villa Quesada, 5000 ft. (1524 m). DISTRIBUTION: N.C. Nicaragua; C. Costa Rica. COMMENT: Subgenus Aporodon; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. Includes nicaraguae; see Jones and Genoways, 1970, Occas. Pap. W. Found. Vert. Zool., 2: 10. ISIS NUMBER: 5301410008047001001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 460, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255.","Jones, J. K., Jr., and H. H. Genoways. 1970. Harvest mice (genus Reithrodontomys) of Nicaragua. Occasional Papers of the Western Foundation of Vertebrate Zoology, 2: 1 - 16."]}

Reithrodontomys Giglioli, 1874. Bull. Soc. Geogr. Ital., Roma, 11:326. REVIEWED BY: M. D. Carleton (MDC); A. V. Linzey (AVL); J. Ramirez-Pulido (JRP)(Mexico); G. Urbano-V. (GUV). COMMENT: Includes Aporodon as a subgenus; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255, Hershkovitz, 1966, in Wenzel and Tipton, eds., Ectoparasites of Panama, pp. 725-752, and Carleton, 1980:125- 126. Karyology reviewed by Carleton and Myers, 1979, J. Mammal., 60:307-313. Revised by Howell, 1914, N. Am. Fauna, 36:1 -97; Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255, revised the Central American species. Subfamily Hesperomyinae; see comment under Cricetidae. ISIS NUMBER: 5301410008047000000., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 460, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255.","Carleton, M. D. 1980. Phylogenetic relationships in neotomine-peromyscine rodents (Muroidea) and a reappraisal of the dichotomy within New World Cricetinae. Miscellaneous Publications, Museum of Zoology, University of Michigan, 157: 1 - 146.","Carleton, M. D., and P. Myers. 1979. Karyotypes of some harvest mice, genus Reithrodontomys. Journal of Mammalogy, 60: 307 - 313.","Howell, A. H. 1914. Revision of the American harvest mice (genus Reithrodontomys). North American Fauna, 36: 1 - 97."]}

Reithrodontomys microdon Merriam, 1901. Proc. Wash. Acad. Sci., 3:548. TYPE LOCALITY: Guatemala, Huehuetenango, Todos Santos, 10,000 ft. (3048 m). DISTRIBUTION: S. Guatemala to C. Chiapas; N.C. Oaxaca; N.E. Michoacan to Distrito Federal (Mexico). COMMENT: Subgenus Aporodon; see Hooper, 1952, Mise. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047012001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 461, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Reithrodontomys gracilis J. A. Allen and Chapman, 1897. Bull. Am. Mus. Nat. Hist., 9:9. TYPE LOCALITY: Mexico, Yucatan, Chichen-Itza. DISTRIBUTION: N.W. Costa Rica to Chiapas and Yucatan (Mexico). COMMENT: Includes insularis; see Jones, 1964, Proc. Biol. Soc. Wash., 77: 123-124. Subgenus Aporodon; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047007001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 460, DOI: 10.5281/zenodo.7353031, {"references":["Jones, J. K., Jr. 1964. Distribution and taxonomy of mammals of Nebraska. University of Kansas Publications, Museum of Natural History, 16: 1 - 356.","Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Reithrodontomys hirsutus Merriam, 1901. Proc. Wash. Acad. Sci., 3:553. TYPE LOCALITY: Mexico, Jalisco, Ameca, 4000 ft. (1219 m). DISTRIBUTION: S. Nayarit and N.W. Jalisco (Mexico). COMMENT: Subgenus Reithrodontomys; see Hooper, 1952, Mise. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047008001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 461, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Elimination of 137-Cs and 59-Fe by three species of wild rodents was measured in laboratory and field experiments to determine whether excretion rates of these nuclides are influenced directly by general metabolic (CO-2 production) rates. Sigmodon hispidus and Peromyscus leucopus were used in both field and laboratory experiments, and Reithrodontomys humulis was investigated only in the laboratory. Final-component biological half-lives (Tb) of 59-Fe for Sigmodon averaged 108 days in winter, 144 days in spring, and means ranged from 176 to 242 days under various laboratory conditions (ambient temperature, cold-exposure, irradiation, and chemical metabolic inhibition); for Peromyscus, values were 50 days in winter 47 days in spring, and 289 days (at ambient temperature only) in the laboratory; for Reithrodontomys mean values ranged from 121 to 178 days at different laboratory treatment levels. Biological half-lives of final-component 137-Cs elimination for Sigmodon averaged 7.5 days in winter, 7.9 days in spring, and means ranged from 7.7 to 8.6 days at the different treatment levels in the laboratory. Laboratory mean values for Reithrodontomys ranged from 3.5 to 3.9 days. For Peromyscus, Tb values averaged 3.4 days in winter, 3.6 days in spring, and 3.5 days in the laboratory. The data suggested that elimination of 59-Fe is influenced by metabolic rates of rodents in the field, but laboratory experiments were unable to demonstrate any predictable relationship. Neither did the rate of final-component 137-Cs loss from rodents appear to be influenced by metabolic rate in the laboratory or in the field. However, final-component Y-axis intercept values of 137-Cs exhibited a linear correlation with metabolic rates, and equations were derived from these intercept values to predict metabolism in the field for two species: for Sigmodon, Daily Average CO-2 Production (ml/hr/g, STP) [5.24-0.9172 (log-ea)] [0.886]; and for Reithrodontomys, = [12.51-1.80 (log-ea)] [0.886].

Reithrodontomys chrysopsis Merriam, 1900. Proc. Biol. Soc. Wash., 13: 152. TYPE LOCALITY: Mexico, Volcan Popocatepetl, 11,500 ft. (3505 m). DISTRIBUTION: S.E. Jalisco to W.C. Veracruz (Mexico). COMMENT: Subgenus Reithrodontomys; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047003001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 460, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Reithrodontomys sumichrasti (Saussure, 1861). Rev. Mag. Zool. Paris, ser. 2, 13:3. TYPE LOCALITY: Mexico, Veracruz, Mirador. DISTRIBUTION: W. Panama to N. Costa Rica; N.W. Nicaragua to S. Tabasco (Mexico); C. Guerrero to S. Oaxaca to C. Veracruz to S. San Luis Potosi and S.W. Jalisco (Mexico). COMMENT: Subgenus Reithrodontomys; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047016001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 462, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Reithrodontomys darienensis Pearson, 1939. Not. Naturae Acad. Nat. Sci. Phila., 6:1. TYPE LOCALITY: Panama, Darien, Santa Cruz de Cana, upper Rio Tuyra, 2000 ft. (610 m). DISTRIBUTION: Panama; perhaps N.W. Colombia. COMMENT: Subgenus Aporodon; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047005001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 460, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Reithrodontomys spectabilis Jones and Lawlor, 1965. Univ. Kans. Mus. Nat. Hist. Misc. Publ., 16(3):413. TYPE LOCALITY: Mexico, Quintana Roo, Cozumel Isl., 2.5 km N. San Miguel. DISTRIBUTION: Cozumel Isl. (Quintana Roo, Mexico). COMMENT: Subgenus Aporodon; see Carleton, 1980:15., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 462, DOI: 10.5281/zenodo.7353031, {"references":["Carleton, M. D. 1980. Phylogenetic relationships in neotomine-peromyscine rodents (Muroidea) and a reappraisal of the dichotomy within New World Cricetinae. Miscellaneous Publications, Museum of Zoology, University of Michigan, 157: 1 - 146."]}

Reithrodontomys rodriguezi Goodwin, 1943. Am. Mus. Novit., 1231:1. TYPE LOCALITY: Costa Rica, Cartago, Volcan de Irazu, 9400 ft. (2865 m). DISTRIBUTION: Known only from the type locality. COMMENT: Subgenus Aporodon; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047015001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 462, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Reithrodontomys mexicanas (Saussure, 1860). Rev. Mag. Zool. Paris, ser. 2, 12: 109. TYPE LOCALITY: Mexico, Veracruz, Mirador. DISTRIBUTION: Andes of W. Colombia and N. Ecuador; W. Panama to Oaxaca to Michoacan and S. Tamaulipas (Mexico). COMMENT: Subgenus Aporodon; see Hooper, 1952, Mise. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047011001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 461, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Reithrodontomys tenuirostris Merriam, 1901. Proc. Wash. Acad. Sci., 3:547. TYPE LOCALITY: Guatemala, Todos Santos, 10,000 ft. (3048 m). DISTRIBUTION: S. Guatemala. COMMENT: Subgenus Aporodon; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047017001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 462, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

In a band of semi-arid grasslands and shrublands of the high basins of the American Southwest, one can find impressive numbers of nocturnal rodents. Species are both diverse and abundant in the traps of the rodent ecologist. One family in particular, the Heteromyidae, a family endemic to North America, has particularly rich associations: its members are usually far more abundant than those of all other families combined and it quite often displays three of its species on the same patch of ground (less than 1/5 hectare) at the same time. In fact, associations of four or even five species are not infrequently encountered and there is a report in the literature of six species taken in about 1/2 hectare (Hoffmeister & Goodpaster, 1954). Often, associations of Heteromyidae are joined by various cricetines including members of the genera Peromyscus, Onychomys, Reithrodontomys, Baiomys, Sigmodon and Neotoma.

Reithrodontomys paradoxus Jones and Genoways, 1970. Occas. Pap. W. Found. Vert. Zool., 2: 12. TYPE LOCALITY: Nicaragua, Carazo, 3 mi. (5 km) N.N.W. Diriamba, about 660 m. DISTRIBUTION: W.C. Nicaragua; C. Costa Rica. COMMENT: Subgenus Aporodon; see Carleton, 1980:15., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 461, DOI: 10.5281/zenodo.7353031, {"references":["Carleton, M. D. 1980. Phylogenetic relationships in neotomine-peromyscine rodents (Muroidea) and a reappraisal of the dichotomy within New World Cricetinae. Miscellaneous Publications, Museum of Zoology, University of Michigan, 157: 1 - 146."]}

Reithrodontomys creper Bangs, 1902. Bull. Mus. Comp. Zool. Harv. Univ., 39:39. TYPE LOCALITY: Panama, Chiriqui, Volcan de Chiriqui, 11,000 ft. (3353 m). DISTRIBUTION: C. Costa Rica; W. Panama. COMMENT: Subgenus Aporodon; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047004001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 460, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Twelve study locations were established in nine habitat types in the vicinity of the proposed reference repository location. Eight species of small mammals were captured. Great Basin pocket mice (Perognathus parvus) comprised the majority of individuals captured, followed by deer mice (Peromyscus maniculatus), Northern pocket gopher (Thomomys talpoides), Western harvest mouse (Reithrodontomys megalotus), Grasshopper mouse (Onychomys leucogaster), Montane vole, (Microtus montanus), House mouse (Mus musculus), and the Bushy-tailed woodrat (Neotoma cinerea). Pocket mice were captured in all habitats sampled; deer mice were obtained in all habitats save hopsage and nearly pure cheatgrass stands. The highese capture rates were found in bitterbrush and riparian habitats. Capture sex ratios for both pocket mice and deer mice were significantly different from equality. Body weights for deer mice and pocket mice exhibited a great deal of heterogeneity across trap sites, although only the heterogeneity for pocket mice was significant. In general, body weights for both species were greater in the sagebrush habitats than elsewhere. These differences are interpreted in light of habitat evaluation methodologies. Six species of reptiles and one species of amphibian were captured. Side-blotched lizards (Uta stansburiana) were by far the most frequently captured species. The predominant snakes captured were the yellow-belliedmore » racer (Coluber constrictor) and the Great Basin gopher snake (Pituophis melanoleucus). Two Great Basin spadefoot toads (Scaphiopus intermontanus) captured at the Rattlesnake Springs trap site. Species diversity was quite low (Shannon-Wiener H )equals) 1.03). Side-blotched lizards were found in all habitats save near the talus on Gable Mountain and on the gravel pad site. The only other lizard species (northern sagebrush lizard (Sceloporus graciosus) and short-horned lizard (Phrynosoma douglasii)) were obtained in bitterbrush habitat. 20 refs., 1 fig., 9 tabs.« less

Reithrodontomys raviventris Dixon, 1908. Proc. Biol. Soc. Wash., 21: 197. TYPE LOCALITY: U.S.A., California, San Mateo Co., Redwood City. DISTRIBUTION: Vicinity of San Francisco Bay (California, U.S.A.). COMMENT: Subgenus Reithrodontomys; see Carleton, 1980:15. Subspecies raviventris and halicoetes thought to be in terminal stages of speciation; see Fisler, 1965, Univ. Calif. Publ. Zool., 77:1 -108, and Shellhammer, 1965, J. Mammal., 48:549-556. PROTECTED STATUS: U.S. ESA - Endangered. ISIS NUMBER: 5301410008047014001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 461, DOI: 10.5281/zenodo.7353031, {"references":["Carleton, M. D. 1980. Phylogenetic relationships in neotomine-peromyscine rodents (Muroidea) and a reappraisal of the dichotomy within New World Cricetinae. Miscellaneous Publications, Museum of Zoology, University of Michigan, 157: 1 - 146.","Fisler, G. F. 1965. Adaptations and speciation in harvest mice of the marshes of San Francisco Bay. University of California Publications in Zoology, 77: 1 - 108."]}

Reithrodontomys montanus (Baird, 1855). Proc. Acad. Nat. Sci. Phila., 7:335. TYPE LOCALITY: U.S.A., Colorado, either Saguache Co., upper end of San Luis Valley or Alamosa Co., Medaño Creek. DISTRIBUTION: N. Durango and N.E. Sonora (Mexico) to N.W. South Dakota, E.C. Texas, and S.W. Missouri (U.S.A.). COMMENT: Subgenus Reithrodontomys; see Hooper, 1952, Mise. Publ. Mus. Zool. Univ. Mich., 77:1 -255. For type locality information see Hall, 1981: 636. ISIS NUMBER: 5301410008047013001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 461, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255.","Hall, E. R. 1981. The mammals of North America. Second ed. John Wiley and Sons, New York, 1: 1 - 600 + 90, 2: 601 - 1181 + 90."]}

Reithrodontomys burti Benson, 1939. Proc. Biol. Soc. Wash., 52: 147. TYPE LOCALITY: Mexico, Sonora, Rio Sonora, Rancho de Costa Rica. DISTRIBUTION: C. Sinaloa to W.C. Sonora (Mexico). COMMENT: Subgenus Reithrodontomys; see Hooper, 1952, Misc. Publ. Mus. Zool. Univ. Mich., 77:1 -255. ISIS NUMBER: 5301410008047002001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 460, DOI: 10.5281/zenodo.7353031, {"references":["Hooper, E. T. 1952. A systematic review of harvest mice (genus Reithrodontomys) of Latin America. Miscellaneous Publications, Museum of Zoology, University of Michigan, 77: 1 - 255."]}

Reithrodontomys humulis (Audubon and Bachman, 1841). Proc. Acad. Nat. Sci. Phila., 1:97. TYPE LOCALITY: U.S.A., South Carolina, Charleston Co., Charleston. DISTRIBUTION: E. Texas and S.E. Oklahoma to S. Ohio, east to the Atlantic coast (U.S.A.). COMMENT: Subgenus Reithrodontomys; see Carleton, 1980:15, and Hall, 1981:637. ISIS NUMBER: 5301410008047009001., Published as part of James H. Honacki, Kenneth E. Kinman & James W. Koeppl, 1982, Order Rodentia (Part 3), pp. 392-476 in Mammal Species of the World (1 st Edition), Lawrence, Kansas, USA :Alien Press, Inc. & The Association of Systematics Collections on page 461, DOI: 10.5281/zenodo.7353031, {"references":["Carleton, M. D. 1980. Phylogenetic relationships in neotomine-peromyscine rodents (Muroidea) and a reappraisal of the dichotomy within New World Cricetinae. Miscellaneous Publications, Museum of Zoology, University of Michigan, 157: 1 - 146.","Hall, E. R. 1981. The mammals of North America. Second ed. John Wiley and Sons, New York, 1: 1 - 600 + 90, 2: 601 - 1181 + 90."]}

Metabolic rates of certain tissues of a shrew, Cryptotis , were lower than had been expected in view of the high total metabolism characteristic of shrews. Similar trends were shown in the rodent Reithrodontomys. The depression of metabolism of some tissues that was observed in these very small mammals may aid them in conserving energy during periods of inactivity.

WILD species of rodents are reported to be more resistant to acute radiation exposure than laboratory strains1. The LD50(30) acute exposure dose for the old-field mouse (Peromyscus polionotus), the cotton mouse (Peromyscus gossypinus) and the harvest mouse (Reithrodontomys humilis) is 1,100 to 1,200 r., for the cotton rat (Sigmodon hispidus) 1,200 to 1,500 r. and for pocket mice (Perognathus formosus and P. longimembris) 1,300 to 1,500 r.2–4. LD50(30) values for laboratory rodents range from 450 to 850 r. when the radiation is delivered as a single acute dose5. Ecologists have tended to interpret this as an advantage conferred by the “wild” condition. Chronic exposure over a long time is, however, less damaging than the same dose given in a short time5, but new results show that wild mice are quite sensitive to damage from chronic exposure in terms of life shortening and reduced fertility.

Relationships between diet of bobcats (Lynx rufus) and season, region, age, and sex were studied in Arkansas, based on contents of 150 stomachs collected between June 1970 and April 1972. Rabbits (Sylvilagus sp.), squirrels (Sciurus niger, S. carolinensis, Tamias striatus, Glaucomys volans), and rats and mice (Sigmodon hispidus, Neotoma floridana, Peromyscus sp., Microtus pinetorum, Reithrodontomys sp.) were found in 39, 22, and 21 percent of stomachs, respectively. Consumption of rabbits and deer (Odocoileus virginianus) peaked in autumn. Occurrence of rabbits (P < 0.025) and rats and mice (P < 0.01) was greater in stomachs from the Gulf Coastal Plain region; occurrence of squirrels (P < 0.005) was greater in the Interior Highlands. Diets of kittens, juveniles, and adults were similar. Occurrence of rats and mice was greater in females than in males (P < 0.025), suggesting that females selected smaller or more abundant

The extent of competition between deer mice, Peromyscus maniculatus, and western harvest mice, Reithrodontomys megalotis, was assessed by a species removal experiment conducted on a relict grassland in Ellis County, Kansas. Vegetation was sampled to determine microhabitats. There was no indication of ecological release for either species when mouse densities were manipulated. Vegetational analysis revealed significant differences in microhabitats utilized by the two species. The cricetine rodent component of the Mixed Prairie in Ellis County, Kansas, consists primarily of two species, deer mice (Peromyscus maniculatus) and western harvest mice (Reithrodontomys megalotis). Both are found in all communities of the mixed grass prairie. P. maniculatus is most abundant in big bluestem-little bluestem communities (Fleharty, 1972; Hansen and Fleharty, 1974; Martin, 1960) whereas R. megalotis is captured most often in lush, weedy habitats and avoids open little bluestem communities (Fleharty, 1972; Martin, 1960). Diets of both species consist of seeds and insects (Brown, 1946). Research conducted in a remnant prairie in Kansas in the late 1960's (Fleharty, 1972) revealed asynchronous fluctuations in population densities of deer mice and western harvest mice. Densities of Peromyscus were greatest in autumn and winter and least in spring and summer, whereas densities of Reithrodontomys were greatest in winter and spring and least in autumn. These asynchronous fluctuations and the fact that both species rely heavily on seeds as a food source suggested the existence ofinterspecific competition. Interspecific competition also has been suggested between the related species Peromyscus gossipinus and Reithrodontomys humilis (Packard, 1968). The purpose of this study was to determine if competition influences fluctuations in density and utilization of microhabitats in areas where deer mice and western harvest mice coexist. This content downloaded from 157.55.39.180 on Mon, 25 Apr 2016 07:05:58 UTC All use subject to http://about.jstor.org/terms VOLUME 91, NUMBERS 3-4 133 MATERIALS AND METHODS The study was conducted on a 14.2-ha remnant grassland located in the southeastern quarter of section 1, T1 4S, R19W, Ellis County, Kansas. This area was described by Martin (1960) and Brock (1968). Six 75 x 75-m plots were established in February 1985. The plots were isolated from surrounding habitats and one another by 15-m mowed strips (Cameron, 1977) except that four plots (3 through 6) were not mowed on one side because adjacent pastures were heavily grazed. Each plot contained 36 trap stations arranged in grid fashion, spaced at 15-m intervals. Trapping was initiated in March 1985 and was conducted monthly through February 1986. A Sherman live trap (7.6 x 8.9 x 22.9 cm) baited with a mixture of rolled oats, raisins, and peanut butter was placed at each station. Traps were set for five consecutive nights during the new moon phase in each census period. Sex was determined and toes were clipped for each captured animal to facilitate future identification. Plots were divided into three treatments with two replications. Deer mice, P. maniculatus, were removed from two plots (2 and 4), harvest mice, R. megalotis, were removed from two plots (3 and 6), and two plots were used as controls (1 and 5). The decision as to which plot would receive which treatment was based on preliminary trapping. The number of rodents occurring on each grid was estimated for each month using the "minimum number known to be alive" method (Krebs, 1966). Microhabitats were characterized by sampling three vegetational variables: plant height at each trap station, mean litter depth at each trap station, and species composition of plants around each trap. Plant height was sampled in June and September with a forage disk (Sharrow, 1984). Four litter-depth samples were measured at right angles 20 cm from each trap and averaged to give mean litter depth. Species composition of plants was obtained using the modified step-point procedure (Owensby, 1973). Eight points, 45 cm from the trap, were sampled in a circular fashion at each station to determine plant frequencies. Trap sites were classified into associations based on plant frequencies using principal component analysis (Ray, 1982) as described by Jeffers (1978) and Greig-Smith (1983). Only plants with frequencies of 20 percent or more were included in principal component analysis. Product moment correlation coefficients (Sokal and Rohlf, 1973) were used to determine to what extent P. maniculatus and R. megalotis were associated with plant species, litter depth, and plant height. Seasonal correlation between mice species was also calculated.

Responses of fulvous harvest mice (Reithrodontomys fulvescens) to habitat patchiness were investigated by experimentally creating 0.2-ha patches with or without a shrub layer. Results based on 555 captures of 230 individual harvest mice indicated that significantly more were captured in patches with shrubs. There were no differences in survival, movement or body mass between the patch types, but there was an excess of reproductive males in patches with shrubs removed on one of the experimental grids. Harvest mice may have avoided the patches with shrubs removed because of a lack of vertical structure which facilitated avoidance of cotton rats inhabiting the same patches, or because of a decrease in insect prey. INTRODUCTION The fulvous harvest mouse (Reithrodontomys fulvescens) is a codominant rodent on the Texas coastal prairie with the hispid cotton rat (Sigmodon hispidus) Uoule and Cameron, 1975). Relatively few population studies have been conducted on this species since Packard's (1968) initial ecological study in E Texas. Several recent studies on the Texas coastal prairie used species removal techniques to ascertain the role of interspecific interactions on resource utilization by R. fulvescens and S. hispidus Uoule and Jameson, 1972; Cameron, 1977a; Joule and Cameron, 1980; Cameron and Kincaid, 1982; Kincaid and Cameron, 1982a). Other aspects of the biology of the fulvous harvest mouse were reviewed by Spencer and Cameron (1982). Reithrodontomys fulvescens was more of a habitat generalist when contrasted with the narrow requirements of the other common coastal prairie rodents, Sigmodon hispidus and the rice rat (Oryzomys palustris) (Kincaid et al., 1983). Reithrodontomys habitat, unlike that of Sigmodon or Oryzomys, was characterized by a positive association with Baccharis halimifolia (sea myrtle), a common shrub on the coastal prairie. Little bluestem grass (Schizachyrium scoparium) was found in association with Baccharis in areas heavily used by R. fulvescens. A related study found that Reithrodontomys were trapped more frequently in Baccharis (by traps set in bushes) in the presence of cotton rats than in areas where cotton rats had been removed; in the latter areas, harvest mice used the ground more frequently (Cameron and Kincaid, 1982). These findings suggested that shrubs are an important component of the habitat of the fulvous harvest mouse. The object of this study was to determine the response of fulvous harvest mice to a patchy habitat created by removing shrubs. In particular, we tested the following hypothesis: that Reithrodontomys density, survival, movement and reproduction differed in areas where shrubs were removed because of decreased cover. In addition, we present new information on the demography of Reithrodontomysfulvescens. METHODS This study was conducted from February 1979 through October 1980 at the University of Houston Coastal Center, 56 km SE of Houston, Texas. To study population dynamics of harvest mice in relation to habitat patchiness, demographic monitoring was conducted on two 1.6-ha fields (Grids 1 and 2). These fields were separated by more than 100 m of low-lying area and were bounded on the N by a mowed fence line and on the S by a water-filled drainage ditch. They were dominated by Schizachyrium scoparium (little bluestem grass), Tripsacum dactyloides (eastern gamagrass) and Spartina spartinae

CONTEXT AND CONTENT. Order Rodentia, Family Cricetidae (considered by some to be only a subfamily of Muridae), Subfamily Cricetinae. The genus Reithrodontomys, which occurs in the New World from southern Canada (in the west), the western Great Lakes states, and the Mid-Atlantic region southward to northwestern South America, contains two subgenera, Reithrodontomys and Aporodon. R. brevirostris is included in the latter and therein in the R. mexicanus group. Two subspecies are recognized

Live-trapping data were analyzed to determine size of the home range of the fulvous harvest mouse (Reithrodontomysfulvescens). Analyses of 381 home ranges showed that males, in general, had larger home ranges than females and that larger animals occupied larger home ranges. Estimates of home range size were affected by both number of captures and length of the capture history of the animal. Smaller home ranges in this study compared to others may have been due to differences in habitat, trapping techniques or home range measurement. Interspecific interactions with the hispid cotton rat (Sigmodon hispidus) did not affect home range area but variation in habitat composition did. Larger home ranges in fields that contained larger proportions of shrubs could indicate that shrubs were used as a source of insect prey, for avoiding interactions with hispid cotton rats, or both.

The effects of interspecific interactions on movements of hispid cotton rats (Sigmodon hispidus) and fulvous harvest mice (Reithrodontomys fulvescens) were examined by experimental removal of species. For both Sigmodon and Reithrodontomys, the average distance moved by individuals (AvD,) was greater for males than females. The average distance moved by the population within trap periods (AvD,) was negatively correlated with Sigmodon density only in a field with low resource abundance whereas the AvDp for Reithrodontomys was negatively correlated with density in all fields. Species removal did not affect AvDp of either species. Seasonal differences in AvDp for R. fulvescens suggested an intraspecific effect on movement. Reithrodontomys used the vertical component of the habitat to a significantly greater extent when Sigmodon was present. There was no difference between experimental and control fields in vertical habitat structure, suggesting an interspecific effect of Sigmodon upon movement of Reithrodontomys. Variation in movement may result from differences in available habitat for Sigmodon, but not for Reithrodontomys.

Three trapping grids, 225 m on a side, where established in the desert of southern New Mexico. On grid I all Dipodomys (Heteromyidae, Rodentia) were removed; on grid 2 all Perognathus (Heteromyidae, Rodentia) were removed; and on grid 3 no rodents were removed. All grids were censused at two-week intervals for six weeks. When the larger Dipodomys (40g) were removed, the Perognathus (15g) population increased 2.56-fold (from 27 to 69 individuals) in two weeks. Removal of Perognathus had no effect on numbers of Dipodomys. Our data allow us to estimate the magnitude of the competition between Dipodomys and Perognathus. About 45 species of heteromyid rodents inhabit the southwestern deserts of North America. Most of these taxa belong to the genera Dipodomys (kanga- roo rats) and Perognathus (pocket mice). All are nocturnal, burrowing, lar- gely granivorous rodents with cheek pouches. At localities of greatest diver- sity, four or five species live syntopically (Brown, 1975). Coexistence in these ecologically similar rodents offers the opportunity to test a basic tenet of competition theory: to what extent can competing spe- cies coexist (Volterra, 1928; Gause, 1934; Levins, 1968; MacArthur and Lev- ins, 1968; May, 1973)? In response to this question, much of the research on heteromyids has centered on quantification of methods of niche separation among syntopic species (Brown, 1975; Lemen and Rosenzweig, 1978; Won- dolleck, 1978; Price, 1978). Relatively few studies (Munger and Brown, 1981; Schroder and Rosenz- wig, 1975) actually try to measure competition directly. Schroder and Rosenzweig (1975) removed rodents from large study plots with the surpris- ing result that little competition exists between two coexisting species of similar size. They concluded that competition had been important in the past, but is not presently affecting interspecific interactions. Munger and Brown (1981) demonstrated the existence of competition in coexisting desert rodents by documenting an increase in the density of small rodents, Perog- nathus (7-17g), Reithrodontomys (1 g) and Peromyscus (17g), in response to the removal of Dipodomys (40g). However, this increase in the density of Perognathus took place only after Dipodomys has been kept off experimen- tal plots for 8 months. We have concentrated on short-term effects of density perturbations. Schroder and Rosenzweig (1975) found it difficult to lower a species' density because after removing most individuals from an experimental grid other individuals of that same species took their places, often within two weeks. This might indicate an intraspecific mechanism for adjusting local popula- tion density that worked very quickly. Our goal was to determine if there is a corresponding short-term mechanism acting intergenerically as well. Here we report an additional experiment to determine the effects of removal on population densities of coexisting heteromyids.