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Resumen: La estructura de una comunidad biologica esta conformada por atributos como la composicion, la riqueza y la abundancia de las especies, e influenciada por los cambios temporales y espaciales, que a su vez, se refleja en la composicion y abundancia de especies de dicha comunidad. El objetivo fue evaluar la variabilidad temporal y espacial de la comunidad de pequenos mamiferos en la selva seca de Chamela, Jalisco, considerando los dos tipos de vegetacion predominantes (selva baja y selva mediana). El muestreo abarco 18 anos y la informacion generada se compilo en una base de datos, en la que se incluyen los registros de precipitacion de los mismos periodos. Con los datos obtenidos se concluye que la abundancia anual de especies vario ano con ano, registrandose 13 especies de pequenos mamiferos en el area ( Tlacuatzin canescens , Megasorex gigas , Spilogale pygmaea , Liomys pictus , Oryzomys melanotis , O. couesi , Nyctomys sumichrasti, Reithrodontomys fulvescens , Osgoodomys banderanus , Peromyscus perfulvus , Baiomys musculus , Sigmodon mascotensis y Xenomys nelsoni ). A pesar de que la estructura y cambios temporales de la vegetacion modificaron de forma distinta a cada tipo de selva, la composicion fue igual para ambas, no obstante la selva mediana es mas rica y diversa en especies que la selva baja. Esta estructura de la comunidad de pequenos mamiferos mostro una variacion a largo plazo tanto en composicion como en riqueza. Por lo que las caracteristicas de la region de Chamela, permiten la coexistencia de las especies haciendo un uso diferencial del habitat. Palabras clave: Pequenos mamiferos, comunidad, selvas secas, Jalisco, Mexico. Abstract: The structure of a biological community consists of attributes such as composition, richness and abundance of species, and influenced by the temporal and spatial changes, which in turn is reflected in the composition and abundance of species of that community. The objective was to evaluate the temporal and spatial variability of the community of small mammals in the dry forest of Chamela, Jalisco, considering the two predominant types of vegetation (lowland and tropical forest). The sample comprised 18 and the information generated is compiled in a database, which includes the precipitation records the same periods. The data obtained showed that the annual abundance of species varied from year to year, recorded 13 species of small mammals in the area ( Tlacuatzin canescens , Megasorex gigas , Spilogale pygmaea , Liomys pictus , Oryzomys melanotis , O. couesi , Nyctomys sumichrasti , Reithrodontomys fulvescens , Osgoodomys banderanus , Peromyscus perfulvus , Baiomys musculus , Xenomys nelsoni and Sigmodon mascotensis ). Although the structure and temporal changes of vegetation changed differently for each type of forest, the composition was the same for both, despite the tropical forest is richer and more diverse in the lowland species. The community structure of small mammals showed a long-term variation in composition and in wealth. So that the characteristics of the region of Chamela allow coexistence of species making a differential use habitat. Key words: small mammals, community, dry forest, Jalisco, Mexico.

Reithrodontomys spectabilis Jones and Lawlor, 1965. Univ. Kansas Pubi., Mus. Nat. Hist., 16:413. TYPE LOCALITY: Mexico, Quintana Roo, Isla Cozumel, 2.5 km N San Miguel. DISTRIBUTION: Restricted to Cozumel Island, Mexico. COMMENTS: Subgenus Aporodon, mexicanus species group. A large insular species, perhaps sharing common ancestry with R. gracilis (Jones and Lawlor, 1965). See Jones (1982, Mammalian Species, 193)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 742, DOI: 10.5281/zenodo.7353098, {"references":["Jones, J. K., Jr., and T. E. Lawlor. 1965. Mammals from Isla Cozumel, Mexico, with description of a new species of harvest mouse. University of Kansas Publications, Museum of Natural History, 16: 409 - 419."]}

Reithrodontomys burti Benson, 1939. Proc. Biol. Soc. Washington, 52:147. TYPE LOCALITY: Mexico, Sonora, Rio Sonora, Rancho de Costa Rica. DISTRIBUTION: WC Sonora to C Sinaloa, Mexico. COMMENTS: Subgenus Reithrodontomys, megalotis species group. A relict species having close affinity to R. montanus (Hooper, 1952)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 740, DOI: 10.5281/zenodo.7353098, {"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 creper Bangs, 1902. Bull. Mus. Comp. Zool., 39:39. TYPE LOCALITY: Panama, Chiriqui Prov., Volcan de Chiriqui, 11,000 ft. DISTRIBUTION: Upper elevations in Cordilleras Central and Talamancae, Costa Rica, to Chiriqui region, W Panama. COMMENTS: Subgenus Aporodon, tenuirostris species group., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on pages 740-741, DOI: 10.5281/zenodo.7353098

Reithrodontomys mexicanus (Saussure, 1860). Rev. Mag. Zool. Paris, Ser. 2, 12:109. TYPE LOCALITY: Mexico, Veracruz, Mirador (as restricted by Hooper, 1952:140). DISTRIBUTION: S Tamaulipas and WC Michoacan, Mexico, south through Middle American highlands to W Panama; Andes of W Colombia and N Ecuador. SYNONYMS: cherrii, costaricensis, garichensis, goldmani, howelli, jalapae, lucifrons, minusculus, ocotepequensis, orinus, potrerograndei, riparius, scansor. COMMENTS: Subgenus Aporodon, mexicanus species group., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on pages 741-742, DOI: 10.5281/zenodo.7353098, {"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 raviventris Dixon, 1908. Proc. Biol. Soc. Washington, 21:197. TYPE LOCALITY: USA, California, San Mateo Co., Redwood City. DISTRIBUTION: Salt marshes around San Francisco Bay, California, USA. STATUS: U.S. ESA and IUCN - Endangered. SYNONYMS: halicoetes. COMMENTS: Subgenus Reithrodontomys, megalotis species group. Morphological and chromosomal differentiation between the subspecies raviventris and halicoetes thought to represent terminal stages of speciation (Fisler, 1965; Shellhammer, 1967). Banded chromosomes and genic data reveal sister-group relationship to R. montanus (Hood et al., 1984; Nelson et al., 1984). See Shellhammer (1982, Mammalian Species, 169)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 742, DOI: 10.5281/zenodo.7353098, {"references":["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.","Shellhammer, H. S. 1967. Cytotaxonomic studies of the harvest mice of the San Francisco Bay region. Journal of Mammalogy, 48: 549 - 556.","Nelson, K., R. J. Baker, H. S. Shellhammer, and R. K. Chesser. 1984. Test of alternative hypotheses concerning the origin of Reithrodontomys raviventris: Genetic analysis. Journal of Mammalogy, 65: 668 - 673.","Shellhammer, H. S. 1982. Reithrodontomys raviventris. Mammalian Species, 169: 1 - 3."]}

Reithrodontomys chrysopsis Merriam, 1900. Proc. Biol. Soc. Washington, 13:152. TYPE LOCALITY: Mexico, Mexico, Volcan Popocatepetl, 11,500 ft. DISTRIBUTION: Transverse Volcanic Range, SE Jalisco to WC Veracruz, Mexico. SYNONYMS: colimae, orizabae, perotensis, tolucae. COMMENTS: Subgenus Reithrodontomys, megalotis species group., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 740, DOI: 10.5281/zenodo.7353098

Reithrodontomys tenuirostris Merriam, 1901. Proc. Washington Acad. Sci., 3:547. TYPE LOCALITY: Guatemala, Huehuetenango Dept., Todos Santos, 10,000 ft. DISTRIBUTION: Mountains of S Chiapas, Mexico, and C Guatemala. SYNONYMS: aureus. COMMENTS: Subgenus Aporodon, tenuirostris species group., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on pages 742-743, DOI: 10.5281/zenodo.7353098

Reithrodontomys gracilis J. A. Allen and Chapman, 1897. Bull. Am. Mus. Nat. Hist., 9:9. TYPE LOCALITY: Mexico, Yucatan, Chichen-Itza. DISTRIBUTION: Yucatan Peninsula and coastal Chiapas, Mexico, south along Pacific watershed to NW Costa Rica. SYNONYMS: anthonyi, harrisi, insularis, pacificus. COMMENTS: Subgenus Aporodon, mexicanus species group. See Young and Jones (1984, Mammalian Species, 218)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 741, DOI: 10.5281/zenodo.7353098, {"references":["Young, C. J., and J. K. Jones, Jr. 1984. Reithrodontomys gracilis. Mammalian Species, 218: 1 - 3."]}

Reithrodontomys brevirostris Goodwin, 1943. Am. Mus. Novit., 1231:1. TYPE LOCALITY: Costa Rica, Alajuela Prov., canyons above Villa Quesada, 5000 ft. DISTRIBUTION: Allopatric populations in highlands of NC Nicaragua (see Jones and Genoways, 1970) and C Costa Rica. SYNONYMS: nicaraguae. COMMENTS: Subgenus Aporodon, mexicanus species group. See Jones and Baldassarre (1982, Mammalian Species, 192)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 740, DOI: 10.5281/zenodo.7353098, {"references":["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.","Jones, J. K., Jr., and G. A. Baldassarre. 1982. Reithrodontomys brevirostris and Reithrodontomys paradoxus. Mammalian Species, 192: 1 - 3."]}

Reithrodontomys humulis (Audubon and Bachman, 1941). Proc. Acad. Nat. Sci. Philadelphia, 1:97. TYPE LOCALITY: USA, South Carolina, Charleston Co., Charleston. DISTRIBUTION: SE USA, from SE Oklahoma and E Texas east to the Atlantic seaboard, from S Maryland to C peninsular Florida. SYNONYMS: carolinensis, dickinsoni, impiger, lecontii, merriami, virginianus. COMMENTS: Subgenus Reithrodontomys, megalotis species group. Karyotype departs markedly from other species of megalotis group (Carleton and Myers, 1979; Engstrom et al., 1981)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 741, DOI: 10.5281/zenodo.7353098, {"references":["Carleton, M. D., and P. Myers. 1979. Karyotypes of some harvest mice, genus Reithrodontomys. Journal of Mammalogy, 60: 307 - 313."]}

Reithrodontomys microdon Merriam, 1901. Proc. Washington Acad. Sci., 3:548. TYPE LOCALITY: Guatemala, Huehuetenango Dept., Todos Santos, 10,000 ft. DISTRIBUTION: Isolated pockets in highlands of N Michoacan and Distrito Federal, N Oaxaca, and C Chiapas, Mexico, and WC Guatemala. SYNONYMS: albilabris, wagneri. COMMENTS: Subgenus Aporodon, tenuirostris species group., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 742, DOI: 10.5281/zenodo.7353098

Reithrodontomys sumichrasti (Saussure, 1861). Rev. Mag. Zool. Paris, Ser. 2, 13:3. TYPE LOCALITY: Mexico, Veracruz, Mirador (as restricted by Hooper, 1952:72). DISTRIBUTION: Allopatric segments in Middle American highlands: SW Jalisco and S San Luis Potosi to C Guerrero and EC Oaxaca, Mexico; C Chiapas, Mexico, to NC Nicaragua; C Costa Rica to W Panama. SYNONYMS: alleni, australis, dorsalis, luteolus, modestus, nerterus, otus, rufescens, seclusus, underwoodi, vulcanius. COMMENTS: Subgenus Reithrodontomys, megalotis species group., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 742, DOI: 10.5281/zenodo.7353098, {"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 fulvescens J. A. Allen, 1894. Bull. Am. Mus. Nat. Hist., 6:319. TYPE LOCALITY: Mexico, Sonora, Oposura, 2000 ft. DISTRIBUTION: SC Arizona to SW Missouri to WC Mississippi, USA, south through Mexico, to W Nicaragua; excluding Yucatan Peninsula and Caribbean coastal lowlands. SYNONYMS: amoenus, aurantius, canus, chiapensis, chrysotis, difficilis, griseoflavus, helvolus, inexspectatus, infernatis, intermedius, laceyi, mustelinus, nelsoni, tenuis, toltecus, tropicalis. COMMENTS: Subgenus Reithrodontomys, fulvescens species group. Chromosomal complement (2n=50) interpreted as primitive for the genus (Robbins and Baker, 1980). See Spencer and Cameron (1982, Mammalian Species, 174)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 741, DOI: 10.5281/zenodo.7353098, {"references":["Robbins, L. W., and R. J. Baker. 1980. G- and C-band studies on the primitive karyotype for Reithrodontomys. Journal of Mammalogy, 61: 708 - 714.","Spencer, S. R., and G. N. Cameron. 1982. Reithrodontomys fulvescens. Mammalian Species, 174: 1 - 7."]}

Reithrodontomys darienensis Pearson, 1939. Not. Naturae, Acad. Nat. Sci. Philadelphia, 6:1. TYPE LOCALITY: Panama, Darien Prov., Santa Cruz de Cana, upper Rio Tuyra, 2000 ft. DISTRIBUTION: E Panama, including Azuero Peninsula, and perhaps adjacent Colombia. COMMENTS: Subgenus Aporodon, mexicanus species group. Hooper (1952) viewed R. darienensis as closely related to R. gracilis., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 741, DOI: 10.5281/zenodo.7353098, {"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 Giglioli, 1874. Bull. Soc. Geogr. Ital., Roma, 11:326. TYPE SPECIES: Reithrodon megalotis Baird, 1858. SYNONYMS: Aporodon, Ochetodon. COMMENTS: Peromyscine. Alpha taxonomy revised by Allen (1895a), Howell (1914), and Hooper (1952), the last of whom framed the currently-used subgeneric division and species groupings. Distributions and species limits of Latin American harvest mice, especially those of the subgenus Aporodon, require renewed systematic attention. Generic relationships investigated by Carleton (1980), Hooper and Musser (1964a), and J. C. Patton et al. (1981). For comparative studies of morphology, see Arata (1964), Carleton (1973, 1980), and Hooper (1952, 1959); of karyology, see Carleton and Myers (1979), Engstrom et al. (1981), Hood et al. (1984), and Robbins and Baker (1980); of genic variation, see Nelson et al. (1984). A key to the species is found in Spencer and Cameron (1982)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 740, DOI: 10.5281/zenodo.7353098, {"references":["Allen, J. A. 1895 a. On the species of the genus Reithrodontomys. Bulletin of the American Museum of Natural History, 7: 107 - 143.","Howell, A. H. 1914. Revision of the American harvest mice (genus Reithrodontomys). North American Fauna, 36: 1 - 97.","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.","Hooper, E. T., and G. G. Musser. 1964 a. The glans penis in Neotropical cricetines (Family Muridae) with comments on classification of muroid rodents. Miscellaneous Publications, Museum of Zoology, University of Michigan, 123: 1 - 57.","Arata, A. 1964. The anatomy and taxonomic significance of the male accessory reproductive glands of muroid rodents. Bulletin of the Florida State Museum, Biological Sciences, 9: 1 - 42.","Carleton, M. D. 1973. A survey of gross stomach morphology in New World Cricetinae (Rodentia, Muroidea), with comments on functional interpretations. Miscellaneous Publications, Museum of Zoology, University of Michigan, 146: 1 - 43.","Hooper, E. T. 1959. The glans penis in five genera of cricetid rodents. Occasional Papers of the Museum of Zoology, University of Michigan, 613: 1 - 11.","Carleton, M. D., and P. Myers. 1979. Karyotypes of some harvest mice, genus Reithrodontomys. Journal of Mammalogy, 60: 307 - 313.","Robbins, L. W., and R. J. Baker. 1980. G- and C-band studies on the primitive karyotype for Reithrodontomys. Journal of Mammalogy, 61: 708 - 714.","Nelson, K., R. J. Baker, H. S. Shellhammer, and R. K. Chesser. 1984. Test of alternative hypotheses concerning the origin of Reithrodontomys raviventris: Genetic analysis. Journal of Mammalogy, 65: 668 - 673.","Spencer, S. R., and G. N. Cameron. 1982. Reithrodontomys fulvescens. Mammalian Species, 174: 1 - 7."]}

Reithrodontomys hirsutus Merriam, 1901. Proc. Washington Acad. Sci., 3:553. TYPE LOCALITY: Mexico, Jalisco, Ameca, 4000 ft. DISTRIBUTION: SC Nayarit and NW Jalisco, Mexico. SYNONYMS: levipes. COMMENTS: Subgenus Reithrodontomys, fulvescens species group., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 741, DOI: 10.5281/zenodo.7353098

Reithrodontomys zacatecae Merriam, 1901. Proc. Washington Acad. Sci., 3:557. TYPE LOCALITY: Mexico, Zacatecas, Sierra de Valparaiso. DISTRIBUTION: W Chihuahua to WC Michoacan, Mexico. SYNONYMS: obscurus. COMMENTS: Subgenus Reithrodontomys, megalotis species group. Hooper (1952) noted the phenetic distinction of zacatecae from R. megalotis saturatus in Jalisco and Michoacan but elected to retain it as a subspecies. Karyotypic divergence of zacatecae reported by Hood et al. (1984), who proposed its elevation to species. Distributional limits, morphological discrimination, and assignment of species-group synonyms deserve amplification., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 743, DOI: 10.5281/zenodo.7353098, {"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 paradoxus Jones and Genoways, 1970. Occas. Pap. W. Found. Vert. Zool., 2:12. TYPE LOCALITY: Nicaragua, Carazo Dept., 3 mi NNW Diriamba, about 660 m. DISTRIBUTION: Isolated records from SW Nicaragua and WC Costa Rica. COMMENTS: Subgenus Aporodon, mexicanus species group. Morphologically closest to R. brevirostris; extent of distribution unknown. See Jones and Baldassarre (1982, Mammalian Species, 192)., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 742, DOI: 10.5281/zenodo.7353098, {"references":["Jones, J. K., Jr., and G. A. Baldassarre. 1982. Reithrodontomys brevirostris and Reithrodontomys paradoxus. Mammalian Species, 192: 1 - 3."]}

Reithrodontomys rodriguezi Goodwin, 1943. Am. Mus. Novit., 1231:1. TYPE LOCALITY: Costa Rica, Cartago Prov., Volcan de Irazu, 9000 ft. DISTRIBUTION: Reported only from Volcan de Irazu, Costa Rica. COMMENTS: Subgenus Aporodon, tenuirostris species group., Published as part of Guy G. Musser & Michael D. Carleton, 1993, Order Rodentia - Family Muridae, pp. 501-755 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on page 742, DOI: 10.5281/zenodo.7353098

Three methods were tested for recovering Borrelia burgdorferi from live mice onto BSK II culture medium. Four laboratory-reared Peromyscus leucopus were inoculated intraperitoneally with the JD-1 isolate of Borrelia burgdorferi. Borrelia burgdorferi spirochetes were recovered from 13 of 20 (65%) samples taken by needle aspiration between days 7 and 40 post-inoculation (PI) and from 1 of 16 samples of skin obtained by ear punch biopsy during the same sampling period. Spirochetes were not recovered from culture media inoculated with mouse blood. The use of needle aspirates for recovering spirochetes was compared among three species of mice: P. leucopus, P. maniculatus, and Reithrodontomys fulvescens. Spirochetes were isolated from 14 of 15 aspiration samples from four P. maniculatus, 12 of 20 from three P. leucopus, and 15 of 20 from four R. fulvescens taken between days 7 and 48 PI. Spirochetes were isolated from only one aspiration sample between days 80 and 95 PI from any of the mice tested. Needle aspiration was an efficient method for repeated recovery of B. burgdorferi from live, experimentally infected mice. We also document R. fulvescens as an experimental host for B. burgdorferi. Based on their susceptibility to infection, all species of mice tested herein may play a role in the epidemiology of Lyme disease where their distribution is compatible with endemic transmission.

Small mammals were live-trapped in pickleweed (Salicornia virginica) habitats near San Francisco Bay, California in order to measure the uptake of several contaminants and to evaluate the potential effects of these contaminants on the endangered salt marsh harvest mouse (Reithrodontomys raviventris). Tissues of house mice (Mus musculus), deer mice (Peromyscus maniculatus), and California voles (Microtus californicus) from nine sites were analyzed for chemical contaminants including mercury, selenium, cadmium, lead, and polychlorinated biphenyls (PCBs). Concentrations of contaminants differed significantly among sites and species. Mean concentrations at sites where uptake was greatest were less than maximum means for the same or similar species recorded elsewhere. Harvest mice (Reithrodontomys spp.) were captured only at sites where concentrations of mercury or PCBs were below specific levels in house mice. Additional studies aimed at the protection of the salt marsh harvest mouse are suggested. These include contaminant feeding studies in the laboratory as well as field monitoring of surrogate species and community structure in salt marsh harvest mouse habitats.

1. 1. Mean urinary protein concentration levels are significantly higher in male Peromyscus leuopus than females (98.4 and 72.4 mg/dl). 2. 2. Only females showed a significant correlation between weight and urinary protein concentration ( r = 0.75 vs 4 = 0.03). 3. 3. In intraspecific sexual electrophoretic comparisons of P. leucopus and P. maiculatus non-denatured urinary protein, four and two common bands were identified, respectively. Males both species showed an extra protein band. 4. 4. Four common electrophoretically separable denatured urinary protein bands were observed between 14,200 and 116,000 mol. wt in male and female P. leucopus and female P. gossypinus . Three of the four major protein bands were also found in P. maniculatus . Male Reithrodontomys megaloits pattern showed none of the major bands.

Patterns of restriction-endonuclease site and length variation at the nuclear rDNA locus (18S + 28S rRNA gene complex) were examined in rodents. Of the 164 restriction sites mapped for seven species, 22 were conserved (mapping to the 18S, 28S, and 5.8S genes and ITS1) in all three Onychomys species as well as in Mus musculus and in three closely related peromyscine rodents, Peromyscus boylii, P. eremicus, and Reithrodontomys megalotis. The nontranscribed spacer (NTS) region revealed most of the variation among these taxa, with the patterns of variation grouping into the following categories, (1) intraindividual variation revealing as many as four site-specific repeat types within an individual, (2) intraspecific and interspecific site variation confined to the NTS, and (3) length variation in both the transcribed and NTS regions. Length variation in the 28S rRNA gene was also examined in 17 additional rodent species, and most size differences mapped to the divergent domain, D8, found in sequence comparisons between Mus and Rattus. The systematic implications of rDNA variation are discussed using the perspective gained from these rodent comparisons.

Resumen: En este trabajo damos a conocer la diversidad de mamiferos en el Parque Nacional Lagunas de Montebello, Chiapas, con informacion sobre su distribucion local por tipos de vegetacion, afinidad de distribucion geografica y estado de conservacion. Los datos se obtuvieron a traves de capturas y observaciones en el campo, completandose con informacion bibliografica y de bases de datos. Se registraron 52 especies de mamiferos silvestres, comprendidos en 7 ordenes, 18 familias y 41 generos, los ordenes mejor representados son Rodentia, Chiroptera y Carnivora. Las familias mas diversas son Muridae y Phyllostomyidae, y los generos mas diversos son Peromyscus y Reithrodontomys . Esta riqueza constituye el 11.2% del total de los mamiferos terrestres de Mexico y el 25.2% de los mamiferos de Chiapas. El 58% de las especies son nuevos registros para el Parque. La mastofauna de Montebello muestra una afinidad Neotropical con una buena representacion de especies mesoamericanas, incluyendo dos especies endemicas de Mexico. La comunidad mas diversa se encuentra en el bosque mesofilo de montana, mostrando un alto nivel de asociacion entre las especies y el tipo de vegetacion. Los mamiferos de Montebello estan poco representados en los diversos listados de estatus de conservacion, ya que algunas de las especies que aparecen en ellos ya estan localmente extintas del area. Palabras clave : mastofauna, diversidad, distribucion, estado de conservacion, Parque Nacional Lagunas de Montebello, Chiapas, Mexico. Abstract: In this paper we summarize the information available on diversity of mammals in the Lagunas de Montebello National Park, Chiapas, Mexico, including data about the local distribution by vegetation types, geographical affinity by their distribution ranges and conservation status. Data were obtained by captures and observations in the field, and were completed with bibliographical as well as data-base information. 52 species of native mammals were recorded, arranged in seven orders, 18 families and 41 genera. This species richness constitutes the 11.2% of terrestrial mammals of Mexico and the 25.2% of the mammal diversity of Chiapas. The 58% of the species are new records for the Park and the orders with more representation are Rodentia, Chiroptera and Carnivora. The more diverse families are Muridae and Phillostomyidae while the most species genera were Peromyscus and Reithrodontomys . The fauna of mammals of Montebello shows a Neotropical affinity and represents a high portion of Mesoamerican mammals including two Mexican endemic species. The most diverse community was encountered in the tropical mountain rainforest, showing a high association between species and the vegetation types. The mammals of Montebello have a relatively little representation in the different lists of conservational status due to the recently local extinctions of species from the area.

Resumen:En el presente trabajo se presentan las relaciones entre dieta y demografía de dos especies de roedores (Reithrodontomys fulvescens y Peromyscus aztecus) en un bosque mesófilo de montaña y en un área perturbada del occidente de México. La información se obtuvo mediante técnicas de captura-recaptura. Las especies difirieron en la densidad poblacional, abundancia y en el tiempo de reproducción. La actividad reproductiva de P. aztecus en bosque mesófilo alcanzó sus máximos valores a mitad de la estación lluviosa y en a mitad de la estación seca-fría en el área perturbada. R. fulvescens registró la mayor actividad reproductiva en la estación húmeda en ambos hábitats. La densidad de P. aztecus mantuvo fluctuaciones a lo largo de todo el año, con picos en los meses de enero y febrero. R. fulvescens mostró el mismo patrón de densidad en ambos hábitats con lo máximos valores al final de la estación húmeda. Los hábitos alimentarios y la sobreposición de la dieta fueron evaluados mediante técnicas microhistológicas. La dieta de P. aztecus en bosque mesófilo estuvo dominada por frutos de Solanaceae, Melastomataceae, Araliaceae y Myrsinaceae. Dicotiledóneas (hojas y tallos), semillas de monocotiledóneas (Zea diploperennis) y de dicotiledóneas (Lupinus y Acacia) dominaron la dieta en R. fulvescens. Los valores más altos de sobreposición de la dieta en bosque mesófilo ocurrieron en la estación húmeda (77.6%) y el valor menor en la estación seca-caliente (25.1%). Las características nutrimentales de la dieta mostraron variación estacional. No existió una relación evidente entre los diferentes nutrimentos y la reproducción.Abstract: The relationship between diet and demography of two rodents (Reithrodontomys fulvescens and Peromyscus aztecus) in clouded forest and disturbed area of western Mexico was described. A live-traps study was conducted to obtain information about population dynamics. Species varied in population density, relative abundance, and reproduction timing, which was seasonal. Reproductive activity for P. aztecus peaked in the middle of the wet season in the clouded forest and in the wet season and middle of the dry-cold season indisturbed areas. R. fulvescens showed reproductive activity in the wet season in both habitats. Density fluctuated annually for P. aztecus in both habitats, with a peak in January - February;R. fulvescens showed the same patterns of density in both habitats with the highest values at the end of the wet season. Food habits and dietary overlap were evaluated by microhistological techniques. The diet of P. aztecus in the clouded forest was dominated by dicot fruits of Solanaceae, Melastomataceae, Araliaceae, and Myrsinaceae species. In disturbed area this species did not prefer a particular food item. Dicots (leaves and stems) dominated the diet, but seeds of monocots (Zea diploperennis) and dicots (Lupinus and Acacia) were also included. Reithrodontomys fulvescens consumed dicots species (seeds, fruits, leaves and stems). The greatest dietary overlap between species occurred in cloud forest during the wet season (77.6%), with less overlap in the dry-hot season (35.2 %). High overlap occurred in disturbed area during the wet season (68.2 %) and low values in the dry-hot season (25.1 %). Nutritional characteristics of diets showed seasonal variation.Palabras clave: Peromyscus aztecus, Reithrodontomys fulvescens, ecología poblacional, hábitos alimentarios, reproducción, occidente de México.

Desert arroyos make up only 2-4% of the desert landscape but may be unique habitat for some wildlife species. Habitat suitability models for small mammals could indicate habitat condition in these uncommon areas and, through monitoring, provide a tool for arid lands wildlife management. During 1993 and 1994, we modeled habitat associations for 18 species of small mammals in 6 habitats associated with desert foothills in the Sacramento Mountains, New Mexico. Habitat associations of small mammals remained relatively consistent through time, although community abundance decreased 34% from spring 1993 to fall 1994. These habitat associations allowed us to use discriminant analysis to model habitat associations based upon designation of habitat as capable of supporting high, moderate, or low relative abundance. The procedure successfully classified 80-93% of habitats as supporting high, moderate, or low abundance of 13 species of heteromyid and murid rodents. Murid rodents (Peromyscus, Reithrodontomys, Neotoma, Sigmodon) were found primarily within arroyos where shrub diversity, canopy cover, and height were greatest compared to surrounding habitats. The modeling approach described herein should be useful to managers because stochastic temporal change in the relative abundance of small mammals is effectively removed from consideration.

RESUMEN. En este trabajo se reportan las preferencias de habitat, dinamica poblacional y estacionalidad repoductiva de Perognathus jlavus, Chaetodipus hispidus, C. nelsoni, C. penicillatus, Dipodomys ordii, D. merriami, Liomys irroratus, Reithrodontomys fulvescens, Peromyscus maniculatus, Onychomys arenicola y Sigmodon hispidus en asociacion con tres sistemas agricolas aridos, sus bordes y sus alrededores no cultivados, en el Altiplano de San Luis Potosi, Mexico. Al parecer, la cubierta herbacea es la caracteristica mas importante del habitat. Los roedores presentaron dos patrones estacionales diferentes: la mayoria tuvo el nivel poblacional mas alto durante el verano, aunque algunos lo presentaron en invierno. A pesar de las diferencias en la estacionalidad de la poblacion, todos los roedores tuvieron su pico reproductivo durante el verano, relacionado en alguna forma con la epoca de lluvias. ABSTRACT. This work reports on the habitat preferences, population dynamics and reproductive seasonality of Perognatusflavus, Chaetodipus hispidus, C. nelsoni, C. penicillatus, Dipodomys ordii. D. merriami, Liomys irroratus, Reithrodontomys fulvescens, Peromyscus maniculatus. Onychomys arenicola and Sigmodon hispidus in association with three dry farming systems and their unfarmed neighboring areas and borders, in the San Luis Potosi Plateau, Mexico. lt was found that herbaceaous cover seemed to be the most important habitat characteristic. Rodents presented two different seasonal patterns: most had their highest populations during the summer. But some did so during the winter. Despite differences in population seasonality, all rodents had their highest reproductive rates during the summer, related in some form with the rainy season. Palabras clave: San Luis Potosi, Mexico, roedores, dinamica poblacional.

Cross-transmission experiments were performed using oocysts of an Eimeria arizonensis-like coccidian from Peromyscus leucopus and Peromyscus truei, an E. arizonensis-like coccidian from Reithrodontomys fulvescens, Eimeria baiomysis and Eimeria taylori from Baiomys taylori, Eimeria albigulae from Neotoma albigula, and Eimeria onychomysis from Onychomys spp., between representatives of the above host genera. The E. arizonensis-like coccidian from R. fulvescens infected Reithrodontomys megalotis, Reithrodontomys montanus, and Peromyscus leucopus. Oocysts of E. arizonensis from P. leucopus could be transmitted to both P. leucopus and R. megalotus. Oocysts of E. baiomysis and E. taylori infected only B. taylori. Oocysts of E. arizonensis from P. truei infected P. truei but not Neotoma mexicana or Onychomys leucogaster. Oocysts of E. albigulae from N. albigula were infective for N. mexicana but not for P. truei or O. leucogaster. Oocysts of E. onychomysis from Onychomys spp. infected O. leucogaster but not N. mexicana or P. truei. These results demonstrate that Peromyscus and Reithrodontomys, genera known to be related very closely evolutionarily, are capable of sharing E. arizonensis, whereas morphologically similar coccidians (E. albigulae, E. baiomysis, and E. onychomysis) from more distantly related hosts, are probably distinct and more stenoxenous. This also is the first report of coccidians infecting species of Reithrodontomys.

Differential abilities of white-footed mice (Peromyscus leucopus), deer mice (P. maniculatus) and fulvous harvest mice (Reithrodontomys fulvescens) to find seeds covered by 0 and 75 g of litter were assessed during laboratory foraging trials. All individuals collected significantly fewer seeds in aquaria with litter. Mean percent reduction in seed harvest between 0 and 75 g of litter was significantly greater for P. leucopus than either P. maniculatus or R. fulvescens, which did not differ significantly. Mean grams of seeds harvested significantly decreased with increased amounts of litter (0, 25, 50, 75, 100 and 125 g) for P. leucopus and R. fulvescens. Interspecific differences for mean percent reduction in seed harvest for sparse (25 g) and deep/dense (100 and 125 g) litter were nonsignificant; however, seed harvest was significantly lower for P. leucopus than R. fulvescens in moderate litter (50 and 75 g). Our results imply that differences in the ability of grassland rodents to collect seeds in plant litter may be partially responsible for species-specific patterns of microhabitat

Small mammals were trapped monthly in wheat fields (Triticum aestivum1), fallow wheat fields, and grazed breaks prairie sites in Lincoln and Russell counties, Kansas from February 1983 to February 1984. The deer mouse (Peromnyscus maniculatus) was the most common species in each of the three habitats (94% of 559 individuals captured in wheat fields; 83% of 760 in fallow wheat fields; 86% of 528 in breaks prairie). Fallow field was the preferred habitat for deer mice, western harvest mice (Reithrodontomys inegalotis), cotton rats (Sigmnodon hispidus), and house mice (Mus musculus); breaks prairie for grasshopper mice (Onychomnys leucogaster) and hispid pocket mice (Chaetodipus hispidus); and wheat and fallow wheat fields for prairie voles (Alicrotus ochrogaster). Data from this and other studies in north-central Kansas suggest that conversion of native prairie to wheat production has shifted the abundance and composition of the assemblage of native prairie rodents. Changes associated with this shift included both greater abundance and greater numerical domination of the assemblage by deer mice, little effect on grasshopper mice, but a reduction in abundance and proportional contribution to the assemblage by western and plains harvest mice, pocket mice, prairie voles, and ground squirrels. One of the changes brought by human settlement was the conversion of forests and grasslands to crop fields, a change that undoubtedly had an impact on native wildlife species including small mammals (Fleharty and Navo, 1983; Houtcooper, 1978a; Navo and Fleharty, 1983; Whittaker, 1967). In north-central Kansas, approximately one-half of the native mixed-grass prairie was converted to cropland following settlement (based on Lincoln and Russell counties; Barker and Hamilton, 1985; Jantz et al., 1982). With increased concerns about the impacts of human activities on wildlife, it is necessary for biologists and conservationists to understand habitat distribution and requirements of native animals, including their use of agricultural lands. Only limited natural history and ecological data on the effects of various land practices are available for small mammals in Kansas. Such This content downloaded from 157.55.39.132 on Thu, 15 Sep 2016 05:48:50 UTC All use subject to http://about.jstor.org/terms VOLUME 93, NUMBERS 1-2 29 information is valuable for developing habitat management practices and for understanding how different land uses affect small mammals. Objectives, herein, are to assess and describe the use of wheat fields (Triticum aestivum) and fallow wheat fields by small mammals in north-central Kansas and to examine how the composition of the prairie rodent assemblage differs between native prairie and cropland used for wheat production. STUDY AREA AND METHODS Small mammals were censused using 150 traplines set in wheat fields, fallow wheat fields, and limestone breaks prairie in T 11S, R 11W; T1 iS, R12W; T12S, Ri 1W; and T12S, R12W in Russell County and TI IS, R10W in Lincoln County, Kansas. Each trapline consisted of 20 stations with a 15 m spacing between stations. Three Museum Special snap traps baited with peanut butter were placed at each station. Traps were set and checked for three consecutive nights each month from February 1983 to February 1984, with the full moon period of each month avoided. In March 1983, a heavy snow prevented the third night of trapping on two lines set in wheat fields, one in fallow field, and two in breaks prairie. Small mammals were censused with 50 traplines set in wheat fields (number of traplines set per month: 0, 4, 4, 4, 4, 4, 8, 4, 4, 4, 2, 4, 4); 49 traplines in fallow wheat fields (6, 5, 5, 3, 4, 2, 2, 4, 4, 4, 2, 4, 4); and 51 in grazed limestone breaks sites (4, 4, 4, 4, 4, 5, 4, 4, 4, 4, 2, 4, 4). Total trap nights were 8880 in wheat fields, 8760 in fallow fields, and 9060 in breaks prairie. Wheat fields consisted of growing wheat during March-May; standing wheat nearly ready to be harvested during June; standing wheat stubble for two lines and recently disked for two lines during July; standing wheat stubble for four lines and recently disked for four lines during August; wheat fields cultivated two or more times in preparation for fall planting during September-October; and growing wheat, planted in October, during NovemberFebruary. Fallow wheat fields in February-August were fields from which wheat had been harvested in late June to early July 1982 and September-February were fields from which wheat had been harvested in late June to early July 1983. During these censuses, sites with standing stubble were 3 of 6 lines in February 1983 and 2 of 5, 2 of 5, 3 of 3, 4 of 4, 0 of 2, 0 of 2, 4 of 4, 4 of 4, 4 of 4, 2 of 2, 2 of 4, and 3 of 4 in succeeding months. The limestone breaks sites were in mixed-grass prairie dominated by a bluestem-grama (Andropogon-Bouteloua) association (Barker and Hamilton, 1985; Kiichler, 1974). All prairie sites were grazed by cattle during the growing season and had been during most of the years since settlement. In breaks sites, traplines followed the curved outcropping of the limestone and, therefore, were not set as straight census lines as in the other two habitat

Sigmodon hispidus and Reithrodontomys fulvescens are the codominant rodent species of the Texas coastal prairie. Eight isolated 1.6 hectare replicated plots were used to study dispersal strategies of these rodents. Each replicate was live-trapped for nineteen months. For two control replicates all captured individuals were identified, sexed, weighed, marked, and released. In two perturbed replicates all Reithrodontomys were removed, in two perturbed replicates all Sigmodon were removed, and in two other perturbed replicates both species were removed. Monthly dispersal of individuals into plots where that species was previously removed was measured. The number of dispersers of both sexes of Sigmodon and Reithrodontomys were positively correlated with monthly changes in control (resident) density. Sex ratio comparisons between dispersers and residents reflected nonsignificant differences for both species. The rank-order of weight (age) classes of dispersers was positively correlated with the classes found in control plots for female Sigmodon and male Reithrodontomys entering both types of perturbed conditions. Pre-emption by Reithrodontomys appeared to inhibit the immigration of the larger (adult) classes of Sigmodon males. Higher proportions of Reithrodontomys females, compared to males, invaded both types of perturbed plots. Resident populations of both species appeared to inhibit conspecific immigration. The rank-order templated dispersal strategy found during this study has the advantage of introducing a stabilized age structure into newly acquired habitat space.

Growth rates and/ or dynamics of body mass for the hispid cotton rat ( Sigmodon hispidus ), fulvous harvest mouse ( Reithrodontomys fulvescens ), and marsh rice rat ( Oryzomys palustris ) were determined from field data. Significant sexual dimorphism was exhibited by all three species when based on average body mass. Growth rates were categorized by sex, season, and size class for Sigmodon and Reithrodontomys. Female Sigmodon grew faster than males, there were no seasonal differences in growth rate for cotton rats, and Reithrodontomys exhibited increased spring female growth and overall decreased growth rate with increased size. The lack of seasonal differences in growth rates was attributed to the mild climate of the area and the continuous availability of resources. Growth rates determined in the field were, on the whole, much lower than growth rates obtained from laboratory colonies.

Experimental species removal was conducted for three years to assess the demographic consequences of interspecific interactions between cotton rats ( Sigmodon hispidus ) and fulvous harvest mice ( Reithrodontomys fulvescens ). Six 1.6-hectare (ha) plots were monitored monthly by live-trapping; two control, two Sigmodon -only, and two Reithrodontomys -only plots were maintained by appropriate species removal. Frequent trapping and habitat discontinuities between plots minimized the effect of interplot movement and maintained the experimental perturbation. Seasonal vegetation analyses were conducted on each field. Density, percent reproduction, and expectation of further life but not survival were significantly lower for both Sigmodon and Reithrodontomys on experimental plots (codominant species removed). Lower density for both species and lower reproduction for Reithrodontomys were significantly correlated to lower abundance of preferred habitat on these plots. Lower expectation of further life reflected increased mobility ( AvD p ) of Sigmodon on experimental plots, thereby contributing to lower densities and decreased reproduction through lower mate contact. Cotton rat mean individual body weight was significantly lower and male harvest mouse mean body weight significantly higher on experimental plots; lower cotton rat body weight reflected immigration onto experimental plots in response to a density gradient. Sigmodon sex ratio was skewed toward males on control plots, whereas Reithrodontomys sex ratio was skewed toward males on both plots; differential movement or trappability by either sex may be responsible for this result. The significantly lower proportion of adults and young adults on Sigmodon experimental plots was due to emigration; there was no between-plot age class difference for Reithrodontomys . Most demographic differences between control and experimental plots are explained by differential movement, survival, or abundance of preferred habitat. However, increased mean body weight of male Reithrodontomys and earlier appearance of Reithrodontomys juveniles on experimental plots remain unexplained. These results suggest interspecific interactions and/or behavioral interactions may be of secondary importance in determining the demographic structure of rodents in this system.

The role of competition among cotton rats ( Sigmodon hispidus ), pigmy mice ( Baiomys taylori ), and fulvous harvest mice ( Reithrodontomys fulvescens ) in determining microhabitat utilization was examined in a species removal field experiment conducted in the postoak savanna habitat of east-central Texas. Presence of cotton rats did not affect microhabitat utilization or population size of fulvous harvest mice during winter or spring, or of pigmy mice during spring. Presence of cotton rats may have reduced pigmy mouse population size during winter. Neither pigmy mice or fulvous harvest mice used a broader range of microhabitats in the absence of cotton rats than in their presence.

S. hispidus, B. taylori et R. fulvescens vivent en sympatrie dans de nombreuses regions du Texas. Leurs microhabitats se chevauchent considerablement dans un habitat de savane. Des etudes experimentales montrent que les interactions comportementales (relations dominance-soumission) influencent la segregation spatiale dans les zones de sympatrie; l'interpretation ecologique de telles interactions est liee au fait que les confrontations entre individus sont renforcees par des conditions artificielles d'habitat

Karyotypes of six species of harvest mice, representing both the sub-genus Reithrodontomys ( humulis, sumichrasti , and fulvescens ) and the subgenus Aporodon ( gracilis, mexicanus , and creper ), are described. The karyotype of R. sumichrasti (2n = 40) resembles those previously reported for R. megalotis and R. raviventris , which possess mainly metacentric chromosomes. Reithrodontomys humulis (2n = 51), R. fulvescens (2n = 50), R. gracilis (2n = 52), R. mexicanus (2n = 52), and R. creper (2n = 52) exhibit a large proportion of acrocentric chromosomes. Karyotypic evidence suggests that intrageneric relationships of Reithrodontomys may not be accurately reflected by use of the subgenera Aporodon and Reithrodontomys .

The population dynamics of three sympatric rodents, Microtus californicus, Mus musculus, and Reithrodontomys megatolis was studied at four sites in coastal southern California. The study was undertaken to determine the extent of local demographic diversity in rodent populations. The populations of all rodent species became extinct on one site, while on another site the populations fluctuated widely and on two other sites the populations remained relatively stable. The most common species, Reithrodontomys, exhibited differences in reproduction, age class structure, recruitment, and survivorship on the two sites which were monitored for relatively long terms. Immigration was the main source of new individuals entering the sites where the Reithrodontomys population was most persistent. On a local scale, some life history characteristics are affected in a density dependent fashion. When viewed on a global scale, the non-equilibrium nature of the rodent populations becomes clear.

G- and C-banded karyotypes of Reithrodontomys raviventris were examined to identify the amount and types of chromosomal change that have occurred in this species. The evolutionary origin and phylogenetic relationships of R. raviventris were evaluated by comparing G- and C-band data with six additional species of Reithrodontomys ( fulvescens, creper, mexicanus, megalotis, montanus , and sumichrasti ). Banding homologies indicate that the low diploid number forms ( raviventris, montanus, megalotis , and sumichrasti ) shared a common ancestry and that a major dichotomy exists among these taxa. R. raviventris and R. montanus share a phylogenetic relationship as indicated by 10 shared-derived chromosomal rearrangement events. R. megalotis and R. sumichrasti represent a second well-defined clade. These chromosomal banding data suggest an alternative hypothesis to the traditionally accepted view that R. raviventris is most closely related to R. megalotis .

1. 1. The activity of l -gulonolactone oxidase (EC 1.1.3.8) in livers of 49 species of eutherian mammals varied intraspecifically among individuals; coefficients of variation were 0.2 to 0.4 in many species. 2. 2. Differences observed in l -gulonolactone oxidase activity among strains of laboratory rats and domestic rabbits are probably genetically controlled. 3. 3. Pronounced sex differences in l -gulonolactone oxidase activity were found in some species, particularly in the genera Peromyscus, Reithrodontomys and Onychomys. 4. 4. Mormota monax exhibited seasonal variation in l -gulonolactone oxidase somewhat like that previously observed in Sylvilagus floridanus; no such seasonal variation was found in Sciurus carolinensis. 5. 5. Hibernation did not affect l -gulonolactone oxidase activity in Spermophilus tridecemlineatus. 6. 6. In four species of rodents, Microtus ochrogaster, Tylomys panamensis, Octodon degus and Sigmodon hispidus, l -gulonolactone oxidase activity was not affected by the level of dietary ascorbate.

The genus Prolistrophorus Fain, 1970 (Acari, Listrophoridae) now comprises, including the new taxa described herein, 26 species grouped in three subgenera. These species live attached permanently to the hairs of their hosts. The whole group is confined to North and South American rodents or South American marsupials. The genus Prolistrophorus is redefined and new characters are provided for the definition of the three subgenera: Prolistrophorus s.st., Aprolistrophorus Fain, 1980 and Beprolistrophorus Fain, 1980. Complete descriptions with figures are given for the first time for eight insufficiently known species: P. grassii (Radford, 1954), P. pernamboucensis Fain, 1973, P. scotinomys Fain & Lukoschus, 1982, P. postscutatus Fain & Lukoschus, 1982, P. reithrodontomys Fain & Lukoschus, 1982, P. lestoros Fain & Lukoschus, 1982, P. cuzcoensis Fain & Lukoschus, 1982 and P. akodon, Fain & Lukoschus, 1982. Four new species are described and depicted: P. primitivus, P. curvistriatus, P. monilistriatus and P. bidentatus. Keys to females and males are provided for all the known species of the genus. The origin and the evolution of this genus are discussed. ac]19830401

We studied the relationship between small mammals, Amblyomma americanum (L.), and Dermacentor variabilis (Say) in an oak/hickory woods and an old-field habitat at Land Between The Lakes, Tennessee. The seven small-mammal species captured were Peromyscus leucopus, Microtus ochrogaster, Microtus pinetorum, Blarina brevicauda, Cryptotis parva, Reithrodontomys humulis, and Mus musculus. Only three subadult A. americanum were collected from small mammals, but high densities of free-living A. americanum were present. Therefore, we concluded that small mammals were not principal hosts of A. americanum. In the woods, 115 P. leucopus were examined for ticks, with a mean of 0.03 nymphal D. variabilis and 1.4 larvae per mouse. In the field, 49 P. leucopus were examined, with 0.3 larvae and 0 nymphs per mouse. We collected a total of 68 larval and 10 nymphal D. variabilis from M. ochrogaster and one larva from M. pinetorum. Although male P. leucopus traveled farther and had more ticks than females, we found no significant difference in numbers of ticks per mouse by sex and no significant correlation in numbers of ticks per mouse by weight, total length, or maximum distance traveled. This was most likely because a small percentage of the mice carried most of the ticks. We concluded that small mammals could reinfest a control area with D. variabilis but not with A. americanum.

The influence of vole cycles on the demography, spatial organization, and abundance of potential rodent competitors was studied in three California rodents in the laboratory and in the field. Population densities ofMicrotus californicus were inversely correlated with reproductive success in two potential competitors (Reithrodontomys megalotis andMus musculus). Additionally, high-density vole populations forced these species into suboptimal habitats. During low-density vole populations,Reithrodontomys andMus left their refugia, expanded their usage of habitat, were more active, and their reproductive success was greater. Thus, this work suggests that during vole population peaks, competition with sympatric species of mice is severe. Conversely, when vole populations decline, competition is relaxed. The temporal and spatial organization of the three-species complex supports models of nonequilibrium and fugitive species coexistence.

Feeding ecology of Long-eared Owls (Asio otus) was investigated in the Snake River Birds of Prey Area, southwestern Idaho, during the breeding seasons of 1980 and 1981. The owls preyed mainly on five genera of small mammals: Peromyscus, Perognathus, Dipodomys, Microtus, and Reithrodontomys. There was considerable variation in prey composition among sites but not between years. In both years the proportion of Perognathus in the diet increased after the young owls fledged. Compared with other North American studies, Long-eared Owls in the Snake River Birds of Prey Area had a wider feeding niche and preyed more extensively on nonmicrotines. The range of prey sizes in Long-eared Owl diets was similar to that in other areas, with most prey weighing less than 100 g. Interlocality differences in the Long-eared Owl feeding niche probably reflect differences in the composition of small mammal faunas. Long-eared Owls in the Snake River Birds of Prey Area appeared to feed opportunistically on a diversity of available small mammals; prey size, rather than prey type, was the most important factor in food selection.

The responses of a population of Reithrodontomys megalotis to fluctuations in density of Microtus californicus were examined at Russell Reservation, Contra Costa Co., California. Reithrodontomys increased in abundance on four permanently established grids during years of low Microtus density but declined to very low numbers or local extinction when vole populations irrupted. The annual spring decline in abundance of harvest mice noted at Russell Reservation also occurred three to four months earlier in the year when vole numbers were rapidly increasing. Reproductive activity was found to be seasonally complementary in the two species. The hypothesis that Microtus density is negatively correlated with Reithrodontomys reproductive activity could not be tested due to the small number of harvest mouse captures during the period of peak vole abundance. However, the only female Reithrodontomys captured during this time that was reproductively active was taken from a 3- × 4-m area from which Microtus had been excluded. Analyses of space use patterns indicated a random association between the two species at low Microtus density, but an increasingly negative association as vole density increased. These data support the hypothesis that interference between Microtus and Reithrodontomys may be relaxed during most years. Behavioral interactions intensify when Microtus density increases, however, and interspecific competition during vole irruptions is severe.

During a 13 month live-trapping study on a 2.3 ha grid located in upland coastal sage scrub near Irvine, California, the food habits of seven species of rodents were determined using fecal analysis. These included four cricetids, Reithrodontomys megalotis , Peromyscus maniculatus , P. eremicus , and P. calif omicus , and three heteromyids, Dipodomys agilis , Perognathus fallax , and P. longimembris . Laboratory feeding experiments using the cafeteria method in autumn 1971 indicated different patterns of food preference from wide acceptance of shrubs, forbs, and grasses ( Dipodomys ) to lower preferences for shrubs and high preferences for grasses (all cricetids except P. maniculatus ) to relatively narrow acceptance of only grasses ( P. longimembris ). Comparison of diet composition by weight with volumetric percentages using fecal analysis of animals in feeding experiments indicated highest correlations for shrubs and forbs in cricetids and shrubs and grasses in heteromyids. Food habit trends revealed a high utilization of insects and Eriogonum fasciculatum by Reithrodontomys , a generalized diet for P. maniculatus , and a specialization on various seeds, flowers, and fruits by P. californicus and to a lesser degree by P. eremicus . The three heteromyids ate large amounts of annual and grass seeds during most months with the most opportunistic feeding shown by Dipodomys on grasses and forbs during winter-spring months. Food habits were most similar among the heteromyids, and P. eremicus-P. californicus . Of these, P. longimembris utilized winter torpor, whereas P. californicus was a seasonal resident. Food habit responses of subordinate cricetids to the spring immigration of P. californicus suggest the presence of both flexible feeding strategies and seasonally abundant resources in spring. These conditions may explain the continued coexistence of the diverse rodent fauna during this period.