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Reintroduction programs that release endangered species back into areas from which they have been extirpated rarely take competitive interactions between species into account. The endangered Pacific pocket mouse (Perognathus longimembris pacificus) is being reintroduced to parts of its former range where multiple species of native rodents have overlapping diets. The granivorous species in this foraging guild compete for seeds exploitatively and through direct interference interactions, and pocket mice are the smallest and least dominant species in the guild. Repeated aggressive interactions from resident heterospecifics could lower the chances of reintroduced pocket mice establishing burrows during the post-release settlement period. As such, temporarily reducing the density of competing species through exclusionary fencing might be an advisable reintroduction strategy, in combination with other interventions, such as predator exclusion. The presence of other members of the seed-foraging guild, however, could have a net benefit for pocket mice, if the pocket mice pilfer from the other species’ seed caches more than the other species pilfer from their caches. To test the frequency of cache pilfering between species, we conducted a field experiment with fluorescent dyed seeds. Two of 10 pocket mice pilfered from heterospecifics, but only 1 of 33 heterospecifics pilfered from pocket mice. In a field-enclosure experiment, we could not conclude that any of the 4 species tested used heterospecific scent to find (or avoid) seed caches, and pocket mice were less efficient in pilfering from artificial caches, recovering fewer seeds than the larger species. We did not find strong evidence that Pacific pocket mice benefit from living in sympatry with larger, dominant species. Although further research is needed to elucidate the relationship between heterospecific density and the prevalence of cache pilfering, a conservative reintroduction approach would be to select receiver sites with low densities of known competitors to benefit pocket mice during the critical post-release establishment phase. © 2019 The Wildlife Society.

Joshua trees (Yucca brevifolia) produce large, indehiscent fruits that contain numerous large seeds. Seed dispersal in this species depends on rodents to dismantle fruits and extract the seeds which they disperse tens of meters from the source. Using camera trapping and fruits tied to bobbins, I show that white-tailed antelope squirrels (Ammospermophilus leucurus) and kangaroo rats (Dipodomys spp.) moved intact, fallen fruits 6 to 7 m from trees before opening them. Pocket mice (Chaetodipus fallax and Perognathus longimembris) and pinyon mice (Peromyscus trueii) dismantled fruits and harvested loose seeds but did not appear to move them although they readily harvested loose seeds. Mobilizing fruits may be an important, overlooked step in the seed dispersal process, especially if the fruits are indehiscent. Fruit-carrying behavior of rodents described in this study adds to the dispersal distance of Joshua tree seeds.

Recruitment of Indian ricegrass (Achnatherum hymenoides) seedlings occurs primarily from surface seed caches made by scatter-hoarding desert rodents of the family Heteromyidae. We used radiolabeled Indian ricegrass seeds in field seed-caching experiments with 5 coexisting heteromyid species (Dipodomys deserti, D. merriami, D. microps, Microdipodops pallidus, and Perognathus longimembris) to compare their potential effectiveness as dispersers. Dipodomys microps individuals deposited seeds almost exclusively in larders rather than in scatter hoards, implying that this species is unlikely to be an important seed disperser. Among the other species, individual caches made by larger species had more seeds than those made by smaller species, but smaller species made more caches. At the level of individual animals, M. pallidus was the most effective disperser in a quantitative sense; they made more caches than other species tested and placed fewer excess seeds in caches relative to optimal cache sizes for Indian ricegrass seedling establishment. However, because D. merriami individuals were considerably more abundant at the study site than other species and were also avid scatter hoarders, D. merriami is likely to be the most quantitatively effective disperser of Indian ricegrass seeds at the species level. Ranking species according to qualitative effectiveness (e.g., by considering effects such as the caching microsite on seedling establishment) was more ambiguous. For example, P. longimembris made relatively shallow caches that most closely match optimal planting depths for Indian ricegrass seedling emergence, but such shallow caches are probably more likely than deeper caches to be discovered by foraging rodents before they can germinate. With the possible exception of D. microps, any of the species we tested may be effective dispersers of Indian ricegrass seeds.

Periods of disuse or physical inactivity increases bone porosity and decreases bone mineral density, resulting in a loss of bone mechanical competence in many animals. Although large hibernators like bears and marmots prevent bone loss during hibernation, despite long periods of physical inactivity, some small hibernators do lose bone during hibernation. Little pocket mice (Perognathus longimembris) remain underground during winter hibernation and undergo bouts of torpor and interbout arousals, but the torpor bout duration is shorter than other rodent hibernators. Additionally, little pocket mice may enter torpor during summer estivation. In this study, cortical and trabecular bone architectural, mineral, and mechanical properties were analyzed for femurs from little pocket mice captured during 8 different months (March to October) to determine seasonal effects on bone. There were no differences in any bone properties between the pre-hibernation month of October and the post-hibernation month of March, suggesting winter hibernation did not adversely affect bone properties. However, cortical area was higher in March than April, May, and June. Bone mechanical and osteocyte lacunar properties were not different between any months. Trabecular bone in the distal femoral epiphysis showed no changes between months. The distal femoral metaphyseal region showed higher trabecular spacing and lower trabecular number in May than August, otherwise, there were no differences in trabecular parameters. The few monthly differences in bone properties may be due to physical inactivity from periodic summer estivation or from the timing of birth and growth in spring and summer months. Anat Rec, 300:2175-2183, 2017. © 2017 Wiley Periodicals, Inc.

Anthropogenic habitat fragmentation typically precedes conservation planning; maintaining remaining linkages among core habitat areas can thus become a key conservation objective. Identifying linkages for dispersal and ensuring those linkages have long-term protection and management are challenging tasks for wildlife managers. These tasks can be especially daunting for smaller species with low mobility, termed corridor dwellers, which must maintain sustainable populations within corridors. Between May 2007 and June 2009, we collected occurrence locations for a corridor dweller, the Palm Springs pocket mouse (Perognathus longimembris bangsii), from museums, previous research, and our own field sampling. We used those data to model their suitable niche space and then identify suitable linkages between proposed conservation areas. We used a partitioned Mahalanobis D2 statistic to create a spatially explicit niche model describing the distribution of a suitable niche space, and we validated the model...

Seed caching by desert rodents in the family Heteromyidae is an important behavioral adaptation for animals living in environments with limited and unpredictable food resources. Heteromyids cache seeds throughout their home ranges, either concentrated in 1 location (larder hoard) or in multiple, small seed piles (scatter hoards). To minimize cache pilferage by other rodents, coexisting species may scatter hoard seeds in distinct microhabitats. We examined interspecific differences in caching and pilfering behaviors of 3 coexisting heteromyid rodents, Merriam's kangaroo rat (Dipodomys merriami), the pale kangaroo mouse (Microdipodops pallidus), and the little pocket mouse (Perognathus longimembris), to determine if caching microhabitat affects likelihood of pilferage. In outdoor enclosures we tracked cache placement and measured pilferage of artificial caches using radiolabeled Indian ricegrass (Achnatherum hymenoides) seeds. M. pallidus and P. longimembris placed seed caches mostly under shrubs, whereas D. merriami placed caches predominately in open microhabitat. However, D. merriami showed a significant preference for pilfering caches under shrubs, whereas P. longimembris did not show a significant preference for pilfering caches in either open or undershrub microhabitats. The 2 species pilfered similar numbers of caches. Coexisting heteroymid rodent species may contribute to spatial heterogeneity of available resources by caching in different microhabitats, thereby reducing but not eliminating cache pilferage by other species.

We used program CAPTURE to analyze 1,535 capture–recapture data sets from 33 species of small mammals for sources of variation in capture probabilities and to characterize species-specific responses to mark–recapture trapping. Program CAPTURE contains 8 models to account for all possible combinations of heterogeneity (h), behavioral response (b), and time (t) effects on capture probabilities. Model Mo (equal capture probabilities) was selected most often by CAPTURE as the most appropriate model for small sample sizes, reflecting the difficulty of detecting unequal probabilities of capture in small data sets. Heterogeneity in capture probabilities among individuals was evident in larger data sets for all species of small mammals examined. Strong behavioral responses were detected in several species. Sylvilagus, Tamias amoenus, Glaucomys sabrinus, Perognathus longimembris, and Microtus ochrogaster were trap shy, whereas Tamias striatus, Tamias townsendii, Spermophilus richardsonii, Perognathus parvus, Reithrodontomys megalotis, Peromyscus maniculatus, Peromyscus truei, Sigmodon hispidus, Microtus californicus, and Microtus pennsylvanicus were trap prone. Time effects were not apparent for most species except where they were accompanied with heterogeneity. Murid species had the highest estimated probabilities of capture, followed by heteromyids, sciurids, and leporids in decreasing order. Estimates of abundance from model Mh were significantly greater than those from models Mb, Mo, and Mt, which likely reflects the negative bias of these latter estimators.

The Perognathus longimembris species group currently consists of 3 species and approximately 23 subspecies. Members of this species group have been of considerable interest to biologists in both physiological and ecological studies, and several members are threatened with extinction. No one has yet attempted a phylogenetic study including several populations from each of these 3 species to test the monophyly of these taxa and to elucidate the relationships among the species and subspecies. Mitochondrial DNA sequences from the cytochrome-b gene were used to assess the genetic variation among these species and to make a 1st approximation of the number of species that should be recognized taxonomically in this species group. Results indicate that the Arizona pocket mouse, P. amplus, and the San Joaquin pocket mouse, P. inornatus, are monophyletic entities, and should remain as single polytypic species, whereas the little pocket mouse, P. longimembris, is paraphyletic in the maximum-likelihood and maximum-parsimony phylogenies, suggesting that it might best be split into 2 polytypic species.

The geographic genetic structure, based onsequence variation of an 810 base pair fragmentof the mitochondrial cytochrome b gene,is described for populations of five subspeciesof the Little Pocket Mouse, Perognathuslongimembris, from Southern California. Oneof these, P. l. pacificus (Pacific PocketMouse), is listed as Endangered by the U.S.Federal Government. Sixty-two uniquehaplotypes were recovered from 99 individualssampled. Phylogenetic analyses of thesevariants do not identify regionallyreciprocally monophyletic lineages concordantwith the current subspecies designations, butmost haplotypes group by subspecies in networksgenerated by either statistical parsimony ormolecular variance parsimony. Moreover, asubstantial proportion of the total pool ofhaplotype variation is attributed to thesesubspecies, or to local populations withingeographic segments of each, indicating theirrelative evolutionary independence. The pooledextant populations of the endangered PacificPocket Mouse exhibit the same levels ofnucleotide and haplotype diversity as other,presumptively less-impacted populations ofadjacent subspecies, although the sample fromDana Point, Orange County, has markedly lowhaplotype diversity in comparison to allothers. These populations also show a geneticsignature of population expansion rather thanone of decline. Both pieces of evidence are atodds with current empirical populationestimates, which reinforces the fact thatpresent-day patterns of genetic diversity arethe product of coalescent history and will notnecessarily reflect recent anthropogenic, orother, perturbations. Comparison of haplotypevariation within and among extant populationsof the Pacific Pocket Mouse with those obtainedfrom museum samples collected more than 70years ago suggests that the pattern ofpopulation differentiation and diversity was inplace before the post-World War II exponentialurbanization of Southern California.

The foraging behavior of a predator species is thought to be the cause of short-term apparent competition among those prey species that share the predator. Short-term apparent competition is the negative indirect effect that one prey species has on another prey species via its effects on predator foraging behavior. In theory, the density-dependent foraging behavior of granivorous rodents and their preference for certain seeds are capable of inducing short-term apparent competition among seed species. In this study, I examined the foraging behavior of two heteromyid rodent species (family Heteromyidae), Merriam’s kangaroo rats (Dipodomys merriami) and little pocket mice (Perognathus longimembris). In one experiment I tested the preferences of both rodent species for the seeds of eight plant species. Both rodent species exhibited distinct but variable preferences for some seeds and avoidance of others. However, the differences in preference appeared to have only an occasional effect on the strength of the short-term apparent competition detected in a field experiment. In another experiment, I found that captive individuals of both rodent species had approximately equal foraging effort (i.e., time spent foraging) in patches that contained a highly preferred seed type (Oryzopsis hymenoides) regardless of seed density and the presence of a less preferred seed type (Astragalus cicer) in the patches. The rodents also harvested a large proportion of O. hymenoides seeds regardless of initial seed density; this precluded a negative indirect effect of A. cicer on O. hymenoides. But there was a negative indirect effect of O. hymenoides on A. cicer caused by rodents having a lower foraging effort in patches that only contained A. cicer seeds than in patches that contained A. cicer and O. hymenoides seeds. The indirect interaction between O. hymenoides and A. cicer thus represented a case of short-term apparent competition that was non-reciprocal. Most importantly, it was caused by the foraging behavior of the rodents.

Cattle grazing has been shown to alter various features of desert communities that may impact microhabitats required by various species of desert rodents, with unknown implications for desert rodent communities. We conducted a series of studies at heavily and lightly grazed sites to investigate effects of cattle grazing on desert rodent relative abundances, home range sizes and microhabitat use in salt desert shrub communities of the western Great Basin Desert. Monitoring of rodent populations with repeated live trapping showed that different levels of grazing were associated with differences in relative abundances of some species of rodents. Specifically, Dipodomys merriami was significantly more abundant in heavily grazed areas, and Perognathus longimembris was significantly more abundant in lightly grazed areas. Our studies showed that cattle, by preferentially feeding on certain plants, can create conditions that are more suitable for some species of rodents, while reducing important microhab...

Storing food is an important adaptation of heteromyid rodents to desert environments of southwestern North America. These rodents store seeds in burrows (larder hoarding) and in small, widely scattered caches buried at shallow depths in soil (scatter hoarding). Laboratory trials were done with five species from one site and two species from two other sites to test the hypothesis that larger species would larder hoard relatively more seeds than smaller species. Subjects were tested in arenas consisting of a sand-filled box for scatter hoarding and a nest box for larder hoarding. Chisel-toothed and Merriam's kangaroo rats ( Dipodomys microps and D. merriami ) from one site larder hoarded more than sympatric dark kangaroo mice ( Microdipodops megacephalus ) and long-tailed and little pocket mice ( Chaetodipus formosus and Perognathus longimembris ). Chisel-toothed kangaroo rats larder hoarded more than Merriam's kangaroo rats and little pocket mice larder hoarded more than dark kangaroo mice. These results were consistent with reported information on the relative aggressive behaviors of the species. For subjects from the other two sites, Ord's kangaroo rats ( D. ordii ) larder hoarded more than the smaller Merriam's kangaroo rats. Pocket mice made larger scatter hoards than kangaroo rats and placed these scatter hoards closer to edges and corners of arenas than kangaroo rats. Differences among species in food-hoarding behavior should be considered in future studies of the community ecology of desert rodents.

Understanding the diet of an endangered species illuminates the animal's ecology, habitat requirements, and conservation needs. However, direct observation of diet can be difficult, particularly for small, nocturnal animals such as the Pacific pocket mouse (Heteromyidae: Perognathus longimembris pacificus). Very little is known of the dietary habits of this federally endangered rodent, hindering management and restoration efforts. We used a metabarcoding approach to identify source plants in fecal samples (N = 52) from the three remaining populations known. The internal transcribed spacers (ITS) of the nuclear ribosomal loci were sequenced following the Illumina MiSeq amplicon strategy and processed reads were mapped to reference databases. We evaluated a range of threshold mapping criteria and found the best-performing setting generally recovered two distinct mock communities in proportions similar to expectation. We tested our method on captive animals fed a known diet and recovered almost all plant sources, but found substantial heterogeneity among fecal pellets collected from the same individual at the same time. Observed richness did not increase with pooling of pellets from the same individual. In field-collected samples, we identified 4-14 plant genera in individual samples and 74 genera overall, but over 50 percent of reads mapped to just six species in five genera. We simulated the effects of sequencing error, variable read length, and chimera formation to infer taxon-specific rates of misassignment for the local flora, which were generally low with some exceptions. Richness at the species and genus levels did not reach a clear asymptote, suggesting that diet breadth remained underestimated in the current pool of samples. Large numbers of scat samples are therefore needed to make inferences about diet and resource selection in future studies of the Pacific pocket mouse. We conclude that our minimally invasive method is promising for determining herbivore diets given a library of sequences from local plants.

A study was carried out to characterize various ecological aspects of small mammals in the Sierra del Pinacate, Sonora, Mexico, during the spring of 1981. A survey of rodents was undertaken in nine different plant association of the Gran Desierto of Sonora, and as a result, sixteen species belonging to nine genera were recorded. The rodent fauna consisted of three species of Sciuridae, one species of Geomyidae, seven species of Heteromyidae, and five species of Cricetidae. The Perognathinae was the richest group, with five species. Rodent distribution was correlated with plant associations and soil substrate. From the total number of species, 16 (94%) dwelled on firm soils, which is the most common substrate. The rock squirrel (SpermophHus variegatus) and the white-throated wood rat (Neotoma albigula] characterized rocky areas, while the desert kangaroo rat (Dipodomys deserti) was restricted to sand dunes, and caracterized the most sandy areas. Habitats were classified according to the presence of rodent species. Perognathus longimembris at\a Neotoma albigula separate within our classification the most diverse habitats from the less diverse. The analysis indicates that riparian vegetation was the most important habitat to most of the rodent species.

A PERIODIC and often diurnal lowering of the body temperature has been reported in birds and bats1, rodents belonging to six different families2, and among marsupials (Eudromicia3;, Cercartetus3,4). The associated inactive state is known as torpor to distinguish it from hibernation and aestivation, which are seasonal phenomena. Bartholomew and Cade5 obtained a continuous record of the temperature during entry into torpor and arousal in the little pocket mouse, Perognathus longimembris, using embedded thermocouples with detachable leads. Rectal thermocouples with leads taped to the tail have been used to measure changes in temperature during arousal in the birch mouse, Sicista betulina6, the ground squirrel, Citellus mohavensis7, the marsupial pigmy possum, Cercaertus (= Cercartetus) nanus3,4 and other species8. Tucker9 kept Perognathus californicus in 200 ml. glass jars fitted with thermocouples, and measured the incidence of torpor from the changes in temperature of the jars. This communication reports on torpor in the marsupial mouse, Sminthopsis larapinta (Spencer). Temperature changes during entry into torpor and arousal were measured using a thermistor fixed in the nest box.

C-, and G-banded chromosomes are presented for Perognathus amplus and Perognathus longimembris from Arizona, USA and Chaetodipus nelsoni from Coahuila, Mexico. The two species of Perognathus reveal similar C-band patterns, and extensive autosomal and X chromosome G-band identity with only pericentric inversions distinguishing pairs 4 and 6 and a difference in the morphology of pair 20. Three pairs of autosomal secondary constrictions were found in P. amplus and only one in P. longimembris. Only 50% of the amplus/longimembris G-banded karyotype could be aligned with that of C. nelsoni indicating extensive chromosomal restructuring has taken place since these genera last shared a common ancestor. A review of the literature suggests variable rates of morphological, chromosomal and molecular evolution in these animals.

Substantiated cases of ring species in mammals are rare. I examined the variation in mitochondrial DNA (mtDNA) of Perognathus amplus and P. longimembris in and around Arizona to test the hypothesis proposed by Hoffmeister (1986) that these two taxa are members of a single ring species demonstrating circular overlap. Through digestion of purified mtDNA from 45 P. amplus and 35 P. longimembris with 16 type II restriction enzymes, I identified 38 distinct haplotypes that belong to eight different evolutionary lineages. I then amplified and directly sequenced a portion of the mitochondrial cytochrome-b region from individuals representative of the lineages identified by restriction fragments, and used these data for phylogeny reconstruction in both a parsimony and neighbor-joining setting. The resulting phylogeny was consistent with the ring hypothesis, but, based on the incompleteness of the ring of subspecies and the apparent timing of evolutionary events in this group, I conclude that P. amplus and P. longimembris are distinct lineages that have completed the speciation process.

Perognathus longimembris (Coues, 1875). Proc. Acad. Nat. Sci. Philadelphia, 27:305. TYPE LOCALITY: USA, California, Kern Co., Tehachapi Mtns, Old Fort Tejon. DISTRIBUTION: SE Oregon and W Utah (USA) south to N Sonora and Baja California Norte (Mexico). STATUS: IUCN - Endangered as subspecies brevinasus and psammophilus. Two California subspecies (brevinasus and pacificus) listed as Species of Special Concern by the State of California Dept, of Fish and Game. SYNONYMS: aestivus Huey, arcus Benson, arenicola Stephens, arizonensis Goldman, bangsi Mearns, bombycinus Osgood, brevinasus Osgood, cantwelli, von Bloeker, elibatus Elliot, gulosus Hall, internationalis Huey, kinoensis Huey, nevadensis Merriam, pacificus Merans, panamintinus Merriam, pericalles Elliot, pimensis Huey, psammophilus von Bloeker, salinensis Bole, tularensis Richardson, venustus Huey, Virginis Huey. COMMENTS: Revised by Osgood (1918); subspecies listed by Hall (1981)., Published as part of James L. Patton, 1993, Order Rodentia - Family Heteromyidae, pp. 477-486 in Mammal Species of the World (2 nd Edition), Washington and London :Smithsonian Institution Press on pages 485-486, DOI: 10.5281/zenodo.7353079, {"references":["Osgood, W. H. 1918. The status of Perognathus longimembris (Coues). Proceedings of the Biological Society of Washington, 31: 95 - 96.","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."]}

1. 1.|Blood pH of an active amphibian ( Bufo valliceps ) and a dormant amphibian ( Scaphiopus couchii ) at different body temperatures was found to resemble the pH-temperature relationship for water. Their pH-temperature coefficients were −0.030 and −0.028 u/°C respectively. The blood pH of a heliothermic lizard ( Dipsosaurus dorsalis ) and a heterothermic mammal ( Perognathus longimembris ) had a lower temperature coefficient, −0.007 and −0.0085 u/°C respectively. Blood pCO 2 of the amphibia, reptile and mammal decreased at low body temperatures, in conformance with the pH regime; the lizard and mammal were, however, acidotic relative to the amphibia, at low temperatures. 2. 2.|Data from the present study, and other studies, suggest that the manner in which vertebrates regulate in vivo pH at different body temperatures is quite variable, and that behavioural/physiological thermoregulators tend to have low temperature-pH coefficients. 3. 3.|The temperature-pH optimum for a tricarboxylic acid cycle enzyme, malate dehydrogenase, from P. longimembris ) was about −0.008 u/°C, which corresponds closely for the temperature-pH coefficient for blood (−0.0085 u/°C). 4. 4.|The pattern of in vivo pH-temperature regulation observed in vertebrates would appear to be intimately correlated with the physico-chemical requirements for the maintenance of cellular metabolism. Neither the temperature-pH coefficient for in vivo pH regulation, or for optimal enzyme activity, necessarily parallel the observed temperature dependence of the pH of water.

Electroencephalogram (EEG), electromyogram (EMG), and brain temperature (Tbr) were recorded from seven pocket mice (Perognathus longimembris) during euthermia and 22 bouts of torpor induced by food deprivation. All but one of a total of 22 entrances into torpor began during slow-wave sleep (SWS), and SWS continued throughout 89% of the entrances, whereas rapid eye movement (REM) sleep was almost completely suppressed. Although EEG amplitude diminished as $T_{br}$ dropped, SWS and wakefulness could still be distinguished at the lowest $T_{br}'s$ of 23-25 C. SWS continued to be preponderant, accounting for 96% of the recordings at these $T_{br}'s$. Thus the association of SWS with declines in $T_{br}'s$ during entry into hibernation or torpor reported for marmots, squirrels, and doves also applies to one of the smallest mammals. However, suppression of REM sleep during hibernation or torpor is not as great in these larger endotherms as in the pocket mouse. $T_{br}$ in a euthermic pocket mouse is strongly af...

The timing of bouts of torpor was continuously monitored in 36 pocket mice,Perognathus longimembris, for as long as 11 months. Animals were kept at 8 °C or 18 °C, with light cycles of LD 12∶12, 10∶14, 15∶9, or continuous darkness. At 8 °C, torpor duration had a polymodal frequency distribution, and the near absence of bouts of torpor lasting exactly 24, 48, 72, and 96 h divided the bouts into discrete classes (one-day, two-day, etc.). The maximum duration of torpor was 2.5 times greater at 8 °C than 18 °C.

The relationship of death and age in pocket mice ( Perognathus longimembris ) was determined in a cohort of 216 animals derived from breeding experiments with field trapped animals. A maximum life span of 8.3 years was found. The pattern of mortality as revealed by a comparison of its qx curve with other rodents seems to be distinctly different. There is a prolongation of moderate mortality at a time when mortality rates of other mammals are tending toward a logarithmic increase. The ramifications of torpor on longevity and ecological strategy are discussed.

1. 1. Nine species of rodents representing three Families were exposed to ionizing radiation or potassium cyanide to determine whether sensitivity to KCN might be used as an index to radiation response of the species, and to document the comparative responses of the species to the stresses. 2. 2. There was a twofold variation between the responses of the most sensitive, Oryzomys palustris (525 rad), and the most resistant species, Perognathus longimembris (1094 rad), following radiation treatment. There was no apparent relationship between radiation responses and taxonomic affinity or adaptation to high altitude. 3. 3. There was a taxonomic ordering of responses to cyanide with members of the Family Heteromyidae most sensitive (4 mg/kg), Muridae intermediate in response, and members of the Family Cricetidae most resistant (9·6 mg/kg). 4. 4. There was no correlation between radiation resistance and KCN toxicity in the Families Muridae and Heteromyidae, but there was a strong positive correlation in the Family Cricetidae. The inconsistent results would preclude use of cyanide toxicity as an index to radiation sensitivity in rodents in general, but might apply in some larger Families. 5. 5. Results of cyanide exposures and sulfur transferase activity suggested that resistance to ionizing radiation could not be totally related to the availability of free sulfhydryl groups.

Selection of seeds with different dispersion patterns, facilitated by the energetic differences between bipedal—hopping and quadrupedal heteromyid rodents, has been proposed as a mechanism of resource allocation for microsympatric species. To test several aspects of this hypothesis, field observations of foraging behavior and laboratory measurements of locomotion costs were made for several species of heteromyids. Neither the field observations nor the laboratory measurements supported predictions generated by the seed—dispersion hypothesis. Locomotion costs of the bipedal—hopping Dipodomys deserti and D. merriami were similar to those predicted for quadrupeds of equal mass. At low speeds, the cost of quadrupedal locomotion was not greater for a small, hopping biped than would be expected for a similar—sized quadruped. Free—living Dipodomys deserti, D. merriami, and Perognathus longimembris spent most of their foraging time either stopped or moving at slow speeds. High—speed locomotion, at which energetic "savings" by bipeds should be greatest, was rare. These results led to the conclusion that the energetic costs of different locomotory modes do not play a major role in resource allocation for Mojave Desert heteromyids.

Removal trapping was used to study lability in microhabitat use by three heteromyid rodents in three widely separated localities. Among all sites, captures from the first night of trapping showed a similar pattern of microhabitat use: Dipodomys merriami was associated with open, sandy microhabitats, whereas Perognathus formosus and Perognathus longimembris were trapped in shrubby areas with, respectively, low and high percentages of sand. Continued removal of individuals (rarefaction) initiated shifts in microhabitats used by Perognathus at the Fallon Site; both species began to frequent the open areas previously occupied by Dipodomys alone. No shifts were detected at the other two sites although trapping was continued at Indian Springs for a much longer period and many more individuals were removed. Site-specific responses to rarefaction suggest that the processes underlying patterns of microhabitat use by rodents may vary geographically. These results weaken the widespread notion that localized studies can be extrapolated to generalizations of community organization over a broad area even when the same species comprise local assemblages.

Home range sizes were estimated seasonally for Microdipodops megacephalus and Perognathus longimembris and biweekly for Dipodomys merriami, D. ordii, D. panamintinus, D. microps , and Peromyscus maniculatus. Mean estimates are also presented for Reithrodontomys megalotis and Onychomys torridus . Principal component analysis was used to calculate home range values because of its ability to deal with a wide variety of home range configurations. All species showed great variability in home range size throughout the year. Shape of home range was similarly variable, although most species tended towards elliptical movement configurations. The heteromyids showed consistency in annual composite home range areas (0.33–0.49 ha) regardless of body size. The generally smaller cricetine rodents exhibited much larger composite home range areas (0.95–1.42 ha). Emphasis is placed on the utility of point-in-time estimates of movements rather than obtaining a single home range value, which subordinates the dynamic nature of small mammal movements.

Long-term patterns of surface activity were monitored in 15 pocket mice, Perognathus longimembris , which constructed burrow systems in dirt-filled terrariums kept at 16°c and 31°c on 12-hour photoperiods. a rhythm, with an average period of about 10 months, was evident in the behavior of the mice at 16°c. During each cycle, these animals spent several months continuously underground even though food was always available on the surface. The transition between the underground and surface active phases of the cycle was usually gradual. However, the mice immediately resumed nightly foraging if the upper layers of the soil were heated each day during this transition time. They did not respond to this stimulus during the middle of the underground phase of the annual cycle. I suggest that in nature the vertical uniformity of soil temperatures in the spring may cue the synchronization of the circannual rhythm with the seasons. The absence of surface activity is apparently unrelated to torpor because mice at 31°c, where torpor does not occur, also spent several months continuously underground. However, the regular 10-month periodicity of the behavioral cycle was disrupted in this hot environment. Torpor was also monitored for up to 20 months in 25 mice at 8°c and 18°c under 9-hour and 15-hour photoperiods, but circannual rhythms of torpor were not evident under these experimental conditions.

Direct observations of free-living individuals were employed to quantify foraging be- havior in Dipodomys desert, D. merriami, and Perognathus longimembris in two Mojave Desert communities. D. merriami and P. longimembris do not partition shrub and open microhabitats, and all three species concentrate their foraging efforts (>75%) near or beneath the canopies of desert shrubs. Results of livetrapping assessments of microhabitat usage (conducted concurrently with for- aging observations) resemble those of earlier studies but differ greatly from observational data; trap- ping may not produce accurate representations of spatial utilization. P. longimembris avoids open areas and utilizes shrubs in a relatively coarse-grained fashion. D. merriami and D. deserti frequently traverse open areas at high speeds and hence utilize shrubs in a relatively fine-grained manner. Beneath shrubs, D. merriami and D. desert are more active and discrete in their foraging than is P. longimembris; both Dipodomys apparently search for large clumps of seeds, while P. Iongimembris forages slowly and continuously, taking individual seeds from scat- tered dispersions. The distinctive morphology of Dipodomys is interpreted as an adaptation that allows fine-grained use of desert shrubs in the face of high predation risk during intershrub transits. Differences in heteromyid body sizes may also reflect two foraging strategies: small size would reduce energy demands, and thus lower the need to move between shrubs and reduce the need for predator avoid- ance; larger size would permit year-round activity (avoidance of torpor), reduce susceptibility to starvation (B. K. McNab, personal communication), increase the range of thermal tolerance, and generally increase abilities to cope with variations in environmental parameters (Boyce 1978). It is concluded that the morphological and behavioral differences between Dipodomys and Perognathus reflect divergent foraging strategies which may reflect equivalent but alternative strategies for ex- ploitation of desert seeds.

Nocturnal, above-ground movement patterns of three desert heteromyid rodents, Dipodomys merriami, Perognathus formosus , and Perognathus longimembris , were studied in a Mohave desert-scrub habitat. Dipodomys merriami moved long distances between stops, remained stationary for long periods of time and collected a low diversity of seeds when compared to the Perognathus . In contrast, both Perognathus moved short distances between stops, spent little time stationary, and collected a wide range of seed types. These differences are consistent with the hypothesis that Dipodomys forage for rich seed clumps, whereas Perognathus forage for more dispersed seed resources. That Dipodomys and Perognathus show differences in the diversity of seeds collected is additional evidence that intergeneric modes of foraging may differ. Differential foraging behaviors leading to the exploitation of seed resources may be one of the mechanisms which facilitates the coexistence of desert rodents.

Twelve species of nocturnal rodents were studied on a 2.7-hectare plot of sagebrush desert in west-central Nevada. Six species, Dipodomys merriami, D. ordii, D. panamintinus, D. microps, Onychomys torridus, and Peromyscus maniculatus, were active throughout the year. Four species, Perognathus longimembris, P. formosus, Microdipodops megacephalus, and Reithrodontomys megalotis, hibernated and were active only in spring, summer, and autumn. Onychomys leucogaster and Neotoma lepida were trapped intermittently throughout the year but were not permanent residents of the area. Differences in time of daily activity were found between potential competitors demonstrating a degree of temporal isolation. Time after sunset and amount of moonlight were the two most important factors correlated to rodent activity. Ambient temperature, wind, cloud cover, precipitation, and water vapor pressure had little effect on activity except when extreme conditions prevailed. (auth)

A comparative study of seasonal food hoarding activity and tactile discriminatory ability in four species of heteromyid rodents (Dipodomys panamintinus, D. merriami, Perognathus longimembris, and P. formosus) was conducted in laboratory test arenas. Animals were tested individually to determine their treatment of seed (white millet) and seed mimics (glass beads and gravel) offered as food. In general, all animals showed low levels of millet hoarding activity during winter months with higher levels in fall and spring. Observations revealed that all species manipulated (with the forepaws) each potential food item prior to eating, pouching, or rejecting it. These tactile cues appear to surpass visual and olfactory cues as critical factors in distinguishing between food and food mimics. Pocket mice (Perognathus) showed high levels of tactile discriminatory ability which may serve as the mechanism by which they achieve high foraging efficiency in nature when "filter-feeding" for widely dispersed seed resources. Kangaroo rats (Dipodomys), on the other hand, are less adept at distinguishing between food and very similar non-food items. The fact that, in nature, kangaroo rats depend heavily on clumped food resources may obviate the need for highly efficient tactile discriminatory abilities.

For 3 yr we studied the reproductive responses of desert rodents in the Owens Valley of eastern California (average annual precipitation 14 cm): four nocturnal heteromyids–the kangaroo rats Dipodomys microps and D. merriami and the pocket mice Perognathus formosus and P. longimembris–and one diurnal sciurid, the antelope ground squirrel, Ammospermophilus leucurus. Reproductive status was assessed by autopsies of adults trapped at approximately monthly intervals. Reproduction differed conspicuously among the five species. Our analysis illustrates effects of body size, phylogenetic association, and adaptation to the desert environment upon reproductive performances and associated life—history parameters. Most breeding occurs in late winter and early spring. Winter rains cause a series of pulses in vegetation growth and an attendant increase in availability of water in food plants, which contribute to rodent reproduction. Among the four heteromyids, onset of breeding is sequential according to body size, wit...

Daily metabolism was calculated from food consumption in pocket mice, Perognathus longimembris, at 80C, 180C, and 310C. At temperatures below thermal neutrality for this species, daily metabolism was related to the amount of time the mice spent in torpor. Ambient temperature has no net effect on the minimum energy expenditure during a typical 5-mo hibernation season. Once an animal has accumulated a food store of 130 g of millet seeds, it has the minimum energy necessary to hibernate at any environmental temperature. Such temperature compensation results from the complex effects of temperature on (1) the ratio of time of euthermy to time of torpor, (2) the energetic cost per hour of torpor, (3) the energetic cost per hour of euthermy, and (4) the energetic cost of arousal from torpor. The amount of time spent in torpor was inversely dependent on the food supply, indicating that euthermia is preferred even during the hibernation season. Mice also maximize the time of euthermia by selecting high environmental temperatures at all times of the year. Torpor probably occurs naturally only during the winter when the highest temperatures available to the mice are below thermal neutrality. The maximization of the time of euthermia reduces the chances of freezing during hibernation and enhances the animal's ability to escape from predators.

Vascular inclusions regularly occur in the lingual dentin of the constantly erupting teeth of the pocket mouse (P. longimembris). The inclusion of a capillary loop and surrounding perivascular tissues is associated with odontoblasts whose cytodifferentiation is relatively immature. These same cells produce dentinal tubules which are more irregular in their course, more arborescent, with more lateral branches, wider in diameter and less numerous than are the tubules of the labial orthodentin. The patent vascular inclusions are surrounded by a broad halo of incompletely mineralized dentin. With further maturation complete obliteration of the vessels occurs, accompanied by complete dental matrix mineralization. A literature review supports the contention that vasodentinogenesis is related operationally to lower stages of odontoblastic cytodifferentiation although the processes by which this occurs are not yet clear.

Communities of granivorous desert rodents may be influenced by either predation risk or resources. To examine the influence of these factors, I manipulated illumination, using lanterns, and resources, using seeds. Foraging behavior is responsive to changes in predation risk; increased illumination reduces foraging in open areas without cover. Foraging behavior is also affected by resource enrichments. Differences among species in habitat selection are correlated with specific abilities to detect and avoid predators. The least vulnerable species, Dipodomys deserti, foraged heavily in the open and was largely unaffected by treatments; the other species of kangaroo rats and kangaroo mice (Dipodomys merriami, Dipodomys microps, and Microdipodops pallidus) also prefer the open, but responded to both risk and resource manipulations; highly vulnerable Peromyscus maniculatus was restricted to bushes, even under the best of circumstances; Perognathus longimembris was displaced from preferred microhabitats by the presence of kangaroo rats. A correlation between auditory bullar volume and use of open habitat by the various species in this community suggests that predation risk provides an axis along which habitat segregation occurs. Predation can structure communities of mobile prey when risk differs among habitats. Animals specializing in predator avoidance and in exploitation of risky environments have reduced interactions with superior competitors; this promotes coexistence.

The foraging strategies of four naturally co-existing heteromyid rodent species were investigated: Dipodomys deserti (≈100 g), D. merriami (≈38 g), Microdipodops pallidus (≈13 g), and Perognathus longimembris (≈7 g). In 208 over-night laboratory foraging trials animals were provided with millet seed distributed in clumped and scattered patterns. Net removal of seeds from the foraging arena and amounts of seeds in cheek pouches and in caches were determined. When alone in an areana none of these species specialized extensively on either clumped or scattered seeds, although each tended to take more clumped than scattered seeds. When placed together with other individuals, animals once again tended to cache more clumped than scattered seeds in all but one paired combination of species: P. longimembris cached more scattered than clumped seeds when opposed by D. deserti. This suggests that the smaller species obtained a less preferred distribution of seeds in the face of competition. The two smaller species showed a great reduction in general foraging success in the presence of either of the two larger species. In general, a species cached less seeds when faced by larger opponent species.

Perognathus longimembris , under a variety of conditions, demonstrated essentially a 24-hr rhythm in oxygen consumption. The amplitude, correlation with light cycle, and duration of periods of high and low metabolism varied. In September, mice provided with food and held at 22–24° C had a rhythm closely synchronized with a 12-hr light cycle (high in dark); mice were hypometabolic 12.5% of the days. In May, mice were more often out of synchrony and were hypometabolic 32.5% of the days. Without food at 22° C, mice became torpid every day; the first period of torpor began in the dark, and the rhythm of oxygen consumption was thereafter reversed. At 10° C without food, mice failed to arouse to a normal metabolic rate every day; sometimes they were deeply hypometabolic for 48–56 hr. A circadian rhythm of reduced amplitude continued, however, and arousals to normal rate occurred approximately on multiples of 24 hr. Arousals continued to occur in mice without food at 10° C despite exposure to or state of animals under the following conditions: constant darkness with or without sound, air with 4.5% CO2, obesity, 9 months' prior conditioning to 10° C, 1,400 R acute whole-body gamma radiation. Mice acclimatized to 10° C had the shortest periods of normal metabolism and obese mice the longest. In P. longimembris (mean wt 10.7 g), P. inornatus (14.6 g) and P. formosus (20.5 g) at 10° C without food, frequency and extent of hypometabolism varied inversely with body weight.

A method for estimating the probability of an animal being in a particular region of the home range is discussed. Data for Perognathus longimembris (Coues) were used to illustrate the use of this method and were transform ed with r ′ = ( r λ − 1)/λ. One-sided tolerance limits were used to assert degrees of confidence γ that given percentages of the recaptures will be within specified distances from the estimated activity center.

A group of 160 female and 40 male captive pocket mice ( Perognathus longimembris ) were examined routinely for reproductive activity during January–June 1965. Limited observations were made throughout the summer and fall. Fifty-eight per cent of the females showed one or more estrous cycles during the routine inspection. Most exhibited polyestrus cycles of approximately 10 days duration. The incidence of first estrus was highest in March. Breeding was accomplished by pairing animals judged by external signs to be receptive. A total of 217 matings were attempted and 57 litters were produced. Five mice produced two litters each. Litters were born from late March through September. Males made sexually active with human chorionic gonadotropin sired several Utters. Information on hormone treatment, estrus, estrous cycles, postpartum and juvenile estrus, mating, gestation, maternal care and nest building is presented.

1. 1. The species studied were: Baiomys taylori , 8 g mature wt; Perognathus longimembris , 10 g; Peromyscus maniculatus , 21·5 g; Mus musculus , 32 g. Metabolic rate of a litter was measured at 1–6-day intervals until it could maintain a “constant” increased metabolism for 1–1.5 hr at T a 20°C, the response here defined as homeometabolism. 2. 2. B. taylori and M. musculus showed no rise of metabolism at T a 20°C until 5–8 days old and 1 day old respectively. The initial ability to increase metabolism may depend on muscular movement in B. taylori , but it does not in the larger species. In all species the ability for sustained increase coincided with the first occurrence of obvious shivering and piloerection, and with 2–4 mm of underfur. 3. 3. The weight at which each species attained homeometabolism is directly related to mature weight, and the age at this time is inversely related to weight. Both a minimum body weight and a minimum time for development after birth are necessary for homeometabolism. 4. 4. B. taylori became homeometabolic at 2·4 g, which is the weight Pearson (1948) predicted as the minimum for homeothermy in mammals. 5. 5. In all species the average ml O 2 ·g −1 hr −1 at T a = 20°C and the minimum at 35°C both increased with growth, up to the point where they equalled adult values. These rates then declined with further growth. Maximum metabolic rate increased with growth to at least four to six times the adult basal rate.