Pocket Mice Research Articles

Rediscovery of Heteromys nelsoni in its type locality after over a century

Abstract We rediscovered a population of Nelson’s spiny pocket mouse (Heteromys nelsoni; Merriam, 1902) in the type locality of Pinabeto in the Mexican state of Chiapas, 121 years after it was last collected. We describe five topotype specimens according to their morphology and external measurements, and we confirm its identity at the species level in the Basic Local Alignment Search Tool (BLAST) of GenBank. As the population of H. nelsoni in Pinabeto is isolated, it is likely to be susceptible to extinction. There is a need to carry out additional scientific studies of this microendemic species in order to obtain more information regarding its biology, ecology and evolutionary history, and to be able to influence environmental policy to protect and conserve this species, as well as the region’s cloud forests.

It's a trap: Optimizing detection of rare small mammals.

Improving detection probabilities for rare species is critical when assessing presence or habitat associations. Our goal was to create a new small mammal trapping protocol that improved detection of rare species, such as the olive-backed pocket mouse (Perognathus fasciatus). We used three trap and bait types and trapped an area 4.4 times larger than the standard grid. We also assessed the effect of captures of non-target species on detection probability of pocket mice. Regardless of species, trap success was higher for Havaharts. We found that bait and trap type selection varied significantly by species, with pocket mice showing strongest selection for Havahart traps baited with bird seed. Increasing grid size, while maintaining a similar trapping effort, resulted in higher detection probability, although our analyses showed that effective grids can be about three-quarters of the size we use to achieve similar results. We were also able to demonstrate that by deploying a combination of different traps and baits it is possible to overcome the potential effect of non-target species (e.g., deer mice, Peromyscus maniculatus) on the detection probability of pocket mice. Our results show that simple changes to standard small-mammal trapping methods can dramatically increase the detectability of rare and elusive small mammals. Increasing detection probability of rare components of a community can improve the results and understanding of future studies.

Divergent behavior amid convergent evolution: A case of four desert rodents learning to respond to known and novel vipers.

Desert communities world-wide are used as natural laboratories for the study of convergent evolution, yet inferences drawn from such studies are necessarily indirect. Here, we brought desert organisms together (rodents and vipers) from two deserts (Mojave and Negev). Both predators and prey in the Mojave have adaptations that give them competitive advantage compared to their middle-eastern counterparts. Heteromyid rodents of the Mojave, kangaroo rats and pocket mice, have fur-lined cheek pouches that allow them to carry larger loads of seeds under predation risk compared to gerbilline rodents of the Negev Deserts. Sidewinder rattlesnakes have heat-sensing pits, allowing them to hunt better on moonless nights when their Negev sidewinding counterpart, the Saharan horned vipers, are visually impaired. In behavioral-assays, we used giving-up density (GUD) to gauge how each species of rodent perceived risk posed by known and novel snakes. We repeated this for the same set of rodents at first encounter and again two months later following intensive “natural” exposure to both snake species. Pre-exposure, all rodents identified their evolutionarily familiar snake as a greater risk than the novel one. However, post-exposure all identified the heat-sensing sidewinder rattlesnake as a greater risk. The heteromyids were more likely to avoid encounters with, and discern the behavioral difference among, snakes than their gerbilline counterparts.

Divergent genetic mechanism leads to spiny hair in rodents.

Spines, or modified hairs, have evolved multiple times in mammals, particularly in rodents. In this study, we investigated the evolution of spines in six rodent families. We first measured and compared the morphology and physical properties of hairs between paired spiny and non-spiny sister lineages. We found two distinct hair morphologies had evolved repeatedly in spiny rodents: hairs with a grooved cross-section and a second near cylindrical form. Compared to the ancestral elliptical-shaped hairs, spiny hairs had higher tension and stiffness, and overall, hairs with similar morphology had similar functional properties. To examine the genetic basis of this convergent evolution, we tested whether a single amino acid change (V370A) in the Ectodysplasin A receptor (Edar) gene is associated with spiny hair, as this substitution causes thicker and straighter hair in East Asian human populations. We found that most mammals have the common amino acid valine at position 370, but two species, the kangaroo rat (non-spiny) and spiny pocket mouse (spiny), have an isoleucine. Importantly, none of the variants we identified are associated with differences in rodent hair morphology. Thus, the specific Edar mutation associated with variation in human hair does not seem to play a role in modifying hairs in wild rodents, suggesting that different mutations in Edar and/or other genes are responsible for variation in the spiny hair phenotypes we observed within rodents.

Interaction between Seed Detectability and Seed Preference Affects Harvest Rates of Granivorous Rodents

Granivorous rodents commonly exhibit preferences for seeds of particular plant species. However, among buried seeds that are available, rodents may find that alternate, less desirable seeds are more easily located by olfaction than preferred seeds. Seeds of Indian ricegrass (Achnatherum hymenoides) are a highly preferred food resource for seed-caching desert heteromyid rodents. We tested relative abilities of heteromyids to locate buried caches of Indian ricegrass seeds versus seeds of another plant species (cheatgrass, Bromus tectorum) that are common in heteromyid diets at a western Nevada field site. Rodents located more cheatgrass than Indian ricegrass seed caches in the field when seeds were unaltered. When ground, however, detectability of preferred Indian ricegrass seeds increased, presumably due to release of volatile compounds inside seeds, and more ground Indian ricegrass seed caches were found and removed compared with ground cheatgrass caches. Grinding cheatgrass seeds did not affect harvest rates of cheatgrass caches. Results of a laboratory cache removal experiment using 2 heteromyid species, Merriam's kangaroo rats (Dipodomys merriami) and long-tailed pocket mice (Chaetodipus formosus), mirrored field cache removal results. Dispersal of Indian ricegrass seeds and establishment of new seedlings occurs largely through emergence of seedlings from heteromyid scatterhoard caches. Our results suggest that Indian ricegrass seeds may have been selected for reduced olfactory detectability to minimize the probability that they are recovered by rodents for later consumption once they have been cached.

Matrilineal genealogies suggest a very low dispersal in desert rodent females

Previous research shows little haplotype diversity in small geographic areas, such as islands and areas where physical barriers interrupt gene flow. The general pattern is the presence of a small number of haplotypes spread across sampling sites. Instead, this paper reports the presence of a large number of haplotypes (Cytb and COI) in the extremely small distribution area (Los Planes basin, Baja California Sur, Mexico) of the Cerralvo pocket mouse, Chaetodipus siccus. Haplotype zoning revealed that haplotypes considered as ancestral are located to the periphery of the distribution area, whereas derived haplotypes are located to the center of the distribution range. Most derivatives are unique haplotypes and many of them exhibit a remarkable characteristic: a separation of not more than 1.7 km between them, which prompts a genetic microstructured population. All these features suggest the presence of a strong philopatric behavior among females.

Body size, not phylogenetic relationship or residency, drives interspecific dominance in a little pocket mouse community

The role of interspecific aggression in structuring ecological communities can be important to consider when reintroducing endangered species to areas of their historic range that are occupied by competitors. We sought to determine which species is the most serious interference competitor of the endangered Pacific pocket mouse, Perognathus longimembris pacificus, and more generally, whether interspecific aggression in rodents is predicted by body size, residency status or phylogenetic relatedness. We carried out simulated territory intrusion experiments between P. longimembris and four sympatric species of rodents (Chaetodipus fallax, Dipodomys simulans, Peromyscus maniculatus, Reithrodontomys megalotis) in a field enclosure in southern California sage scrub habitat. We found that body size asymmetries strongly predicted dominance, regardless of phylogenetic relatedness or the residency status of the individuals. The largest species, D. simulans, was the most dominant while the smallest species, R. megalotis, was the least dominant to P. longimembris. Furthermore, P. longimembris actively avoided encounters with all species, except R. megalotis. One management recommendation that follows from these results is that P. longimembris should not be reintroduced to areas with high densities of D. simulans until further research is carried out to assess the fitness consequences of the interactions. Our finding that the species least similar in body size is the most serious interference competitor of P. longimembris highlights an important distinction between interference and exploitative competition in rodent communities.

Dominance by extremely high aggressive behaviors in relation to genetic microstructure in matrilines

Dominance is an important element of life history. It assures access to resources, which, in turn, affects fitness. By establishing a hierarchy, females may monopolize resources while remaining philopatric. Our genetic study of the sandy pocket mouse, Chaetodipus siccus, has shown a genetic microstructure with private haplotypes in the extremely small species range (∼270km2). To explore these results we evaluate patterns of aggressive–submissive behavior among female C. siccus based on direct dominance, dominance over encounters and dominance based on the defense of food resources. Our findings suggest the presence of aggressive behaviors resulting in the establishment of dominant-subordinate relationship; this relationship remains constant even after a process of visual, auditory and olfactory contact and during the defense of food resources. These results may be linked to a strong territorial behavior that permits the formation of matrilineal nuclei that could be related to a genetic microstructure.

Anthropogenic water sources and the effects on Sonoran Desert small mammal communities.

Anthropogenic water sources (AWS) are developed water sources used as a management tool for desert wildlife species. Studies documenting the effects of AWS are often focused on game species; whereas, the effects on non-target wildlife are less understood. We used live trapping techniques to investigate rodent abundance, biomass, and diversity metrics near AWS and paired control sites; we sampled vegetation to determine rodent-habitat associations in the Sauceda Mountains of the Sonoran Desert in Arizona. A total of 370 individual mammals representing three genera and eight species were captured in 4,800 trap nights from winter 2011 to spring 2012. A multi-response permutation procedure was used to identify differences in small mammal community abundance and biomass by season and treatment. Rodent abundance, biomass, and richness were greater at AWS compared to control sites. Patterns of abundance and biomass were driven by the desert pocket mouse (Chaetodipus penicillatus) which was the most common capture and two times more numerous at AWS compared to controls. Vegetation characteristics, explored using principal components analysis, were similar between AWS and controls. Two species that prefer vegetation structure, Bailey’s pocket mouse (C. baileyi) and white-throated woodrat (Neotoma albigula), had greater abundances and biomass near AWS and were associated with habitat having high cactus density. Although small mammals do not drink free-water, perhaps higher abundances of some species of desert rodents at AWS could be related to artificial structure associated with construction or other resources. Compared to the 30-year average of precipitation for the area, the period of our study occurred during a dry winter. During dry periods, perhaps AWS provide resources to rodents related to moisture.

Hibernating Little Pocket Mice Show Few Seasonal Changes in Bone Properties

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.

Species’ traits help predict small mammal responses to habitat homogenization by an invasive grass

Invasive plants can negatively affect native species, however, the strength, direction, and shape of responses may vary depending on the type of habitat alteration and the natural history of native species. To prioritize conservation of vulnerable species, it is therefore critical to effectively predict species' responses to invasive plants, which may be facilitated by a framework based on species' traits. We studied the population and community responses of small mammals and changes in habitat heterogeneity across a gradient of cheatgrass (Bromus tectorum) cover, a widespread invasive plant in North America. We live-trapped small mammals over two summers and assessed the effect of cheatgrass on native small mammal abundance, richness, and species-specific and trait-based occupancy, while accounting for detection probability and other key habitat elements. Abundance was only estimated for the most common species, deer mice (Peromyscus maniculatus). All species were pooled for the trait-based occupancy analysis to quantify the ability of small mammal traits (habitat association, mode of locomotion, and diet) to predict responses to cheatgrass invasion. Habitat heterogeneity decreased with cheatgrass cover. Deer mouse abundance increased marginally with cheatgrass. Species richness did not vary with cheatgrass, however, pocket mouse (Perognathus spp.) and harvest mouse (Reithrodontomys spp.) occupancy tended to decrease and increase, respectively, with cheatgrass cover, suggesting a shift in community composition. Cheatgrass had little effect on occupancy for deer mice, 13-lined ground squirrels (Spermophilus tridecemlineatus), and Ord's kangaroo rat (Dipodomys ordii). Species' responses to cheatgrass primarily corresponded with our a priori predictions based on species' traits. The probability of occupancy varied significantly with a species' habitat association but not with diet or mode of locomotion. When considered within the context of a rapid habitat change, such as caused by invasive plants, relevant species' traits may provide a useful framework for predicting species' responses to a variety of habitat disturbances. Understanding which species are likely to be most affected by exotic plant invasion will help facilitate more efficient, targeted management and conservation of native species and habitats.

Sonoran Desert rodent abundance response to surface temperature derived from remote sensing

Nocturnal rodents play a key role in the Sonoran Desert ecosystem as consumers, prey and reservoirs of disease-yet rodent distribution remains poorly mapped. We use surface temperature extracted from the Landsat Thematic Mapper thermal infrared band to model rodent abundance obtained from trapping data at the Organ Pipe Cactus National Monument in southwest Arizona. We produce response curves that describe the effects of surface temperature on species abundance. Daytime surface temperature derived from images collected in June across thirty rodent trapping grids ranged from 318 K (45.0 °C) to 332 K (59.2 °C). Results show peak seasonal surface temperature splits high species abundances into two groups: Merriam's kangaroo rat, Arizona pocket mouse, desert pocket mouse and southern grasshopper mouse species prefer habitat characterized by higher surface temperatures; and white-throated wood rat, cactus mouse, rock pocket mouse and Bailey's pocket mouse species prefer habitat characterized by lower temperatures. Abundances for the high and low temperature habitat groupings correlate linearly with surface temperature (r = +0.66 and −0.75, respectively, p < 0.001). Surface temperature integrates multiple landscape characteristics (e.g. topography, vegetation cover and soil properties) that define the dominant habitats of ORPI rodents. These results prove that simple models can inform complex ecological processes.

Rodent Removal of Fallen Joshua Tree (Yucca brevifolia) Fruits

Abstract 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.

Metabarcoding of Fecal Samples to Determine Herbivore Diets: A Case Study of the Endangered Pacific Pocket Mouse.

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.

Identification of Bartonella Species Isolated from Rodents from Yucatan, Mexico, and Isolation of Bartonella vinsonii subsp. yucatanensis subsp. nov.

Bartonella species are highly endemic among wild rodents in many parts of the world. Blood and/or blood clot cultures from 38 rodents, including 27 Yucatan deer mouse (Peromyscus yucatanicus), 7 Gaumer's spiny pocket mouse (Heteromys gaumeri), 2 black rats (Rattus rattus) and 2 big-eared climbing rats (Ototylomys phyllotis) captured near Merida, Yucatan, Mexico, led to the isolation in 3-4 days of small gram-negative bacilli, which were identified as Bartonella spp. based on colony morphology. DNA extraction and PCR testing were also performed from heart samples of 35 of these 38 rodents. Overall, Bartonella spp. were isolated from the blood/blood clots of 22 (58%) rodents. All Bartonella-positive rodents were Yucatán deer mice from San José Pituch. Sequencing of a fragment of the gltA gene showed that all but one rodent isolates were closest to B. vinsonii subsp. vinsonii and one isolate was intermediate between B. vinsonii subsp. berkhoffii and B. vinsonii subsp. arupensis. Further analysis of concatenated housekeeping genes (gltA, ftsZ, rpoB, and 16S rRNA) suggests that this outlier isolate is a new subspecies within the B. vinsonii genogroup, for which we proposed the name B. vinsonii subsp. yucatanensis.

Ecología poblacional de Heteromys pictus (Rodentia: Heteromyidae), en un bosque tropical caducifolio con perturbación humana en la costa de Oaxaca, México.

Spiny pocket mice Liomys and Heteromys are forest-dwelling granivorous rodents distributed in seasonally dry forest or thorn scrub along the Pacific lowlands or xeric regions in the Mexican Plateau. We analyzed the population dynamics of the spiny pocket mouse Heteromys pictus, in the coast of Oaxaca, Mexico, in two sites of tropical deciduous forest with different degrees of disturbance: ZPP = less disturbed site, and ZMP = more disturbed site. Two plots were established in each area with 66 trap stations; we used the capture-recapture method and trapping for 12 periods for one year. Population density was estimated using the method of Minimum Number of Individuals Known Alive (MNKA). We captured 706 individuals, 290 for the ZPP and 416 for the ZMP. The population density ranged from 28 to 142 ind./ha for both zones, but it was higher for the ZMP (54 against 142 ind./ha). The population density for both areas increased during the rainy season and coincided with the increased recruitment of adults. Reproductive activity occurred throughout the study period in both areas, but it was higher for the ZMP. The sex ratio in the ZPP was 1:1 while in the ZMP was 1:0.75. In the ZMP we found a higher population density and reproductive activity in females, compared to the ZPP. These results suggest that H. pictus prefers the ZMP, indicating that thespeciesisnot significantly affected by human disturbance in the studied location.

Effects of exurban development on trophic interactions in a desert landscape

Mechanisms of ecosystem change in urbanizing landscapes are poorly understood, especially in exurban areas featuring residential or commercial development set in a matrix of modified and natural vegetation. We asked how development altered trophic interactions and ecosystem processes in the matrix. We examined the effect of varying degrees of exurban development (housing density) on a trophic system that included an apex mammalian predator (coyote, Canis latrans), mammalian herbivores (lagomorphs and rodents), and herbaceous plants. We tested the hypothesis that plant recruitment would be negatively affected by exurban development due either to increases in herbivores associated with increased resource availability (a bottom–up effect) or to a reduction in predators that avoid humans (a top–down effect). In Las Cruces, New Mexico, USA, four replicate sites were located in each of three urbanization levels: high density exurban, low density exurban, and wildland dominated by Chihuahuan Desert vegetation. Seedling trays measured herbivory rates, live trapping estimated abundance of pocket mice and kangaroo rats, and remotely-triggered wildlife cameras estimated the activity of lagomorphs and coyotes. Increased herbivory on seedlings and decreased herbaceous plant recruitment were observed in high density exurban areas. Overall rodent abundance, seed consumption rates, and activity of the lagomorph Lepus californicus did not vary with urbanization level. Activity by another lagomorph, Sylvilagus audubonii, and coyotes was highest in dense exurban areas, consistent with a bottom–up effect. Exurban development can have important indirect effects on trophic interactions occurring in adjacent, untransformed ecosystems. Similar to earlier studies, such effects in the Chihuahuan Desert may be mediated by bottom–up processes associated with anthropogenic inputs.

Fleas, Lice, and Epifaunistic Pseudoscorpions of Some Native Mammals in Northwestern Costa Rica

ABSTRACT: Two species of chewing lice (Eutrichophilus mexicanus and Neotrichodectes mephiditis), 4 species of sucking lice (Fahrenholzia fairchildi, Fahrenholzia ferrisi, Fahrenholzia n. sp., and Hoplopleura mendezi), 4 species of fleas (Kohlsia traubi, Polygenis roberti beebei, Rhopalopsyllus australis australis, and Rhopalopsyllus lugubris), and 1 species of epifaunistic pseudoscorpion (Epichernes guanacastensis) were recorded from native mammals in the Area de Conservacion Guanacaste in northwestern Costa Rica during a parasite All Taxa Biodiversity Inventory from 1996 to 2004. All 6 species of lice were host specific. Fleas were less host specific and included a record of a rodent flea (R. a. australis) from a jaguar, Panthera onca. Epifaunistic pseudoscorpions were recorded only from Salvin’s spiny pocket mouse, Liomys salvini, on which they appear to be mutualistic with the host by preying on ectoparasites in the host pelage. Eutrichophilus mexicanis, N. mephiditis, F. ferrisi, H. mendezi, K. traub...

Intercontinental-wide consequences of compromise-breaking adaptations: the case of desert rodents

Desert rodent assemblages from around the world provide convergent, but independent crucibles for testing theory and deducing general ecological principles. The heteromyid rodents of North America and the gerbils of the Middle East and their predators provide such an example. Both sets of rodents face predation from owls and vipers, but the North American species possess unique traits that may represent macroevolutionary breakthroughs: rattlesnakes have infra-red sensitive sensory pits, and heteromyids have cheek pouches. To test their significance, we brought together two gerbils (Middle East), two heteromyid rodents (a kangaroo rat and a pocket mouse; North America) in a common setting (a vivarium in the Negev Desert), and quantified the “opinions” of the rodents towards the North American sidewinder rattlesnake and the Middle Eastern Saharan horned viper and the foraging behavior of each in the face of these snake predators plus owl predators. Gerbils are fairly evenly matched in their anti-predator abilities, while the heteromyids differ widely, and these seem to match well with and may determine the types of mechanisms of species coexistence that operate in the communities of each continent. Evolutionary history, macroevolutionary traits, and risk management therefore combine to determine the characteristics of the organisms and the organization of their communities.

A mast-seeding desert shrub regulates population dynamics and behavior of its heteromyid dispersers.

Granivorous rodent populations in deserts are primarily regulated through precipitation‐driven resource pulses rather than pulses associated with mast‐seeding, a pattern more common in mesic habitats. We studied heteromyid responses to mast‐seeding in the desert shrub blackbrush (Coleogyne ramosissima), a regionally dominant species in the Mojave–Great Basin Desert transition zone. In a 5‐year study at Arches National Park, Utah, USA, we quantified spatiotemporal variation in seed resources in mast and intermast years in blackbrush‐dominated and mixed desert vegetation and measured responses of Dipodomys ordii (Ord's kangaroo rat) and Perognathus flavescens (plains pocket mouse). In blackbrush‐dominated vegetation, blackbrush seeds comprised >79% of seed production in a mast year, but 0% in the first postmast year. Kangaroo rat abundance in blackbrush‐dominated vegetation was highest in the mast year, declined sharply at the end of the first postmast summer, and then remained at low levels for 3 years. Pocket mouse abundance was not as strongly associated with blackbrush seed production. In mixed desert vegetation, kangaroo rat abundance was higher and more uniform through time. Kangaroo rats excluded the smaller pocket mice from resource‐rich patches including a pipeline disturbance and also moved their home range centers closer to this disturbance in a year of low blackbrush seed production. Home range size for kangaroo rats was unrelated to seed resource density in the mast year, but resource‐poor home ranges were larger (P < 0.001) in the first postmast year, when resources were limiting. Blackbrush seeds are higher in protein and fat but lower in carbohydrates than the more highly preferred seeds of Indian ricegrass (Achnatherum hymenoides) and have similar energy value per unit of handling time. Kangaroo rats cached seeds of these two species in similar spatial configurations, implying that they were equally valued as stored food resources. Blackbrush mast is a key resource regulating populations of kangaroo rats in this ecosystem.