Sylvilagus Audubonii Research Articles

Dryland state transitions alter trophic interactions in a predator-prey system.

Environmental change is expected to alter trophic interactions and food web dynamics with consequences for ecosystem structure, function and stability. However, the mechanisms by which environmental change influences top-down and bottom-up processes are poorly documented. Here, we examined how environmental change caused by shrub encroachment affects trophic interactions in a dryland. The predator-prey system included an apex canid predator (coyote; Canis latrans), an intermediate canid predator (kit fox; Vulpes macrotis), and two herbivorous lagomorph prey (black-tailed jackrabbit, Lepus californicus; and desert cottontail, Sylvilagus audubonii) in the Chihuahuan Desert of New Mexico, USA. We evaluated alternative hypotheses for how shrub encroachment could affect habitat use and trophic interactions, including (i) modifying bottom-up processes by reducing herbaceous forage, (ii) modifying top-down processes by changing canid space use or the landscape of fear experienced by lagomorph prey and (iii) altering intraguild interactions between the dominant coyote and the intermediate kit fox. We used 7 years of camera trap data collected across grassland-to-shrubland gradients under variable precipitation to test our a priori hypotheses within a structural equation modelling framework. Lagomorph prey responded strongly to bottom-up pulses during years of high summer precipitation, but only at sites with moderate to high shrub cover. This outcome is inconsistent with the hypothesis that bottom-up effects should be strongest in grasslands because of greater herbaceous food resources. Instead, this interaction likely reflects changes in the landscape of fear because perceived predation risk in lagomorphs is reduced in shrub-dominated habitats. Shrub encroachment did not directly affect predation pressure on lagomorphs by changing canid site use intensity. However, site use intensity of both canid species was positively associated with jackrabbits, indicating additional bottom-up effects. Finally, we detected interactions between predators in which coyotes restricted space use of kit foxes, but these intraguild interactions also depended on shrub encroachment. Our findings demonstrate how environmental change can affect trophic interactions beyond traditional top-down and bottom-up processes by altering perceived predation risk in prey. These results have implications for understanding spatial patterns of herbivory and the feedbacks that reinforce shrubland states in drylands worldwide.

Neighborhood ethnicity is related to mammal occupancy and activity across a desert metropolitan area

AbstractCities support abundant human and wildlife populations that are shaped indirectly and directly by human decisions, often resulting in unequal access to environmental services and accessible open spaces. Urban land cover drives biodiversity patterns across metropolitan areas, but at smaller scales that matter to local residents, neighborhood socio‐cultural factors can influence the presence and abundance of wildlife. Neighborhood income is associated with plant and animal diversity in some cities, but the influence of other social variables is less well understood, especially across desert ecosystems. We explored wildlife distribution across gradients of neighborhood ethnicity in addition to income and landscape characteristics within residential areas of metropolitan Phoenix, Arizona, USA. Utilizing data from 38 wildlife cameras deployed in public parks and undeveloped open spaces within or near suburban neighborhoods, we estimated occupancy and activity patterns of common mammal species, including species native to the Sonoran Desert (coyote [Canis latrans] and desert cottontail rabbit [Sylvilagus audubonii]), and non‐native domestic cat (Felis catus). Neighborhood ethnicity (percentage of Latino residents) appeared to exhibit a negative relationship with occupancy for coyotes and cottontail rabbits. Additionally, daily activity patterns of coyotes occurred later in the evenings and mornings in neighborhoods with higher proportions of Latino residents, but activity was unaffected by differences in neighborhood income. This study is one of the first to show that social‐ecological mechanisms associated with patterns of neighborhood ethnicity as well as income may help to shape wildlife distribution in cities. These findings have implications for equitable management and provisioning of ecosystem services for urban residents and highlight the importance of considering a range of social covariates to better understand biodiversity outcomes in urban and urbanizing areas.

SEASONAL AND HOST-ASSOCIATED VARIATION IN BOT FLY (OESTRIDAE: CUTEREBRINAE) PARASITISM OF LAGOMORPHS ACROSS AN ARID-LAND ECOSYSTEM IN SOUTHERN NEW MEXICO.

Bot flies (Oestridae: Cuterebrinae) are obligate mammalian parasites that complete the larval stage of their life cycle under the skin of their host. Most detailed studies of bot fly larval disease ecology have been conducted in temperate deciduous zone rodent systems. To understand the relative importance of seasonal and spatial factors, as well as factors intrinsic to the host, in underpinning the likelihood and extent of parasitism by bot flies in non-rodent hosts as well as in arid-land ecosystems, we examined the dynamic for black-tailed jackrabbit (Lepus californicus) and desert cottontail (Sylvilagus audubonii) parasitism by bot fly larvae (Cuterebra spp.) across 7 repeatedly sampled sites spread across approximately 500 km of the Chihuahuan Desert ecoregion of southern New Mexico. This environment is characterized by a climate that includes hot dry summers and cool to cold dry winters, as well as strongly seasonal summer monsoonal rains. Lagomorphs are a common mid-sized mammal in these landscapes. Bot fly parasitism was strongly seasonal, with peak prevalence and abundance in the spring, and there was spatial variation in the extent of parasitism between collection sites. Additionally, jackrabbits in better body condition were less likely to be parasitized (as indicated by kidney fat index). We did not find sex-based differences in bot fly parasitism between male and female jackrabbits. Thus, in arid-land ecoregions, abiotic factors are likely the primary driver of the bot fly-host interaction, whereas factors intrinsic to the host were of secondary importance for characterizing the interactions of bot flies and lagomorphs.

Rickettsial antibodies and Rickettsia bellii detection in lagomorphs and their ectoparasites in Northern Baja California, Mexico.

Lagomorphs-principally rabbits and hares-have been implicated as hosts for vectors and reservoirs for pathogens associated with multiple rickettsial diseases. Western North America is home to diverse rickettsial pathogens which circulate among multiple wild and domestic hosts and tick and flea vectors. The purpose of this study was to assess lagomorphs and their ectoparasites in 2 locations in northern Baja California, Mexico, for exposure to and infection with rickettsial organisms. In total, 55 desert cottontail rabbits (Sylvilagus audubonii) (Baird) and 2 black-tailed jackrabbits (Lepus californicus) (Gray) were captured. In Mexicali, ticks were collected from 44% (14/32) of individuals, and were exclusively Haemaphysalis leporispalustrisNeumann (Acari: Ixodidae); in Ensenada, ticks were collected from 70% (16/23) individuals, and 95% were Dermacentor parumapertus. Euhoplopsyllus glacialis affinisBaker (Siphonaptera: Pulicidae) fleas were collected from 72% of rabbits and 1 jackrabbit from Mexicali, while the few fleas found on hosts in Ensenada were Echidnophaga gallinaceaWestwood (Siphonaptera: Pulicidae) and Cediopsylla inaequalis(Siphonaptera: Pulicidae). Rickettsia bellii was the only rickettsial organism detected and was identified in 88% of D. parumapertus and 67% of H. leporispalustris ticks from Ensenada. A single tissue sample from a jackrabbit was positive for R. belli (Rickettsiales: Rickettsiaceae). Hosts in Ensenada had a significantly higher prevalence of rickettsial antibodies than hosts in Mexicali (52.3% vs. 21.4%). Although R. bellii is not regarded as pathogenic in humans or other mammals, it may contribute to immunity to other rickettsiae. The marked difference in distribution of ticks, fleas, and rickettsial exposure between the 2 locations suggests that disease transmission risk may vary markedly between communities within the same region.

Fruit Production and Seed Dispersal of Opuntia phaeacantha (Cactaceae) in the Southwest Mojave Desert

Mode of reproduction in the genus Opuntia varies among species but often includes both vegetative and sexual reproduction, with the latter often facilitated by animal seed dispersal. In this multi-year study, we examined fruit and seed production and seed dispersal in the Mojave prickly pear (Opuntia phaeacantha) at two sites in the southwest Mojave Desert. Between 2015–2020 we counted fruits on randomly selected cactus patches, quantified fruit losses from those patches over time, collected fruits, and extracted and counted seeds. To assess seed dispersal, we collected fresh mammal pellets in belt transects at one site from 2016–2018; pellets were examined for Opuntia seeds. To assess animal fruit consumption and removal, we installed camera traps at one site. We baited selected patches with fruits and photographed animals that consumed or removed fruits. Fruit numbers varied widely among years and sites, although fruit production was not significantly correlated with climatic variables. Fruit losses were high at both sites, occurring more slowly in years of high fruit production. Seeds per fruit also varied with means ranging from 65 to 125 seeds. Rabbit and deer (Odocoileus hemionus) pellets were abundant at one site where we found 0.02 seeds per rabbit pellet but none in deer pellets. Camera traps baited with fruits revealed that they disappeared more quickly from patch edges than from patch interiors. Desert cottontails (Sylvilagus audubonii) and California jackrabbits (Lepus californicus) dominated photographs at patch edges while nearly all interior photographs were of white-tailed antelope squirrels (Ammospermophilus leucurus). In summary, although the number of seeds produced by O. phaeacantha is highly variable, the total number per site is high in some years, and fruits are consumed and seeds spread by animal dispersers.

Microplastic abundance in feces of lagomorphs in relation to urbanization

The presence of microplastics (MPs) in marine environments has been extensively documented. However, studies of terrestrial species are scarce. Fecal samples (105) of lagomorphs were collected at sites with different levels of urbanization in the Baja California Chaparral and analyzed to quantify and characterize MPs found in the feces. The lagomorph species recorded in the study area are the desert cottontail rabbit (Sylvilagus audubonii), brush rabbit (Sylvilagus bachmani), and black-tailed jackrabbit (Lepus californicus), which play important roles in the food web of the chaparral ecosystem. Microplastics were identified using attenuated total reflectance Fourier transform infrared spectroscopy. Microplastics were detected in 49 % of the samples, with fibers being the dominant shape found (72 %). Most (75 %) of the MPs were <1 mm in size, with a mean length of 0.93 ± 0.99 mm (median 0.60 mm, range 0.02 – <5 mm). Polyamide was the dominant polymer (54 %), indicating that MPs are likely derived from textiles; polyethylene was also abundant (27 %). A difference was also observed in the abundance of MPs in feces from sites with different levels of urbanization, with the highest abundance in feces from the urban sites.

Molecular Characterization of a Novel Relapsing Fever Borrelia Species from the Desert Cottontail (Sylvilagus audubonii) in New Mexico, USA.

The Borrelia genus comprises vector-borne, spirochete bacteria infecting vertebrates worldwide. We characterized a novel relapsing fever Borrelia species from a desert cottontail (Syvilagus audubonii) from New Mexico, US, using an established multilocus sequence analysis approach. Phylogenetic analysis of the flagellin gene (flaB) and four other protein-coding loci (clpX, pepX, recG, rplB) grouped the novel Borrelia species with hard tick relapsing fever borreliae Borrelia lonestari, Borrelia theileri, and Borrelia miyamotoi. The identity of the vectors and other vertebrate hosts, geographic distribution, and zoonotic potential of this novel Borrelia species deserve further investigation.

Status of Desert Cottontails (Sylvilagus audubonii) in Arizona, 1955-2020

More than 60 years of survey and hunt data indicate declining trends in Arizona's desert cottontail (Sylvilagus audubonii) populations. Survey numbers, hunter participation, harvests, and hunt success for this species after 1990 are considerably less than prior to the 1980s. Summer surveys conducted in the 1950s and repeated in 2019 and 2020 showed that populations were not uniform and related to winter precipitation amounts (r2=0.71, p=0.07). Although one population in 2020 was at an historic low, others were as robust as in the 1950s. Although declines in hunter numbers may be due to sociological factors, the reasons for declining trends in cottontail survey numbers and hunt success are more difficult to evaluate. Precipitation amounts and temperature data suggest that population declines might have been caused by increased mortality due to climate change, increases in predator populations, and/or the presence of disease.

Early circulation of rabbit haemorrhagic disease virus type 2 in domestic and wild lagomorphs in southern California, USA (2020-2021).

Rabbit haemorrhagic disease virus type 2 (RHDV2) causes a severe systemic disease with hepatic necrosis. Differently from classic RHDV, which affects only European rabbits (Oryctolagus cuniculus), RHDV2 can affect many leporid species, including hares (Lepus spp.) and cottontail rabbits (Sylvilagus spp.). RHDV2 emerged in Europe in 2010 and spread worldwide. During the last 5 years, there have been multiple outbreaks in North America since the first known event in 2016 in Quebec, Canada, including several detections in British Columbia, Canada, between 2018 and 2019, Washington State and Ohio, USA, in 2018 and 2019, and New York, USA, in 2020. However, the most widespread outbreak commenced in March 2020 in the southwestern USA and Mexico. In California, RHDV2 spread widely across several southern counties between 2020 and 2021, and the aim of this study was to report and characterize these early events of viral incursion and circulation within the state. Domestic and wild lagomorphs (n = 81) collected between August 2020 and February 2021 in California with a suspicion of RHDV2 infection were tested by reverse transcription quantitative real-time PCR on the liver, and histology and immunohistochemistry for pan-lagovirus were performed on liver sections. In addition, whole genome sequencing from 12 cases was performed. During this period, 33/81 lagomorphs including 24/59 domestic rabbits (O. cuniculus), 3/16 desert cottontail rabbits (Sylvilagus audubonii), and 6/6 black-tailed jackrabbits (Lepus californicus) tested positive. All RHDV2-positive animals had hepatic necrosis typical of pathogenic lagovirus infection, and the antigen was detected in sections from individuals of the three species. The 12 California sequences were closely related (98.9%-99.95%) to each other, and also very similar (99.0%-99.4%) to sequences obtained in other southwestern states during the 2020-2021 outbreak; however, they were less similar to strains obtained in New York in 2020 (96.7%-96.9%) and Quebec in 2016 (92.4%-92.6%), suggesting that those events could be related to different viral incursions. The California sequences were more similar (98.6%-98.7%) to a strain collected in British Columbia in 2018, which suggests that that event could have been related to the 2020 outbreak in the southwestern USA.

Burrow webs: Clawing the surface of interactions with burrows excavated by American badgers.

Ecosystem engineers are organisms that influence their environment, which includes alterations leading to habitat provisioning for other species. Perhaps the most well‐examined guild of species provisioning habitat for other species is tree cavity excavators or woodpeckers (Picidae). Many studies have examined the suite of secondary cavity users that rely on woodpeckers, and how the ecological network of secondary users, collectively referred to as the nest web, changes across communities. Despite similar habitat provisioning processes, fewer studies have assessed the suite of species associated with burrowers providing access to subterranean habitat. Here, we begin to characterize the burrow web provisioned by American badgers (Taxidea taxus) and evaluate the diversity and frequency of species interactions we detected at abandoned badger burrows in Wyoming, USA. We deployed camera traps at 23 badger burrows and identified interactions with the burrow by birds, mammals, and reptiles. Overall, we discovered 31 other species utilizing badger burrows, consisting of 12 mammals, 18 birds, and 1 reptile. Mammals, other than American badgers themselves and other fossorial species such as ground squirrels (Urocitellus sp.), frequently using burrows included mice (Peromyscus sp.), long‐tailed weasel (Mustela frenata), pygmy rabbit (Brachylagus idahoensis), and desert cottontail (Sylvilagus audubonii). Of the 18 bird species detected, most accounted for <5% of overall detections, besides chipping sparrows (Spizella passerina) at 7.2%–11.5% of detections. The most common category of detection by bird species was foraging, contrary to mammals, which used the burrow frequently and were commonly observed entering and exiting the burrow. This work provides additional context on the ecological role of American badgers within their environment. More broadly, this work scratches the surface of many remaining questions to explore with the aim of advancing our understandings about burrow webs across the diversity of burrowing species and the communities in which they occur.

Pathology of Lagovirus europaeus GI.2/RHDV2/b (Rabbit Hemorrhagic Disease Virus 2) in Native North American Lagomorphs.

Rabbit hemorrhagic disease, a notifiable foreign animal disease in the US, was reported for the first time in wild native North American lagomorphs in April 2020 in the southwestern US. Affected species included the desert cottontail (Sylvilagus audubonii), mountain cottontail (Sylvilagus nuttallii), black-tailed jackrabbit (Lepus californicus), and antelope jackrabbit (Lepus alleni). Desert cottontails (n=7) and black-tailed jackrabbits (n=7) collected in April and May 2020 were necropsied at the US Geological Survey National Wildlife Health Center and tested positive for Lagovirus europaeus GI.2, also known as rabbit hemorrhagic disease virus 2 (GI.2/RHDV2/b), by real-time PCR at the US Department of Agriculture's Foreign Animal Disease Diagnostic Laboratory. Gross and microscopic lesions were similar to those reported in European rabbits (Oryctolagus cuniculus) and other hare (Lepus) species with GI.2/RHDV2/b infection; they included epistaxis (12/13; 92%); massive hepatocellular dissociation (14/14; 100%) and necrosis or apoptosis (11/11; 100%); pulmonary congestion (12/12; 100%), edema (12/13; 92%), and hemorrhage (11/12; 92%); and acute renal tubular injury (3/8; 38%). As in previous reports, massive hepatocellular dissociation and necrosis or apoptosis was the most diagnostically distinct finding. As North American Sylvilagus and Lepus species appear to be susceptible to fatal GI.2/RHDV2/b infection, additional work is needed to understand the host range, pathogenicity, and potential population effects of GI.2/RHDV2/b in North America.

Outbreak of rabbit hemorrhagic disease virus 2 in the southwestern United States: first detections in southern California.

An outbreak of rabbit hemorrhagic disease virus 2 (RHDV2)-associated disease occurred in the southwestern United States following its first detection in New Mexico in March 2020. The disease spread throughout several states and was diagnosed for the first time in California on May 11, 2020, in a black-tailed jackrabbit (Lepus californicus). The following day, the California Department of Food and Agriculture (CDFA) issued an order banning the entrance into California of several lagomorph species and their products from any state in which the disease had been detected in the last 12 mo. RHDV2 is a threat to wild lagomorph species in California, including the endangered riparian brush rabbit (Sylvilagus bachmani riparius). Therefore, the California Department of Fish and Wildlife (CDFW) started tracking any mortality event in wild lagomorph populations. As of August 9, 2020, RHDV2 had been detected in wild and domestic lagomorphs of several counties in southern California that were submitted to the California Animal Health and Food Safety laboratory system by the CDFA or the CDFW. These positive cases included 2 additional black-tailed jackrabbits and 3 desert cottontail rabbits (Sylvilagus audubonii). In addition, the infection spilled over to domestic populations, whereby it was confirmed on July 10, 2020, in a domestic rabbit (Oryctolagus cuniculus).

Trypanosoma (Herpetosoma) diversity in rodents and lagomorphs of New Mexico with a focus on epizootological aspects of infection in Southern Plains woodrats (Neotoma micropus).

Protozoan parasites of the genus Trypanosoma infect a broad diversity of vertebrates and several species cause significant illness in humans. However, understanding of the phylogenetic diversity, host associations, and infection dynamics of Trypanosoma species in naturally infected animals is incomplete. This study investigated the presence of Trypanosoma spp. in wild rodents and lagomorphs in northern New Mexico, United States, as well as phylogenetic relationships among these parasites. A total of 458 samples from 13 rodent and one lagomorph species collected between November 2002 and July 2004 were tested by nested PCR targeting the 18S ribosomal RNA gene (18S rRNA). Trypanosoma DNA was detected in 25.1% of all samples, with the highest rates of 50% in Sylvilagus audubonii, 33.1% in Neotoma micropus, and 32% in Peromyscus leucopus. Phylogenetic analysis of Trypanosoma sequences revealed five haplotypes within the subgenus Herpetosoma (T. lewisi clade). Focused analysis on the large number of samples from N. micropus showed that Trypanosoma infection varied by age class and that the same Trypanosoma haplotype could be detected in recaptured individuals over multiple months. This is the first report of Trypanosoma infections in Dipodomys ordii and Otospermophilus variegatus, and the first detection of a haplotype phylogenetically related to T. nabiasi in North America in S. audubonii. This study lends important new insight into the diversity of Trypanosoma species, their geographic ranges and host associations, and the dynamics of infection in natural populations.

Body Weight as an Indicator of Vulnerability to Domestic Cat Predation for Juveniles of Three Species of Cottontail Rabbits (Sylvilagus spp.) in Colorado, USA: Implications for Release Criteria.

Cottontail rabbits (Sylvilagus spp.) are frequently admitted to wildlife rehabilitation facilities due to predation by domestic cats (Felis catus). Our retrospective study (2015-19) of three species (Sylvilagus audubonii, Sylvilagus floridanus, and Sylvilagus nuttallii) indicated that once juveniles reached a weight over 220 g, they were unlikely to present due to domestic cat interactions. This information should be incorporated into release criteria for these species.

Shrub encroachment creates a dynamic landscape of fear for desert lagomorphs via multiple pathways

AbstractShrub encroachment is transforming arid and semiarid grasslands worldwide. Such transitions should influence predator–prey interactions because vegetation cover often affects risk perception by prey and contributes to their landscape of fear. We examined how the landscape of fear of two desert lagomorphs (black‐tailed jackrabbit,Lepus californicus; desert cottontail,Sylvilagus audubonii) changes across grassland‐to‐shrubland gradients at Jornada Basin Long Term Ecological Research site in the Chihuahuan Desert of southern New Mexico. We test whether shrub encroachment shapes risk differently for these two lagomorphs because of differences in body size and predator escape tactics. We also examine whether an ecosystem engineer of grasslands (banner‐tailed kangaroo rat,Dipodomys spectabilis) mediates risk perception through the creation of escape refuge and whether trade‐offs exist between shrub encroachment and the local reduction of banner‐tailed kangaroo rats caused by shrub expansion. We measured perceived predation risk with flight initiation distances (FIDs) and then used structural equation modeling to tease apart the hypothesized direct and indirect pathways for how shrub encroachment could affect perceived risk. A total negative effect of shrub cover on FID was supported for jackrabbits and cottontails, suggesting both species perceive shrubbier habitat as safer. Increases in fine‐scale concealment also reduced risk for cottontails, but not jackrabbits, likely because cottontails rely on crypsis to avoid predator detection whereas jackrabbits rely on speed and agility to outrun predators. Perceived risk was reduced when individuals were near kangaroo rat mounds only for cottontails because the smaller species can use banner‐tailed kangaroo rat mounds as refuge. Shrub encroachment greatly reduced the availability of mounds. Thus, a trade‐off exists for cottontails in which shrub encroachment directly reduced perceived risk, but indirectly increased perceived risk through the local extirpation of an ecosystem engineer. Our work illustrates how the expansion of shrub encroachment can create a dynamic landscape of fear for populations of prey species involving direct and indirect pathways contingent on prey body size, escape tactics, and activities of an ecosystem engineer.

Longitudinal Study of Bacterial Infectious Agents in a Community of Small Mammals in New Mexico.

Background and Objectives: Vector-borne bacterial diseases represent a substantial public health burden and rodents have been recognized as important reservoir hosts for many zoonotic pathogens. This study investigates bacterial pathogens in a small mammal community of the southwestern United States of America. Methods: A total of 473 samples from 13 wild rodent and 1 lagomorph species were tested for pathogens of public health significance: Bartonella, Brucella, Yersinia, Borrelia, Rickettsia spp., and Anaplasma phagocytophilum. Results: Three animals were positive for Yersinia pestis, and one Sylvilagus audubonii had a novel Borrelia sp. of the relapsing fever group. No Brucella, Rickettsia, or A. phagocytophilum infections were detected. Bartonella prevalence ranged between 0% and 87.5% by animal species, with 74.3% in the predominant Neotoma micropus and 78% in the second most abundant N. albigula. The mean duration of Bartonella bacteremia in mark-recaptured N. micropus and N. albigula was 4.4 months, ranging from <1 to 18 months, and differed among Bartonella genogroups. Phylogenetic analysis of the Bartonella citrate synthase gene (gltA) revealed 9 genogroups and 13 subgroups. Seven genogroups clustered with known or previously reported Bartonella species and strains while two were distant enough to represent new Bartonella species. We report, for the first time, the detection of Bartonella alsatica in North America in Sylvilagus audubonii and expand the known host range of Bartonella washoensis to include Otospermophilus variegatus. Interpretation and Conclusion: This work broadens our knowledge of the hosts and geographic range of bacterial pathogens that could guide future surveillance efforts and improves our understanding of the dynamics of Bartonella infection in wild small mammals.

A protocol for differentiating late Quaternary leporids in southern California with remarks on Project 23 lagomorphs at Rancho La Brea, Los Angeles, California, USA

Leporid remains are common in Quaternary fossil assemblages and are useful paleoenvironmental indicators. Identifying leporid fossils to species is challenging, though previous work has shown that identifications are more feasible if fossils can be narrowed down to a subset of potential species occurring across limited spatial scales. We sampled 120 adult and nine juvenile dentaries of six extant western North American species (Lepus americanus, L. californicus, L. townsendii, Sylvilagus audubonii, S. bachmani, and S. nuttallii) to establish useful characters for genus and species-level identification of late Quaternary leporid fossils in California. Most individuals can be differentiated from individuals of other species using a combination of lower third premolar enamel folding patterns and dental measurements. However, it is difficult to discriminate dental elements among L. californicus and L. townsendii and elements of S. nuttallii from S. audubonii, S. bachmani, and L. americanus. Here we present criteria for differentiating western leporid dental remains, apply the criteria to identify specimens recovered from several late Quaternary fossil deposits at Rancho La Brea (RLB), California, collectively known as Project 23, and reconstruct changes in relative fossil leporid abundances there. Using our criteria, we identified two extant species, S. audubonii and S. bachmani, among the Project 23 fossils. In addition to relative abundance changes across several RLB deposits, S. audubonii and S. bachmani generally become larger through time, possibly in response to local environmental changes. Establishing region-specific identification criteria as done here may prove useful for discerning morphologically similar species at prehistoric sites elsewhere.

TEMPORAL NICHE SEPARATION OF DESERT COTTONTAILS (SYLVILAGUS AUDUBONII) AND BLACK-TAILED JACKRABBITS (LEPUS CALIFORNICUS) IN THE CHIHUAHUAN DESERT

Desert cottontails (Sylvilagus audubonii) and black-tailed jackrabbits (Lepus californicus) occur in sympatry throughout the southwestern United States and northern Mexico, including in the Chihuahuan Desert. Their ecological niches are similar but separated by variations of diet and microhabitat. To determine if niche separation may be supplemented by differing times of foraging activity, I first tested various lures and baits and determined the optimal attractant for camera stations to be alfalfa hay and apple juice. I then observed desert cottontail and black-tailed jackrabbit activity at baited and control camera stations. Peak seasonal foraging activity occurred in winter for desert cottontails and in spring for black-tailed jackrabbits. Early morning activity peaked in black-tailed jackrabbits 1 h later than in desert cottontails, but otherwise general diel activity levels were similar between the two species. However, times of peak feeding, as determined by comparisons of baited and control stations, were clearly separated. Thus, niche separation between desert cottontails and black-tailed jackrabbits in the Chihuahuan Desert may be increased by differing time distributions of foraging activity.

A Comparison of Diurnal Resting Sites Used by Sylvilagus audubonii and Lepus californicus in the Chihuahuan Desert

Sylvilagus audubonii (desert cottontail) and Lepus californicus (black-tailed jackrabbit) occur in sympatry in the southwestern United States and northern Mexico. During the daytime, both species occupy shallow excavations under shrubs known as forms. Comparisons of form and shrub characteristics between the 2 species can provide insights into connections between body size, physiology, and behavior. I examined forms of the 2 species in the Chihuahuan Desert in southern New Mexico, USA, from 2014 to 2016. In response to temperature, S. audubonii varied the structure of its forms and dug burrows, whereas L. californicus did not. Sylvilagus audubonii forms were most commonly located in the centers of patches of shrubs, whereas L. californicus forms were most commonly on the edges of patches. Overhead canopy depth and exposure to direct sunlight were not different between the 2 species, but canopy heights were less at S. audubonii forms than at L. californicus forms. Sylvilagus audubonii individuals were less visible to predators than L. californicus individuals at predator eye level in all directions, and the horizontal extent of canopies was greater at S. audubonii forms than at L. californicus forms in all directions except to the left side. An asymmetry was evident in the exposure of S. audubonii to predators, which may be the result of brain lateralization. Although distance to nearest neighbor shrubs was not different between the 2 species, open space around L. californicus forms was greater than around S. audubonii forms. Lepus californicus forms were located under Larrea tridentata in proportion to its availability and more often than forms of S. audubonii, which were located under L. tridentata less often than it was available. These observations are consistent with concordant ensembles of adaptations in which S. audubonii is smaller, more sensitive to heat, and more inclined to hide rather than run from predators in comparison with L. californicus.

Vertebrate herbivory on shrub seedlings in California sage scrub: important but understudied interactions

Herbivory is poorly characterized in the endangered California sage scrub ecosystem, because previous studies were conducted only in winter and spring. To better understand vertebrate herbivore impacts, we first examined if and when vertebrate herbivores influence Artemisia californica seedling survivorship by examining differences in mortality between caged and uncaged seedlings. Then, we examined: (1) vertebrate herbivore preference of common sage scrub shrub species, and (2) which vertebrate species constitute important herbivores in the ecosystem. We found that mortality for uncaged A. californica seedlings was twice that of caged seedlings, and occurred in the summer and early fall, when previous studies in the system were not conducted. Short leaved shrubs, Artemisia californica and Eriogonum fasciculatum, were more susceptible to herbivory than broader leaved Salvia apiana and Eriodictyon trichocalyx. However, susceptibility likely depends on the herbivore assemblage, as the three main herbivore species [Sylvilagus audubonii (desert cottontail), Zonotrichia leucophrys (white-crowned sparrow; a bird, not a mammal), and Otospermophilus beecheyi (California gray squirrel)] all had different shrub preferences. Our results contrast with previous studies that suggests that native vertebrate herbivores facilitate shrub seedling survivorship by highlighting that late-season vertebrate herbivory may negatively affect shrub seedling survivorship. We demonstrate the complex but understudied role herbivores play in the sage scrub ecosystem, and highlight that further study of these key ecological interactions is warranted.