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Abstract The availability and quality of food resources can alter the intensity of competition and predation pressure within communities. Understanding species capacity to respond to global change‐driven shifts in resource distribution is therefore crucial for biodiversity conservation. Small mammal communities are often structured by competition for food resources, but understanding and monitoring these processes are currently hindered by lack of functional dietary trait information in these hard‐to‐sample systems. In this study, we collected a comprehensive suite of gastrointestinal (GI) measurements from 26 small mammal species (including some never reported), compared them with more traditional craniodental traits in predicting dietary guild, and used them in a novel way to understand how diet structures 22 small mammal communities across the Appalachian Mountains of eastern North America. As predicted, we found GI traits to be effective dietary trait proxies; they were equally or more accurate than craniodental proportions in predicting the dietary guild of individual species. Furthermore, at the community level, we found that both the mean and functional dispersion of GI length were positively correlated with latitude and measures of temperature seasonality. Our results indicate that small mammal communities in more seasonal environments are filtered to include species with longer GI tracts (on average) as well as those that can partition food resources more finely, as expected based on the lower productivity of these regions. Conversely, communities in less seasonal environments display functional redundancy from the addition of species with short to intermediate GI lengths. Proportions of the GI tract represent novel dietary traits that can illuminate community assembly processes across regional environmental gradients and in the face of changing timing and availability of resources. 

Abstract The “small-eared” species group of Urocitellus ground squirrels (Sciuridae: Xerinae: Marmotini) is endemic to the Great Basin, United States, and surrounding cold desert ecosystems. Most specific and subspecific lineages in this group occupy narrow geographic ranges, and some are of significant conservation concern; despite this, current taxonomy remains largely based on karyotypic or subtle pelage and morphological characteristics. Here, we leverage 2 multilocus DNA sequence data sets and apply formal species delimitation tests alongside morphometric comparisons to demonstrate that the most widespread small-eared species (U. mollis Kennicott, 1863 sensu lato; Piute Ground Squirrel) is comprised of 2 nonsister and deeply divergent lineages. The 2 lineages are geographically separated by the east-west flowing Snake River in southern Idaho, with no sites of sympatry currently known. Based on robust support across the nuclear genome, we elevate populations previously attributed to U. mollis from north of the Snake River to species status under the name Urocitellus idahoensis (Merriam 1913) and propose the common name “Snake River Plains Ground Squirrel” for this taxon. We delimit 2 subspecies within U. idahoensis; U. i. idahoensis (Merriam 1913) in western Idaho and U. i. artemesiae (Merriam 1913) in eastern Idaho. Urocitellus idahoensis is endemic to Idaho and has a maximal range area of roughly 29,700 km2 spanning 22 counties but occurs discontinuously across this area. Our work substantially expands knowledge of ground squirrel diversity in the northern Great Basin and Columbia Plateau and highlights the difficulty in delimiting aridland mammals whose morphological attributes are highly conserved. 

Dehnel’s phenomenon describes a seasonal and reversible winter decrease in body size, which is a trait that predicts total energy demand. However, the phenomenon remains less well- studied than common energy-saving or energy-seeking strategies of mammals. Here, we explore the generality of Dehnel’s phenomenon in Sorex shrews on three continents. First, we use new field sampling to document seasonal phenotypic change in masked shrews (Sorex cinereus) in North America at the lowest latitude yet investigated for this species (35.7°). This includes the first documentation of appendicular skeleton remodification in Sorex. Summer-to- winter decreases in S. cinereus body mass, braincase height, and femur length were 13%, 11.5%, and 8.7%, respectively, with subsequent increases of each in second-year individuals. Second, we compile a comprehensive dataset of Dehnel’s-relevant studies to test whether seasonal plasticity in Sorex globally is related to climate, demonstrating that body and braincase plasticity are functions of cold season temperatures. Meta-analytical models for both these traits generalized by a) applying at both inter- and intraspecific scales, and b) predicting the seasonal change newly observed for S. cinereus. Our results support body size plasticity as an environmentally-responsive innovation in these very small, homeothermic mammals. 

Chiggers are larval mites that pose a significant health risk globally via the spread of scrub typhus. However, fundamental studies into the bacterial microbiome in North America have never been considered. In this investigation, chiggers were collected in the wild from two locally common rodent host species (i.e.,Sigmodon hispidusandPeromyscus leucopus) in three different ecoregions of North Carolina (NC), United States to investigate the composition of their bacterial communities, including potential pathogens. DNA was extracted from the chiggers, and the V3-V4 regions of the bacterial 16S rRNA gene were sequenced using next-generation sequencing (NGS). Alpha diversity metrics revealed significant differences in bacterial diversity among different collection counties. Beta diversity metrics also revealed that bacterial communities across counties were significantly different, suggesting changes in the microbiome as the environment changed. Specifically, we saw that the two western NC collection counties had similar bacterial composition as did the two eastern collection counties. In addition, we found that the chigger microbiome bacterial diversity and composition differed between rodent host species. The 16S rRNA sequence reads were assigned to 64 phyla, 106 orders, 199 families, and 359 genera. The major bacterial phylum was Actinobacteria. The most abundant species were in the generaCorynebacterium,Propionibacterium, class ZB2, andMethylobacterium. Sequences derived from potential pathogens within the generaOrientiaandRickettsiawere also detected. Our findings provide the first insights into the ecology of chigger microbiomes in the US. Further research is required to determine if the potential pathogens found detected in chiggers are a threat to humans and wildlife. 

ABSTRACT Understanding animal movement is at the core of ecology, evolution and conservation science. Big data approaches for animal tracking have facilitated impactful synthesis research on spatial biology and behavior in ecologically important and human-impacted regions. Similarly, databases of animal traits (e.g. body size, limb length, locomotion method, lifespan) have been used for a wide range of comparative questions, with emerging data being shared at the level of individuals and populations. Here, we argue that the proliferation of both types of publicly available data creates exciting opportunities to unlock new avenues of research, such as spatial planning and ecological forecasting. We assessed the feasibility of combining animal tracking and trait databases to develop and test hypotheses across geographic, temporal and biological allometric scales. We identified multiple research questions addressing performance and distribution constraints that could be answered by integrating trait and tracking data. For example, how do physiological (e.g. metabolic rates) and biomechanical traits (e.g. limb length, locomotion form) influence migration distances? We illustrate the potential of our framework with three case studies that effectively integrate trait and tracking data for comparative research. An important challenge ahead is the lack of taxonomic and spatial overlap in trait and tracking databases. We identify critical next steps for future integration of tracking and trait databases, with the most impactful being open and interlinked individual-level data. Coordinated efforts to combine trait and tracking databases will accelerate global ecological and evolutionary insights and inform conservation and management decisions in our changing world. 

Amid global challenges like climate change, extinctions, and disease epidemics, science and society require nuanced, international solutions that are grounded in robust, interdisciplinary perspectives and datasets that span deep time. Natural history collections, from modern biological specimens to the archaeological and fossil records, are crucial tools for understanding cultural and biological processes that shape our modern world. At the same time, natural history collections in low and middle-income countries are at-risk and underresourced, imperiling efforts to build the infrastructure and scientific capacity necessary to tackle critical challenges. The case of Mongolia exemplifies the unique challenges of preserving natural history collections in a country with limited financial resources under the thumb of scientific colonialism. Specifically, the lack of biorepository infrastructure throughout Mongolia stymies efforts to study or respond to large-scale environmental changes of the modern era. Investment in museum capacity and training to develop locally-accessible collections that characterize natural communities over time and space must be a key priority for a future where understanding climate scenarios, predicting, and responding to zoonotic disease, making informed conservation choices, or adapting to agricultural challenges, will be all but impossible without relevant and accessible collections. 

Abstract Anthropogenically-driven climate warming is a hypothesized driver of animal body size reductions. Less understood are effects of other human-caused disturbances on body size, such as urbanization. We compiled 140,499 body size records of over 100 North American mammals to test how climate and human population density, a proxy for urbanization, and their interactions with species traits, impact body size. We tested three hypotheses of body size variation across urbanization gradients: urban heat island effects, habitat fragmentation, and resource availability. Our results demonstrate that both urbanization and temperature influence mammalian body size variation, most often leading to larger individuals, thus supporting the resource availability hypothesis. In addition, life history and other ecological factors play a critical role in mediating the effects of climate and urbanization on body size. Larger mammals and species that utilize thermal buffering are more sensitive to warmer temperatures, while flexibility in activity time appears to be advantageous in urbanized areas. This work highlights the value of using digitized, natural history data to track how human disturbance drives morphological variation. 

Abstract Effects of global climate change on population persistence are often mediated by life‐history traits of individuals, especially the timing of somatic growth, reproductive development, and reproduction itself. These traits can vary among age groups and between the sexes, a result of differential life‐history tactics and levels of lifetime reproductive investment. Unfortunately, the trait data necessary for revealing sex‐specific breeding behaviors and use of breeding cues over reasonably large geographic areas remain sparse for most taxa. In this study, we assembled and analyzed a new reproductive trait base for the North American deer mouse (Peromyscus maniculatus) from digitized natural history specimens and field censuses. We used the data to reconstruct sex‐specific breeding phenologies and their drivers within and among North American ecoregions. Male and female phenologies varied across the geographic range of this species, with discordance in timing and intensity being highest in regions of lower seasonality (and longer breeding seasons). Reliance on environmental variables as breeding cues also appeared to vary in a sex‐specific manner, being most similar for photoperiod and least similar for temperature (positive male response and negative female response); in addition, model validation indicated that phenological models generalized better for males than for females. Finally, our individual‐level trait data also show that male reproductive investment (quantified as relative testis size) varies across the vastly different abiotic and social (i.e., female breeding) contexts studied here. By harmonizing across a broad set of digital data resources, we demonstrate the potential to uncover drivers of phenological variation within species and inform global change predictions at multiple scales of biological organization. 

Abstract While museum voucher specimens continue to be the standard for species identifications, biodiversity data are increasingly represented by photographic records from camera traps and amateur naturalists. Some species are easily recognized in these pictures, others are impossible to distinguish. Here we quantify the extent to which 335 terrestrial nonvolant North American mammals can be identified in typical photographs, with and without considering species range maps. We evaluated all pairwise comparisons of species and judged, based on professional opinion, whether they are visually distinguishable in typical pictures from camera traps or the iNaturalist crowdsourced platform on a 4-point scale: (1) always, (2) usually, (3) rarely, or (4) never. Most (96.5%) of the 55,944 pairwise comparisons were ranked as always or usually distinguishable in a photograph, leaving exactly 2,000 pairs of species that can rarely or never be distinguished from typical pictures, primarily within clades such as shrews and small-bodied rodents. Accounting for a species geographic range eliminates many problematic comparisons, such that the average number of difficult or impossible-to-distinguish species pairs from any location was 7.3 when considering all species, or 0.37 when considering only those typically surveyed with camera traps. The greatest diversity of difficult-to-distinguish species was in Arizona and New Mexico, with 57 difficult pairs of species, suggesting the problem scales with overall species diversity. Our results show which species are most readily differentiated by photographic data and which taxa should be identified only to higher taxonomic levels (e.g., genus). Our results are relevant to ecologists, as well as those using artificial intelligence to identify species in photographs, but also serve as a reminder that continued study of mammals through museum vouchers is critical since it is the only way to accurately identify many smaller species, provides a wealth of data unattainable from photographs, and constrains photographic records via accurate range maps. Ongoing specimen voucher collection, in addition to photographs, will become even more important as species ranges change, and photographic evidence alone will not be sufficient to document these dynamics for many species.