Arthur D. Middleton’s research while affiliated with University of California, Berkeley and other places

Ungulates play vital roles in ecological systems, shaping plant biomass and diversity via herbivory and impacting soil properties through trampling and nutrient deposition. As ungulate communities fluctuate across the globe, the extent to which wild ungulates and domestic livestock can play similar ecological roles is an increasingly vital - and fraught - question. Here, we synthesized the literature directly comparing wild and domestic ungulate effects on above- and belowground ecosystem responses to assess the direction and relative strength of species’ impacts within shared environments. We then investigated the intrinsic and extrinsic mechanisms researchers identified as driving differences in ecosystem responses to wild and domestic ungulates. Overall, our synthetic review revealed that surprisingly few studies directly compare the effects of wild and domestic ungulates, and even fewer explicitly consider the mechanisms underlying observed outcomes. We found that wild and domestic ungulate effects on plant and soil variables are overwhelmingly similar in kind, differing in intensity rather than direction, with domestic ungulates exhibiting stronger effects on ecosystem responses. Specifically, livestock appear to reduce plant biomass and cover more than wild species, but wild ungulates exhibit more positive effects on plant diversity. Diet and stocking density were by far the most frequently referenced mechanisms explaining differences between wild and domestic ungulates, and other mechanisms (e.g. behavior, movement, veterinary treatments) were rarely considered, let alone tested explicitly. Thus, more intentional study of the intrinsic and extrinsic factors underlying ungulate effects on ecosystems, and particularly on belowground processes, is necessary for a more complete understanding of the functional interchangeability - or irreplaceability - of wild and domestic ungulates in a rapidly changing world.

Many ungulates migrate between distinct summer and winter ranges, and identifying, mapping, and conserving these migration corridors have become a focus of local, regional, and global conservation efforts. Brownian bridge movement models (BBMMs) are commonly used to empirically identify these seasonal migration corridors; however, they require location data sampled at relatively frequent intervals to obtain a robust estimate of an animal's movement path. Fitting BBMMs to sparse location data violates the assumption of conditional random movement between successive locations, overestimating the area (and width) of a migration corridor when creating individual and population‐level occurrence distributions and precluding the use of low‐frequency, or sparse, data in mapping migration corridors. In an effort to expand the utility of BBMMs to include sparse GPS data, we propose an alternative approach to model migration corridors from sparse GPS data. We demonstrate this method using GPS data collected every 2 h from four mule deer (Odocoileus hemionus) and four elk (Cervus canadensis) herds within Wyoming and Idaho. First, we used BBMMs to estimate a baseline corridor for the 2‐h data. We then subsampled the 2‐h data to one location every 12 h (a proxy for sparse data) and fitted BBMMs to the 12‐h data using a fixed motion variance (FMV) value, instead of estimating the Brownian motion variance empirically. A range of FMV values was tested to identify the value that best approximated the baseline migration corridor. FMV values within a species‐specific range (mule deer: 400–1200 m²; elk: 600–1600 m²) successfully delineated migration corridors similar to the 2‐h baseline corridors; overall, lower values delineated narrower corridors and higher values delineated wider corridors. Optimal FMV values of 800 m² (mule deer) and 1000 m² (elk) decreased the inflation of the 12‐h corridors relative to the 2‐h corridors from traditional BBMMs. This FMV approach thus enables using sparse movement data to approximate realistic migration corridor dimensions, providing an important alternative when movement data are collected infrequently. This approach greatly expands the number of datasets that can be used for migration corridor mapping—a useful tool for management and conservation across the globe.

Private lands support much of the biodiversity in North America, but supporting wildlife can be costly for landowners. Innovative tools are needed to reduce the risks that wildlife pose to private landowners while conserving biodiversity. Here, we present a range of innovative tools that have effectively been used to “de‐risk” wildlife occupancy of private lands in the Greater Yellowstone Ecosystem. Lessons learned from these risk reduction strategies inform conservation more broadly by highlighting the importance of economic and risk‐management considerations to wildlife conservation on private lands. Incorporating de‐risking tools into the wildlife conservation toolbox can help conservation practitioners more strategically allocate resources to benefit wildlife and the private lands that help support them.

Context Widespread globally, roads impact the distribution of wildlife by influencing habitat use and avoidance patterns near roadways and disrupting movement across them. Wildlife responses to roads are known to vary across species; however within species, the response to roads may depend on the season or the individual’s behavioral state. Objectives We assess the movement behavior and space use of the most widespread large herbivore in Patagonia, the guanaco (Lama guanicoe). We estimated the preference or avoidance to paved or unpaved roads (the proximity effect) and the preference or avoidance to traverse them (the crossing effect). Methods Using GPS collar data, we combined Hidden Markov Models with an integrated step selection analysis to segment guanaco movement trajectories into individual behaviors and test for differences in road effects on movement. Results We found that guanacos display distinct movement responses to different types of roads depending on their behavioral state. Guanacos select for proximity to paved roads while foraging, but against them when traveling. Yet, guanacos select for unpaved roads when traveling. Despite the selection for proximity to paved roads, guanacos avoid crossing them, irrespective of their behavioral state. Conclusion Our findings offer significant implications for guanaco distribution and management across Patagonia. The selection for roads strongly influences the distribution of guanacos, which could concentrate grazing in some areas while freeing others. Despite potential benefits such as increased vegetation near roadsides, increased association with roads while foraging may result in an ecological trap. Finally, the strong aversion to crossing paved roads raises concerns about habitat loss and connectivity.

Animal carcass decomposition is an often-overlooked component of nutrient cycles. The importance of carcass decomposition for increasing nutrient availability has been demonstrated in several ecosystems, but impacts in arid lands are poorly understood. In a protected high desert landscape in Argentina, puma predation of vicuñas is a main driver of carcass distribution. Here, we sampled puma kill sites across three habitats (plains, canyons, and meadows) to evaluate the impacts of vicuña carcass and stomach decomposition on soil and plant nutrients up to 5 years after carcass deposition. Soil beneath both carcasses and stomachs had significantly higher soil nutrient content than adjacent reference sites in arid, nutrient-poor plains and canyons, but not in moist, nutrient-rich meadows. Stomachs had greater effects on soil nutrients than carcasses. However, we did not detect higher plant N concentrations at kill sites. The biogeochemical effects of puma kills persisted for several years and increased over time, indicating that kills do not create ephemeral nutrient pulses, but can have lasting effects on the distribution of soil nutrients. Comparison to broader spatial patterns of predation risk reveals that puma predation of vicuñas is more likely in nutrient-rich sites, but carcasses have the greatest effects on soil nutrients in nutrient-poor environments, such that carcasses increase localized heterogeneity by generating nutrient hotspots in less productive environments. Predation and carcass decomposition may thus be important overlooked factors influencing ecosystem functioning in arid environments.

For various temperate ungulate species, recent research has highlighted the potential for spring vegetation phenology ("green-up") to influence individual condition, with purported benefits to population productivity. However, few studies have been able to measure the benefit on vital rates directly, and fewer still have investigated the comparative influence of other phenological periods on ungulate vital rates. In this study, we tracked phenological changes throughout the duration of the growing season and examined how their timing affected the probability of pregnancy in an ungulate population. We did this for elk (Cervus canadensis) across the Greater Yellowstone Ecosystem (GYE) by sampling 1106 adult females in winter at 25 sites over a 13-year period and assessing sources of variation in pregnancy using a Bayesian hierarchical model. Pregnancy rates were generally high across the GYE (82.4%), and the primary influences on probability of pregnancy were the timing of vegetation senescence (“brown-down”) in autumn and exposure to the reproductive disease brucellosis. Earlier forage brown-down in fall negatively influenced the probability of pregnancy of elk aged 6–9 years by an estimated 17.2% within the range (ca. 32 days) of observed brown-down end dates. While summer habitat quality has been inferred to influence elk pregnancy previously, our findings specify the key influence of foraging conditions later in the seasonal cycle, immediately before the breeding season. The reproductive disease brucellosis was also an important factor, reducing the probability of pregnancy by 12.4% in elk in the 6- to 9-year age class. Because pregnancy was tested before most disease-induced abortions occur, the apparent mechanism for this effect is a prolonged reduction in fertility beyond the period of initial exposure in which fetal mortality is typically expected. Our results prompt greater scrutiny of the combined effects of late-season phenology and disease on reproductive rates and population productivity in temperate ungulates.

Prey often induce antipredator behaviors when balancing food acquisition against safety. The starvation–predation hypothesis (SPH) posits that, during food shortages, the risk of starvation requires prey to forego antipredator behavior to increase feeding rates. Such shifts in antipredator behavior may further increase the risk of predation and therefore kill rates by predators. We tested the SPH and its consequences for kill rates in a single large prey, single large predator system. In the Argentine Andes, we evaluated whether risk avoidance by vicuñas ( Vicugna vicugna ) decreased during periods of food scarcity. From three years of GPS relocations collected simultaneously from vicuñas and pumas ( Puma concolor ), resource selection functions revealed that vicuñas increased their exposure to pumas during nongrowing seasons by reducing the avoidance of canyons and increasing selection for meadows, both of which offer more food of higher quality than relatively safe plains. However, and despite vicuñas becoming more risk‐prone during nongrowing seasons, kill rates by pumas did not change between growing and nongrowing seasons. Contrary to evidence from mesocosm experiments, relaxation of antipredator behavior by prey did not translate into increased kill rates by predators. Our results enhance understanding of the interplay between food limitation and predator–prey interactions within ecosystems and may improve ecologists' ability to predict when and where behaviorally mediated trophic cascades are more likely to occur.

Human activity and associated landscape modifications alter the movements of animals with consequences for populations and ecosystems worldwide. Species performing long-distance movements are thought to be particularly sensitive to human impact. Despite the increasing anthropogenic pressure, it remains challenging to understand and predict animals' responses to human activity. Here we address this knowledge gap using 1206 Global Positioning System movement trajectories of 815 individuals from 14 red deer (Cervus elaphus) and 14 elk (Cervus canadensis) populations spanning wide environmental gradients, namely the latitudinal range from the Alps to Scandinavia in Europe, and the Greater Yellowstone Ecosystem in North America. We measured individual-level movements relative to the environmental context, or movement expression, using the standardized metric Intensity of Use, reflecting both the directionality and extent of movements. We expected movement expression to be affected by resource (Normalized Difference Vegetation Index, NDVI) predictability and topography, but those factors to be superseded by human impact. Red deer and elk movement expression varied along a continuum, from highly segmented trajectories over relatively small areas (high intensity of use), to directed transitions through restricted corridors (low intensity of use). Human activity (Human Footprint Index, HFI) was the strongest driver of movement expression, with a steep increase in Intensity of Use as HFI increased, but only until a threshold was reached. After exceeding this level of impact, the Intensity of Use remained unchanged. These results indicate the overall sensitivity of Cervus movement expression to human activity and suggest a limitation of plastic responses under high human pressure, despite the species also occurring in human-dominated landscapes. Our work represents the first comparison of metric-based movement expression across widely distributed populations of a deer genus, contributing to the understanding and prediction of animals' responses to human activity.