Biology subjects

Stahler, D. R.

Publications and source records attributed to Stahler, D. R..

13 recordsLinked to original sources

bioRxiv2026

Prey age modifies risk-taking behavior in a multi-predator environment

Many species of animals undergo senescence, impacting predator-prey relationships, yet how senescing prey adjust their risk-taking behavior is poorly understood. We used integrated step selection analysis to quantify risk-taking from empirical data. A graphical framework of age-dependent adaptive risk-taking predicted - and our empirical analysis found - a reduction in female elk (Cervus canadensis) risk-taking with age toward wolves (Canis lupus) but not cougars (Puma concolor), underscoring the role of predator hunting mode in ecological dynamics. We estimated average risk-taking toward wolves would be 42% lower in a population with median age 10 versus 4 years, highlighting how a prey populations age structure likely impacts risk-induced trait responses and the potential emergence of predation-risk effects. Our findings suggest that altered risk-taking may be an adaptive behavioral shift rather than a passive consequence of physical decline. Such adaptive changes to risk-taking may represent an underappreciated link between individual behavior and community-level coexistence.

ecology↗

bioRxiv2024

Species-specific interactions with apex carnivores yield unique benefits and burdens for mesocarnivores

Mesocarnivores navigate a complex risk-reward continuum in ecosystems shared with their apex counterparts, balancing scavenging opportunities with risks of mortality. However, the risks to mesocarnivores in multi-carnivore systems are not uniform--often varying with specific apex-meso pairings. Using camera traps and GPS-telemetry, we examined space-use, temporal activity, fine-scale interactions, and scavenging behavior of apex (wolves, cougars) and mesocarnivores (red foxes, coyotes) in northern Yellowstone National Park, USA. Coyote space use was positively linked to wolf presence, while red fox space use was positively linked to cougar presence. Notably, photo-detection rates of mesocarnivores doubled within 24 hours of apex carnivore detections--except for coyotes following cougars. Coyotes were more frequent scavengers at wolf and cougar kills than red foxes, but they also suffered the highest mortality rates. Over 60% of wolf caused coyote mortalities were linked to wolf kill-sites, though wolves rarely consumed the coyotes themselves. In contrast, cougars hunted and consumed coyotes as prey, posing an additional risk of predation. These findings highlight how divergent hunting strategies and habitat preferences between canid and felid apex carnivores create separate risks for mesocarnivores. Our study offers new insights into the species-specific behavioral dynamics that can shape trophic interactions in multi-carnivore systems.

ecology↗

bioRxiv2023

Prions in carnivore feces: recovery from spiking experiments and detection in free-ranging carnivores

Chronic wasting disease (CWD) is a highly contagious, fatal neurodegenerative disease caused by infectious prions (PrPCWD) affecting wild and captive cervids. Although experimental feeding studies have demonstrated prions in feces of crows (Corvus brachyrhynchos), coyotes (Canis latrans), and cougars (Puma concolor), the role of scavengers and predators in CWD epidemiology remains poorly understood. Here we applied the real-time quaking-induced conversion (RT-QuIC) assay to detect PrPCWD in feces from cervid consumers, to advance surveillance approaches, which could be used to improve disease research and adaptive management of CWD. We assessed recovery and detection of PrPCWD by experimental spiking of PrPCWD into carnivore feces from 9 species sourced from CWD-free populations or captive facilities. We then applied this technique to detect PrPCWD from feces of predators and scavengers in free-ranging populations. Our results demonstrate that spiked PrPCWD is detectable from feces of free-ranging mammalian and avian carnivores using RT-QuIC. Results show that PrPCWD acquired in natural settings is detectable in feces from free-ranging carnivores, and that PrPCWD rates of detection in carnivore feces reflect relative prevalence estimates observed in the corresponding cervid populations. This study adapts an important diagnostic tool for CWD, allowing investigation of the epidemiology of CWD at the community-level.

ecology↗

bioRxiv2022

Density-dependent habitat selection alters drivers of population distribution in northern Yellowstone elk

Although it is well established that density dependence drives changes in organismal abundance over time, relatively little is known about how density dependence affects variation in abundance over space. We tested the hypothesis that spatial tradeoffs between food and safety can change the drivers of population distribution, caused by opposing patterns of density-dependent habitat selection (DDHS) that are predicted by the multidimensional ideal free distribution. We addressed this using winter aerial survey data of northern Yellowstone elk (Cervus canadensis) spanning four decades. Supporting our hypothesis, we found positive DDHS for food (herbaceous biomass) and negative DDHS for safety (openness and roughness), such that the primary driver of habitat selection switched from food to safety as elk density decreased from 9.3 to 2.0 elk/km2. Our results demonstrate how population density can drive landscape-level shifts in population distribution, confounding habitat selection inference and prediction, and potentially affecting community-level interactions.

ecology↗

bioRxiv2022

Investigating tri-trophic interactions using bio-energetic demographic models

A central debate in ecology has been the long running discussion on the role of apex predators in affecting the abundance and dynamics of their prey. In terrestrial systems, research has primarily relied on correlational approaches, due to the challenge of implementing robust experiments with replication and appropriate controls. A consequence of this is that we largely suffer from a lack of mechanistic understanding of the population dynamics of interacting species that can be surprisingly complex. Mechanistic models offer an opportunity to examine the causes and consequences of some of this complexity. We present a bioenergetic mechanistic model of a tri-trophic system where the primary vegetation resource follows a seasonal growth function, and the herbivore and carnivore species are modelled using two integral projection models (IPMs) with body mass as the phenotypic trait. Within each IPM, the demographic functions are structured according to bioenergetic principles, describing how animals acquire and transform resources into body mass, energy reserves and breeding potential. We parameterise this model to reproduce the population dynamics of grass, elk and wolves in northern Yellowstone (USA), and investigate the impact of wolf reintroduction on the system. Our model generated predictions that closely matched the observed population sizes of elk and wolf in Yellowstone prior to and post wolf reintroduction. The introduction of wolves into our basal grass-elk bioenergetic model resulted in a population of 99 wolves, and a reduction in elk numbers by 61% (from 14,948 to 5,823) at equilibrium. In turn, vegetation biomass increased by approximately 25% in the growing season and more than 3-fold in the non-growing season. The addition of wolves to the model caused the elk population to shift from being food-limited to being predator-limited, and had a stabilising effect on elk numbers across different years. Wolf predation also led to a shift in the phenotypic composition of the elk population, via a small increase in elk average body mass. Our model represents a novel approach to the study of predator-prey interactions. Explicitly considering and linking bioenergetics, population demography and body mass phenotypes can provide novel insights into the mechanisms behind complex ecosystem processes.

ecology↗

bioRxiv2022

High retention of genomic variation and fitness-related traits in the effective population of reintroduced wolves in Yellowstone National Park

Cooperatively breeding species exhibit numerous strategies to avoid mating with close relatives, inherently reducing effective population size. For species of management concern, accurate estimates of inbreeding and trait depression are crucial for the species future. We utilized genomic and pedigree data for Yellowstone National Park gray wolves to investigate the contributions of foundation stock lineages, genetic architecture of the effective population, and putative fitness consequences of inbreeding. Our dataset spans 25 years and seven generations since reintroduction, encompassing 152 nuclear families and 329 litters. We found over 87% of the pedigree foundation genomes persisted and report influxes of allelic diversity from two translocated wolves from a divergent source in Montana. As expected for group-living species, mean kinship significantly increased over time, although we found high retention of genetic variation. Strikingly, the effective population carried a significantly lower level of genome-wide inbreeding coefficients and autozygosity with shorter decays for linkage disequilibrium relative to the non-breeding population. Lifespan and heterozygosity were higher in the effective population, although individuals who had their first litter at an older age also had higher inbreeding coefficients. Our findings highlight genetic contributions to fitness, and the importance of effective population size and gene flow to counteract loss of genetic variation in a wild, free-ranging social carnivore. It is crucial for managers to mitigate factors that significantly reduce effective population size and genetic connectivity, which supports the dispersion of genetic variation that aids in rapid evolutionary responses to environmental challenges.

evolutionary biology↗

bioRxiv2021

Breeding displacement in gray wolves (Canis lupus): Three males usurp breeding position and pup rearing from a neighboring pack in Yellowstone National Park

Gray Wolves (Canis lupus) are territorial, group living carnivores that live in packs typically consisting of a dominant breeding pair and their offspring. Breeding tenures are relatively short and competitive, with vacancies usually occurring following a breeders death, and are often filled by unrelated immigrants or by relatives of the previous breeder. The frequency and conditions of active breeder displacements are poorly understood. Position changes in the dominance hierarchy are common yet rarely documented in detail. We describe a turnover in male breeding position in a wolf pack by males from a neighboring pack in mid-summer 2016 in Yellowstone National Park. Over the course of two months, three males from the Mollies pack displaced the breeding male of the neighboring Wapiti Lake pack, joined the packs two adult females, and subsequently raised the previous males four approximately three-month old pups. In the four years following the displacement (2017 to 2020), at least one of the intruding males has successfully bred with the dominant female and most years with a subordinate female (who was one of the pups at the time of displacement). The pack reared pups to adulthood each year. Male breeding displacements are likely influenced by male-male competition and female mate choice. These changes are the result of individuals competing to improve breeding position and may lead to increased pack stability and greater reproductive success. We report in detail on the behavior of a closely observed breeding displacement and we discuss the adaptive benefits of the change.

animal behavior and cognition↗

bioRxiv2020

Experimental assessment of K locus effects on the gray wolf response to virus

In North American gray wolves, black coat color is dominantly inherited via a three base pair coding deletion in the canine beta defensin 3 (CBD103) gene. This three base pair deletion, called the KB allele, was introduced through hybridization with dogs and subsequently underwent a selective sweep that increased its frequency in wild wolves. Despite apparent positive selection, KBB wolves have significantly lower fitness than wolves with the KyB genotype, even though the two genotypes show no observable differences in black coat color. Thus, the KB allele is thought to have pleiotropic effects on as-yet unknown phenotypes. Given the role of skin-expressed CBD103 in innate immunity, we hypothesized that the KB allele influences the gene regulatory response to viral infection. To test this hypothesis, we developed a panel of primary epidermal keratinocyte cell cultures from 24 wild North American gray wolves (both Kyy and KyB genotypes) and generated immortalized Kyy and CBD103 knockout lines. We assessed the transcriptome-wide responses of wolf keratinocytes to polyinosinic:polycytidylic acid (polyI:C), which mimics infection by a double-stranded RNA virus, and to live canine distemper virus. Keratinocytes with the KyB genotype and with the Kyy genotype had similar gene regulatory responses to viral infection, suggesting that this response does not explain pleiotropic effects of the KB allele on fitness. This study supports the feasibility of using cell culture methods to investigate the phenotypic effects of naturally occurring genetic variation in wild mammals.

evolutionary biology↗

bioRxiv2019

Tooth fracture frequency in gray wolves reflects prey availability

Exceptionally high rates of tooth fracture in large Pleistocene carnivorans imply intensified interspecific competition, given that tooth fracture rises with increased bone consumption, a behavior that likely occurs when prey are difficult to acquire. To assess the link between prey availability and dental attrition, we documented dental fracture rates over decades among three well-studied populations of extant gray wolves that differed in prey:predator ratio and levels of carcass utilization. When prey:predator ratios declined, kills were more fully consumed, and rates of tooth fracture more than doubled. This supports tooth fracture frequency as a relative measure of the difficulty of acquiring prey, and reveals a rapid response to diminished food levels in large carnivores despite risks of infection and reduced fitness due to dental injuries. More broadly, large carnivore tooth fracture frequency likely reflects energetic stress, an aspect of predator success that is challenging to quantify in wild populations.

ecology↗

bioRxiv2018

Mountain lion genomes provide insights into genetic rescue of inbred populations

Introduction paragraph/AbstractAcross the geographic range of mountain lions, which includes much of North and South America, populations have become increasingly isolated due to human persecution and habitat loss. To explore the genomic consequences of these processes, we assembled a high-quality mountain lion genome and analyzed a panel of resequenced individuals from across their geographic range. We found strong geographical structure and signatures of severe inbreeding in all North American populations. Tracts of homozygosity were rarely shared among populations, suggesting that assisted gene flow would restore local genetic diversity. However, the genome of an admixed Florida panther that descended from a translocated individual from Central America had surprisingly long tracts of homozygosity, indicating that genomic gains from translocation were quickly lost by local inbreeding. Thus, to sustain diversity, genetic rescue will need to occur at regular intervals, through repeated translocations or restoring landscape connectivity. Mountain lions provide a rare opportunity to examine the potential to restore diversity through genetic rescue, and to observe the long-term effects of translocation. Our methods and results provide a framework for genome-wide analyses that can be applied to the management of small and isolated populations.

evolutionary biology↗

bioRxiv2018

Rediscovery of red wolf ghost alleles in a canid population along the American Gulf Coast

Rediscovering species once thought to be extinct or on the edge of extinction is rare. Red wolves have been extinct along the Gulf Coast region since 1980, with their last populations found in coastal Louisiana and Texas. We report the rediscovery of red wolf ghost alleles in a canid population on Galveston Island, Texas. We analyzed over 7,000 SNPs in 60 canid representatives from all legally recognized North American Canis species and two phenotypically ambiguous canids from Galveston Island. We found notably high Bayesian cluster assignments of the Galveston canids to captive red wolves with extensive sharing of red wolf private alleles. Today, the only known extant wild red wolves persist in a reintroduced population in North Carolina, which is dwindling amongst political and taxonomic controversy. Our rediscovery of red wolf ancestry after almost 40 years introduces both positive opportunities for additional conservation action and difficult policy challenges.

genomics↗

bioRxiv2017

Diel predator activity drives a dynamic landscape of fear

AO_SCPLOWBSTRACTC_SCPLOWA landscape of fear (LOF) is a map that describes continuous spatial variation in an animals perception of predation risk. The relief on this map reflects, for example, places that an animal avoids to minimize risk. Although the LOF concept is a potential unifying theme in ecology that is often invoked to explain the ecological and conservation significance of fear, quantified examples of a LOF over large spatial scales are lacking as is knowledge about the daily dynamics of a LOF. Despite theory and data to the contrary, investigators often assume, implicitly or explicitly, that a LOF is a static consequence of a predators mere presence. We tested the prediction that a LOF in a large-scale, free-living system is a highly-dynamic map with peaks and valleys that alternate across the diel (24-hour) cycle in response to daily lulls in predator activity. We did so with extensive data from the case study of Yellowstone elk (Cervus elaphus) and wolves (Canis lupus) that was the original basis for the LOF concept. We quantified the elk LOF, defined here as spatial allocation of time away from risky places and times, across nearly 1000-km2 of northern Yellowstone National Park and found that it fluctuated with the crepuscular activity pattern of wolves, enabling elk to use risky places during wolf downtimes. This may help explain evidence that wolf predation risk has no effect on elk stress levels, body condition, pregnancy, or herbivory. The ability of free-living animals to adaptively allocate habitat use across periods of high and low predator activity within the diel cycle is an underappreciated aspect of animal behavior that helps explain why strong antipredator responses may trigger weak ecological effects, and why a LOF may have less conceptual and practical importance than direct killing.

ecology↗

bioRxiv2017

Limited evidence for proactive and reactive spatial responses of prey to an active predator

O_LIThe extent to which prey space use actively minimises predation risk continues to ignite controversy. Methodological reasons that have hindered consensus include inconsistent measurements of predation risk, biased spatiotemporal scales at which responses are measured, and lack of robust null expectations.\nC_LIO_LIWe addressed all three challenges in a comprehensive analysis of the spatiotemporal responses of adult female elk (Cervus elaphus) to the risk of predation by grey wolves (Canis lupus) during winter in northern Yellowstone, USA.\nC_LIO_LIWe quantified spatial overlap between the winter home ranges of GPS-collared elk and three measures of predation risk: the intensity of wolf space use, the distribution of wolf-killed elk and vegetation openness. We also assessed whether elk varied their use of areas characterised by more or less predation risk across hours of the day, and estimated encounter rates between simultaneous elk and wolf pack trajectories. We determined whether observed values were significantly lower than expected if elk movements were random with reference to predation risk using a null model approach.\nC_LIO_LIAlthough a small proportion of elk did show a tendency to minimise use of open vegetation at specific times of the day, overall we highlight a notable absence of spatiotemporal response by female elk to the risk of predation posed by wolves in northern Yellowstone.\nC_LIO_LIOur results suggest that predator-prey interactions may not always result in strong spatiotemporal patterns of avoidance.\nC_LI

ecology↗