Biology subjects

MacNulty, D. R.

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

6 recordsLinked to original sources

bioRxiv2026

Livestock depredation frequency is negatively associated with wolf body mass

Foraging theory predicts that behavioral decisions are state-dependent, with individuals expected to alter foraging strategies according to physiological condition. Although livestock depredation by carnivores is often attributed to seasonal changes in prey availability and livestock exposure, less attention has been given to predator state. We evaluated whether seasonal variation in wolf body mass was associated with monthly livestock depredation frequency using 17 years of monitoring data from gray wolves (Canis lupus) in Oregon, USA. Using 329 body-mass measurements from 274 wolves, we modeled age- and season-related variation in body mass and generated standardized monthly population-level predictions. Predicted body mass declined through spring and summer, reached its lowest values in late summer, and increased into winter. Monthly depredation frequency decreased as predicted population-level body mass increased; a one-standard-deviation increase in predicted mass was associated with a 36.7% decrease in expected monthly depredation frequency (95% confidence interval: 22.7-48.1% decrease). The negative association persisted across sensitivity analyses based on predicted population-level body mass. When season was modeled explicitly, the association remained negative, but uncertainty increased substantially because predicted body mass and season contained limited independent temporal information. Livestock depredations were therefore most frequent during the portion of the annual cycle when wolves were predicted to have their lowest body mass. The observed association is consistent with state-dependent foraging theory, but the available data could not determine whether body mass itself contributed to depredation frequency or whether other seasonal ecological processes drove the association. Our results identify predator state as a potentially important but understudied component of carnivore-livestock interactions. Integrating measures of predator state with established drivers of conflict, including livestock exposure, husbandry, native prey, and landscape conditions, may help determine whether predator state provides additional information for understanding and anticipating carnivore-livestock conflict.

animal behavior and cognition↗

bioRxiv2026

Parental death destabilizes wolf packs despite the benefits of larger pack size

1. Cooperative breeding is a fundamental feature of many animal family groups. However, few studies have quantified whether variation in group size meaningfully buffers social and reproductive consequences following parental death. 2. Using 17 years of data from a gray wolf (Canis lupus) population in Oregon, USA, we evaluated how parental death (the death of one or both parents) influenced pack dissolution, reproductive failure, and pup recruitment, and whether larger pack sizes mitigated these effects. 3. Across 303 pack-years, we recorded 69 parental deaths, 39 pack dissolutions, and 112 reproductive failures. Packs that experienced parental death were nearly five times more likely to dissolve (95% CI: 2.12-11.12), nearly 16 times more likely to fail reproductively (95% CI: 5.34-47.26), and recruited 66% fewer pups (95% CI: 49-78% fewer) than packs in which both parents survived. 4. Larger packs were associated with improved demographic outcomes overall, but these group-size benefits were insufficient to fully offset the elevated risks associated with parental death. 5. Our results show that numerous individuals can provide generalized pack-level demographic resilience but do not functionally replace parental roles, highlighting the importance of evaluating social structure in addition to population size. 6. By clarifying the limits of social buffering in a cooperatively breeding carnivore, this study advances understanding of how social systems respond to parental death.

animal behavior and cognition↗

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↗

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↗

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↗