A human-neutral large carnivore? No patterns in the body mass of gray wolves across a gradient of anthropization

**Background:** The gray wolf (Canis lupus) has expanded its distribution in Europe over recent decades, increasingly colonizing human-dominated landscapes. Understanding whether anthropization affects fitness-related traits like body mass is critical for forecasting future range expansion and planning management. Body mass is linked to survival, reproduction, and dispersal capacity. The authors hypothesized that anthropization could act through two mechanisms: (1) affecting growth during the first year of life via early-life conditions and food availability, and (2) influencing sexual dimorphism in adults, as males are typically ~20% larger than females due to selective pressures for hunting large prey and intergroup aggression.

**Methods:** The study included 175 dead wolves recovered in Italy (Emilia-Romagna, Tuscany, and Abruzzo regions) between 1999 and 2021. Age was estimated via dental development, body size, and weight. Body mass (kg) was the response variable. Anthropization was quantified using the Human Footprint Index (HFI) at 1-km resolution, with median HFI calculated within a 6-km radius buffer (~113 km²) around each recovery location. Confounders controlled included total body length, year found, day of year, and geographic area. Bayesian models were fitted using the brms R package with Student's-t distribution, 5000 MCMC iterations, and 1000 burn-in. Model selection used leave-one-out cross-validation. Sensitivity analyses tested different buffer radii (4–16 km) and collapsibility of confounders.

**Key Results:** For first-year wolves (n=53), the best model explained 79.0% of variability in body mass. Body mass increased with age but the interaction between age and anthropization was mild (estimate: -0.09, SE: 0.06, 95% CI: -0.20 to 0.03). Wolves in more anthropized areas had slightly higher body mass at 3–5 months but smaller overall variation during the first year. For adult wolves (n=121), the model explained 57.8% of variability. Sexual dimorphism showed a mild increase with anthropization driven by increased male body mass (Sex[Male] * Anthropization estimate: 0.15, SE: 0.13, 95% CI: -0.12 to 0.40), while female body mass did not change. All credibility intervals overlapped with zero, indicating no statistically clear effects. Sensitivity analyses confirmed robustness to buffer size and confounder removal.

**Clinical Implications:** The absence of clear negative effects of anthropization on wolf body mass suggests that wolves in Italy can cope with human-dominated landscapes without apparent fitness costs in terms of body condition. This implies that wolves could potentially re-occupy most of their historical European range, including anthropized areas, necessitating management and coexistence policies across vast spatial scales. However, the authors caution that Italy has among the highest densities of wild ungulates in Europe, and results may differ in regions with different prey availability, livestock practices, or waste management. The study's limited sample size (n=53 for growth, n=121 for dimorphism) means small but biologically important effects cannot be ruled out. Replication studies with larger samples and in other European regions are urgently needed, along with collaborative data-sharing initiatives and harmonized collection protocols.