Long-Term Changes in Richness and Diversity of Wild Mammal Roadkill

We assessed the temporal changes in the richness and diversity of wild mammal roadkill by analysing officially recorded wildlife–vehicle collision data from Lithuania between 2002 and 2025. We calculated annual taxon richness, abundance-sensitive diversity, and community composition from a species frequency matrix. To account for significant variations in annual sample size, diversity was standardised using individual-based rarefaction to 218 registered individuals, employing Hill numbers (q = 0, 1, and 2). Observed richness increased from seven taxa in 2002 to 18 in 2023, while the number of registered individuals increased markedly, particularly after 2013. Rarefied richness also exhibited a significant positive temporal trend, suggesting that the rise in recorded richness was not solely due to an expanding sample size. In contrast, rarefied Shannon and inverse Simpson diversity declined, indicating increasing dominance by a smaller number of abundant taxa. The proportion of roe deer (Capreolus capreolus) records increased from 72.1% in 2002–2009 to 83.7% in 2018–2025, which contributed significantly to temporal community restructuring. These results demonstrate long-term changes in the recorded wild mammal roadkill assemblage while highlighting the need to account for reporting and detection processes when interpreting administrative roadkill data.