Shrinking giants: the impact of hunting on body size and population viability of Pteropus rufus (Chiroptera: Pteropodidae) on Madagascar

Abstract

Fruit bats play a central role in Madagascar’s ecosystems through seed dispersal, yet Pteropus rufus faces increasing pressure from habitat loss and largely unregulated hunting. Commercial harvest of this species expanded in the 1980s to mid-1990s, but its long-term biological effects have not been formally quantified. Using cranial and dental measurements from historical and contemporary museum specimens spanning more than 150 yr, we tested whether intensified harvest has altered morphology and age structure in this slow-reproducing species. Sexual dimorphism across traits was minimal, and age-related differences followed expected patterns, with larger values in older individuals. After the onset of commercial hunting, clear directional reductions emerged across multiple cranial measurements in adults. Dental traits showed mixed responses, with most declining and one increasing, indicating nonuniform odontic change. Multivariate analyses revealed significant temporal divergence in both cranial and dental morphospace independent of age structure. Temporal modeling showed a significant decline in cranial PC1 over the past century, whereas dental PC1 also changed significantly but less consistently. Quantile regressions indicated that cranial shrinkage was concentrated at the median of the adult size distribution—consistent with sustained removal of adults under hunting pressure. Together, these results show that large-scale exploitation is actively reshaping P. rufus morphology. The downward shift in adult body size, combined with low reproductive output and ongoing habitat loss and hunting, raises serious concern for long-term population viability and underscores the need for strengthened protection, monitoring, and formal viability assessment.