Density-dependent decline of early horn growth in European mouflon

Abstract

The development of horns in Caprinae can be largely influenced by food-limiting factors such as population density and climate, as well as by negative evolutionary responses to size-selective harvesting. In this study, we investigated the effects of population density, environmental covariates and trophy hunting on horn development in a population of European mouflon Ovis aries musimon introduced to the Mediterranean region of Croatia in the early 1980s. The study population was subject to commercial trophy hunting on males since the mid-1980s. This allowed to analyse the temporal trend in early horn growth in 341 rams legally culled. Cohort-based linear model and analysis of deviance (ANODEV) revealed a significant negative trend in early horn growth, with a decline of ca. 10% over only 15 cohorts (1993–2007). The increase in population density (by ca. 600%) and summer temperature, selected via LASSO regression, explained about 61% and 13% of the decline in early horn growth, as revealed by the ANODEV R2. Our results suggest a prominent role of food-limiting factors in the decline of weapon size. We also found a negative relationship between age at death and early horn growth in our study population, which suggests the occurrence of hunters’ selectivity towards large horns. The effect of trophy hunting on the decline in horn size, however, is difficult to quantify. Our analysis was largely influenced by the rapid increase of mouflon density after introduction, thereby limiting the possibility to detect potential effects of hunting selection, although the large number of rams shot before 5 years of age may possibly lead to undesirable consequences of trophy hunting on mating success. To clarify the consequences of commercial trophy hunting on the mouflon population, the long-term pattern of horn growth and the age-dependent male siring success should be further investigated.