Ecological factors affecting Alpine chamois population recruitment: remote sensing can support adaptive management

The analysis of ecological factors able to affect the life history traits of ungulates is important to reveal key information on population dynamics of wild herbivores. As regard to bovids, it is often crucial for juveniles and yearlings to gain quickly body size and mass, as such growths primarily increase chance to reach re- productive maturity (i.e., an increase in the survival probability). Accordingly, we modeled a set of ecological factors accounting for the variation of Alpine chamois (Rupicapra rupicapra) population recruitment through three indexes: i) the ratio kids/adult females (NK/NF), ii) the ratio yearlings/adult females (NY/NF), and iii) the yearlings eviscerated body mass (YBM). These indexes were derived respectively from block count census and from hunting records in the last 45 years in different ecological contexts in the South-West Trento province. These indexes were associated to forage quality/quantity, winter harshness, and local chamois density. In detail, we considered NDVI (Normalized Difference Vegetation Index) as a proxy for the quality of Alpine meadows used by chamois in spring and summer and snow cover data belonging to the National Aeronautics and Space Ad- ministration (NASA) remote sensing dataset (TERRA-MODIS). The reproductive success of these populations was strongly influenced both by the quality of meadows during births period (May) and by the space-time pattern of growth and maturation of Alpine pastures in spring and summer periods. Even winter harshness played an important role in this process. In particular, i) the NK/NF was positively influenced by the average quality of the grazing season previous to the births period and by the maximum NDVI value recorded in May (i.e., births period); ii) the NY/NF was negatively affected by the extent of snow cover in the first winter of kids and positively related to the average quality of the pasture in the subsequent spring and summer (i.e., the feed intake period in which individuals had to recover weight loss derived from previous winter); and iii) the YBM revealed a negative trend during the study period suggesting a difficult adaptation to climate and environmental changes taking place. Contrary to our expectations, local density was not able to influence these variables. This result may suggest that local density are not exceedingly high in the study area and therefore are not able to promote density dependent phenomena. In conclusion, these results contribute to increase the knowledge of the mechanisms underlying Alpine chamois population dynamics and give insights to plan adaptive management and conservation of this species.