Diet composition and habitat use in red deer (Cervus elaphus) populations in the northeastern iberian peninsula: relations with phenotypic plasticity in dental roots, group ethology and stress hormones

Abstract

[eng] Deer populations are increasing in recent times. One of the main causes is the abandonment of agriculture and extensive livestock farming. This thesis focuses on expanding our knowledge about the biology of red deer (Cervus elaphus) on the following aspects: diet composition and habitat use, phenotypic plasticity in dental roots, group ethology, and stress. First, we determined the composition of the diet and the habitat use in order to help properly manage these populations and conserve the habitats that are newly available to them. The results indicated that the population of Axial Pyrenees were on average more grazers and the one of the Pre- Pyrenees more browsers. We also found that there was no seasonal pattern in the Axial Pyrenees. In the case of the Pre-Pyrenees, the consumption of woody plants was higher for females, which has not been found in the literature. Parallel to this study, we analysed the movements of 7 red deer using GPS tracking collars. The differences found in diet composition and habitat use between the two areas were reflected in their movements. The individuals from the Axial Pyrenees descend in unfavourable seasons and ascend in the favourable ones. These oscillations were due to the low food availability. In the Pre-Pyrenees, we did not observe such altitudinal migration. On the other hand, we found similar results of habitat use in as a refuge and in Pre-Pyrenees was for feeding, which was related to the harshness of the climate in the northernmost area. Our second objective was to analyse the influence of several factors, including sex, origin and lineage of deer populations, and type of habitat, on the prevalence of supernumerary roots in molars. The highest prevalence of supernumerary roots found in deciduous teeth was in pm3 (14%), and in permanent teeth in M1 (3%). We found significant differences between areas, lineages and geology. We suggest that the high prevalence of supernumerary roots in M1 may be related to the wear caused by a grazer condition. Thus, the Axial Pyrenean population had the higher prevalence in agreement with a mostly grazing population. Contrarily, we associated a high prevalence in deciduous teeth as a response to a hard diet, a dry climate condition and a harsh weaning period, with the Pre-Pyrenees, which is a browser population, as one of the populations with this higher prevalence. Additionally, we found that individuals that consumed more graminoids and fewer woody species also showed better body condition, which we attributed to a higher nutritional quality of graminoids. The third objective was pioneering in comparing the size and type of deer groups in five ecologically distinct areas simultaneously. Our results showed that deer group size varied with food availability, with large groups forming in unfavourable periods and small groups forming in favourable periods. On the other hand, the values of mixed group size found during the rutting season are among the lowest reported, and one of the reasons attributed to this is that, being a favourable period, individuals have prioritized feeding over reproduction and have dispersed due to the abundance of food everywhere. In the last objective focused on hormone stress levels, our results indicated that prior climatic conditions best explained the variations of cortisol within seasons and among years. We also found differences between adult males and the other individuals in cortisol and T3 hormones. We found neither a contribution of nutritional stress to physiological stress nor an effect of the ecotourism influx in this population. Our results highlight the high adaptability of the red deer to ecosystems differing widely in food quality and availability as well as climate conditions. Food and climate stand out as two of the main factors determining the ecology in these predator-free ecosystems.