Abstract
Population dynamics studies and harvesting strategies often take advantage of body size measurements. Selected elements of the skeletal system such as mandibles, are often used as retrospective indices to describe body size. The variation in mandibular measurements reflects the variation in the ecological context and hence the variation in animal performance. We investigated the length of the anterior and posterior sections of the mandible in relation to the conditions experienced by juveniles of 8–10 months of age during prenatal and early postnatal life and we evaluated these parameters as ecological indicators of juvenile condition as well as female reproductive condition in a roe deer population living in the southern part of the species range. We analyzed a sample of over 24,000 mandibles of roe deer shot in 22 hunting districts in the Arezzo province (Tuscany, Central Italy) from 2005 to 2015 per age class. Mandible total length in juveniles is equal to 90% of total length in adults. In this stage of life the growing of the mandible’s anterior section is already completed while that of the posterior section is still ongoing. Environmental conditions conveyed by forest productivity, agricultural land use, local population density and climate strongly affected the growth of the anterior and posterior sections of the mandibles. Conditions experienced both by pregnant females and offspring played an important role in shaping the length of the anterior section, while the size of the posterior section was found to be related to the conditions experienced by offspring. Temporal changes of the length of the anterior section are a particularly suitable index of growth constraints. Anterior section length in fact differs according to more or less advantageous conditions recorded not only in the year of birth, but also in the previous year. Similarly, the sexual size dimorphism of the anterior section of the roe deer mandible can be used to describe the quality of females above two years of age, as well as habitat value. Hence the anterior section length of the mandible and its sexual size dimorphism are indexes that can provide cues of population performance, because they capture the system’s complexities, while remain simple enough to be easily and routinely used in the majority of European countries where roe deer hunting period extends from early autumn to late spring.
Highlights
The anterior section showed a very low sexual size dimorphism that remained practically constant during the first winter of life
Given the increase of roe deer populations in Europe, assessing the relationship between a population and its habitat shall be necessary in order to make appropriate management decisions on a quantitative basis [78]
The length of the mandible has generally been used as index of quality and Mandible growth in roe deer performance of individuals in a population
Summary
Body size is correlated with juvenile/adult survival (e.g. Toigo and Gaillard [1] on ungulates in general; Clutton-Brock et al [2] on Soay sheep Ovis aries, Gaillard et al [3,4] on roe deer Capreolus capreolus, Loison et al [5] on red deer Cervus elaphus, Coteand Festa-Bianchet [6] on mountain goat Oreamnos americanus, Festa Bianchet et al [7] on bighorn sheep Ovis canadensis) and reproductive success (e.g. Mc Elligott et al 2001 on fallow deer Dama dama [8], Douhard et al [9] and Flajsman et al [10] on roe deer, Albon et al [11] and Bertouille and De Crombrugghe [12] on red deer, Albon et al [13] on red deer and moose Alces alces). Demographic performance, and contribution to population growth, depends on body condition [14]. The assessment of the causes of variation in body size is essential for the management and conservation of sustainable ungulate populations. Females may rely on stored resources to sustain the costs of reproduction (capital breeders), or may not accumulate body reserves and rather use the energy acquired during the reproductive period (income breeders; see Stephens et al [20]). Small ungulates like roe deer belong to the group of high expenditure species, and are closer to the income breeder strategy of energy utilization [21]. Across its pan-European distribution, the species faces a wide diversity of environmental and climatic conditions and the female characteristics and their reproductive performance depends on these conditions [10,23]. The environmental and climatic influence on pregnant female condition has been little studied in wild populations, and there is currently no consensus about the expected direction of variations in this condition as a function of environmental and climatic harshness [25]
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