Age-dependent differences in mean eviscerated body mass and potential reproductive output (number of CL, including infertile individuals) in roe deer females in Slovenia (n = 1312).

<p>Error bars denote 95% confidence intervals of the mean. Note that age was estimated using macroscopic inspection of tooth-wear, a method that is less accurate (especially) in older animals.</p

Age-related effects of body mass on fertility and litter size in roe deer

<div><p>We analysed effects of females’ body mass and age on reproductive capacity of European roe deer (<i>Capreolus capreolus</i>) in a large sample set of 1312 females (305 yearlings and 1007 adults), hunted throughout Slovenia, central Europe, in the period 2013–2015. Body mass positively affected probability of ovulation and potential litter size (number of corpora lutea), although its effect was more pronounced in yearlings than in adults. Between age groups, we found clear differences in responses of both reproductive parameters to body mass which influences primarily reproductive performance of younger, and in particular, lighter individuals: at the same body mass yearlings would at average have smaller litters than adults, and at lower body mass also young to middle-aged adults would have smaller litters than old ones. In addition, while yearlings have to reach a critical threshold body mass to attain reproductive maturity, adult females are fertile (produce ova) even at low body mass. However, at higher body mass also younger individuals shift their efforts into the reproduction, and after reaching an age-specific threshold the body mass does not have any further effects on the reproductive output of roe deer females. Increased reproductive capacity at more advanced age, combined with declining body mass suggests that old does allocate more of their resources in reproduction than in body condition.</p></div

Potential reproductive output (number of CL, including infertile individuals) of roe deer females in relation to body mass by age category.

<p>Age categories are as follows: yearlings (15–19 months old), young to middle-aged adults (2–7 years old), and older adults (8+ years old). Samples were pooled based on the body mass of individuals into five groups with an equal number of units across the total sample set (for intervals, see marks above the X axis). In the case of the first and the last body mass groups, dots are horizontally positioned on the mean body mass of all individuals in these two groups. Error bars denote 95% confidence intervals of the mean.</p

Bivariate analyses of the effects of age and body mass on the reproductive potential (fertility, potential litter size) of roe deer females in Slovenia.

<p>Relations between variables (their categories are listed in parentheses) were analysed by tests for homogeneity. The results of each of eight analyses are presented in each row.</p

Generalized linear models of fertility (n = 1007) and potential litter size (n = 993) of adult roe deer females in Slovenia (2013–2015).

<p>The independent variables were age (2–7 years <i>vs</i>. 8+ years), body mass (covariate), body mass × age interaction, and year (2013, 2014 <i>vs</i>. 2015; fixed factor). Model selection was performed using the Akaike information criteria (AIC). For the best model, basic statistics are displayed, while for other models with ΔAIC < 2 only the model structure and ΔAIC are shown.</p

Relative frequencies of the number of CL in roe deer females of different age classes in Slovenia in the period 2013–2015 (n = 1312).

<p>Note that age was estimated using macroscopic inspection of tooth-wear, a method that is less accurate (especially) in older animals.</p

Generalized linear models of fertility (n = 1312) and potential litter size (n = 1280) of subadult and adult roe deer females in Slovenia (2013–2015).

<p>The independent variables were age (yearlings <i>vs</i>. adults), body mass (covariate), body mass × age interaction, and year (2013, 2014 <i>vs</i>. 2015; fixed factor). Model selection was performed by the Akaike information criteria (AIC). For the best model, basic statistics are displayed, while for other models with ΔAIC < 2 only the model structure and ΔAIC are shown.</p