The cooler the better? Indirect effect of spring–summer temperature on fecundity in a capital breeder

Abstract

Female reproductive performance is a central component of ungulate population dynamics, and it can be influenced by individual, social, and environmental factors. Researchers have often assumed direct effects of different predictors on reproduction, yet more complex relationships should be considered when investigating temporal variations in life‐history traits within a broader eco‐evolutionary context. In this study, we explored direct effects of individual, social, and environmental predictors on female reproductive performance and investigated potential causal chains among variables. We analyzed the variation in fecundity, measured as the probability of being pregnant, in 215 adult female deer Cervus elaphus culled on the Italian Alps, with respect to age, body mass, kidney fat, jaw length, lactation status, population size, temperature and precipitation in spring–summer, temperature and snow depth in winter, and the delayed effect of spring–summer temperature. We used random forest and logistic regression models to select variables whose direct effects best explained variation in fecundity. Path analysis was used to test for alternative hypotheses of direct/indirect effects between pre‐selected weather (spring–summer temperature) and individual (age, kidney fat index [KFI]) predictors. The most important direct predictors of fecundity were age, kidney fat, and the interaction between kidney fat and spring–summer temperature. Path analysis supported the hypothesis that higher spring–summer temperature had negative, indirect effects on the probability of being pregnant, mediated by decreasing values of KFI. Our study revealed some complex, cause–effect relationships between weather stochasticity, body condition, and reproduction, possibly suggesting a conditional trade‐off between opportunity for reproduction and survival, and emphasizing how environmental variations and individual characteristics may interact to shape life‐history traits in ungulate populations.

Reflections of ecological differences? Stress responses of sympatric Alpine chamois and red deer to weather, forage quality, and human disturbance

“…Male Alpine ibex ( Capra ibex ), for example, reduce daytime feeding activity with increasing temperature (Aublet et al, 2009 ), and Mason et al ( 2014 ) demonstrated a negative effect of higher temperatures on time spent foraging in Alpine chamois ( Rupicapra rupicapra ) independent of time of day. Moreover, reductions in female red deer body condition and thus fecundity have been linked with elevated spring–summer temperatures (Corlatti et al, 2018 ), and red deer calves have been shown to experience reduced growth rates under heat stress (Pérez‐Barbería et al, 2020 ). Such stress responses should be reflected in higher glucocorticoid concentrations with increasing temperature during summer, which might provide an early warning sign for population‐level consequences of climate change.…”

Climatic changes and the fate of mountain herbivores

“…Climate change patterns may vary between geographical regions in terms of snow and rain (Parmesan and Matthews 2006), with a global increase of temperatures (Hegerl et al 2018), sometimes even having locally contrasting effects on population dynamics of mountain ungulates (Loison et al 1999), thus making it difficult to predict a general pattern. In spite of local variations, it has been suggested that warmer weather during the vegetative season may have particularly negative effects on body mass (Rughetti and Festa-Bianchet 2012;Mason et al 2014a), fecundity of females (Corlatti et al 2018) and offspring survival (Douhard et al 2018;Ferretti et al 2018), affecting population dynamics of mountain herbivores.…”

Disentangling demographic effects of red deer on chamois population dynamics

“…In our study area, birth rate was positively influenced by spring-summer precipitation in the previous year, but not in the same year (see methods); this suggests an indirect effect of spring-summer weather on birth rate through improved maternal conditions (cf. Chirichella et al, 2021; see also Corlatti et al, 2018 for red deer).…”