Omar Lenzi , Kurt Grossenbacher, Silvia Zumbach, Beatrice Lüscher, Sarah Althaus, Marco Thoma, Daniela Schmocker, Helmut Recher, Arpat Ozgul, Benedikt R. Schmidt

1. Vital rates of individuals in natural populations, such as survival and breeding probabilities, can be affected by abiotic (i.e. environmental conditions), biotic (e.g. population density), and individual factors (i.e. individual traits). Many studies often consider the direct effects of one or two of these sources of vital-rate variations, but taking them all into account might reveal important relationships, including indirect trait-mediated effects.

2. We estimated survival and breeding probability in a high-elevation population of an ectotherm species while accounting for the effects of these three types of factors: abiotic (in the form of the length of the active season and temperature at emergence from hibernation), biotic (population size), and individual factors (body size). We expect this population living at the extreme range of the species’ distribution to be affected mainly by abiotic factors, given the harsh environmental conditions experienced.

3. Using 28 years of capture-mark-recapture data and individual body size measurements on an alpine population of the common toad (Bufo bufo), we estimated male survival probability with a Bayesian Cormack-Jolly-Seber model, female survival and female breeding probability with a Bayesian multistate model, and we estimated sex-specific growth curves.

4. Our findings reveal significant negative impacts of all three factor types on survival. Moreover, breeding probability exhibited a Markovian pattern, notably breeding biennially, with temperature at hibernation emergence, an abiotic factor, affecting the probability of skipping a breeding season, and population density, a biotic factor, influencing the resuming of breeding. We also found indication for the presence of indirect effects, with both abiotic and biotic factors potentially affecting asymptotic growth, and thus by extension, survival through changes in body size.

5. Our study reveals interesting and novel results for a population in a context seldom studied. It also highlights the complexity of factors affecting vital rates directly and indirectly, as well as the importance of long-term studies, especially in understudied habitats and taxa.