Contrasting patterns of environmental fluctuation contribute to divergent life histories among amphibian populations

Abstract

International audienceBecause it modulates the fitness returns of possible options of energy expenditure at each ontogenetic stage, environmental stochasticity is usually considered a selective force in driving or constraining possible life histories. Divergent regimes of envi- ronmental fluctuation experienced by populations are expected to generate differences in the resource allocation schedule between survival and reproductive effort and outputs. To our knowledge, no study has previously examined how different regimes of stochastic variation in environmental conditions could result in changes in both the temporal variation and mean of demographic parameters, which could then lead to intraspecific variation along the slow–fast continuum of life history tactics. To investigate these issues, we used capture–recapture data collected on five populations of a long-lived amphibian (Bombina variegata) experiencing two distinct levels of stochastic environmental variation: (1) constant availability of breeding sites in space and time (predictable environment), and (2) variable spatio-temporal availability of breeding sites (unpredictable environment). We found that female breeding propensity varied more from year to year in unpredictable than in pre- dictable environments. Although females in unpredictable environments produced on average more viable offspring per year, offspring production was more variable between years. Survival at each ontogenetic stage was slightly lower and varied significantly more from year to year in unpredictable environments. Taken together, these results confirm that increased environmental stochasticity can modify the resource allocation schedule between survival and reproductive effort and outputs and may lead to intraspecific variation along the slow–fast continuum of life history tactics

Demographic response to patch destruction in a spatially structured amphibian population

“…The model had a robust design structure (Pollock, ), including both a primary period (years) and secondary sessions (capture sessions within years). We therefore made the assumption that survival probability was 1 between secondary sessions; this assumption was previously verified in this population (Cayuela, Arsovski, et al., 2016; see appendix 2 of the paper). To specify the state–state transitions at each step, a matrix was used in which the rows corresponded to the individual's state at t − 1, and the columns the possible states of arrival at t .…”

“…Considering the most realistic life cycle for the yellow‐bellied toad (Figure ) used in previous studies (e.g., Cayuela et al., ), we used a three age‐class (juveniles, subadults, and adults), female‐dominant, prebreeding Leslie matrix (Caswell, ) (Figure ). We used the prebreeding survival probability (juvenile survival, S 1 = 0.60; subadult survival, S 2 = 0.74) estimated in a previous study on this population (Cayuela, Arsovski, et al., 2016). Fecundity F was possible only for adult females and consisted of an estimation of recruitment, that is, the number of recruited juvenile females at t per breeding female at t − 1 ( F = 0.79) (Cayuela, Arsovski, et al., 2016).…”

“…We used the prebreeding survival probability (juvenile survival, S 1 = 0.60; subadult survival, S 2 = 0.74) estimated in a previous study on this population (Cayuela, Arsovski, et al., 2016). Fecundity F was possible only for adult females and consisted of an estimation of recruitment, that is, the number of recruited juvenile females at t per breeding female at t − 1 ( F = 0.79) (Cayuela, Arsovski, et al., 2016). For adult survival S 3 , we used female survival estimate resulting from the CR data analysis previously described ( S 3 = 0.79, when no patch destruction occurs).…”

“…For adult survival S 3 , we used female survival estimate resulting from the CR data analysis previously described ( S 3 = 0.79, when no patch destruction occurs). In addition, we also considered the possibility that females may skip breeding opportunities; in this population, a previous study showed that females’ skipping breeding probability B was 0.15 (Cayuela, Arsovski, et al., 2016). Moreover, we also included facultative dispersal D in our simulations; we used female facultative dispersal estimate resulting from the CR data analysis (i.e., 0.22).…”

“…In the temperate forests of Europe and North America, many amphibians breed in temporary waterbodies resulting from natural disturbance (i.e., flooding or windstorms) (DeMaynadier & Hunter, ; Joly & Morand, ). Over the last century, rapid changes in forest management practices have deeply impacted the population dynamics of amphibians inhabiting these landscapes by modifying the characteristics of their breeding habitats (see for instance, Cayuela, Arsovski, et al., 2016; Cayuela, Boualit, et al., 2016). On the one hand, silviculture has led to the disappearance of natural early successional waterbodies by altering the pattern of natural disturbances (i.e., reduction of the frequency of flooding and windstorm damage).…”