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

Abstract

Because 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 environmental 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 predictable 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.

Survival cost to relocation does not reduce population self‐sustainability in an amphibian

“…Yet, in contrast to their parents born in captivity, locally born individuals do not experience decreased survival at the adult stage in the new forest-grassland habitat; we did not detect survival difference with individuals from the source population. In addition, the survival of the locally born adults (0.79) was close to that of individuals from forest (ranging from 0.71 to 0.75 in various populations of B. variegata; see Cayuela et al 2016a) and grassland environments (0.77, Cayuela et al 2016a), suggesting similar survival-related performances regardless of the environmental context. This indicates that, once the second generation is established, survival is similar to that in natural populations.…”

“…No scientific evaluation (e.g., viability analysis) was conducted prior to the operation. The demographic parameters (i.e., age-dependent survival and female fecundity) required to perform such an analysis was unknown at this time; the first inferences of demographic rates of B. variegata were published in 2014 (Cayuela et al 2014(Cayuela et al , 2016a. In 2018, we took advantage of this relocation program to investigate post-relocation demographic processes.…”

“…The control population is located in a harvested woodland in northeast France, close to Verdun (Cayuela et al 2018a). In this population, reproduction takes place in a set of 189 sites (i.e., groups of ruts) and dispersal is high between the sites (Cayuela et al 2016a).…”

“…Intra-annual survival probability was set at 1 as is typical in robust design models Nichols 1995, Kendall andNichols 2002). This assumption was realistic in our study system as intra-annual survival probability in B. variegata is usually >0.9 (Cayuela et al 2016a).…”

“…By contrast, relocated populations always have small sizes and therefore are subject to demographic stochasticity (Armstrong and Seddon 2008). Hence, for each year, demographic parameter values were randomly sampled in a Gaussian distribution centered on the estimates provided by the CR analysis and standard deviation inferred in two previous studies (Cayuela et al 2016a(Cayuela et al , 2018b. The standard deviation values were: 0.05 for u juv , 0.03 for u sub , 0.01 for u adu , 0.02 for F.…”