Abstract
Yellow-bellied toad populations (Bombina variegata) show a wide fast–slow continuum of the life-history trait longevity ranging from 5 to 23 years. We investigated populations in Germany (n = 8) and Austria (n = 1) to determine their position within the continuum of longevity and the potential drivers of adult survival at the local and the continental scale. Intrinsic and extrinsic factors considered were local weather, nutritional state, allocation of ingested energy to somatic growth, pathogen prevalence, and geographical clines (latitude, altitude, and longitude). Capture-mark-recapture (CMR) monitoring and direct age assessment by skeletochronology allowed for reliable estimates of longevity and adult survival. Raw and corrected recapture rates as well as a probabilistic estimate of the lifespan of the eldest 1% adults of a cohort (CMR data) were used as surrogates for adult survival and thus longevity in a population. Additionally, survival rates were calculated from static life tables based on the age structure (skeletochronological data) of eight populations. Populations in Germany were short-lived with a maximum lifespan of annual cohorts varying from 5 to 8 years, whereas the population in Austria was long-lived with a cohort longevity of 13 to 23 years. We provide evidence that annual survival rates and longevity differ among years and between short- and long-lived populations, but there was no decrease of survival in older toads (i.e. absence of senescence). Variation of weather among years accounted for 90.7% of variance in annual survival rates of short-lived populations, whereas the sources of variation in the long-lived population remained unidentified. At the continental scale, longevity variation among B. variegata populations studied so far did not correspond to geographical clines or climate variation. Therefore, we propose that a population’s position within the fast–slow continuum integrates the response to local environmental stochasticity (extrinsic source of variation) and the efficiency of chemical antipredator protection determining the magnitude of longevity (intrinsic source of variation).
Highlights
Variation of life-history traits related to reproduction is shaped by the interaction of environmental variability and constraints of the organism such as trade-offs between size, fecundity and longevity (Stearns, 2000)
To test for a general pattern underlying the fast–slow continuum of longevity throughout the geographical range, we identified published information on longevity estimates for B. variegata basing on CMR or on skeletochronology
Our case study on B. variegata provides evidence that the magnitude of longevity is a fixed attribute of a population, which varies among the cohorts of a population by integrating the influence of environmental stochasticity on annual survival rates during the cohorts’ lifetime
Summary
Variation of life-history traits related to reproduction is shaped by the interaction of environmental variability and constraints of the organism such as trade-offs between size, fecundity and longevity (Stearns, 2000). Most of life-history variation among species falls on a fast–slow continuum, with low fecundity, slow growth and long lifespan at one end and the opposite combination of traits at the other end (Stearns, 1983; Gaillard et al, 1989; Ricklefs & Wikelski, 2002). There are strong size-independent correlations among life-history variables, e.g., species with late age at maturity have often low rates of juvenile and adult mortality and small litters with large neonates (Bielby et al, 2007; for an exception see Kraus et al, 2005). Long-lived species are commonly less affected by climate variability than their short-lived counterparts because longevity buffers adult survival against temporal environmental variation (Gaillard & Yoccoz, 2003; Morris et al, 2008)
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