Unbiased survival estimates and evidence for skipped breeding opportunities in females

Abstract

Summary 1.Estimates of demographic parameters for females, in many organisms, are sparse. This is particularly worrisome as more and more species are faced with high extinction probabilities and conservation increasingly depends on actions dictated by complex predictive models that require accurate estimates of demographic parameters for each sex and species. 2. This study assesses demographic parameters, specifically temporary emigration and survival, for females, a class that has been difficult to investigate historically because of lack of data. Amphibians provide a particularly good example because there is global concern about amphibian decline; yet most demographic parameter estimates are based on data from males, which we show can lead to erroneous conclusions. 3. We use 10 years of capture-recapture data from boreal toads (Bufo boreas) and the multi-state open robust design model to provide evidence for the occurrence of skipped breeding opportunities (i.e. temporary emigration) in females. This is the first time that the open robust design model has been applied to an analysis of an amphibian population that we are aware of. 4. We determined that the transition from breeder to non-breeder is obligate and the probability of a non-breeder remaining a non-breeder is 64%; thus, temporary emigration is first-order Markovian in nature, where breeding probability is dependent on the previous year's activity, i.e. if a female did not breed in year one, there is a 36% chance that she will breed in year two. With temporary emigration accounted for, we estimated between-year female survival at 87%. 5. Establishing the occurrence of temporary emigration not only reduces bias in estimates of survival probabilities but also provides information about expected breeding attempts by females, a critical element in understanding the ecology of an organism and the impacts of outside stressors and conservation actions.

Compensatory effects of recruitment and survival when amphibian populations are perturbed by disease

“…As predicted, survival rates were higher in the Bd ‐negative (77%, DC), compared to the Bd ‐positive (52%, BR), population. Previous work shows similar survival rates for male and female boreal toads (Scherer, Muths & Lambert 2008; Muths, Scherer & Lambert 2010), such that results from this study (male data only) may be applicable to other boreal toad populations.…”

“…Funk et al. 2005; Gibson, Van der Marel & Starzomski 2009), skip breeding opportunities (Muths, Scherer & Lambert 2010), and have less opportunity to behaviourally regulate their body temperature (potentially combating disease, Woodhams, Alford & Marantelli 2003). Recent work by McCaffery & Maxell (2010) reported increased survival and breeding probability with less severe winters, reminding us that even without disease, the environment can be stressful.…”

“…Although we collected data for males and females, data on females were too sparse to be used in the analysis. Furthermore, female toads tend to show Markovian breeding probabilities (Muths, Scherer & Lambert 2010) which can cause bias in estimates of parameters in the Pradel model (Williams, Nichols & Conroy 2002; Schmidt, Feldmann & Schaub 2005). We used the parameterization of the Pradel model that contained the following parameters: apparent survival probability (Φ), recruitment rate ( f ) and capture probability ( p ) to elucidate the effects of Bd on Φ and f at the population level.…”

Body reserves mediate trade-offs between life-history traits: new insights from small pelagic fish reproduction

“…Contrary to longer-lived species able to safeguard their own survival by ceasing to breed at any time (e.g. amphibian [78] and reptile [79]), such a strategy could greatly affect other small pelagic life-history traits and explain the recent reduction of growth rates and sardine adult survival highlighted by Van Beveren et al . [33].…”

Influence of demography and environment on persistence in toad populations

“…After breeding, they move away from the breeding pond to forage and find hibernacula (Hammerson ). Their habitat is further characterized by a short growing season (May through late Sep), with synchronous breeding aggregations occurring from May to July depending on elevation and snowmelt (Carey et al , Muths et al ).…”