Abstract
While the population growth rate in long‐lived species is highly sensitive to adult survival, reproduction can also significantly drive population dynamics. Reproductive parameters can be challenging to estimate as breeders and nonbreeders may vary in resighting probability and reproductive status may be difficult to assess. We extended capture–recapture (CR) models previously fitted for data on other long‐lived marine mammals to estimate demographic parameters while accounting for detection heterogeneity between individuals and state uncertainty regarding reproductive status. We applied this model to data on 106 adult female bottlenose dolphins observed over 13 years. The detection probability differed depending on breeding status. Concerning state uncertainty, offspring were not always sighted with their mother, and older calves were easier to detect than young‐of‐the‐year (YOY), respectively, 0.79 (95% CI 0.59–0.90) and 0.58 (95% CI 0.46–0.68). This possibly led to inaccurate reproductive status assignment of females. Adult female survival probability was high (0.97 CI 95% 0.96–0.98) and did not differ according to breeding status. Young‐of‐the‐year and 1‐year‐old calves had a significantly higher survival rate than 2‐year‐old (respectively, 0.66 CI 95% 0.50–0.78 and 0.45 CI 95% 0.29–0.61). This reduced survival is probably related to weaning, a period during which young are exposed to more risks since they lose protection and feeding from the mother. The probability of having a new YOY was high for breeding females that had raised a calf to the age of 3 or lost a 2‐year‐old calf (0.71, CI 95% 0.45–0.88). Yet, this probability was much lower for nonbreeding females and breeding females that had lost a YOY or a 1‐year‐old calf (0.33, 95% CI 0.26–0.42). The multievent CR framework we used is highly flexible and could be easily modified for other study questions or taxa (marine or terrestrial) aimed at modeling reproductive parameters.
Highlights
Population dynamics studies rely on the estimation of several de‐ mographic parameters, such as survival by age class and fecundity (Caswell, 2001), which may contribute differently to the population growth rate (Kroon, Plaisier, Groenendael, & Caswell, 1986)
In long‐ lived species, several studies have demonstrated that the population growth rate, and population viability, is much more sensitive to variations in adult survival than to reproductive parameters
The concept of environmental canalization (Gaillard & Yoccoz, 2003) states that demographic parameter with high sensitivity to population viability is less sensitive to environmental variations as this species usually developed some morphology, physiological, or behavioral ad‐ aptations to limit survival variations
Summary
Population dynamics studies rely on the estimation of several de‐ mographic parameters, such as survival by age class and fecundity (Caswell, 2001), which may contribute differently to the population growth rate (Kroon, Plaisier, Groenendael, & Caswell, 1986). Detection issues in estimating demographic parameters are traditionally dealt with capture–recapture models (CR hereafter, Lebreton, Burnham, Clobert, & Anderson, 1992) These methods are largely used to provide unbiased estimates of population size or sur‐ vival probability (Kendall & Pollock, 1992), with a recent and growing focus on reproductive parameters for species breeding and calving on land (Desprez, Gimenez, McMahon, Hindell, & Harcourt, 2018; Desprez et al, 2014; Garnier, Gaillard, Gauthier, & Besnard, 2016; Oosthuizen, Pradel, Bester, & Bruyn, 2019). No previous publicly available study has accounted for calf age and fate in breeding probability in ceta‐ cean species; in small cetacean species, maternal care can last several years after a calf's birth (Oftedal, 1997) To this end, we studied a bottlenose dolphin (Tursiops truncatus) population in France. We used a descriptive method based on Tezanos‐Pinto et al (2014) to estimate calf survival proba‐ bility while not taking detection issues into account
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