Abstract
Increased environmental stochasticity due to climate change will intensify temporal variance in the life‐history traits, and especially breeding probabilities, of long‐lived iteroparous species. These changes may decrease individual fitness and population viability and is therefore important to monitor. In wild animal populations with imperfect individual detection, breeding probabilities are best estimated using capture–recapture methods. However, in many vertebrate species (e.g., amphibians, turtles, seabirds), nonbreeders are unobservable because they are not tied to a territory or breeding location. Although unobservable states can be used to model temporary emigration of nonbreeders, there are disadvantages to having unobservable states in capture–recapture models. The best solution to deal with unobservable life‐history states is therefore to eliminate them altogether. Here, we achieve this objective by fitting novel multievent‐robust design models which utilize information obtained from multiple surveys conducted throughout the year. We use this approach to estimate annual breeding probabilities of capital breeding female elephant seals (Mirounga leonina). Conceptually, our approach parallels a multistate version of the Barker/robust design in that it combines robust design capture data collected during discrete breeding seasons with observations made at other times of the year. A substantial advantage of our approach is that the nonbreeder state became “observable” when multiple data sources were analyzed together. This allowed us to test for the existence of state‐dependent survival (with some support found for lower survival in breeders compared to nonbreeders), and to estimate annual breeding transitions to and from the nonbreeder state with greater precision (where current breeders tended to have higher future breeding probabilities than nonbreeders). We used program E‐SURGE (2.1.2) to fit the multievent‐robust design models, with uncertainty in breeding state assignment (breeder, nonbreeder) being incorporated via a hidden Markov process. This flexible modeling approach can easily be adapted to suit sampling designs from numerous species which may be encountered during and outside of discrete breeding seasons.
Highlights
Intermittent breeding is widespread among vertebrate taxa
The multievent‐robust design model we describe here is a general model that combines multistate open robust design capture data collected during discrete breeding seasons with auxiliary live observations made at other times of the year
Our results indicated that breeding probabilities subsequent to first reproduction best corresponded to a Markovian process, where breeders in year t tended to have a higher probability to breed again in the year than females that were nonbreeders
Summary
Intermittent breeding is widespread among vertebrate taxa (e.g., fish: Jørgensen, Ernande, Fiksen, & Dieckmann, 2006, amphibi‐ ans: Muths, Scherer, & Lambert, 2010, reptiles: Baron, Le Galliard, Ferrière, & Tully, 2013, birds: Cam, Hines, Monnat, Nichols, & Danchin, 1998 and mammals: Pilastro, Tavecchia, & Marin, 2003). Many other long‐ lived species are prone to annual reproduction, but females may intermittently fail to breed because of impairment during the early stages of the reproductive cycle. The proximate regulator of inter‐ mittent breeding is thought to closely couple with an individual's energy balance, with reproductive skipping more prevalent among individuals in poor condition (Drent & Daan, 1980). Adaptive ex‐ planations of intermittent breeding postulate that, under certain circumstances, reproductive skipping may increase average life‐ time reproductive success above what could be achieved through persistent attempts at annual reproduction (Bull & Shine, 1979). According to the prudent parent hypothesis (Drent & Daan, 1980), intermittent breeding is adaptive when the energetic savings asso‐ ciated with skipped breeding opportunities can be diverted to im‐ prove an individual's survival probability or subsequent fecundity. Nonadaptive explanations suggest that intermittent breeding is itself not advantageous, but instead an unavoidable consequence of ecological or social constraints
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