Limitation of population recovery: a stochastic approach to the case of the emperor penguin


  • Stéphanie Jenouvrier,

  • Christophe Barbraud,

  • Henri Weimerskirch,

  • Hal Caswell

S. Jenouvrier ( and H. Caswell, Biology Dept, MS-34, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA. – SJ, C. Barbraud and H. Weimerskirch, Centre d'Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, FR–79360 Villiers en Bois, France.


Major population crashes due to natural or human-induced environmental changes may be followed by recoveries. There is a growing interest in the factors governing recovery, in hopes that they might guide population conservation and management, as well as population recovery following a re-introduction program. The emperor penguin Aptenodytes forsteri population in Terre Adélie, Antarctica, declined by 50% during a regime shift in the mid-1970s, when abrupt changes in climate and ocean environment regimes affected the entire Southern Ocean ecosystem. Since then the population has remained stable and has not recovered. To determine the factors limiting recovery, we examined the consequences of changes in survival and breeding success after the regime shift. Adult survival recovered to its pre-regime shift level, but the mean breeding success declined and the variance in breeding success increased after the regime shift. Using stochastic matrix population models, we found that if the distribution of breeding success observed prior to the regime shift had been retained, the emperor penguin population would have recovered, with a median time to recovery of 36 years. The observed distribution of breeding success after the regime shift makes recovery very unlikely. This indicates that the pattern of breeding success is sufficient to have prevented emperor penguin population recovery. The population trajectory predicted on the basis of breeding success agrees with the observed trajectory. This suggests that the net effect of any facors other than breeding success must be small. We found that the probability of recovery and the time to recovery depend on both the mean and variance of breeding success. Increased variance in breeding success increases the probability of recovery when mean success is low, but has the opposite effect when the mean is high. This study shows the important role of breeding success in determining population recovery for a long-lived species and demonstrates that demographic mechanisms causing population crash can be different from those preventing population recovery.