Galapagos Sea Lions and Fur Seals, Adapted to a Variable World

Galapagos otariids (Galapagos sea lions Zalophus wollebaeki, and Galapagos fur seal Arctocephalus galapagoensis) have developed a number of behavioral adaptations to living in a tropical ecosystem exemplified by high environmental variability and subsequent oceanographic disturbances that lead to unpredictable marine productivity. Both species have been subject to selection pressures to reduce overall body size and energy requirements compared to otariids living in more predictably productive systems. The environmental stochasticity also appears to have modified both reproductive and foraging behavior. Galapagos otariids respond to limited food supplies with prolonged lactation, thus enhancing the chances of pup survival, and have developed trophic specialization with a high level of flexibility that reduces interspecific competition, combined with prey-switching during El Nino events. Galapagos fur seal mothers adjust the length of foraging trips and the duration of visits to attend pups in response to fluctuations in food. Galapagos sea lions reduce competition among individuals by displaying diverse foraging strategies in relation to prey availability. These mechanisms make life viable in the Galapagos Islands. Although the populations of these otariids have slightly increased in the last 5 years, they may not have recovered yet from the drastic reductions caused by El Nino events during the years 1982/83 and 1997/98. This shows the high vulnerability of these otariids to temporal changes in environmental conditions of the region and how the natural climatic variation of this ecosystem is an important stressor factor of their populations.