Social structure of Atlantic spotted dolphins, Stenella frontalis, following environmental disturbance and demographic changes

Abstract

Extreme environmental events and demographic changes can have variable effects on the social structure of animal populations. This study compared the social structure of a community of Atlantic spotted dolphins in the Bahamas before and after two hurricanes. Approximately 36% of the individuals were lost, with no subsequent increase in immigration. The majority of the social structure characteristics were consistent with results from a long‐term study covering the previous 12 yr, including community structure with definitive social clusters, sex preferences and overall association patterns. However some changes occurred, though still constrained within sex preferences. Posthurricane there was a decrease in social differentiation and increased cohesion within clusters and across age class. Males retained or made new first order alliances, however, only one second order alliance was evident, revealing a simplified alliance structure. Juvenile individuals made alliance level associations, unprecedented from long‐term analysis. Although other studies have shown stark restructuring, this study showed that less drastic changes within overall social structure stability can occur. Persistence and evolutionary changes in populations through environmental and/or demographic perturbations may depend on the social structure of a population or community. Understanding the processes involved in social development is paramount for conservation of diverse populations.

Changes in interspecies association patterns of Atlantic bottlenose dolphins, Tursiops truncatus, and Atlantic spotted dolphins, Stenella frontalis, after demographic changes related to environmental disturbance

“…, Elliser and Herzing ). Data were collected between May and early September each year, 2005–2007 (for effort 2002–2007 see Elliser and Herzing ) aboard a 62 ft power catamaran research vessel. Observations for sighting dolphin groups were conducted in all but rough weather conditions (over Beaufort 3 and/or intense rain squalls) from 0700 to 2000 in one person/one hour shifts, scanning forward 180° while the boat was underway, and 360° while anchored.…”

“…, ), and community definition and social structure (Herzing and Brunnick ; Rossbach and Herzing ; Rogers et al . ; Elliser and Herzing ; Elliser and Herzing , , b). Both species show social structure characteristics similar to other well studied bottlenose dolphin studies where long‐term affiliations are correlated with age, sex, and reproductive status.…”

“…Environmental disasters can alter animal populations in a variety of ways, including changes in behavior, death, emigration/immigration, food abundance/distribution, and social structure (Elliser and Herzing ). In particular, losses of individuals can subtly or greatly affect associations and social structure (chimpanzees, Pan troglodytes verus , Lehmann and Boesch ; bottlenose dolphins, Elliser and Herzing ; spotted dolphins, Elliser and Herzing ; killer whales, Orcinus orca , Matkin et al . ).…”

“…The spotted dolphin community suffered the greatest loss of individuals (36%), including 16 females and 20 males, with no subsequent immigration. Although the losses were fairly consistent over age classes, the percentage loss per age class decreased with increasing age (Elliser and Herzing ). Community structure (consisting of three social clusters), sex preferences and overall association patterns remained consistent with previous long‐term analyses, however some changes did occur (Elliser and Herzing ).…”

“…Although the losses were fairly consistent over age classes, the percentage loss per age class decreased with increasing age (Elliser and Herzing ). Community structure (consisting of three social clusters), sex preferences and overall association patterns remained consistent with previous long‐term analyses, however some changes did occur (Elliser and Herzing ). Decreased social differentiation and increased cohesion within social clusters and across age class, reduced prevalence of second‐order alliances, and unprecedented juvenile alliance level associations were documented, revealing social structure changes within overall stability after the demographic changes (Elliser and Herzing ).…”