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

Abstract

Animal populations can be affected by environmental disturbances in many ways including demographic and behavioral changes. This can affect interspecies associations for regularly interacting sympatric species, like bottlenose and spotted dolphins in the Bahamas (observed since 1985 and interspecies associations analyzed since 1993). After two hurricanes in 2004 each species lost roughly 30% of their respective communities resulting in differing social structure and behavioral changes. During mixed species encounters (MSE) group sizes for spotted dolphins (truexfalse¯ = 14.1 ± 9.2) were significantly larger than bottlenose dolphins (truexfalse¯ = 6.0 ± 7.3; F = 11.74, df = 1, P < 0.001), however, t‐tests revealed no differences between aggressive vs. affiliative encounters. Sexual/aggressive behavior regularly seen previously was not observed posthurricanes and aggressive encounters were greatly reduced. Generally results were similar to prehurricane data including high resightings of spotted dolphins with male alliances prevalent (including new juvenile alliances seen only posthurricane), and individualized bottlenose participation with few male alliances. However temporal associations varied compared to prehurricane. Interspecies association and behavior patterns were altered and likely affected by the changes in intraspecies association patterns following the hurricanes. However both species still participated in MSE, suggesting this is an important component of their ability to coexist as sympatric species.

Exodus! Large-scale displacement and social adjustments of resident Atlantic spotted dolphins (Stenella frontalis) in the Bahamas

“…This provides further support to the finding of [ 14 ] that the clusters are an integral part of the community structure, remaining in some capacity regardless of demographic changes. It may also take longer than three years for the individuals to adapt to the new conditions; in this study site it took more than five years for ‘normal’ aggressive behaviors during interspecies encounters to re-occur following hurricanes and social restructuring [ 22 ], thus future research may reveal nonrandom associations and a similar or different social structure. Regardless of time frame however, the changes observed will have important implications regarding survivability of individuals, social clusters/social structure, and community as a whole if outside individuals and genes are not integrated (see genetic section below).…”

“…Following demographic upheaval after hurricane disturbance in 2004, differing social structure changes also occurred on LBB between the two closely related sympatric species of resident Atlantic spotted dolphins and bottlenose dolphins [ 3 , 14 ]. The long-term interspecies interactions of these two stable communities of dolphins have been documented [ 19 – 21 ], along with changes following the hurricanes [ 22 ].…”

Effects of intense storm events on dolphin occurrence and foraging behavior

“…Should dolphins experience range shifts due to direct displacement or in search of prey, they may be exposed to changes in pollutants, pathogens 45 , and predators 48 . Interspecific dynamics 20 and biodiversity have also been affected by range shifts in these top predators 48 . Bottlenose dolphin and spotted dolphin (Stenella frontalis) populations in the Bahamas decreased in size by 30% following two hurricanes, likely due to death and/or emigration 20 .…”

“…Storm events were considered the direct cause of bottlenose dolphin (Tursiops truncatus) movement into shallower waters 17,18 and lower adult survival probabilities for manatees (Trichechus manatus latirostris) in years with intense hurricanes 19 . Following two hurricanes, Bahamian dolphin populations experienced 30% population loss, but it is not known whether this was due to emigration and/or mortality 20 . Hurricanes in the Mississippi Sound area had variable effects on short 21 and long-term dolphin foraging activities 22 .…”

Exploration of Horizontal Information Transmission through Social Learning in Juvenile Atlantic Spotted Dolphins (Stenella frontalis)

“…The bottom is primarily sandy, with zones of rock, reef and patches of seagrass (Thalassia testudimum). The life history, including non-invasive genetic analysis, (Elliser & Herzing, 2012, 2013, 2016a, 2016bGreen, Herzing & Baldwin, 2007 and the development and use of social and acoustic behaviors of this community of Atlantic spotted dolphins have been documented extensively Herzing, 2000Herzing, , 2004Herzing, , 2005Herzing & Brunnick, 1997;Herzing & dos Santos, 2004;Herzing & Johnson, 1997;Herzing, Moewe & Brunnick, 2003;Lammers, Au & Herzing, 2003;Miles & Herzing, 2003;Welsh & Herzing, 2008).…”