Kovacs Carolyn J, Perrtree Robin M, Cox Tara M
Marine Sciences Program, Department of Marine & Environmental Sciences, Savannah State University, Savannah, Georgia, United States of America.
PLoS One. 2017 Feb 1;12(2):e0170151. doi: 10.1371/journal.pone.0170151. eCollection 2017.
Both natural and human-related foraging strategies by the common bottlenose dolphin (Tursiops truncatus) have resulted in social segregation in several areas of the world. Bottlenose dolphins near Savannah, Georgia beg at an unprecedented rate and also forage behind commercial shrimp trawlers, providing an opportunity to study the social ramifications of two human-related foraging behaviors within the same group of animals. Dolphins were photo-identified via surveys conducted throughout estuarine waterways around Savannah in the summers of 2009-2011. Mean half-weight indices (HWI) were calculated for each foraging class, and community division by modularity was used to cluster animals based on association indices. Pairs of trawler dolphins had a higher mean HWI (0.20 ± 0.07) than pairs of non-trawler dolphins (0.04 ± 0.02) or mixed pairs (0.02 ± 0.02). In contrast, pairs of beggars, non-beggars, and mixed pairs all had similar means, with HWI between 0.05-0.07. Community division by modularity produced a useful division (0.307) with 6 clusters. Clusters were predominately divided according to trawler status; however, beggars and non-beggars were mixed throughout clusters. Both the mean HWI and social clusters revealed that the social structure of common bottlenose dolphins near Savannah, Georgia was differentiated based on trawler status but not beg status. This finding may indicate that foraging in association with trawlers is a socially learned behavior, while the mechanisms for the propagation of begging are less clear. This study highlights the importance of taking into account the social parameters of a foraging behavior, such as how group size or competition for resources may affect how the behavior spreads. The positive or negative ramifications of homophily may influence whether the behaviors are exhibited by individuals within the same social clusters and should be considered in future studies examining social relationships and foraging behaviors.
普通宽吻海豚（Tursiops truncatus）的自然觅食策略和与人类相关的觅食策略，在世界上的几个地区都导致了社会隔离。佐治亚州萨凡纳附近的宽吻海豚以前所未有的速度乞讨，还在商业捕虾拖网渔船后面觅食，这为研究同一动物群体内两种与人类相关的觅食行为的社会影响提供了机会。通过在2009 - 2011年夏季对萨凡纳周围河口航道进行的调查，对海豚进行了照片识别。计算了每个觅食类别的平均半体重指数（HWI），并使用基于模块性的群落划分方法，根据关联指数对动物进行聚类。拖网渔船附近的海豚对的平均HWI（0.20±0.07）高于非拖网渔船附近的海豚对（0.04±0.02）或混合对（0.02±0.02）。相比之下，乞讨者对、非乞讨者对和混合对的平均HWI都相似，在0.05 - 0.07之间。基于模块性的群落划分产生了一个有用的划分（0.307），分为6个集群。集群主要根据拖网渔船状态划分；然而，乞讨者和非乞讨者在各集群中混合分布。平均HWI和社会集群都表明，佐治亚州萨凡纳附近普通宽吻海豚的社会结构是根据拖网渔船状态而非乞讨状态分化的。这一发现可能表明，与拖网渔船一起觅食是一种通过社会学习获得的行为，而乞讨行为传播的机制尚不清楚。这项研究强调了考虑觅食行为的社会参数的重要性，例如群体大小或资源竞争如何可能影响行为的传播方式。同类相吸的积极或消极影响可能会影响同一社会集群内的个体是否表现出这些行为，并应在未来研究社会关系和觅食行为时予以考虑。
