Biggerstaff Michael T, Lashley Marcus A, Chitwood M Colter, Moorman Christopher E, DePerno Christopher S
Warnell School of Forestry and Natural Resources, University of Georgia, 180 E Green Street, Athens, GA 30602, United States.
Department of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Box 9690, Mississippi State, MS 39759, United States.
Behav Processes. 2017 Mar;136:36-42. doi: 10.1016/j.beproc.2017.01.003. Epub 2017 Jan 6.
Nearly all species of sexually dimorphic ungulates sexually segregate. Several hypotheses have been proposed to explain this phenomenon, including the social-factors hypothesis (SFH) and the predation hypothesis (PH). Interestingly, previous studies have accepted and rejected each hypothesis within and across species but few studies have simultaneously tested both hypotheses in the same population. In August 2011 and 2012 using 7680 photographs taken with camera traps in standardized forage patches, we tested two predictions of the SFH: 1) foraging efficiency of both sexes would decrease when foraging rate in mixed-sex groups relative to single-sex groups, and 2) activity patterns (i.e., the pattern of temporal use of forage patches on a diel scale) of the sexes would decrease in temporal overlap at the forage patch level (i.e., social segregation) compared to the overall temporal overlap of activity patterns of the population. Also, we tested two predictions of the +PH : 1) the relationship between feeding rates of each sex, and 2) temporal activity overlap would change with changing risk level of forage patches as a result of differing risk perception between sexes. In support of the SFH for temporal segregation, when in mixed-sex groups, mature males and all females decreased feeding rate 30% and 10%, respectively; further, the sexes had similar activity patterns overall (94-95% overlap), though temporal overlap was lower in individual forage patches (68-74% overlap). In multi-male mixed sex groups, at least one male exhibited aggressive posture toward females during all foraging bouts suggesting intersex aggression was the cause of the observed decrease in foraging rates. In support of the PH , the sexes adjusted feeding rate differently in response to changing risk level of a forage patch, encouraging spatial segregation; however, the PH was not supported for temporal segregation because temporal activity pattern overlap did not vary as a function of predation risk. Coupling our results with previous reports indicates that the SFH is supported for only temporal segregation of forage patch use, and the PH may only be supported for spatial segregation in forage patch use. Thus, both social factors and predation risk may interact to encourage sexual segregation.
几乎所有两性异形的有蹄类动物都会进行性别隔离。人们提出了几种假说来解释这一现象，包括社会因素假说（SFH）和捕食假说（PH）。有趣的是，以往的研究在物种内部和跨物种研究中对每个假说都有接受和否定的情况，但很少有研究在同一群体中同时检验这两种假说。在2011年8月和2012年，我们利用在标准化觅食区域用相机陷阱拍摄的7680张照片，检验了社会因素假说的两个预测：1）当混合性别群体的觅食率相对于单性别群体降低时，两性的觅食效率都会下降；2）与种群活动模式的总体时间重叠相比，两性在觅食区域层面的活动模式（即一天内对觅食区域的时间利用模式）的时间重叠会减少（即社会隔离）。此外，我们还检验了捕食假说的两个预测：1）两性的进食率之间的关系；2）由于两性对风险的认知不同，随着觅食区域风险水平的变化，时间活动重叠也会发生变化。为支持社会因素假说中关于时间隔离的观点，当处于混合性别群体中时，成年雄性和所有雌性的进食率分别降低了30%和10%；此外，两性总体上有相似的活动模式（重叠率为94 - 95%），尽管在单个觅食区域的时间重叠较低（重叠率为68 - 74%）。在多雄性混合性别群体中，在所有觅食过程中至少有一只雄性对雌性表现出攻击姿态，这表明两性间的攻击行为是观察到的觅食率下降的原因。为支持捕食假说，两性会根据觅食区域风险水平的变化不同程度地调整进食率，这促使了空间隔离；然而，捕食假说在时间隔离方面未得到支持，因为时间活动模式重叠并未随捕食风险而变化。将我们的结果与之前的报告相结合表明，社会因素假说仅在觅食区域使用的时间隔离方面得到支持，而捕食假说可能仅在觅食区域使用的空间隔离方面得到支持。因此，社会因素和捕食风险可能相互作用，促使性别隔离。
