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Ugandag のキバンガ国立公園でのチンパンジー群の内戦について、研究者たちが報告しています。約200匹のNGOGO チンパンジーは、長年にわたり調和して生活していましたが、2015年6月に西側と中心部のグループ間で対立が発生し、以降8年間にわたる内戦状態に陥りました。BBCによると、自2018年から24件の殺人事件（うち17件は幼児）が記録されており、主に中心部グループが西側グループを攻撃しています。
研究者たちは以下のような要因を挙げています：
- 2014年に不明な理由で5匹の成年雄と1匹の成年雌が死亡し、社会ネットワークが崩れ、 subgroup間の関係が弱まったこと
- 領導者の変更（2016年）と西側と中心部グループの最初の分断時期が一致したこと
- 2017年の呼吸器疫病により25匹が死亡し、そのうちの一人はグループをつなぐ最後の個体となったこと
これらの要因が「資源競争」や「雄との雄間の繁殖競争」といった複数の要素によって内戦状態に至ったと考えられています。研究結果は学術誌Scienceに掲載されました。
Researchers say the world's largest known wild chimpanzee community in Uganda fractured into rival factions and has been locked in a vicious "civil war" for the last eight years. "It is not clear exactly why the once close-knit community of Ngogo chimpanzees at Uganda's Kibale National Park are at loggerheads, but since 2018 the scientists have recorded 24 killings, including 17 infants," reports the BBC. From the report: [O]ver several decades, [lead author Aaron Sandel] said the nearly 200 Ngogo chimpanzees had lived in harmony. There were divided into two sets - known to researchers as Western and Central - but they had existed overall as a cohesive group. Sandel said he first noticed them polarizing in June 2015, when the Western chimpanzees ran away and were chased by the Central group. "Chimpanzees are sort of melodramatic," he said, explaining that following arguments there would ordinarily be "screaming and chasing" and then later, they would grooming and co-operating.
But following the 2015 dispute, the researchers saw that there was a six-week avoidance period between the two sets, with interactions becoming more infrequent. When they did occur, Sandel said they were "a little more intense, a little more aggressive." Following the emergence of the two distinct groups in 2018, members of the Western group started attacking the Central chimpanzees. In 24 targeted attacks since the split, at least seven adult males and 17 infants from the Central chimps have been killed, the study found, although the researchers believe the actual number of deaths are higher. The researchers believe many factors such as the group size and subsequent competition of resources, and "male-male competition" for reproducing may be to blame.
But they say there were three likely catalysts:
- The first, were the deaths of five adult males and one adult female -- for reasons unknown -- in 2014, which could have disrupted social networks and weakened social ties across the subgroups
- The following year, there was a change in the alpha male, which the study says coincided with the first period of separation between the Western and Central groups. "Changes in the dominance hierarchy can increase aggression and avoidance in chimpanzees," it explained
- The third factor was the deaths of 25 chimpanzees, including four adult males and 10 adult females, as a result of a respiratory epidemic, in 2017, a year before the final separation. One of the adult males who died was "among the last individuals to connect the groups," the research paper said. The study has been published in the journal Science.
Read more of this story at Slashdot.
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