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ウガンダのキバレ国立公園で最大規模の野生 chimpanzee 群が、8 年間続く内戦状態にあるという研究結果が公表されました。2015年以降、このグループは「西」と「中央」の 2 つの派閥に分かれ、2018 年からは攻撃的な行動が多く見られるようになりました。科学者らは過去 8 年間に 24 回の殺人事件を記録しており、その内の 17 件が幼児でした。
研究責任者のアラオン・サンデル氏によると、このグループは数十年間で共存していたものの、2015年に西派から追放された出来事以降、6週間の回避期間があり、その後の対立はより激しくなったと説明しています。主な要因として、2014年の 5人の成年雄と 1 人の成年雌の死亡（理由不詳）、2017年に起きた呼吸系流行による 25頭の死（その内の 1頭がグループをつなぐ最後の人間）と 2018 年に新たな alpha メス性の変更が挙げられています。これらの要因は社会ネットワークを崩壊させ、資源競争や繁殖における男性間の競争につながったと考えられます。
この研究結果は学術誌 Science に発表されています。
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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