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Ugandasのキバリ国立公園で、世界最大規模の野生チンパンジー集団が8年間 terse 戦いを続けていると研究者が報告しました。このグループは約200頭おり、これまでに24件の殺人事件が報告されており、そのうち17頭は幼児でした。
リーダーのAaron Sandel氏によれば、これらのチンパンジーは数十年間にわたり調和していましたが、2015年に西部集団と中央集団の間で対立が起こり、その後6週間の回避期間がありました。さらに2018年には2つのグループが分断され、西部集団のメンバーが中央集団を攻撃する事件が頻発しました。
研究者らは、このような内戦の原因として、以下の3点を挙げています:
- 2014年に不明な理由で5頭の雄と1頭の雌が死亡し、社会ネットワークが乱れ、社会的つながりが弱まったこと
- アルファメスの変更が2018年早々に2つのグループ間の分断を引き起こした可能性
- 2017年に呼吸器疾患により25頭が死亡し、そのうちの雄4頭と雌10頭はグループをつなぐ最後の個体だったこと
この研究結果はScience誌に発表されました。
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.