🤖 AI Summary
ウガンダのキバイレ国立公園で世界最大規模の野生チンパンジー集団が、約8年間にわたる「内戦」に陥っていると研究者たちは報告しています。 Ngogoという約200匹いるチンパンジーはこれまで和睦を続けていましたが、2015年に西部グループと中央グループの対立が始まり、2018年に二つに分裂しました。その結果、24件以上の攻撃事件が発生し、少なくとも7匹の雄と17匹の未成体が死亡しています。
研究者たちは、集団の大きさ、リソース競争、「雄対雄」の繁殖競争などが原因と考えています。また、3つの可能性がある要因として以下を挙げています:
- 2014年に不明な理由から5匹の成年男性と1匹の成年女性が死亡し、社会ネットワークやグループ間のつながりが損なわれたこと
- 成長順位の変化により、西部グループと中央グループの最初の分断期が生じたことが指摘されています
- 2017年の呼吸器症候群の流行で25匹が死亡し、そのうち雄4匹と雌10匹は最後に集団をつなぐ存在でした
これらの研究結果は学術誌「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.