一項新研究發現，瀕臨滅絕的維龍加山地大猩猩，其受脅狀況可能因全球暖化加劇，提高健康問題和早逝的風險。
利用在野外採集的糞便樣本，研究人員發現，當連月均溫和降雨量高於平均水準，維龍加大猩猩的受脅程度便會提高。作者在研究論文中寫道，這顯示維龍加大猩猩「對暖化趨勢的敏感程度比過去研究結果更高」。
一位靈長類動物學家告訴Carbon Brief，這份研究結果為氣候變遷如何提升動受脅狀況提供了強而有力的證據。「我們還不知道這種生理反應的長期影響是什麼，但可能是降低存活率或生育率的前兆。」
山地大猩猩（Gorilla beringei beringei）是大猩猩中瀕危的亞種，生活在非洲大湖區破碎化的森林。
約有1000隻山地大猩猩分布在兩區之間。「維龍加山地大猩猩」一詞指的是居住在維龍加山區的族群，這是一片由茂密的雲霧森林覆蓋的火山鏈。該地區橫跨盧安達、烏干達和剛果民主共和國。
維龍加大猩猩面臨的威脅包括狩獵、棲息地破壞和人獸衝突。幸好，保育工作使個體數量從1980年代的250隻左右上升到2016年的604隻。
這項新研究發表在《生態與演化》期刊。
兩年多來，研究人員定期蒐集115隻大猩猩的糞便樣本，以持續監測動物的壓力激素（糖皮質素）分泌。
接著科學家將這些結果與當地月均溫和降雨紀錄比較，並將一系列可能影響壓力的社會因素納入評估，包括大猩猩的群成員數，以及與競爭群的相似度。
研究結果顯示，在最高和最低溫高於平均值以及降雨量較高的月份，維龍加大猩猩的壓力激素都比較高。
研究人員並沒有探討為什麼大猩猩在溫暖或潮濕的環境中壓力比較大。然而研究人員指出，炎熱和陽光強時，山地大猩猩經常在植被中尋找遮蔭，導致進食時間減少。
下大雨時，山地大猩猩會靜靜坐在一起，但如果雨一直不停，牠們將恢復進食並補回減少的進食時間。這可能會增加壓力，因為大猩猩花更多精力保持穩定的體溫，以抵消雨水降溫的影響。
研究結果顯示，維龍加大猩猩因應更大幅的升溫和極端降雨時，可能更加辛苦。
在中高溫室氣體排放情境下（SRES A2），到2090年，大猩猩棲息地氣溫可能會增加高達3.6°C。此外，作者指出，屆時降雨將分布更不均，乾濕季節之間會有更多極端波動。
Global warming could cause stress to endangered Virunga mountain gorillas, potentially raising the risk of health problems and early death, a new study suggests.
Using fecal samples taken in the wild, researchers found that Virunga gorillas show elevated stress levels in months with higher-than-average temperatures and rainfall.
This suggests that Virunga gorillas “might be more sensitive to warming trends than previous research has suggested”, the authors write in their research paper.
The findings provide “robust” evidence of how climate change could heighten the animals’ stress levels, a primatologist tells Carbon Brief. “We don’t know yet what the long-term impact of this physiological response will be, but it could be a harbinger of reduced survival or fertility.”
Mountain gorillas (Gorilla beringei beringei) are an endangered subspecies living in fragmented forests across the Great Lakes region of Africa.
The total population of around 1,000 individuals is split between two regions. The term “Virunga mountain gorilla” refers to the group that live across the Virunga massif, a chain of volcanoes covered by dense cloud forest. The region spans Rwanda, Uganda and the Democratic Republic of Congo.
Virunga gorillas face severe ongoing threats from hunting, habitat destruction and the impacts of nearby human conflicts. However, major conservation efforts have seen population numbers rise from around 250 in the 1980s to 604 in 2016.
The new study, published in the journal Ecology and Evolution.
Over two years, researchers routinely collected fecal samples from 115 Virunga gorillas. This allowed them to continuously monitor the animals’ stress hormone(glucocorticoid) levels.
The scientists then compared these results to local records of monthly temperature and rainfall data. They also considered a range of social factors that can influence stress levels, including gorilla group size and proximity to rival groups.
The findings show that baseline stress levels of Virunga gorillas were raised in months with higher-than-average maximum and minimum temperatures, as well as in months with higher rainfall.
The researchers did not study the reasons why gorillas might have experienced more stress in warmer or wetter conditions.
However, the researchers note that “on hot and sunny days, mountain gorillas often seek shade in vegetation”, leading to “reduced time spent feeding”.
When rain is heavy, “mountain gorillas sit still in a huddle, but if rain persists, they will resume feeding and compensate for lost feeding time”, the authors say. This could raise stress as “gorillas work harder to maintain a stable body temperature” to counteract the rain’s cooling impact.
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The findings suggest that Virunga gorillas “may have a harder time coping with warmer temperatures and more extreme rainfall”.
Local temperatures in the gorillas’ habitat could increase by up to 3.6C by 2090, relative to 1990 levels, under a moderately high greenhouse gas emissions scenario (SRES A2).
In addition, rainfall is expected to become “less evenly distributed”, with “more extreme swings between the wet and dry seasons”, the authors say.
※ 全文及圖片詳見：Carbon Brief
