Department of Biology, Colorado State University, Fort Collins, Colorado, 80523, USA.
Department of Biology, Evolutionary Ecology Laboratories, and Monte L. Bean Museum, Brigham Young University, Provo, Utah, 84602, USA.
Ecology. 2018 Feb;99(2):312-321. doi: 10.1002/ecy.2090. Epub 2018 Jan 5.
Long-term observations of ecological communities are necessary for generating and testing predictions of ecosystem responses to climate change. We investigated temporal trends and spatial patterns of soil fauna along similar environmental gradients in three sites of the McMurdo Dry Valleys, Antarctica, spanning two distinct climatic phases: a decadal cooling trend from the early 1990s through the austral summer of February 2001, followed by a shift to the current trend of warming summers and more frequent discrete warming events. After February 2001, we observed a decline in the dominant species (the nematode Scottnema lindsayae) and increased abundance and expanded distribution of less common taxa (rotifers, tardigrades, and other nematode species). Such diverging responses have resulted in slightly greater evenness and spatial homogeneity of taxa. However, total abundance of soil fauna appears to be declining, as positive trends of the less common species so far have not compensated for the declining numbers of the dominant species. Interannual variation in the proportion of juveniles in the dominant species was consistent across sites, whereas trends in abundance varied more. Structural equation modeling supports the hypothesis that the observed biological trends arose from dissimilar responses by dominant and less common species to pulses of water availability resulting from enhanced ice melt. No direct effects of mean summer temperature were found, but there is evidence of indirect effects via its weak but significant positive relationship with soil moisture. Our findings show that combining an understanding of species responses to environmental change with long-term observations in the field can provide a context for validating and refining predictions of ecological trends in the abundance and diversity of soil fauna.
长期的生态群落观测对于生成和检验生态系统对气候变化的响应预测是必要的。我们在南极麦克默多干谷的三个地点，沿着相似的环境梯度进行了土壤动物的时间趋势和空间格局的研究，这三个地点跨越了两个截然不同的气候阶段：从 20 世纪 90 年代初到 2001 年 2 月的南极夏季，持续了十年的降温趋势，随后是当前夏季变暖、更频繁的离散变暖事件的趋势。2001 年 2 月之后，我们观察到优势物种（线虫 Scottnema lindsayae）的减少，以及较少见的类群（轮虫、缓步动物和其他线虫物种）的丰度增加和分布范围扩大。这种不同的响应导致了类群的略微更高的均匀度和空间同质性。然而，土壤动物的总丰度似乎在下降，因为目前较少见的物种的正趋势尚未弥补优势物种数量的下降。在优势物种中幼体比例的年际变化在各地点是一致的，而丰度趋势则变化更大。结构方程模型支持这样的假设，即观察到的生物趋势是由优势和较少见的物种对增强冰融化导致的水分可用性脉冲的不同响应引起的。没有发现夏季平均温度的直接影响，但有证据表明，通过其与土壤水分的微弱但显著的正关系，存在间接影响。我们的研究结果表明，将对环境变化的物种响应的理解与野外的长期观测相结合，可以为验证和完善土壤动物丰度和多样性的生态趋势预测提供背景。
