Petrin Zlatko, Englund Göran, Malmqvist Björn
Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
Proc Biol Sci. 2008 May 22;275(1639):1143-8. doi: 10.1098/rspb.2008.0023.
Large-scale human activities including the extensive combustion of fossil fuels have caused acidification of freshwater systems on a continental scale, resulting in reduced species diversity and, in some instances, impaired ecological functioning. In regions where acidity is natural, however, species diversity and functioning seem to be less affected. This contrasting response is likely to have more than one explanation including the possibility of adaptation in organisms exposed to natural acidity over evolutionary time scales and differential toxicity due to dissimilarities in water chemistry other than pH. However, empirical evidence supporting these hypotheses is equivocal. Partly, this is because previous research has mainly been conducted at relatively small geographical scales, and information on ecological functioning in this context is generally scarce. Our goal was to test whether anthropogenic acidity has stronger negative effects on species diversity and ecological functioning than natural acidity. Using a meta-analytic approach based on 60 datasets, we show that macroinvertebrate species richness and the decomposition of leaf litter -- an important process in small streams -- tend to decrease with increasing acidity across regions and across both the acidity categories. Macroinvertebrate species richness, however, declines three times more rapidly with increasing acidity where it is anthropogenic than where it is natural, in agreement with the adaptation hypothesis and the hypothesis of differences in water chemistry. By contrast, the loss in ecological functioning differs little between the categories, probably because increases in the biomass of taxa remaining at low pH compensate for losses in functionality that would otherwise accompany losses of taxa from acidic systems. This example from freshwater acidification illustrates how natural and anthropogenic stressors can differ markedly in their effects on species diversity and one aspect of ecological functioning.
包括大量燃烧化石燃料在内的大规模人类活动已导致淡水系统在大陆范围内酸化，造成物种多样性降低，在某些情况下还损害了生态功能。然而，在酸度为自然形成的地区，物种多样性和功能似乎受影响较小。这种截然不同的反应可能有不止一种解释，包括在进化时间尺度上暴露于自然酸度的生物可能产生适应性，以及除pH值外水化学差异导致的不同毒性。然而，支持这些假设的实证证据并不明确。部分原因在于，此前的研究主要在相对较小的地理尺度上进行，在这种情况下关于生态功能的信息通常很少。我们的目标是检验人为酸度对物种多样性和生态功能的负面影响是否比自然酸度更强。基于60个数据集采用元分析方法，我们发现大型无脊椎动物物种丰富度以及落叶分解——小溪中的一个重要过程——往往会随着酸度在不同地区和不同酸度类别中的增加而降低。然而，大型无脊椎动物物种丰富度在人为酸度增加时下降的速度比自然酸度增加时快三倍，这与适应性假设和水化学差异假设相符。相比之下，生态功能的损失在不同类别之间差异不大，可能是因为在低pH值下仍存在的类群生物量增加弥补了酸性系统中类群损失本应伴随的功能损失。淡水酸化的这个例子说明了自然和人为压力源在对物种多样性和生态功能的一个方面的影响上可能存在显著差异。
