Kleijn David, Raemakers Ivo
Alterra, Centre for Ecosystem Studies, Droevendaalsesteeg 3, P.O. Box 47, 6700 AA, Wageningen, The Netherlands.
Ecology. 2008 Jul;89(7):1811-23. doi: 10.1890/07-1275.1.
Understanding population declines has been the objective of a wide range of ecological studies. When species have become rare such studies are complicated because particular behavior or life history traits may be the cause but also the result of the decline of a species. We approached this problem by studying species' characteristics on specimens that were collected before the onset of their decline and preserved in natural history museums. In northwestern Europe, some bumble bee species declined dramatically during the 20th century whereas other, ecologically similar, species maintained stable populations. A long-standing debate focuses on whether this is caused by declining species having stricter host plant preferences. We compared the composition of pollen loads of five bumble bee species with stable populations and five with declining populations using museum specimens collected before 1950 in Belgium, England, and The Netherlands. Prior to 1950, the number of plant taxa in pollen loads of declining species was almost one-third lower than that in stable species even though individuals of stable and declining species generally originated from the same areas. There were no systematic differences in the composition of pollen loads between stable and declining species, but the plant taxa preferred by declining species before 1950 had experienced a stronger decline in the 20th century than those preferred by stable species. In 2004 and 2005, we surveyed the areas where bumble bees had been caught in the past and compared the composition of past and present pollen loads of the stable, but not of the by now locally extinct declining species. The number of collected pollen taxa was similar, but the composition differed significantly between the two periods. Differences in composition reflected the major changes in land use in northwestern Europe but also the spread of the invasive plant species Impatiens glandulifera. The main question now is why declining species apparently were not able to switch to less preferred food plants when stable species were. This study shows that natural history collections can play an important role in improving our understanding of the ecological mechanisms driving species population change.
了解种群数量下降一直是众多生态研究的目标。当物种变得稀有时，此类研究就会变得复杂，因为特定的行为或生活史特征可能既是物种数量下降的原因，也是其结果。我们通过研究在物种数量下降开始之前收集并保存在自然历史博物馆中的标本的物种特征来解决这个问题。在欧洲西北部，一些熊蜂物种在20世纪急剧减少，而其他生态习性相似的物种则保持了稳定的种群数量。长期以来的争论焦点在于，这是否是由于数量下降的物种对寄主植物有更严格的偏好所致。我们使用1950年之前在比利时、英国和荷兰收集的博物馆标本，比较了五种种群数量稳定的熊蜂物种和五种种群数量下降的熊蜂物种的花粉载量组成。在1950年之前，数量下降的物种的花粉载量中的植物分类单元数量比稳定物种的低近三分之一，尽管稳定物种和数量下降物种的个体通常来自相同的区域。稳定物种和数量下降物种的花粉载量组成没有系统差异，但数量下降物种在1950年之前偏好的植物分类单元在20世纪的减少幅度比稳定物种偏好的更大。在2004年和2005年，我们对过去捕获熊蜂的区域进行了调查，并比较了稳定物种（而非现已在当地灭绝的数量下降物种）过去和现在的花粉载量组成。收集到的花粉分类单元数量相似，但两个时期的组成有显著差异。组成上的差异既反映了欧洲西北部土地利用的主要变化，也反映了入侵植物物种凤仙花的扩散。现在的主要问题是，为什么数量下降的物种在稳定物种能够做到的时候显然无法转向不太偏好的食物植物。这项研究表明，自然历史藏品在增进我们对驱动物种种群变化的生态机制的理解方面可以发挥重要作用。
