Indirect effects of large herbivores on snakes in an African savanna.
Indirect effects of large herbivores on snakes in an African savanna.
复制标题
大型食草动物对非洲稀树草原蛇的间接影响。
作者：
D. McCauley;F. Keesing;T. Young;B. Allan;R. Pringle
许多大型哺乳动物物种在非洲稀树草原上正在减少，但我们对这些减少如何影响其他物种的了解相对较少。先前的研究表明，从大规模的重复实验地块中移除大型草食性哺乳动物会导致小型哺乳动物的密度急剧增加，这种增加归因于啮齿动物和大型草食性动物之间对食物资源的竞争放松。为了评估是否去除大型食草动物也影响了捕食者的小型哺乳动物，我们测量了丰富的当地常见的橄榄嘶嘶蛇，Psammophis mossambicus，在19个月的时间内，在情节和没有大型食草动物。在大型食草动物被清除且啮齿动物数量较多的地块中，莫桑比克沙蛇的数量明显更加丰富。根据猛禽调查和植被覆盖测量的结果，蛇密度的差异似乎不是由捕食蛇的速度差异所驱动的。相反，蛇似乎是响应数量更大的小型哺乳动物猎物的地区，大型食草动物已被排除在外。这是大型食草动物对蛇丰度的间接影响的第一个实证，并提出了一个有趣的例子，说明优势物种和关键物种的影响如何通过食物网传播。
Many large mammal species are declining in African savannas, yet we understand relatively little about how these declines influence other species. Previous studies have shown that the removal of large herbivorous mammals from large-scale, replicated experimental plots results in a dramatic increase in the density of small mammals, an increase that has been attributed to the relaxation of competition between rodents and large herbivores for food resources. To assess whether the removal of large herbivores also influenced a predator of small mammals, we measured the abundance of the locally common olive hissing snake, Psammophis mossambicus, over a 19-mo period in plots with and without large herbivores. Psammophis mossambicus was significantly more abundant in plots where large herbivores were removed and rodent numbers were high. Based on results from raptor surveys and measurements of vegetative cover, differences in snake density do not appear to be driven by differences in rates of predation on snakes. Instead, snakes appear to be responding numerically to greater abundances of small-mammal prey in areas from which large herbivores have been excluded. This is the first empirical demonstration of the indirect effects of large herbivores on snake abundance and presents an interesting example of how the influence of dominant and keystone species can move through a food web.