Wise David H, Chen Benrong
Department of Entomology, S-225 Agricultural Science Bldg. - North, University of Kentucky, Lexington, KY 40546-0091, USA e-mail:
Oecologia. 1999 Oct;121(1):129-137. doi: 10.1007/s004420050914.
We investigated the impact of variation in densities of a guild of generalist predators on survival of young wolf spiders of the genus Schizocosa. Numbers of other spiders and centipedes were reduced by >80% in fenced 4-m plots in an experiment that was replicated twice in each of three forest locations. Schizocosa survival during the 1st month was low (<50%) in all three locations, but did not differ between predator-reduction and control plots. By the end of the 1st month, densities of the manipulated predators had converged in control and perturbed treatments, most likely because of reduced per capita mortality from lowered rates of intraguild predation and cannibalism in the experimental treatment. During the 2nd month of the experiment, centipedes and spiders other than Schizocosa again were removed from the experimental plots and, unlike the earlier period, numbers of intraguild predators in the predator-removal treatment remained lower than in control plots. Reducing densities of intraguild predators during the 2nd month improved survival of older juvenile Schizocosa by 75% in two of three locations on the forest floor. In addition to this evidence that intraguild predation can affect older juvenile Schizocosa, survival of Schizocosa during the last half of the experiment was negatively correlated with spatial variation in densities of gnaphosid and ctenid spiders. These two abundant families of cursorial spiders preyed on Schizocosa at a high rate in laboratory trials. Thus, variation in densities of intraguild predators did not influence the youngest Schizocosa, but did influence the survival of older juveniles, most likely due to variations in densities of other cursorial spiders.
我们研究了多食性捕食者群落密度变化对裂腹蛛属幼狼蛛生存的影响。在三个森林地点中的每个地点都进行了两次重复实验，在4米见方的围栏地块中，其他蜘蛛和蜈蚣的数量减少了80%以上。在所有三个地点，裂腹蛛在第一个月的存活率都很低（<50%），但在捕食者减少的地块和对照地块之间没有差异。到第一个月末，在对照处理和干扰处理中，被操控的捕食者密度趋于一致，这很可能是由于实验处理中种内捕食和同类相食率降低导致人均死亡率下降。在实验的第二个月，除裂腹蛛外的蜈蚣和蜘蛛再次从实验地块中被清除，与早期不同的是，捕食者清除处理中的种内捕食者数量仍低于对照地块。在第二个月降低种内捕食者的密度，使森林地面三个地点中的两个地点的大龄幼体裂腹蛛存活率提高了75%。除了种内捕食会影响大龄幼体裂腹蛛这一证据外，在实验的最后半个阶段，裂腹蛛的存活率与褛网蛛科和栉足蛛科蜘蛛密度的空间变化呈负相关。在实验室试验中，这两个丰富的游猎蜘蛛科对裂腹蛛的捕食率很高。因此，种内捕食者密度的变化并没有影响最年幼的裂腹蛛，但确实影响了大龄幼体的生存，这很可能是由于其他游猎蜘蛛密度的变化所致。
