Wagner J D, Wise David H
Department of Entomology, College of Agriculture, University of Kentucky, Lexington, KY 40546-0091, USA, , , , , , US.
Oecologia. 1997 Feb;109(3):474-482. doi: 10.1007/s004420050107.
Because cannibals are potentially both predator and prey, the presence of conspecifics and alternative prey may act together to influence the rate at which cannibals prey upon each other or emigrate from a habitat patch. Wolf spiders (Lycosidae) are cannibalistic-generalist predators that hunt for prey with a sit-and-wait strategy characterized by changes in foraging site. Little information is available on how both prey abundance and the presence of conspecifics influence patch quality for these cursorial, non-web-building spiders. To address this question, laboratory experiments were conducted with spiderlings and older juveniles of the lycosid genus Schizocosa. The presence of insect prey consistently reduced rates of spider emigration when spiders were housed either alone or in groups. Solitary juvenile Schizocosa that had been recently collected from the field exhibited a median giving-up time (GUT) of 10 h in the absence of prey (Collembola); providing Collembola increased the median GUT to 64 h. For solitary spiders, the absence of prey increased by about fourfold the rate of emigration during the first 24 h. In contrast, for spiders in patches with a high density of conspecifics, the absence of prey increased the 24-h emigration rate by only 1.6-fold. For successful cannibals in the no-prey patches, the presence of conspecifics improved patch quality by providing a source of food. Mortality by cannibalism was affected by both prey availability and openness of the patch to net emigration. In patches with no net emigration, the presence of prey reduced rates of cannibalism from 79% to 57%. Spiders in patches open to emigration but not immigration experienced a rate of cannibalism (16%) that was independent of prey availability. The results of these experiments indicate that for a cannibalistic forager such as the wolf spider Schizocosa, (1) the presence of conspecifics can improve average patch quality when prey are absent, and (2) cannibalism has the potential to be a significant mortality factor under natural field conditions because cannibalism persisted in prey patches that were open to emigration.
由于同类相食者既可能是捕食者，也可能是猎物，同种个体和替代猎物的存在可能共同影响同类相食者相互捕食或从栖息地斑块迁出的速率。狼蛛（狼蛛科）是具有同类相食习性的广食性捕食者，它们采用坐等策略捕食猎物，其特点是觅食地点会发生变化。关于猎物丰度和同种个体的存在如何影响这些善于奔跑、不结网蜘蛛的斑块质量，目前所知甚少。为了解决这个问题，我们对狼蛛属裂跗蛛的幼蛛和大龄若蛛进行了实验室实验。当蜘蛛单独或成群饲养时，昆虫猎物的存在持续降低了蜘蛛的迁出率。最近从野外采集的独居裂跗蛛若蛛在没有猎物（跳虫）的情况下，中位放弃时间（GUT）为10小时；提供跳虫后，中位GUT增加到64小时。对于独居蜘蛛来说，没有猎物会使前24小时内的迁出率增加约四倍。相比之下，对于同种个体密度高的斑块中的蜘蛛，没有猎物只会使24小时迁出率增加1.6倍。对于无猎物斑块中成功进行同类相食的蜘蛛来说，同种个体的存在通过提供食物来源提高了斑块质量。同类相食导致的死亡率受猎物可获得性和斑块对净迁出的开放性的影响。在没有净迁出的斑块中，猎物的存在使同类相食率从79%降至57%。对迁出开放但对迁入不开放的斑块中的蜘蛛来说，同类相食率（16%）与猎物可获得性无关。这些实验结果表明，对于像狼蛛裂跗蛛这样的同类相食性觅食者来说，（1）在没有猎物时，同种个体的存在可以提高平均斑块质量；（2）在自然野外条件下，同类相食有可能成为一个重要的死亡因素，因为在对迁出开放的猎物斑块中同类相食现象持续存在。
