Juliano Steven A, Lawton John H
Department of Biological Sciences, Ecology Group, Illinois State University, Felmley 206, 61761-6901, Normal, IL, USA.
Department of Biology, University of York, Heslington, YO1 5DD, York, UK.
Oecologia. 1990 Jul;83(4):535-540. doi: 10.1007/BF00317206.
We use field and laboratory experiments to determine whether Hyphydrus ovatus, a predatory aquatic beetle, is food limited, and whether any food shortage results from depletion of prey by these predators (intrinsic food shortage) or is independent of predation by these beetles (extrinsic food shortage). In the laboratory, differences in feeding rate influence body fat content, thus making fat content a useful index of recent feeding history. H. ovatus collected during the breeding season have fat contents significantly greater than those of H. ovatus starved for 25 days, but not significantly different from those of H. ovatus fed ad libitum for 25 days, indicating that natural feeding rates are near the maximum possible. H. ovatus confined at a density 60 times greater than natural show reduced fat content and feeding rate relative to natural, indicating that at very high densities H. ovatus is capable of depleting its prey. Addition of supplemental natural prey (primarily Cladocera) to experimental enclosures resulted in an order of magnitude increase in prey availability, and a significant increase in fat content and feeding rate of confined H. ovatus. Adults of this species do not appear to be food limited during the breeding season, and extraordinarily high densities of adults seem to be necessary to produce intrinsic food shortage. These results suggest that feeding links between H. ovatus an its principal prey do not have major effects on population dynamics under typical field conditions, and call into question the assumption that closely coupled predator-prey interactions are the sole explanation for observed food-web patterns.
我们通过野外和实验室实验来确定捕食性水生甲虫卵形沼梭是否受到食物限制，以及任何食物短缺是由这些捕食者对猎物的消耗导致的（内在食物短缺），还是与这些甲虫的捕食无关（外在食物短缺）。在实验室中，摄食率的差异会影响体脂含量，因此使脂肪含量成为近期摄食历史的一个有用指标。繁殖季节采集的卵形沼梭的脂肪含量显著高于饥饿25天的卵形沼梭，但与自由摄食25天的卵形沼梭无显著差异，这表明自然摄食率接近可能的最大值。与自然密度相比，卵形沼梭的饲养密度高出60倍时，其脂肪含量和摄食率相对于自然状态有所降低，这表明在非常高的密度下，卵形沼梭能够耗尽其猎物。向实验围隔中添加补充性天然猎物（主要是枝角类动物），使猎物可利用量增加了一个数量级，并使饲养的卵形沼梭的脂肪含量和摄食率显著增加。在繁殖季节，该物种的成虫似乎不受食物限制，而且似乎需要极高的成虫密度才会导致内在食物短缺。这些结果表明，在典型的野外条件下，卵形沼梭与其主要猎物之间的摄食联系对种群动态没有重大影响，并对紧密耦合的捕食者 - 猎物相互作用是观察到的食物网模式的唯一解释这一假设提出了质疑。
