Hirvonen Heikki, Ranta Esa
Integrative Ecology Unit, Division of Population Biology, Department of Ecology and Systematics, University of Helsinki, P.O. Box 17, FIN-00014, Finland.
Oecologia. 1996 May;106(3):407-415. doi: 10.1007/BF00334569.
We investigated foraging behaviour of larval dragonflies Aeshna juncea in order to examine the significance of prey density and body size in predator-prey dynamics. A. juncea were offered separately three size-classes of Daphnia magna at low and high densities. The data were collected with direct observations of the foraging individuals. We found that large A. juncea larvae could better enhance their intake of prey biomass as prey size and prey density increased than their smaller conspecifics. However, increasing feeding efficiency of both larval instars was constrained by declining attack success and search rate with increasing prey size and density. With small D. magna, in contrast to large A. juncea, small A. juncea increased their searching efficiency as prey density increased keeping D. magna mortality rate at a constant level. In a predator-prey relationship this indicates stabilizing potential and feeding thresholds set by both prey density and prey-predator size ratio. Attack success dropped with prey size and density, but did not change in the course of the foraging bout. For both A. juncea sizes prey handling times increased as more medium and large prey were eaten. The slope of the increase became steeper with increasing prey-predator size ratio. These observations indicate that components of the predator-prey relationship vary with prey density, contrary to the basic assumptions of functional response equations. Moreover, the results suggest that the effects of prey density change during the ontogeny of predators and prey.
我们研究了幼虫豆娘（Aeshna juncea）的觅食行为，以检验猎物密度和体型在捕食者 - 猎物动态关系中的重要性。分别以低密度和高密度向A. juncea提供三种大小等级的大型溞（Daphnia magna）。通过直接观察觅食个体来收集数据。我们发现，随着猎物大小和猎物密度的增加，大型A. juncea幼虫比其较小的同种个体能够更好地提高猎物生物量的摄入量。然而，随着猎物大小和密度的增加，攻击成功率和搜索率下降，这限制了两个龄期幼虫摄食效率的提高。与大型A. juncea相反，小型A. juncea在捕食小型大型溞时，随着猎物密度的增加提高了搜索效率，使大型溞的死亡率保持在恒定水平。在捕食者 - 猎物关系中，这表明猎物密度和猎物 - 捕食者体型比设定了稳定潜力和摄食阈值。攻击成功率随猎物大小和密度下降，但在觅食过程中没有变化。对于两种大小的A. juncea，随着更多中型和大型猎物被吃掉，猎物处理时间增加。随着猎物 - 捕食者体型比的增加，增加的斜率变得更陡。这些观察结果表明，捕食者 - 猎物关系的组成部分随猎物密度而变化，这与功能反应方程的基本假设相反。此外，结果表明猎物密度的影响在捕食者和猎物的个体发育过程中会发生变化。
