Eklöv P
Animal Ecology, Department of Ecology and Environmental Science, Umeå University, S-901 87 Umeå, Sweden e-mail:
Oecologia. 2000 May;123(2):192-199. doi: 10.1007/s004420051005.
Chemical signals are used as information by prey to assess predation risk in their environment. To evaluate the effects of multiple predators on prey growth, mediated by a change in prey activity, I exposed small and large bullfrog (Rana catesbeiana) larvae (tadpoles) to chemical cues from different combinations of bluegill sunfish (Lepomis macrochirus) and larval dragonfly (Anax junius) predators. Water was regularly transferred from predation trials (outdoor experiment) to aquaria (indoor experiment) in which activity and growth of tadpoles was measured. The highest predation mortality of small bullfrog larvae in the outdoor experiment was due to Anax, and it was slightly lower in the presence of both predators, probably resulting from interactions between predators. There was almost no mortality of prey with bluegill. The activity and growth of small bullfrog larvae was highest in the absence of predators and lowest in the presence of Anax. In the presence of bluegill only, or with both predators, the activity and growth of small bullfrog tadpoles was intermediate. Predators did not affect large tadpole activity and growth. Regressing mortality of small bullfrog tadpoles against activity and growth of bullfrog tadpoles revealed a significant effect for small bullfrog larvae but a non-significant effect for large bullfrog larvae. This shows that the response of bullfrog tadpoles to predators is related to their own body size. The experiment demonstrates that chemical cues are released both as predator odor and as alarm substances and both have the potential to strongly alter the activity and growth of prey. Different mechanisms by which chemical cues may be transmitted to species interactions in the food web are discussed.
猎物利用化学信号作为信息来评估其所处环境中的捕食风险。为了评估多种捕食者通过猎物活动变化对猎物生长的影响，我将大小不同的牛蛙（Rana catesbeiana）幼体（蝌蚪）暴露于蓝鳃太阳鱼（Lepomis macrochirus）和蜻蜓幼虫（Anax junius）捕食者不同组合的化学线索中。定期将捕食试验（室外实验）中的水转移到水族箱（室内实验）中，在水族箱中测量蝌蚪的活动和生长情况。室外实验中，小型牛蛙幼体的最高捕食死亡率是由蜻蜓幼虫导致的，在两种捕食者都存在的情况下死亡率略低，这可能是由于捕食者之间的相互作用。蓝鳃太阳鱼作为捕食者时，猎物几乎没有死亡。小型牛蛙幼体在没有捕食者时活动和生长最高，在有蜻蜓幼虫时最低。仅在有蓝鳃太阳鱼时，或两种捕食者都存在时，小型牛蛙蝌蚪的活动和生长处于中间水平。捕食者对大型蝌蚪的活动和生长没有影响。将小型牛蛙蝌蚪的死亡率与牛蛙蝌蚪的活动和生长进行回归分析，结果显示对小型牛蛙幼体有显著影响，而对大型牛蛙幼体没有显著影响。这表明牛蛙蝌蚪对捕食者的反应与其自身的体型大小有关。该实验表明，化学线索既作为捕食者气味释放，也作为警报物质释放，两者都有可能强烈改变猎物的活动和生长。文中还讨论了化学线索可能传递到食物网中物种相互作用的不同机制。
