Sih Andrew, Krupa James J
Center for Ecology, Evolution and Behavior, T.H. Morgan School of Biological Sciences, University of Kentucky, 40506-0225, Lexington, KY, USA.
Oecologia. 1996 Jan;105(2):179-188. doi: 10.1007/BF00328544.
Previous studies have shown that green sunfish, Lepomis cyanellus, have strong effects on the activity, habitat use, social interactions and mating dynamics of a stream-dwelling water strider, Aquarius remigis (family Gerridae, hence, gerrids). In nature, however, stream pools often contain not just sunfish and water striders, but also smaller fish such as minnows. Here, we used factorial experiments in seminatural streams to document the direct and indirect effects of sunfish and fathead minnows, Pimephales promelas, on water strider survival and behavior. Sunfish, minnows and gerrids all consume surface prey (here, crickets); thus these three species are potential food competitors. Sunfish eat minnows. Accordingly, the presence of sunfish caused minnows to increase their schooling behavior and shift their activity from the surface toward the bottom substrate. The presence of sunfish was also associated with an increase in the number of missing gerrids, whereas minnows caused relatively little gerrid disappearance. Most interestingly, the presence of minnows decreased the effect of sunfish on gerrid disappearance rates; that is, minnows apparently had an indirect positive effect on water strider survival. We suggest that this indirect positive effect reflects the fact that minnows are alternative prey for sunfish. The effects of sunfish and minnows on gerrid mortality explained the influence of these fish on gerrid behavior. Sunfish caused decreases in male gerrid activity, female availability, mating activity, mating frequency and mating duration. Larger males had a mating advantage over smaller males only in pools with sunfish and no minnows. Sunfish also caused a borderline significant decrease in the large female mating advantage. These results were all observed in previous studies and can be viewed as adaptive responses to predation risk. These patterns were not consistent with the expected effects of sunfish as food competitors with water striders. In contrast, minnows had relatively little influence on water strider behavior and the few significant effects were the opposite of those of sunfish. Minnows caused increases in female activity and in mating duration, a decrease in the large male mating advantage and an increase in the large female mating advantage. These patterns fit the view that minnows caused an increase in gerrid hunger, i.e., that minnows acted as food competitors with gerrids. Finally, planned contrasts against controls showed that, in the presence of both sunfish and minnows, water striders showed no significant behavioral responses to fish (i.e., gerrid behavior in pools with sunfish and minnows did not significantly differ from behavior in fishless pools). The most likely mechanism explaining this pattern is a dilution of sunfish predation risk due to the presence of minnows serving as alternative prey for sunfish.
先前的研究表明，蓝鳃太阳鱼（Lepomis cyanellus）对一种栖息于溪流的水黾（Aquarius remigis，黾蝽科，即黾蝽）的活动、栖息地利用、社会互动和交配动态有强烈影响。然而，在自然环境中，溪流池塘通常不仅有太阳鱼和水黾，还存在如米诺鱼等较小的鱼类。在此，我们在半自然溪流中进行析因实验，以记录太阳鱼和黑头呆鱼（Pimephales promelas）对水黾生存和行为的直接和间接影响。太阳鱼、米诺鱼和水黾都捕食水面猎物（这里是蟋蟀）；因此这三个物种是潜在的食物竞争者。太阳鱼会捕食米诺鱼。相应地，太阳鱼的存在导致米诺鱼增加集群行为，并将其活动从水面转移到底层基质。太阳鱼的存在还与失踪水黾数量的增加有关，而米诺鱼导致的水黾消失相对较少。最有趣的是，米诺鱼的存在降低了太阳鱼对水黾消失率的影响；也就是说，米诺鱼显然对水黾的生存有间接的积极影响。我们认为这种间接的积极影响反映了米诺鱼是太阳鱼的替代猎物这一事实。太阳鱼和米诺鱼对水黾死亡率的影响解释了这些鱼类对水黾行为的影响。太阳鱼导致雄性水黾活动减少、雌性可利用性降低、交配活动、交配频率和交配持续时间减少。只有在有太阳鱼且没有米诺鱼的池塘中，较大的雄性水黾才比小雄性水黾具有交配优势。太阳鱼还导致大型雌性水黾的交配优势出现临界显著下降。这些结果在先前的研究中均有观察到，可被视为对捕食风险的适应性反应。这些模式与太阳鱼作为水黾食物竞争者的预期影响不一致。相比之下，米诺鱼对水黾行为的影响相对较小，少数显著影响与太阳鱼的影响相反。米诺鱼导致雌性活动增加和交配持续时间增加，大型雄性水黾的交配优势降低，大型雌性水黾的交配优势增加。这些模式符合米诺鱼导致水黾饥饿感增加的观点，即米诺鱼作为水黾的食物竞争者发挥作用。最后，与对照组的计划对比表明，在同时存在太阳鱼和米诺鱼的情况下，水黾对鱼类没有显著的行为反应（即有太阳鱼和米诺鱼的池塘中的水黾行为与无鱼池塘中的行为没有显著差异）。解释这种模式最可能的机制是，由于米诺鱼作为太阳鱼的替代猎物的存在，稀释了太阳鱼的捕食风险。
