Wahlström E, Persson L, Diehl S, Byström P
Department of Ecology and Environmental Science, Umeå University, S-90187 Umeå, Sweden e-mail:
Oecologia. 2000 Apr;123(1):138-148. doi: 10.1007/s004420050999.
To examine size-dependent food web interactions in systems with cannibalism, we compared the abundances of zooplankton and phytoplankton over 2 years in four lakes with cannibalistic perch (Perca fluviatilis) of which two also supported the top predator pike (Esox lucius). The abundance of perch 2 years and older was lower in lakes with pike than in lakes with only perch. In contrast, the abundance of small perch (young-of-the-year and 1-year old) was lower in lakes with only perch suggesting that intense cannibalism reduced these size classes to low levels in lakes lacking pike. Functional response experiments with differently sized perch and zooplankton showed that the attack rate of small perch susceptible to cannibalism was much higher than that of large cannibalising perch. The optimal body size of perch with respect to attack rate was also lower for small zooplankton prey than for large zooplankton. The zooplankton communities in lakes with only perch were dominated by the relatively small species Ceriodaphnia quadrangula and Bosmina spp. and total zooplankton biomass was higher in these lakes than in lakes with both pike and perch. In contrast, the mean size of cladoceran zooplankton was largest in lakes with both pike and perch owing to a dominance of the large zooplankton species Holopedium gibberum in these lakes. We relate these patterns to (1) the low foraging efficiency of large perch on small zooplankton and (2) the low abundance of small zooplanktivorous perch (due to cannibalism) in lakes with only perch. The differences in zooplankton community structure also resulted in different seasonal dynamics of phytoplankton between lakes. Cannibalism introduces a vertical heterogeneity to food webs that causes consumer-resource dynamics that are not predictable from linear food chain models.
为了研究存在同类相食现象的系统中与体型相关的食物网相互作用，我们在4个湖泊中对浮游动物和浮游植物的丰度进行了为期2年的比较，这些湖泊中有食肉类鲈鱼（河鲈），其中两个湖泊还有顶级捕食者梭子鱼（白斑狗鱼）。在有梭子鱼的湖泊中，2岁及以上鲈鱼的数量比只有鲈鱼的湖泊要少。相反，在只有鲈鱼的湖泊中，小鲈鱼（当年幼鱼和1岁鱼）的数量较少，这表明在没有梭子鱼的湖泊中，强烈的同类相食现象将这些体型等级的鲈鱼数量减少到了很低的水平。对不同体型的鲈鱼和浮游动物进行的功能反应实验表明，易被同类相食的小鲈鱼的攻击率远高于大型同类相食鲈鱼的攻击率。对于小型浮游动物猎物而言，鲈鱼攻击率的最佳体型也比大型浮游动物的要小。仅含有鲈鱼的湖泊中的浮游动物群落以相对较小的四角盘肠溞和薄皮溞属物种为主，这些湖泊中的浮游动物总生物量高于同时含有梭子鱼和鲈鱼的湖泊。相反，在同时含有梭子鱼和鲈鱼的湖泊中，枝角类浮游动物的平均体型最大，这是因为这些湖泊中大型浮游动物物种透明薄皮溞占主导地位。我们将这些模式与以下两点相关联：（1）大型鲈鱼对小型浮游动物的觅食效率较低；（2）在只有鲈鱼的湖泊中，小型浮游动物食性鲈鱼的数量较少（由于同类相食）。浮游动物群落结构的差异也导致了不同湖泊中浮游植物季节性动态的差异。同类相食给食物网引入了垂直异质性，从而导致了消费者 - 资源动态，这是线性食物链模型无法预测的。
