Functional significance of crayfish in stream food webs: roles of omnivory, substrate heterogeneity and sex
Functional significance of crayfish in stream food webs: roles of omnivory, substrate heterogeneity and sex
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小龙虾在溪流食物网中的功能意义：杂食性、基质异质性和性别的作用
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发表时间：
2002
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影响因子：
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通讯作者：
C. Townsend
中科院分区：
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作者：
N. Usio;C. Townsend
食物网中物种间相互作用的异质性不仅与上层消费者的属性有关，还与底物的特性有关。我们进行了一个河边通道实验，以评估小龙虾对碎屑（叶包）和藻类为基础的食物网（硬底）的低营养水平的影响。43天后，雄性和雌性小龙虾都大大促进了叶子的分解，雄性处理材料的速度更快。然而，叶加工率的差异是不相关的男性活动水平更高。尽管与性别有关的差异，残留的叶干质量，密度无脊椎动物在叶包同样低的存在下的小龙虾的性别，由于资源消耗，物理驱逐（生物扰动）和/或捕食。叶包组合中没有明显的营养级联。在硬底组合，结果证实了间接的现场证据表明，小龙虾减少捕食Tanypodinae和间接增加收集者-采集者Chironominae的预测营养级联。然而，由于小龙虾对藻类丰度的直接影响（通过直接消费和生物扰动），没有间接促进其他类群。总体而言，小龙虾对较低的营养水平的影响更明显的结构复杂，碎屑为基础的组合比在其硬底，藻类为基础的对应。这与预期的净捕食效应应该是较弱的结构复杂性更大，但主要是一个深刻的工程效果的小龙虾在减少殖民基板时，他们撕碎和干扰碎屑材料的后果。因此，小龙虾的影响可能会以不同的方式传播，并根据基质的不同而具有不同的强度。此外，工程活动和捕食的小龙虾似乎已经压倒性的意义与微妙的性别差异，叶加工率未能导致无脊椎动物密度的差异。
Heterogeneity of species interactions in food webs can result from characteristics of substrates as well as attributes of top consumers. We performed a streamside channel experiment to evaluate the impact of crayfish on lower trophic levels in detritus-based (leaf packs) and algal-based food webs (hard-bottoms). After 43 days, both male and female crayfish had dramatically promoted leaf decomposition, with males processing material at a faster rate. However, the difference in leaf processing rates was not related to a greater level of male activity. Despite the sex-related difference in residual leaf dry mass, densities of invertebrates in leaf packs were similarly low in the presence of crayfish of either sex, due to resource consumption, physical dislodgment (bioturbation) and/or predation. No trophic cascade was evident in the leaf pack assemblage. In the hard-bottom assemblage, the results confirmed circumstantial field evidence that crayfish reduce predatory Tanypodinae and indirectly increase collector-gatherer Chironominae following the prediction of a trophic cascade. However, no other taxa were indirectly facilitated, because of strong direct effects of crayfish on algal abundance (through direct consumption and bioturbation). Overall, impacts of crayfish on lower trophic levels were more pronounced in the structurally complex, detritus-based assemblages than in its hard-bottom, algal-based counterpart. This conflicts with the expectation that net predation effects should be weaker where structural complexity is greater but is mainly a consequence of the profound engineering effects of crayfish in reducing colonisable substrate when they shred and disturb detrital material. Effects of crayfish may therefore propagate differently and with varying strength depending on substrate. Moreover, engineering activities and predation by crayfish appear to have been of overwhelming significance with subtle sex differences in leaf processing rates failing to lead to differences in invertebrate densities.