Sato Takuya, Watanabe Katsutoshi
The Hakubi Center for Advanced Research, Kyoto University, Yoshida-Ushinomiya-cho, Sakyo-ku, Kyoto, 606-8302, Japan.
Department of Zoology, Division of Biological Science, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto, 606-8502, Japan.
J Anim Ecol. 2014 Jul;83(4):907-15. doi: 10.1111/1365-2656.12192. Epub 2014 Feb 5.
Resource subsidies often weaken trophic cascades in recipient communities via consumers' functional response to the subsidies. Consumer populations are commonly stage-structured and may respond to the subsidies differently among the stages yet less is known about how this might impact the subsidy effects on the strength of trophic cascades in recipient systems. We show here, using a large-scale field experiment, that the stage structure of a recipient consumer would dampen the effects of terrestrial invertebrate subsidies on the strength of trophic cascade in streams. When a high input rate of the terrestrial invertebrates was available, both large and small fish stages switched their diet to the terrestrial subsidy, which weakened the trophic cascade in streams. However, when the input rate of the terrestrial invertebrates was at a moderate level, the terrestrial subsidy did not weaken the trophic cascade. This discrepancy was likely due to small fish stages being competitively excluded from feeding on the subsidy by larger stages of fish and primarily foraging on benthic invertebrates under the moderate input level. Although previous studies using single fish stages have clearly demonstrated that the terrestrial invertebrate input equivalent to our moderate input rate weakened the trophic cascade in streams, this subsidy effect might be overestimated given small fish stage may not switch their diet to the subsidy under competition with large fish stage. Given the ubiquity of consumer stage structure and interaction among consumer stages, the effects we saw might be widespread in nature, requiring future studies that explicitly involve consumer's stage structure into community ecology.
资源补贴通常会通过消费者对补贴的功能反应削弱受援群落中的营养级联效应。消费者种群通常具有阶段结构，并且在不同阶段对补贴的反应可能不同，但对于这可能如何影响补贴对受援系统中营养级联强度的效应，我们了解得较少。我们在此通过一项大规模田间实验表明，受援消费者的阶段结构会抑制陆地无脊椎动物补贴对溪流中营养级联强度的影响。当有高输入率的陆地无脊椎动物时，大小不同的鱼类阶段都会将其食物选择转向陆地补贴，这削弱了溪流中的营养级联。然而，当陆地无脊椎动物的输入率处于中等水平时，陆地补贴并未削弱营养级联。这种差异可能是由于小鱼阶段在竞争中被大鱼阶段排除在食用补贴之外，并且在中等输入水平下主要以底栖无脊椎动物为食。尽管之前使用单一鱼类阶段的研究已经清楚地表明，与我们的中等输入率相当的陆地无脊椎动物输入会削弱溪流中的营养级联，但考虑到小鱼阶段在与大鱼阶段竞争时可能不会将其食物选择转向补贴，这种补贴效应可能被高估了。鉴于消费者阶段结构的普遍性以及消费者阶段之间的相互作用，我们所观察到的效应在自然界中可能很普遍，这就需要未来的研究将消费者的阶段结构明确纳入群落生态学。
