Fagan William F, Siemann Evan, Mitter Charles, Denno Robert F, Huberty Andrea F, Woods H Arthur, Elser James J
Department of Biology, Arizona State University, Tempe, Arizona 85287, USA.
Am Nat. 2002 Dec;160(6):784-802. doi: 10.1086/343879.
Disparities in nutrient content (nitrogen and phosphorus) between herbivores and their plant resources have lately proven to have major consequences for herbivore success, consumer-driven nutrient cycling, and the fate of primary production in ecosystems. Here we extend these findings by examining patterns of nutrient content between animals at higher trophic levels, specifically between insect herbivores and predators. Using a recently compiled database on insect nutrient content, we found that predators exhibit on average 15% greater nitrogen content than herbivores. This difference persists after accounting for variation from phylogeny and allometry. Among herbivorous insects, we also found evidence that recently derived lineages (e.g., herbivorous Diptera and Lepidoptera) have, on a relative basis, 15%-25% less body nitrogen than more ancient herbivore lineages (e.g., herbivorous Orthoptera and Hemiptera). We elaborate several testable hypotheses for the origin of differences in nitrogen content between trophic levels and among phylogenetic lineages. For example, interspecific variation in insect nitrogen content may be directly traceable to differences in dietary nitrogen (including dilution by gut contents), selected for directly in response to the differential scarcity of dietary nitrogen, or an indirect consequence of adaptation to different feeding habits. From some functional perspectives, the magnitude rather than the source of the interspecific differences in nitrogen content may be most critical. We conclude by discussing the implications of the observed patterns for both the trophic complexity of food webs and the evolutionary radiation of herbivorous insects.
食草动物与其植物资源之间的养分含量（氮和磷）差异最近已被证明对食草动物的生存、消费者驱动的养分循环以及生态系统中初级生产的命运具有重大影响。在此，我们通过研究更高营养级动物之间的养分含量模式，特别是昆虫食草动物和捕食者之间的养分含量模式，扩展了这些发现。利用最近汇编的昆虫养分含量数据库，我们发现捕食者的平均氮含量比食草动物高15%。在考虑了系统发育和异速生长的变异后，这种差异仍然存在。在食草昆虫中，我们还发现有证据表明，与较古老的食草动物谱系（如食草直翅目和半翅目）相比，最近分化出的谱系（如食草双翅目和鳞翅目）相对而言体内氮含量少15%-25%。我们阐述了几个关于营养级之间以及系统发育谱系之间氮含量差异起源的可检验假设。例如，昆虫氮含量的种间差异可能直接归因于饮食氮的差异（包括被肠道内容物稀释），这是直接针对饮食氮的不同稀缺性而选择的，或者是适应不同取食习性的间接结果。从某些功能角度来看，氮含量种间差异的大小而非来源可能最为关键。我们通过讨论观察到的模式对食物网营养复杂性和食草昆虫进化辐射的影响来结束本文。
