Thompson Ross M, Hemberg Martin, Starzomski Brian M, Shurin Jonathan B
School of Biological Sciences and Australian Centre for Biodiversity, Monash University, Clayton, Melbourne, Vic 3800, Australia.
Ecology. 2007 Mar;88(3):612-7. doi: 10.1890/05-1454.
The concept of trophic levels is one of the oldest in ecology and informs our understanding of energy flow and top-down control within food webs, but it has been criticized for ignoring omnivory. We tested whether trophic levels were apparent in 58 real food webs in four habitat types by examining patterns of trophic position. A large proportion of taxa (64.4%) occupied integer trophic positions, suggesting that discrete trophic levels do exist. Importantly however, the majority of those trophic positions were aggregated around integer values of 0 and 1, representing plants and herbivores. For the majority of the real food webs considered here, secondary consumers were no more likely to occupy an integer trophic position than in randomized food webs. This means that, above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores. Omnivory was most common in marine systems, rarest in streams, and intermediate in lakes and terrestrial food webs. Trophic-level-based concepts such as trophic cascades may apply to systems with short food chains, but they become less valid as food chains lengthen.
营养级的概念是生态学中最古老的概念之一，它有助于我们理解食物网中的能量流动和自上而下的控制，但它因忽视杂食性而受到批评。我们通过检查营养级位置模式，测试了在四种栖息地类型的58个真实食物网中营养级是否明显。很大一部分分类单元（64.4%）占据整数营养级位置，这表明离散的营养级确实存在。然而，重要的是，这些营养级位置中的大多数都聚集在0和1的整数值周围，分别代表植物和食草动物。对于这里考虑的大多数真实食物网来说，次级消费者占据整数营养级位置的可能性并不比随机食物网更高。这意味着，在食草动物营养级之上，食物网更适合被描述为一个由杂食动物组成的纠结网络。杂食性在海洋系统中最为常见，在溪流中最为罕见，在湖泊和陆地食物网中处于中间水平。基于营养级的概念，如营养级联，可能适用于食物链较短的系统，但随着食物链的延长，它们的有效性会降低。
