Abstract
Food chain length (FCL) is a critical measure of food web complexity that influences the community structure and ecosystem function. The FCL of large subtropical rivers affected by dams and the decisive factors are far beyond clear. In this study, we used stable isotope technology to estimate the FCL of fish in different reaches of the main stream in the Yangtze River and explored the key factors that determined the FCL. The results showed that FCL varied widely among the studied areas with a mean of 4.09 (ranging from 3.69 to 4.31). The variation of FCL among river sections in the upstream of the dam was greater than that in the downstream. Regression analysis and model selection results revealed that the FCL had a significant positive correlation with ecosystem size as well as resource availability, and FCL variation was largely explained by ecosystem size, which represented 72% of the model weight. In summary, our results suggested that ecosystem size plays a key role in determining the FCL in large subtropical rivers and large ecosystems tend to have a longer food chain. Additionally, the construction of the Three Gorges Dam has been speculated to increase the FCL in the impoundment river sections.
Highlights
Food chain length (FCL) is a fundamental and measurable property in complex food web relationships [1], which represents the nutritional progression of the food web in the ecosystem from primary producer to top predator, reflecting the vertical structure of the food web [2,3]
FCL variation was best explained by ecosystem size, which represented 72% of the model weight, followed by resource availability, which represented 27% (Table 2)
Our results showed that the FCL in the main stream of the Yangtze River was 4.09 and similar to other large and medium rivers
Summary
Food chain length (FCL) is a fundamental and measurable property in complex food web relationships [1], which represents the nutritional progression of the food web in the ecosystem from primary producer to top predator, reflecting the vertical structure of the food web [2,3]. The study of FCL and its change mechanism may provide a quantifiable framework for the community composition and energy flow pattern of the food web [4] and an important way for an ecosystem response to the environment and the management of biological resources, such as the assessment of pollutant concentration in predators or species regulation in proliferation and release [5,6]. Utilizing nitrogen stable isotopes (δ15 N), the trophic position of organisms within a food web can be determined without the time-consuming process of constructing a fully delineated energy web [5,7]. With the calibration of primary consumers as the stable isotope baseline, the comparison of FCL among multiple ecosystems becomes feasible [9,10,11]. Research on FCL is not limited to the determination of FCL in a single ecosystem but can be applied to multiple ecosystems in order to make comparisons [12,13] or explore the influence of environmental factors on FCL [14,15,16,17]
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