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How River Food Chains Fare During Drought and Flood

NSF Award:

Collaborative Research: Food-Chain Length in Streams-Testing the Role of Ecosystem Size, Resource Availability and Disturbance  (Arizona State University)

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A team led by John Sabo from Arizona State University has found that variability in the volume and flow of a river can regulate the length of the food chain that conducts energy and matter from a lowly alga to a top-predator fish.

Climate change and direct human activity such as irrigation and damming can alter the timing and amount of river discharge. Factors that control food chain length correspondingly affect the flow of nutrients as well as contaminants through ecosystems. This study illustrates that the impacts of flood or drought could extend beyond the long-term health and survival of individual species.

The length of any food chain is simply a count of the number of steps between organisms in the chain. But more than that, food chain length reflects the pathway taken by energy and matter through an ecosystem. It can influence the rate and geography of nutrient cycling or the accumulation of heavy metals and other contaminants as each organism's tissues store them away in progressively greater quantities.

Past ecological theory predicted that inefficiencies in energy transfer were the primary determinants of food chain length, but this proved false. More recently, attention has focused on correlations with total ecosystem size, but no clear mechanism for this connection was established.

After conducting a survey of 36 rivers in North America, these scientists found that streams with intermittent drying periods were typically missing species of top, large-bodied fish. Further analysis revealed that larger watersheds could accommodate and mitigate the effects of their less stable areas, allowing longer food chains to develop and persist.

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  • river in the Grand Canyon
Navigating a Grand Canyon study site.
John L. Sabo, ASU

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