Do stable habitats support longer food chains?

Posted on December 16, 2014

Food chain length (the height of the food web, or the number of trophic transfers from basal food resources to top predators) affects ecosystem productivity, trophic cascades and the bioaccumulation of toxins. Food chain length varies widely across aquatic systems, but the reasons for these differences, and how they are affected by environmental conditions, are elusive. Canadian researchers monitored nine temporary ponds, which filled with snowmelt in early spring and lost water as summer progressed, between April and August. They mapped the pond outlines and sampled biological communities each month. Because stable isotope ratios of nitrogen are known to increase predictably up the food chain, they were used to estimate the trophic positions of top predators (in this case, insects and amphibians). The food chain length for a given pond was then defined as the maximum trophic position held by any of these species. Food chains were longer in ponds that retained water for more extended periods of time, a finding that agreed with a theoretical prediction that shorter, more resilient food chains should be more common in disturbed habitats. In contrast, food chain length wasn’t related to the size of a pond, a result which offered no support for a competing hypothesis that large ecosystems should support longer food chains because they have a greater array of species and habitats. These results suggested that habitat stability can have a strong influence on foodweb structure as well as on community composition and diversity.

Reference: Schriever, T.A. & Williams, D.D. 2013. Influence of pond hydroperiod, size, and community richness on food-chain length. Freshwater Science 32(3), 964–975.