How interaction strength affects the role of functional and redundant connections in food webs

Links in food webs can be classified as functional, which affect robustness, and redundant, which seem not to do so. We explore whether this topologically based distinction may still be informative when interaction strength is considered. In 81 weighted food webs we identified functional and redundant links by exploiting the method of generalized dominators, and tested whether the two groups could be patterned according to link strength. Overall, redundant connections are weaker than functional links. However this pattern does not hold for every food web. Also, the difference in strength between functional and redundant links seems to depend on food web topology. In fact the systems in which redundant connections are significantly weaker than functional ones show greater connectance than systems in which the difference in strength between the two groups is not significant. We observed that redundant connections are fundamental in the formation of omnivory modules that have been described as being crucial for the stability/persistence of food webs. Although stability can be promoted by the specific arrangement of links magnitude within these modules, it does not necessarily imply that redundant links have to be weaker than functional connections at the whole web scale.