Reliable flows and preferred patterns in food webs

We analyse the structure of food webs from a reliability theoretical point of view. The reliability of the network flow is the probability that source s are connected to sinks. With a fixed number of species and connectance, r eliability depends on the pattern of links. We construct all of the possibl e sink web graphs with given numbers of species and links and calculate the reliability of the network flow for each hypothetical sink web. Patterns f avourable for reliable flows are characterized. Having compared our results with real web data, we conclude that the structure of natural webs contain s mostly such patterns. Thus, the reliability of the network flow seems to be an important factor governing food web structure. Our results show that short chains, a high level of omnivory, a high prey-predator ratio and a lo w number of specialists are favourable for reliable network flows. These co nclusions support the reticulate nature of food webs and the rethinking of the traditional, linearized view.