Predator/prey alteration and connectance modification in food webs

            Food webs and matrices are important tools assisting in the understanding of feeding relationships and ecology. One way of presenting the direct relationships between predators and prey is with an adjacency matrix, a binary matrix with direct links shown as one’s and no direct links shown as zero’s. Species linkage alterations were performed on a variety of published food webs ranging from pine forests in the United States to tussock grasslands in New Zealand. This produced a diverse set of food webs varying in number of distinguishable taxa present, functional diversity; and from various climates and habitats. Predators and prey were chosen from observed food webs by using those which best fit linkage density for the given system and altered them into universal predators and universal prey. By artificially creating a universal predator species as well as a universally consumed prey species the number of indirect paths of length n as well as indirect relationships throughout the systems increased. When a universal prey species was created, however, a greater number of nodes experienced indirect links and a greater number of total paths were observed. Creation of a universal predator also increased paths but this effect was more localized to top predators than was observed with the creation of a universal prey item. Additional manipulations with species feeding at various trophic levels as well as to varying degrees have shown a similar pattern.