A reliability theoretical quest for keystones

Species are not equally important for the functioning of communities. This fact is widely recognized and the term 'keystone species' has been introduced for the most important members of communities. In a recent paper, Power et al. claim for methods suitable for a priori identification of keystone species, which is an urgent problem in conservation biology. Another problem is the scarcity of their quantitativedescription. In this paper, we propose an index for characterizing keystone species reflecting their role in food web flow networks. We present some calculations for characterizing the role of keystones in weighted webs and discuss some problems of food web dynamics. Our keystone index refers well to keystones only if trophic interactions areof prime importance in a community. We further analyze the relationship between keystone species and the reliability of network flow. Keystones make network flow less reliable. Finally, we discuss some problems of stability and reliability in ecological systems. [ABSTRACT FROM AUTHOR]