  To better understand and manage complex systems like ecosystems it is
critical to know the relative contribution of system components to system
functioning. Ecologists and social scientists have described many ways that
individuals can be important; This paper makes two key contributions to this
research area. First, it shows that throughflow, the total energy-matter
entering or exiting a system component, is a global indicator of the relative
contribution of the component to the whole system activity. It is global
because it includes the direct and indirect exchanges among community members.
Further, throughflow is a special case of Hubbell status as defined in social
science. This recognition effectively joins the concepts, enabling ecologists
to use and build on the broader centrality research in network science. Second,
I characterize the distribution of throughflow in 45 empirically-based trophic
ecosystem models. Consistent with expectations, this analysis shows that a
small fraction of the system components are responsible for the majority of the
system activity. In 73% of the ecosystem models, 20% or less of the nodes
generate 80% or more of the total system throughflow. Four or fewer dominant
nodes are required to account for 50% of the total system activity. 121 of the
130 dominant nodes in the 45 ecosystem models could be classified as primary
producers, dead organic matter, or bacteria. Thus, throughflow centrality
indicates the rank power of the ecosystems components and shows the power
concentration in the primary production and decomposition cycle. Although these
results are specific to ecosystems, these techniques build on flow analysis
based on economic input-output analysis. Therefore these results should be
useful for ecosystem ecology, industrial ecology, the study of urban
metabolism, as well as other domains using input-output analysis.
