In this paper a population ecology approach is adopted to measure direct competition among hospitals starting from the concept of niche overlap. Organizational niches specify how competitive processes vary as functions of environmental dependencies. Overlapping resource requirements represent common dependencies from the same resources spaces represented by geographical areas where admitted patients live for health care organizations. We employ longitudinal models for relational data collected on 35 hospitals in the Abruzzo Region. The results reported describe the evolution of the competitive network at the regional level and assess the impact of provider attributes on the evolution of competitive interdependencies among hospitals