"Software ecosystems'' are gaining importance in commercial software development; the iPhone iOS and Salesforce.com ecosystems are examples of this. In contrast to traditional forms of software reuse, such as common platforms or product lines, software ecosystems have a heterogeneous set of actors sharing and collaborating over one or more technological platforms and business model(s) that serve the actors. However, little research has investigated the properties of actual software ecosystems.
In this paper, we present an exploratory study of software ecosystems using the formalizations and metrics of the "network ecology'' approach to the analysis of natural ecosystems. In doing so, we mine the Maven central Java repository and analyze two OSGi ecosystems: Apache Felix and Eclipse Equinox. In particular, we define the concept of an ecosystem ``neighborhood'', apply network ecology metrics to these neighborhoods (including a keystone index that identifies the importance of elements in the ecosystem), and compare the ecosystems.