The use of the term ecosystem in the context of extensible software platforms and third-party developers or user communities has made us ponder about the similarities between software ecosystems and natural ecosystems. We therefore compare software ecosystems and natural ecosystems to present an agenda for further research by analyzing some key characteristics of both types of ecosystems. We discuss the regulatory factors and mechanisms existing in nature, and then deduce key challenges that need to be dealt with, in order to achieve healthy operation of software ecosystems. Categories and Subject Descriptors D.2.9 Management; D.2.11 Software Architectures - Domainspecific architectures; D.2.13 Reusable Software - Reuse models General Terms Management, Measurement, Design, Economics, Experimentation, Human Factors, Theory. Keywords Ecosystem, Software, Nature.