Software startups play an important role to foster innovation, economic growth, and job creation in a region. Startups are likely to increase their odds of thriving if they are embedded in a startup ecosystem. Actors of an ecosystem cocreate value, share resources, and support the prosperous evolution of peers. In recent years, software startups have been the focus of intensive research by the software engineering community. In this paper, we conducted a tertiary study to synthesise literature in the field of requirements engineering in startups. We concluded that there are limited empirical studies reporting an in-depth contextual analysis on how software startups perform requirements engineering. In parallel, we conducted a case study of startups based at Digital Port ecosystem. Our empirical results confirm what has been presented by literature that startups adopt requirements practices in a flexible and informal manner. In fact, as novel empirical evidence, we observed that even as startups evolve by acquiring the first paying customers and growing the customer base, requirements practices remain very pragmatic. Our results also reveal how actors of the studied ecosystem interact to support the co-evolution of startups.