Two recent observations within the strategy field are that firms are embedded in a business ecosystem and that it is becoming increasingly difficult for firms to sustain their superior performance. In this study, we link these two observations and explore how firms’ ability to sustain their superior performance is impacted by the structural and evolutionary features of the ecosystem. Specifically, we first consider the structure of the firm’s interdependence with other actors in the ecosystem based on the number of unique components and subsystems that interact with the firm’s product. We refer to this structural feature of the ecosystem as ecosystem complexity. Second, we consider the evolutionary shifts in the ecosystem as a result of technology transitions initiated by platform firms. We explore our arguments in the context of the U.S. smartphone industry, and we focus on the extent to which application software (app) developers sustain their superior performance across two dominant rival ecosystems — Apple’s iOS and Google’s Android. We find that higher ecosystem complexity helps app developers sustain their superior performance and that this effect is stronger for more experienced firms. In contrast, technology transitions initiated by platform firms make it more difficult for app developers to sustain their performance superiority, and this effect is exacerbated by the extent of ecosystem complexity.