As part of an increasing scientisation of political processes, epistemic communities have been identified as a unique category of social actors, who exclusively rely on their knowledge resources to shape the preferences of decision-makers. Whereas most authors expect that an expert-driven policy process facilitates the implementation of technically complex policies, critical scholars hint to an evolving technocracy, whose scientific dogmatism may end up in policies that aggravate social problems. In this paper, these countervailing assumptions are empirically assessed for the epistemic community on biodiversity and its role in Brazil and India. At least in this case, it seems that the impact experts' influence depends on the configuration of the policy arena. If experts are institutionally compelled to debate their positions with potential critics, the members of an epistemic community seem to engage in a rather deliberative discourse that widens the policy space for all stakeholders involved. Under the conditions of an elitist closure, however, policy experts seem to adapt to the preferences of the most powerful actors but refrain from any critical self-reflection that might seriously challenge their own convictions.