Establishing and managing protected areas (national parks, nature reserves and other sites of conservation value) represent the most common approach to conserving species and ecosystems, but these areas are vulnerable to global environmental change. Recently, Golden Kroner et al. (2019) suggested protected area downgrading, downsizing, and degazettement (PADDD) as one of the main threats to biodiversity conservation. However, there are several other elements, of similar concern, that threaten conservation efforts in protected areas, such as climate change and pollution. Here, in a commentary to the Golden Kroner et al. (2019) paper, we address an additional important element affecting protected area dynamics and robustness that was overlooked by these authors – invasions by alien species. We argue that invasive alien species (IAS) contribute directly to the pressures of biodiversity loss by competing with native species and modifying the characteristics of the invaded ecosystems, and virtually no protected areas are free from these effects. Therefore, excluding IAS from legal instruments and policy frameworks underpinning current conservation approaches in protected areas presents a great risk for nature conservation. Consequently, this aligns poorly with the idea of protected areas being a cornerstone for conservation at local, regional and national levels. For that reason and to paint a more complete picture of the effectiveness of protected areas, we argue that when other factors threatening the existence and functioning of protected areas are discussed, we also need to account for biological invasions. This will ensure that adaptive conservation management strategies protect a wide range of species, ecosystems, and landscapes. Hence, this commentary aims to be of general interest for policymakers, managers and researchers.
