Alien species in a warming climate: a case study of the nutcracker and stone pines

Species are predicted to shift their geographic range with climate change, which increases the need for good conservation planning and management practices. Not only may climate change increase the number of invasive species in parts of the world, it may also lead to some species becoming invasive under new, more preferable, climatic conditions. This study investigates whether climate change may enhance the spread of alien species by another alien species. I use the interaction between the alien slender-billed nutcracker and alien, potentially invasive, stone pines as a case-study and specifically aim to quantify to which extent the potential spread of stone pine species in Sweden in a warming climate is augmented by its dispersal agent: the slender-billed nutcracker. I found that accounting for the future climatic niche of the slender-billed nutcracker, and therefore for its potential presence, significantly augmented the increase of the predicted future range of the stone pines under climate change. This result does not only stress the importance of accounting for species interactions when assessing the impact of climate change on species' future geographic ranges, it also stresses the need for nature conservationists and managers to incorporate species interactions and climate change when designing appropriate plans with regard to invasive species. Although the implications of the predicted future spread of the slender-billed nutcracker might be limited, since the very similar thick-billed nutcracker is native to Sweden, the effects of the stone pines should not be neglected. They are currently classified as potentially invasive in parts of the Nordic region.