Modelling the future distribution of rare bryophytes in Scotland: the importance of the inclusion of habitat loss

Background: Species distribution models (SDMs) have been widely used to predict species ranges and their future distribution under climate change scenarios, mostly using only climatic variables. An important factor that is usually neglected, is the habitat of the species that are being modelled. Even when included, it is often considered a fixed factor, but in reality, it is also subjected to changes. Aims: In this study, we assessed if this omission can lead to different projected distributions of the species. Methods: For this purpose, we applied an ensemble of SDMs, and we projected the distribution of rare bryophyte species in Scotland in the 2050s. Bryophytes are generally very climate-reliant and lend themselves to bioclimatic studies, and we selected species different grades of affinity with blanket bogs, which are threatened by climate change. Blanket bog extension was included in the model as an explanatory variable, and the models were run for three 2050s scenarios: once with the current blanket bog distribution and twice using the blanket bog distribution derived from two bioclimatic models (Lindsay modified and Blanket Bog Tree model), under the same climate change projections. Results: The results showed some differences in the predicted future distribution of those species with a strong relationship with blanket bogs, when habitat changes were accounted for. For example, Sphagnum majus, the species with the highest affinity with blanket bog in our study, was not predicted to change its future distribution when blanket bog is held constant at the current level, but was predicted to lose up to 60% of its current suitable area when the projected loss of blanket bog is included. Conclusion: Our results suggest that adding future habitat changes could improve the reliability of SDMs in the first steps of planning for conservation and restoration.