Biotic interactions influence the projected distribution of a specialist mammal under climate change

Aim: To measure the effects of including biotic interactions on climate-based species distribution models (SDMs) used to predict distribution shifts under climate change. We evaluated the performance of distribution models for an endangered marsupial, the northern bettong (Bettongia tropica), comparing models that used only climate variables with models that also took into account biotic interactions. Location: North-east Queensland, Australia. Methods: We developed separate climate-based distribution models for the northern bettong, its two main resources and a competitor species. We then constructed models for the northern bettong by including climate suitability estimates for the resources and competitor as additional predictor variables to make climate + resource and climate + resource + competition models. We projected these models onto seven future climate scenarios and compared predictions of northern bettong distribution made by these differently structured models, using a 'global' metric, the I similarity statistic, to measure overlap in distribution and a 'local' metric to identify where predictions differed significantly. Results: Inclusion of food resource biotic interactions improved model performance. Over moderate climate changes, up to 3.0 °C of warming, the climate-only model for the northern bettong gave similar predictions of distribution to the more complex models including interactions, with differences only at the margins of predicted distributions. For climate changes beyond 3.0 °C, model predictions diverged significantly. The interactive model predicted less contraction of distribution than the simpler climate-only model. Main conclusions: Distribution models that account for interactions with other species, in particular direct resources, improve model predictions in the present-day climate. For larger climate changes, shifts in distribution of interacting species cause predictions of interactive models to diverge from climate-only models. Incorporating interactions with other species in SDMs may be needed for long-term prediction of changes in distribution of species under climate change, particularly for specialized species strongly dependent on a small number of biotic interactions.