(a) Devil facial tumour disease (DFTD) causes large tumours on the face and mouth of Tasmanian devils (photo: David Hamilton). (b) The main steps involved in our modelling strategy. We first produced maps of the pre-DFTD devil population based on spotlighting data before the discovery of DFTD, and then used this map in a diffusion simulation of DFTD spread across Tasmania (blue box). In a second modelling stage, we used an interpolated map of DFTD spread as a predictor variable in a Bayesian joint-likelihood model, which jointly modelled 35 years of spotlighting data and 21 years of devil density estimates derived from spatially explicit capture-recapture (orange box). From the best joint-likelihood model, we produced maps of devil density, quantified historical changes in the total abundance of the species, and forecasted to the scenario where DFTD will occupy all of the devil’s geographic range.