Megasdm: Modelling Species Ranges in The Past And Future

Abstract

As we enter the Anthropocene, unprecedented climatic and landscape changes are leading to global extinctions and the reorganization of many species’ ranges. Understanding how species ranges have changed through time can contextualize long-term interactions between geography and ecology, offer insight into how they may change in the future, and inform conservation of vulnerable species. Species distribution models (SDMs) can be an important method for examining these range shifts, both in the future and through the past, by providing hypotheses about the responses of species’ ranges to certain scenarios. Here, I present several avenues for exploring hypotheses on range shifts using the megaSDM R package. This package facilitates realistic spatiotemporal SDM analyses by incorporating dispersal probabilities, creating time-step maps of range change dynamics, and efficiently handling large datasets and intensive subsampling techniques, while still allowing model-specific tuning. Using megaSDM, with the ongoing expansion of the nine-banded armadillo (Dasypus novemcinctus) as an example, I show how dispersal rate constraints can be incorporated into predictions of range shifts through time, introducing the concept of “invadable suitability”. Comparing dispersal-constrained to unconstrained models, I establish the importance of considering the dispersal ability of a species when projecting its range through time. Finally, I demonstrate the effects of transient range dynamics (e.g., a momentary range contraction in a period of prolonged expansion) on modelled species distributions, showing that these dynamics can be accounted for by incorporating many incremental time steps. These improvements in SDMs allow us to test and refine hypotheses that forecast or hindcast species range shifts. They are small but important steps towards treating conservation as a dynamic, rather than static, field and bringing a paleontological perspective to the preservation of life on Earth.