A process-based dynamic occupancy model to study range dynamics under non-equilibrium conditions

Abstract

Failing to account for ecological processes such as dispersal and connectivity when modeling distributions can lead to biased inference about environmental drivers and reduced predictive performance. Spatial dynamic occupancy models are promising to study range dynamics while accounting for dispersal and connectivity, but they currently rely on restrictive formulations of the colonization process, and computational constraints prevent their application at large spatial scales. Here, we propose a process-based dynamic occupancy model to study the distribution of range-expanding species while accounting for connectivity and effects of the environment. We introduce a formulation based on dispersal-pressure that provides a flexible and ecologically interpretable representation of the colonization process, and develop a computational approach based on sparse distance matrices that enables its application to national and transnational scales. We conducted a simulation study that showed unbiased parameter estimation across various ecological scenarios. We also applied our model to two range-expanding carnivores offering complementary insights: the grey wolf and the Eurasian otter. Our model revealed contrasting colonization dynamic, with wolves primarily constrained by altitude and forest cover while otters where only marginally affected by the environment, suggesting that their distribution is limited by dispersal history rather than habitat preferences. By explicitly disentangling the influence of dispersal and environment on distributions, our model provides better insight into occupancy-environment relationships under non-equilibrium conditions, and help identifies what limits species distributions. In light of the increasing availability of large-scale biodiversity data, our framework offers opportunities to study range dynamics using mechanistic approaches across entire landscapes.