Tracking change: Integrating animal movement into biodiversity indicators

Movement is essential to life and biodiversity, enabling animals to access resources and avoid risks, underlying species interactions and population dynamics, and facilitating gene flow and various ecosystem services. As such, while movement is a recognized Essential Biodiversity Variable in the class of species’ traits, it also scales up from individual responses to interactions and ecosystem functions. Yet, among the current biodiversity indicators, which provide standardized methods for monitoring biodiversity change under anthropogenic impacts, only one integrates movement data (the Protected Area Isolation Index). Here, we evaluate animal movement metrics for their potential as informative biodiversity indicators. To do so, we assess whether fifteen common movement metrics - standardized calculations of movement traits and movement model parameters - have a generalizable response to human disturbance as measured by the Human Footprint Index. Our analysis uses data from ungulates across the globe: White-bearded wildebeest (Connochaetes taurinus), all four giraffe species (Giraffa spp.), red deer (Cervus elaphus), mule deer (Odocoileus hemionus), Mongolian gazelle (Procapra gutturosa), and guanaco (Lama guanicoe). Of the tested metrics, individuals responded most consistently to increases in human disturbance via a shift in diurnality, a measure of the daily timing of animal movement. All species became more nocturnal in more disturbed landscapes. We therefore suggest that diurnality is a promising candidate for development into a movement-informed biodiversity indicator. Using tracking data from red deer populations monitored for 8-18 years, we then showcase how diurnality can be used to monitor ecological change over time. In particular, we demonstrate that changes in diurnality can capture the effects of management strategies or conservation interventions, a prerequisite for a biodiversity indicator. Lastly, we discuss practical considerations for implementing a movement-based biodiversity indicator like diurnality, highlighting how animal movement offers a powerful, underutilized opportunity to detect the impacts of human disturbance and to inform strategies for mitigating biodiversity loss.