Context-dependent movement or methodological artefact in freshwater ecosystems? Platypus (Ornithorhynchus anatinus) movement dampens under flow regulation but expands in urbanised freshwater environments

Abstract

Understanding how freshwater species move through changing environments is critical for conservation, yet movement in riverine systems is shaped by interacting hydrological, landscape and biological processes that are difficult to disentangle across studies. For semi-aquatic species, these challenges are compounded by methodological differences and limitations in tracking approaches, sampling duration and study design, which can obscure ecological patterns and limit inference across environmental contexts. Using the platypus (Ornithorhynchus anatinus) as a model semi-aquatic mammal, we synthesised 530 movement records from 17 studies (1971–2024) using a bias-aware modelling framework to examine how demography, land use, flow regulation and season shape movement while accounting for methodological variation. Land-use differences were pronounced in unregulated systems, with the largest home ranges occurring in urban systems. Differences were comparatively weak in regulated rivers. Males consistently exhibited larger home ranges and greater daily movement distances than females, while juvenile movement varied seasonally. Study duration varied systematically across methods and environmental contexts and weakly influenced cumulative movement metrics. These findings demonstrate that movement responses in freshwater systems emerge from interactions among hydrology, landscape context and species biology and may differ from the widespread movement reductions reported for terrestrial mammals in human-modified landscapes. Freshwater conservation will require movement monitoring that spans environmental gradients, flow regimes, seasons and life stages, while explicitly accounting for methodological variation. Integrating ecological and methodological perspectives in this way can improve our ability to distinguish biological responses to environmental change from sampling effects and establish robust movement benchmarks for increasingly modified freshwater ecosystems.