Drying landscape and interannual herbivory-driven habitat degradation control semiaquatic mammal population dynamics

Semiaquatic muskrat (Ondatra zibethicus) are in decline throughout their native range. We report on the environmental and behavioural mechanisms responsible for a half-century of muskrat decline in a model system floodplain region of the Peace-Athabasca Delta (Delta). Using the Landsat satellite record, trapping and population survey records, and ecological field studies of muskrat, we develop conceptual and quantitative models to investigate mechanisms driving muskrat population decline at Egg Lake, an archetypal Delta region. Simulation results show processes occurring over nested timescales control population decline: Multidecadal drying has diminished shoreline habitat, and inter-annual shoreline habitat deterioration resulted from excessive herbivory by muskrat thereby exacerbating their die-off. Simulations without herbivory feedback show peak population values up to 73% higher than simulations with herbivory. Simulation results also suggest that trapping is not the primary cause of declines in muskrat abundance. The process model highlights factors responsible for long-term decline and rapid die-off, providing insights into mechanisms for observed muskrat population decline.