Connectivity, Fire, and Land Use: Understanding Platypus (Ornithorhynchus anatinus) Persistence in Fragmented Watersheds

Justine Ohlrich , Gilad Bino, Tahneal Hawke, Tamielle Brunt, Simon Hart

Aim: Effective biodiversity conservation requires improved understanding of species distributions, and of the influence of threatening processes on those distributions. This is particularly important for freshwater species, which are difficult to survey even as they are exposed to disproportionately high levels of threat. Here we address this issue for the platypus (Ornithorhynchus anatinus), an evolutionarily-distinct, ecologically-important species whose threat status is jurisdiction dependent and subject to conjecture. We aim to improve our understanding of platypus distribution across a large, little-studied region, and to quantify the association between occurrence and environmental metrics, including those thought to influence population viability.
Location: Central-eastern Australia, including south-eastern Queensland and northern New South Wales.
Methods: We used environmental DNA to survey for platypus at 174 sites distributed across 43 waterways and seven river basins in the central part of the species’ range. We related platypus occurrence to local food availability (deduced from our multispecies eDNA samples), and to remotely-sensed data on water availability, river fragmentation, recent fire severity, land use, vegetation cover, and topographic metrics.
Results: Platypuses were not detected at 89 sites (51%), of which 56 had nearby historic sightings (within 25km), suggestive of a potentially significant range decline. We also detected platypus in seven locations with no known historical sightings, likely reflecting previously undocumented populations in areas with low historical survey effort. Platypus had lower occurrence in south-eastern Queensland (in the north). Occurrence was positively related to unobstructed river length and had scale-dependent associations with fire severity.
Main conclusions: Our findings highlight the urgent need to improve our understanding of the conservation status of this iconic, cryptic species. Improving our knowledge of the viability of populations in heavily fragmented watersheds and in response to extreme events such as droughts and fire is crucial for developing conservation strategies to halt further declines.