Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Biodiversity Conservation, Biodiversity & Conservation, aquatic invasive species management, droplet digital PCR, eDNA applications, freshwater systems, habitat suitability, invasion dynamics, pond-breeding amphibian, LITHOBATES-CATESBEIANUS, RANA-CATESBEIANA, DNA, LANDSCAPE, CONSERVATION, ERADICATION, POPULATION, FEATURES, ECOLOGY, SPREAD, 1S01822N#56751510, 0501 Ecological Applications, 0502 Environmental Science and Management, 4102 Ecological applications, 4104 Environmental management

Abstract:

The American bullfrog (Lithobates catesbeianus [Shaw, 1802]) is one of the hundred most destructive Alien Invasive Species (AIS) worldwide that has invaded more than 40 countries across 4 continents. In Belgium, bullfrogs have occupied a large area in a relatively short period of time despite a decade of intensive management interventions. Acquiring better insights into the distribution, abundance, and spatial spread of this invasive frog species is an important first step towards a successful management strategy. In this study, we sampled 382 permanent water bodies and combined environmental DNA (eDNA)-based analyses using quantitative droplet digital PCR (ddPCR) with assessments of habitat characteristics to generate an overview of the present distribution of bullfrogs in Flanders (Northern Region of Belgium) and the type of water bodies they have invaded. Our results revealed a fragmented distribution pattern covering an area of 364.76 km² that consisted of eight metapopulations located in five different river valleys, suggesting the occurrence of multiple anthropogenically-mediated introductions. Bullfrogs appeared to be firmly established in the valley of the Grote Nete, where invaded waterbodies have been found along 72% of the length of this river, divided into three distinct metapopulations. Unlike refuge sites, bullfrogs were found to be highly selective in their choice of breeding sites, which were characterised by abundant emergent vegetation and sparse tree cover along the shoreline. The division of the vast occupied area into well-defined, accurately delineated metapopulations facilitates the identification of functional management units. Furthermore, the obtained knowledge of the patterns of range expansions and the spatial configuration and associated environmental features of breeding sites can be used to prioritise management interventions in strategically located invasion hubs. Overall, we conclude that eDNA-based monitoring combined with environmental assessments provide important information that can be used to manage widespread aquatic AIS more effectively.