Ecological Niche Modeling of Invasive Amphibians

Invasive amphibians represent a globally significant threat to native herpetofaunal biodiversity through predation,
competition, habitat modification, and pathogen transmission -- most critically the chytrid fungus Batrachochytrium
dendrobatidis (Bd), which is strongly associated with the range expansion of the American bullfrog (Lithobates
catesbeianus) in Europe. This study developed ensemble ecological niche models (MaxEnt, Random Forest, BRT) for
five invasive amphibian species -- Lithobates catesbeianus, Xenopus laevis, Trachemys scripta, Rana ridibunda (sensu
lato), and Discoglossus pictus -- in their European invasion ranges, projecting current and future (2050, 2070 under
SSP2-4.5 and SSP5-8.5) climatically suitable habitat. Ensemble models performed strongly (mean AUC = 0.91 +- 0.03;
TSS = 0.78 +- 0.04). Current climatically suitable area across Europe ranged from 142,000 km2 (X. laevis) to 1,840,000
km2 (L. catesbeianus). Under SSP5-8.5 by 2070, all five species projected range expansions into currently unsuitable
northern European regions (mean increase +28.4 +- 6.2% in suitable area), while simultaneously experiencing
contraction in southern Mediterranean areas driven by increasing summer aridity. Overlap analysis between modelled
invasive species ranges and native amphibian biodiversity hotspots (Iberian Peninsula, Balkans, Caucasus) identified 84
native amphibian species with >= 40% of their European range overlapping with current or projected invasive species
habitat, constituting the highest-priority conservation conflict zones. Bd co-distribution modelling confirmed significant
spatial overlap between L. catesbeianus invasion front and Bd-naive native species populations across central and
eastern Europe. These results provide spatially explicit early-warning maps for biosecurity management and targeted
monitoring deployment under the EU Regulation 1143/2014 on Invasive Alien Species.