Invasion Patterns and Niche Dynamics of the Pollinivorous Florida Calligrapher, Toxomerus floralis (Diptera: Syrphidae) in the Afrotropical Region

ABSTRACT

The rapid spread of Toxomerus floralis (Fabricius, 1798) (Diptera: Syrphidae) within the Afrotropical region is described. We characterise and compare the climatic niches of T. floralis in its native (Southern North America, Central America and South America) and invaded (Afrotropical Region) range to assess the potential for further expansion across Africa and beyond, and included future global climate models and socioeconomic pathways as projections. Occurrence data for native and invaded ranges were obtained from field sampling by authors, major collections of Afrotropical Syrphidae, collections records and occurrence data from the Global Biodiversity Information Facility (GBIF), including iNaturalist data. Single and ensemble species distribution modelling was performed utilising the ‘biomod2’ package, and the ‘ecospat’ package was used to determine the Continuous Boyce Index and niche dynamics of the species. Current and global climate models (GCM) Worldclim 2.1 data were used as environmental variables. Ensemble models showed high predictive accuracy (native: TSS = 0.824, CBI R _s  = 0.982; expanded: TSS = 0.805, CBI R _s  = 0.997), Bio18 and Bio2 Worldclim 2.1 variables proving the most important predictors. Niche dynamics showed primarily niche conservatism (76.4%) as well as a degree of expansion (23.6%, p  = 0.048). Models predict high probability of further spread throughout Africa, with potential expansion into other Ecoregions. Future climate projections suggest continued range expansion through 2100 under most scenarios. The species' potential distribution shows spatial overlap with its larval host plants, however, since host distributions were not integrated into the modelling framework, the relative roles of climatic and biotic factors in limiting distribution cannot be directly evaluated from current analyses. It is predicted that T. floralis will invade the tropical regions of Asia and Australia in the near future. Citizen science data proved invaluable for tracking the expansion of T. floralis , highlighting the value of such platforms for monitoring non‐native species expansions.