Niche Conservatism Shapes Invasion Patterns of Opuntia Species Despite Interspecific Differences in Expansion...

Opuntia cacti rank among the most widespread and ecologically damaging plant invaders globally, yet it remains unclear whether their invasion success is driven by niche conservatism or niche shifts. Here, we investigated niche dynamics between native and invaded ranges for four Opuntia species (O. dillenii, O. ficus-indica, O. monacantha, and O. humifusa) that differ in climatic origin and invasion history. Using biomod2 ensemble models combined with principal component analysis in environmental space (PCA-env) and multivariate environmental similarity surface (MESS) analysis, we found that all four species exhibit strong niche conservatism, with high niche stability (89.6%-98.2%) and significant niche similarity between native and invaded ranges. Model projections indicated broad climatically suitable areas (10.4-22.5 million km²), with invasive occurrences largely confined to native environmental conditions. Niche expansion was limited (1.9%-10.4%) and restricted to marginal environmental conditions. Soil nutrient availability further contributed to distribution patterns in several species, highlighting the role of edaphic factors in shaping niche structure. Despite this overall conservatism, species differed markedly in niche dynamics and geographic expansion, indicating that invasion processes vary substantially among species. Overall, our results suggest that Opuntia are primarily characterized by environmental tracking rather than widespread niche shifts, while species-specific differences in adaptation and spread highlight the importance of assessing invasion risk at the species level.