Contrasting climate signals between native and introduced annual and perennial floras

Annual versus perennial life histories represent a fundamental axis of plant strategy, with empirical evidence showing that the proportion of annuals is greater in hot, arid, or variable climates. Crucially, introduced species, a group that disproportionately includes annuals, are expanding in number and range across the globe. Whether introduced richness is governed by the same climatic controls as native richness remains untested at continental scales. For 19,299 native (12% annual) and 2,802 introduced (34% annual) Australian plant species, we show that native annual richness tracks climate far more tightly than introduced annual richness. Both floras largely follow the global pattern: the annual fraction rises in dry and seasonal climates. However, hotspots of native and introduced annual richness are completely different.

Introduced annuals (28% of all annual species) concentrate in wet, populated areas with low precipitation seasonality, whereas native annual richness is fairly evenly distributed, with the highest diversity in the seasonal tropics. The current continental-scale pattern is thus the sum of a long interaction between the native flora’s life histories and in situ climate, with dynamic, path-dependent introductions layered on top. As introductions and range expansions continue, they will reshape the annual-to-perennial balance along pathways of human influence.