Rapid range expansion of invasive plants is thought to be facilitated by their ability to quickly adapt to novel environmental conditions they experience in their new ranges. However, fitness trade-offs may constrain adaptation, especially at the geographic range periphery where genetic diversity may be low, thereby, restricting further range expansion. Life history theory predicts flowering early will result in smaller sizes, decreasing reproductive output. Using a common garden of the globally distributed, invasive plant Johnsongrass (Sorghum halepense) we tested whether populations from the range periphery exhibit adaptive trade-offs output.
Results/Conclusions
We found the periphery populations were half the size of the other populations and flowered 10 days earlier, but we did not find evidence of reduced reproductive output in the periphery populations. This suggests that there is a trade-off between flowering time and investment in growth. Our results suggest that Johnsongrass has the adaptive and reproductive potential to continue expanding its range north, though this expansion may be limited by other abiotic factors, such as cold temperature. It will become increasingly important to understand the factors facilitating and limiting range expansion of invasive species to better inform risk assessment and impact mitigation.