1 Department of Bioscience - Plant Biology, Department of Bioscience, Science and Technology, Aarhus University2 Department of Bioscience - Aquatic Biology, Department of Bioscience, Science and Technology, Aarhus University3 State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, 200062, China4 Department of Natural Resources Science , University of Rhode Island , Kingston, RI 02881 , USA.5 Department of Bioscience, Science and Technology, Aarhus University6 Department of Bioscience - Aquatic Biology, Department of Bioscience, Science and Technology, Aarhus University7 Department of Bioscience, Science and Technology, Aarhus University
After its introduction into North America, Euro-Asian Phragmites australis became an aggressive invasive wetland grass along the Atlantic coast of North America. Its distribution range has since expanded to the middle, south and southwest of North America, where invasive P. australis has replaced millions of hectares of native plants in inland and tidal wetlands. Another P. australis invasion from the Mediterranean region is simultaneously occurring in the Gulf region of the USA and some countries in South America. Here, we analysed the occurrence records of the two Old World invasive lineages of P. australis (Haplotype M and Med) in both their native and introduced ranges using environmental niche models (ENMs) to assess (i) whether a niche shift accompanied the invasions in the New World; (ii) the role of biologically relevant climatic variables and human influence in the process of invasion; and (iii) the current potential distribution of these two lineages. We detected local niche shifts along the East Coast of North America and the Gulf Coast of the USA for Haplotype M and around the Mississippi Delta and Florida of the USA for Med. The new niche of introduced Haplotype M accounts for temperature fluctuations and increased precipitation. The introduced Med lineage has enlarged its original subtropical niche to the tropics-subtropics, invading regions with a high annual mean temperature (> c. 10 °C) and high precipitation in the driest period. Human influence is an important factor for both niches. We suggest that an increase in precipitation in the 20(th) century, global warming and human-made habitats have shaped the invasive niches of the two lineages in the New World. However, as the invasions are on-going and human and natural disturbances occur concomitantly, the future distribution ranges of the two lineages may diverge from the potential distribution ranges detected in this study.