The roles of dispersal limitation, climatic niches and glacial history in endemism of the North American bryophyte flora

Abstract

Premise: Bryophytes (mosses, liverworts, and hornworts) tend to have very large geographic ranges, which impedes progress toward understanding the drivers of diversification and extinction. This study aimed to investigate whether North American endemics differ geographically from more widespread species and whether differences in climatic niche or traits related to dispersal and establishment differ between endemics and more widespread species. Methods: All available herbarium records of bryophytes from North America north of Mexico (10 6 collections) were used. Traits related to dispersal were obtained from the literature. Analyses tested whether range sizes and extents differed between endemics and nonendemics, and whether trait differences were associated with endemism. Climate data were used to determine whether differences in niche breadth are present between endemics and nonendemics, and whether suitable climate for endemics occurs outside North America. Results: Nonendemics have range sizes twice as large as endemics and they occur farther north and have greater longitudinal extents. However, they do not have the widest niche breadths and do not differ in spore size (with few exceptions) or sexual condition. Asexual propagules are more prevalent among nonendemics. Climatic models indicate that substantial areas of climate suitable for endemics exist outside of North America. Conclusions: Distributions of endemics and nonendemics are consistent with an important role of glaciation in shaping the North American bryophyte flora. Endemics are not limited to the continent based on a lack of suitable climate elsewhere or by spore size or sexual condition.

Spatial phylogenetic patterns in the North American moss flora are shaped by history and climate

“…This discrepancy indicates that the evolutionary connection of the interior west to the north is greater than might be expected based on species turnover. This is largely consistent with an idea that has been alluded to though not explicitly stated (Carter, 2021; Carter et al, 2016; Schofield, 1980) that the flora of the interior represents an extension of more northern lineages despite high species similarity with the mountainous regions along the pacific coast. This illustrates the utility in comparing patterns of phylogenetic turnover with traditional species‐based metrics to provide a more nuanced understanding of biogeographic patterns.…”

“…Processes at geological timescales are clearly important in North America as well, and Schofield (1980) and Carter (2021) argued for the importance of Pleistocene refugia in the development of current patterns of endemism in the flora. Northern North America was nearly completely glaciated at the last glacial maximum, and though both remained unglaciated through the Pleistocene, the east and west have distinctly different histories from each other.…”

“…The importance of the southeast as a refuge for more tropical floristic elements throughout the Tertiary has been well documented with plant fossils (Manchester, 1999;Tiffney, 1985aTiffney, , 1985bWolfe, 1975) and has been largely supported by a meta-analysis of plant phylogenies (Manos & Meireles, 2015). Although relevant fossil data for bryophytes are largely lacking (reviewed by Carter, 2021), bryologists have long noted that the southeast bears a similar signal of tertiary relictualism for bryophytes (Anderson, 1971;Anderson & Zander, 1973;Crum, 1972;Frahm & Vitt, 1993;Schofield, 1980). In the following discussion of PD and RPD in the three primary moss phytoregions, it is important to keep in mind that we are currently unable to fully disentangle the relative importance of current climatic differences and different geological histories of the regions.…”

“…Dispersal limitation is not likely to explain the floristic differences across regions. Despite the strong floristic differences among regions, approximately 81% of bryophyte species in North America are also native to another continent (Carter, 2021), and genetic studies often find evidence of intercontinental dispersal (Patiño & Vanderpoorten, 2018). The fact that there are distinct regional floristic differences, even though many species have the potential to disperse across long distances, suggests that abiotic filtering is important.…”

“…We constructed a molecular phylogram for 935 moss species, approximately (67%) of the species known from North America (Carter, 2021). We conducted a hierarchical analysis of the NCBI GenBank plant sequence database (compiled 5 November 2020) using PyPHLAWD (Smith & Walker, 2018) to create a molecular dataset for phylogenetic analysis.…”