Latitudinal variation in global range‐size of aquatic macrophyte species shows evidence for a Rapoport effect

Abstract

1. To test hypotheses concerning the applicability of the Rapoport effect (RE: "species that occur at higher latitudes tend to have greater geographical range-size than species which have ranges limited to latitudes closer to the equator") to aquatic macrophytes at global scale, we analysed the world latitudinal distribu

Patterns and mechanisms underlying ecoregion delineation in North American freshwater plants

“…Based on a previous study on global variation in community similarity of lake plants (Alahuhta et al, 2017), we also expected (H2) that within–ecoregion and across–ecoregion heterogeneity would be caused by species replacements rather than by differences in species richness. Similarly, we predicted (H3) that climatic forcing would explain a great deal of variation in the robustness of freshwater plant ecoregions (Heino, 2011; Chappuis et al, 2012; Alahuhta et al, 2021, 2020; García–Girón et al, 2020a, 2020b), with topography, Pleistocene Ice Age legacies, human footprint, water alkalinity, availability of inland waterbodies and the surface area of individual regions playing an important supplementary role (Lacoul & Freedman, 2006; Chappuis et al, 2014; Iversen et al, 2019; Murphy et al, 2019, 2020). Finally, we hypothesised (H4) that ecoregions would be a more robust and useful classification for floating–leaved and submerged plants.…”

“…Unexpectedly, species replacement and richness difference explained equal amount of variation for ecoregion robustness. Recent studies have clearly shown that species replacement primarily structures freshwater plants independent of spatial scale and study region (Alahuhta et al, 2017; Murphy et al, 2020; Alahuhta et al, 2021). However, these previous exercises utilised an alternative measure of richness difference (i.e., nestedness), which does not consider overall difference in species richness explicitly (Legendre 2014; Schmera et al, 2020).…”

“…In brief, distribution maps of 180 freshwater plants were digitalised from the Flora of North America (Flora of North America Editorial Committee, 1993–2007) for a study region that was restricted to the main continental areas of the United States and Canada, excluding Mexico and remote islands. We strictly focused on vascular plant species that are strongly associated with freshwater habitats, removing peatland and marine species following Crow & Hellquist (2000), Flora of North America Editorial Committee (1993–2007), Lichvar (2014) and Murphy et al, (2019, 2020). Hence, riparian, shoreline and semi–aquatic plant species were also excluded from our study.…”

“…Here, we calculated terrain ruggedness (m) as implemented in the MERIT–Digital Elevation Model (DEM) from the Geomorpho90m global dataset (Amatulli et al, 2020), which uses the NASA Shuttle Radar Topographical Mission (SRTM) to provide topographical variables at 3 arc–second resolution. Although no consensus exists on the influence of Late Quaternary history on freshwater plant diversity (Alahuhta et al, 2020, Murphy et al, 2020), we also calculated the average velocity of climate change from the Last Glacial Maximum (LGM) to present day (expressed as m yr −1 , i.e., the speed at which species must migrate over the Earth’s surface to maintain constant climatic conditions, Hamann et al, 2015) from a set of transient simulations at c. 1/5 degrees resolution (see Sandel et al, 2011 for details).…”

Global-scale drivers of ploidy state in aquatic macrophytes

“…Mean, median and standard deviation for climate variables per gridcell were obtained using a 10°g ridcell shapefile and the Zonal statistics tool in QGIS (version 3.4.9-Madeira). The area occupied by each agricultural land use category (and subsequently total agricultural land cover) per gridcell was obtained using the above-mentioned shapefile and the Zonal Histogram tool in the ArcMap Spatial Analyst toolbox using ArcMap v. 9.3.1, see Murphy et al (2019Murphy et al ( , 2020 for further details. All-species richness and ecozone-endemic species richness values were obtained from Murphy et al (2019).…”