DOI: 10.5061/dryad.tqjq2bvvf
title: Latitudinal patterns of species richness and range size of ferns along elevational gradients at the transition from tropics to subtropics

description: Aim: To assess the range size patterns of ferns and lycophytes along
 elevational gradients at different latitudes in an ecographical transition
 zone and search for predictors of range size from a set of environmental
 factors. Location: Mexico, from 15° to 23° N. Taxon: Ferns and lycophytes.
 Methods: All terrestrial and epiphytic species were recorded in 658 plots
 of 400 m2 along eight elevational gradients. To test if the range size
 within assemblages increases with elevation and latitude, we calculated
 the latitudinal range using the northern and southern limits of each
 species and averaged the latitudinal range of all species within
 assemblages weighted by their abundances. We related climatic factors and
 the changes with latitude and elevation with range size using linear
 mixed-effects models. Results: Species richness per plot increased with
 elevation up to about 1500-2000 m, with strong differences in overall
 species richness between transects and a reduction with increasing
 latitude. The mean weighted range size of species within assemblages
 declined with elevation, and increased with latitude, as predicted by
 theory. However, we also found marked differences between the Atlantic and
 Pacific slopes of Mexico, as well as low range size in humid regions. The
 best models described about 76-80 % of the variability in range size and
 included the seasonality in both temperature and precipitation, and annual
 cloud cover. Main conclusion: Latitudinal and elevational patterns of
 range size in fern assemblages are driven by an interplay of factors
 favouring wide-ranging species (higher latitudes with increasing
 temperature seasonality; dryer habitat conditions) and those favouring
 species with restricted ranges (higher elevations; humid habitat
 conditions), with additional variation introduced by the specific
 conditions of individual mountain ranges. Climatically stable, humid
 habitats apparently provide favourable conditions for small-ranged fern
 species, and should accordingly be given high priority in regional
 conservation planning.
description: <strong>Study area: </strong>The Mexican transition
 zone is the complex area where the Neotropical and Nearctic biotas
 overlap, and in a strict sense corresponds to the mountain highlands of
 Mexico, Guatemala, El Salvador and Nicaragua (Halffter & Morrone,
 2017). We here present data from eight elevational gradients at a range of
 0 m to 3500 m elevation at 15-23° latitude N on both the Pacific and
 Atlantic (Gulf of Mexico) sides of Mexico (Figure 1, Table S4 in
 appendices). Three transects have been considered in previous studies: Los
 Tuxtlas (Krömer et al., 2013; Acebey, Krömer, & Kessler, 2017),
 Perote (Carvajal-Hernández & Krömer, 2015; Carvajal-Hernández,
 Krömer, López‐Acosta, Gómez‐Díaz, & Kessler, 2017), and Oaxaca
 (Hernández-Rojas et al., 2018). Los Tuxtlas including abundances was not
 published before (“Los Tuxtlas a”). Both transects from Los Tuxtlas were
 combined for the majority of the analysis.
 <strong>Fern sampling: </strong>On each gradient, we
 sampled the fern assemblages at regular elevational intervals of 100-300 m
 (every 500 m at Perote), depending on accessibility. At each elevation,
 depending on the suitability of the slope, 4-8 plots of 20 x 20 m (400
 m<sup>2</sup>) were sampled with a consistent, standardized
 methodology (Kessler & Bach, 1999; Karger et al., 2014). The plots
 were established in natural zonal forest, avoiding special structural
 features like canopy gaps, ridges, ravines, riparian areas, tree fall
 gaps, landslides, and other disturbed areas whenever possible, which all
 change microenvironmental conditions and have special fern assemblages. In
 each plot, all fern species and their abundances were recorded for
 terrestrial (soil, rocks, and dead wood) and for epiphytic substrates.
 Species with long creeping rhizomes were counted as patches. Epiphytes
 were sampled up to heights of 8 m with trimming poles and recorded at
 greater heights by using binoculars, climbing lower parts of trees, and
 searching recently fallen trees and branches within and adjacent to the
 plots (Gradstein, Nadkarni, Krömer, Holz, & Nöske, 2003; Sarmento
 Cabral et al., 2015).
description: # Latitudinal patterns of species richness and range size of ferns along
 elevational gradients at the transition from tropics to subtropics
 [https://doi.org/10.5061/dryad.tqjq2bvvf](https://doi.org/10.5061/dryad.tqjq2bvvf) ## Description of the data and file structure This is our raw data (**Ferns 9Transects Mexico.xlsx**) containing all species of ferns and lycophytes registered in eight mountains or elevational gradients in Mexico, including a total of 8197 registers. All terrestrial and epiphytic species of ferns and lycophytes, were recorded in 658 plots of 400 m2 (plots of 20 x 20 m) along this eight elevational gradients at a range of 0 m to 3500 m elevation at 15-23° latitude N on both the Pacific and Atlantic (Gulf of Mexico) sides of Mexico, in the Mexican Transition Zone, a complex area where the Neotropical and Nearctic biotas overlap. The Mexican transition zone, in a strict sense, corresponds to the mountain highlands of Mexico, Guatemala, El Salvador and Nicaragua (Halffter & Morrone, 2017). On each mountain or gradient, we sampled the fern assemblages at regular elevational intervals of 100-300 m (every 500 m at Perote), depending on accessibility. At each elevation, depending on the suitability of the slope, 4-8 plots of 20 x 20 m (400 m2) were sampled with a consistent, standardized methodology (Kessler & Bach, 1999; Karger et al., 2014). The plots were established in natural zonal forest, avoiding special structural features like canopy gaps, ridges, ravines, riparian areas, tree fall gaps, landslides, and other disturbed areas whenever possible, which all change microenvironmental conditions and have special fern assemblages. ### Files and variables #### File: Dryad\_Ferns\_9Transects\_Mexico.xlsx **Description:** **Variables** * **Transect:** indicates the mountain, locality, place or state in Mexico where the ferns and lycophytes where sampled along different elevational bands. It contains a total of eight mountains or elevational gradients and many localities as elevational bands sampled in every mountain: | **No.** | **Transect name** | **State in Mexico** | **Name oft he área** | **Latitude (mean between plots)** | | :---------- | :---------------- | :------------------ | :---------------------------------------------- | :-------------------------------- | | 1 | Cielo | Tamaulipas | Reserva del La biosfera El Cielo | 23.106 N, - 99.204 W | | 2 | Nayarit | Nayarit | La Noria – Volcan San Juán, Xalisco | 21.483 N, - 104.979 W | | 3 | Manantlán | Jalisco | Sierra de Manantlán | 19.577 N, - 104.249W | | 4 | Perote\* | Veracruz | Parque Nacional Cofre de Perote – La Mancha | 19.558 N, - 96.903 W | | 5 | Tuxtlasa | Veracruz | Reserva de la Biosfera Los Tuxtlas (San Martín) | 18.568 N, - 95.125 W | | Tuxtlas b\* | Veracruz | | | | | 6 | Oaxaca\* | Oaxaca | Sierra de Juárez | 17.659 N, - 96.427 W | | 7 | ChiapasN | Chiapas | Cerro Huitepec al norte de Chiapas | 17.105 N, - 93.062 W | | 8 | Triunfo | Chiapas | Reserva de la Biosfera El triunfo | 15.643 N, - 92.822 W | * **Plot**: indicates the plot number where the ferns and lycophytes were sampled. The name of this column is a code that includes the two first letters of the name of the transect (but sometimes the name of a locality inside of the corresponding transect), the elevational band originally registered (0-3000 m asl) and the plot number (1-8) * **Elevation**: registered elevation (m asl) of the corresponding plot in fieldwork * **Specie**: valid scientific name * **Latitude:**  registered latitude (decimal degrees) of the corresponding plot in field work * **Longitude:** registered longitude (decimal degrees) of the corresponding plot in field work * **Elevational band:** elevational band (m asl) used to do the analysis of this research ## Code/software Excel (Windows10) ## Access information Other publicly accessible locations of the data: * Data was derived from the following sources: \* Three transects have been considered in previous studies: * Los Tuxtlas (Krömer et al., 2013; Acebey, Krömer, & Kessler, 2017), * Perote (Carvajal-Hernández & Krömer, 2015; Carvajal-Hernández, Krömer, López‐Acosta, Gómez‐Díaz, & Kessler, 2017), and * Oaxaca (Hernández-Rojas et al., 2018). Los Tuxtlas including abundances was not published before (“Los Tuxtlas a”). Both transects from Los Tuxtlas were combined for the majority of the analysis.