Iberian–Balearic fern regions and their explanatory variables

Abstract

This article delineates the compositional regions present in the Iberian-Balearic fern flora and compares these regions to previously proposed biogeographic units. It also assesses the extent to which environmental variables could explain the regions and the fern species richness gradients found within them. A combination of 40 previously published and new maps were used to compile the distribution of 123 pteridophytes on a 50 9 50 km UTM grid. Cluster analysis of the resulting 257 squares was used to classify 10 regions based on fern species assemblages. Discriminant function analysis identified the environmental variables that best explained these fern composition regions. Using generalized linear models; the number of species in each square was regressed against topography, climate, geology, environmental diversity, land use and spatial variables within each region. Two main latitudinal pteridophyte zones can be recognized in the Iberian Peninsula. These two zones are longitudinally subdivided into two sub zones. The 10 regions established significantly differ both in species richness and influential environmental variables. Climatic variables discriminate the most among regions, followed by topography, heterogeneity and geology. Pteridophyte richness varies, with richer areas being located along the coast and the main mountain ranges and the poorest areas being in the central plateaus and some north eastern and south western river basins. Species richness variation in Iberia is positively correlated with altitude range, precipitation, maximum altitude and area with siliceous soils. It is negatively correlated with the total annual days of sun, however. The fact that species richness is explained by different variables within each of the 10 regions indicates that the specific factors determining the spatial distribution of species richness vary from region to region. Some coastal regions are poorly explained by the model, and display a negative correlation with the selected causal factors. This finding suggests that persistent historic effects might play a local role in determining species assemblages in these regions.

Area–heterogeneity tradeoff and the diversity of ecological communities

“…evidence supports this prediction and shows that the qualitative shape of the heterogeneity-diversity relationship may vary among different groups of organisms in the same region (20), within the same group of organisms among different regions (21), and within the same group of species and the same region when the data are analyzed at different scales (22). Furthermore, Tamme et al (23) recently showed that negative effects of habitat heterogeneity on species richness are significantly more common at small spatial scales, a finding fully consistent with our simulations (Fig.…”

Relating landscape structure, environment and management to biodiversity indicators estimated from forest inventory data in Catalonia (NE Spain)

“…The primary cause underlying this relationship is accepted to be the decrease in the length of the growing season and in vegetation productivity with altitude, which determines a lower number of plant species being able to colonise the highest altitudinal ranges. However, several authors found the contrary phenomenon in the Iberian Peninsula (Castro-Parga et al, 1996;Lobo et al, 2001;Moreno-Saiz and Lobo, 2008), arguing that, under a Mediterranean climate, the climatic conditions in the upper mountain areas are not constraining biodiversity, but on the contrary, are the extreme temperatures and low precipitations occurring at lower altitude which, through hydric stress, might limit plant productivity and diversity. The presence of mountains has also been suggested to be a potential surrogate of many factors that might influence positively plant species richness (see Vetaas and Ferrer-Castán, 2008), like the increase in surface area, the higher geological heterogeneity, or its role as refuge during the last glacial periods.…”

Using endemic-plant distribution, geology and geomorphology in biogeography: the case of Sardinia (Mediterranean Basin)

“…In this sense, distribution patterns of the vascular flora (e.g. Rivas-Mart ınez et al, 2002;Moreno Saiz & Lobo, 2008;Moreno Saiz et al, 2013), and in particular of endemic flora (e.g. Rivas Mart ınez et al, 1997; Garc ıa Barros et al, 2002;Santa Anna Del Conde et al, 2009;MedinaCazorla et al, 2010;Gonz alez-Orozco et al, 2013) has often been used to describe biogeographical schemes.…”