Influence of elevation on the species–area relationship

Abstract

Aim Species–area relationships (SARs) are among the best investigated patterns in ecology, yet the shape of the function that should describe SARs and the biological meaning of the function parameters are disputed. Elevational gradients offer the opportunity of investigating how biodiversity responds to large variations in environmental characteristics within small geographical areas. We asked which function describes SARs at different elevations and explored how variations in environmental characteristics influence SAR shape. Location Alborz Mountains (Iran). Taxon Vascular plants. Methods We used sets of nested plots (0.001 to 100 m2) placed at 100 m intervals from 2,000 to 4,500 m elevation to construct series of nested SARs as species accumulation curves. Then, we used these curves to assess the appropriateness of different SAR functions at different elevations. We investigated how parameters of the power function varied along the elevational gradient in response to variation in environmental parameters (ruggedness, temperature, precipitation, exposed rock, percentages of soil sand and total nitrogen, and productivity, expressed by the normalized difference vegetation index). Results The most frequently observed best fit model was the power function, which is controlled by two parameters: z (the velocity in species accumulation with sampled area) and c (the species richness per unit area). z was positively influenced by temperature and soil nitrogen, decreasing with elevation. c was positively influenced by temperature and soil nitrogen, and negatively by rock cover, decreasing with elevation. Main conclusions The decrease in c‐values with elevation is consistent with the altitudinal decrease in species richness and is explained by the increase in bare rock. By contrast, c was positively influenced by temperature and total nitrogen, which are two factors promoting plant growth. Similarly, z‐values decreased with elevation, thus indicating a decrease in beta diversity.

Scale‐dependent patterns and drivers of plant diversity in steppe grasslands of the Central Alborz Mts., Iran

“…Furthermore, mean and maximum richness values in our study were markedly higher across all grain sizes than the values reported in a recent multi-scale study from Alamkuh Mt. on the northern slope of the Alborz mountains (Moradi et al, 2020; see Table 3). This unexpected difference might be due to underestimation of species richness in the latter study.…”

“…However, our value was higher compared to the z ‐value recently reported for steppes of northern slopes of the Alborz Mts. (0.21; Moradi et al, 2020). We found the highest local z ‐value for the transition of 0.01–0.1 m 2 which coincides with findings for grasslands in Transylvania (Turtureanu et al, 2014), Siberia (Polyakova et al, 2016) and Italy (Baumann et al, 2016).…”

“…Mean annual temperature was also the most important TA B L E 3 Species richness in different plot sizes (n = 23 for 1,000 m 2 ; n = 46 for 0.0001-10 m 2 ) and comparison with corresponding values for another part of the Alborz Mts. (Moradi et al, 2020) and for palaearctic grasslands in general (Biurrun et al, 2019;Dengler et al, 2020b) Grain predictor for the richness of the other functional groups, always with unimodal relationships (Table 4). However, the peak position of the different life forms and functional groups clearly varied, from hemicryptophytes at 4.6°C to therophytes at 11.3°C and other forbs with a predicted value of 14.3°C, thus above the modelled range of temperatures (Appendix S4; Figure 3).…”

“…are covered by diverse types of grasslands, ranging from lowland semi‐desert grasslands in the submontane zone via (sub‐)alpine thorn‐cushion grasslands in the montane zone to scree vegetation at the top in the alpine region (Akhani et al, 2013; Noroozi, 2020). While there are relatively many studies on the flora and vegetation of these grasslands (Klein, 1982, 1987, 1999; Kashipazha et al, 2007; Naqinezhad et al, 2009; Noroozi et al, 2010, 2014; Naderi et al, 2012; Ravanbakhsh et al, 2015) only few studies have dealt with biodiversity patterns (Mahdavi et al, 2013; Moradi et al, 2020).…”

Investigating elevational gradients of species richness in a Mediterranean plant hotspot using a published flora

“…Historically, species richness trends have been associated with available area and environmental gradients. An increase in species richness with increasing area is one of the most robust ecological generalizations (Rosenzweig 1995, Lomolino 2000, and a vast literature has been published on species−area relationships (e.g., Karger et al 2011, Dengler et al 2019, Moradi et al 2020, Matthews et al 2021. Species richness patterns have also been evaluated along several environmental gradients (Gaston 2000), such as temperature, productivity, potential evapotranspiration, etc.…”