Distribution of vascular plant species richness and endemic richness along the Himalayan elevation gradient in Nepal

Abstract

Aim Species richness and endemic richness vary along elevation gradients, but not necessarily in the same way. This study tests if the maxima in gamma diversity for flowering plants and the endemic subset of these plants are coherent or not. LocationThe study was conducted in Nepal, between 1000 and 5000 m a.s.l. MethodsWe used published data on distribution and elevational ranges of the Nepalese flora to interpolate presence between maximum and minimum elevations. Correlation, regression and graphical analyses were used to evaluate the diversity pattern between 1000 and 5000 m a.s.l. ResultsThe interval of maximum species endemic to Nepal or the Himalayas (3800 -4200 m) is above the interval of maximum richness (1500 -2500 m). The exact location of maximum species density is uncertain and its accuracy depends on ecologically sound estimates of area in the elevation zones. There is no positive statistically significant correlation between log-area and richness (total or endemic). Total richness is positively correlated with log-area-adjusted, i.e. estimated area adjusted for the degree of topographic heterogeneity. The proportion of endemic species increases steadily from low to high elevations. The peak in endemism (c. 4000 m) corresponds to the start of a rapid decrease in species richness above 4000 m. This may relate to the last glacial maximum (equilibrium line at c. 4000 m) that penetrated down to 2500-3000 m. This dynamic hard boundary may have caused an increase in the extinction rate above 4000 m, and enhanced the probability of isolation and facilitated speciation of neoendemics, especially among genera with a high proportion of polyploids. Main conclusionsThe results reject the idea of corresponding maxima in endemic species and species richness in the lowlands tentatively deduced from Stevens' elevational Rapoport effect. They confirm predictions based on hard boundary theory, but hard-boundaries should be viewed as dynamic rather than static when broad-scale biogeographical patterns with a historical component are being interpreted.

Plant Species Richness, Evenness, and Composition along Environmental Gradients in an Alpine Meadow Grazing Ecosystem in Central Tibet, China

“…Species richness increased linearly with elevation. This is not consistent with other studies where species richness decreases monotonically (Stevens, 1992) or shows a hump-backed pattern along elevation gradients (Rahbek, 1995;Vetaas and Grytnes, 2002). Our elevation gradient only covered 300 m, but the posi-FIGURE 2.…”

“…tion of the gradient (4800-5105 m) was well above the elevation at which the maximum number of species occurred in other alpine regions located in a similar latitudinal range (Vetaas and Grytnes, 2002;Tang et al, 2006;Wang et al, 2007). Thus, we would expect a decreasing rather than increasing trend of species richness with altitude.…”

“…Since quadrats within each plot were not independent, we defined plot as a random variable in the LME models (Crawley, 2007). The quadratic terms were used because the response variables could exhibit unimodal relationships to the explanatory variables, depending on ecosystem properties (Rahbek, 1995;Vetaas and Grytnes, 2002). We used backward elimination to find the best model for each response variable by removing the least significant terms, starting with interaction terms, followed by quadratic and then linear terms (Crawley, 2007).…”

Structure, Composition and Diversity of Forest Along the Altitudinal Gradient in the Himalayas, Nepal

“…Between 1,500 and 2500 m, little change in the number of species has been observed, but above this altitude, a decrease in species richness is evident (Vetaas and Grytnes, 2002). The results of this study also reflect this general trend found in plant diversity of mountain forests in Himalaya.…”

Relationships between environmental variables and vegetation across mountain wetland sites, N. Iran

“…More phytogeographically widespread species are confined mainly to lower altitudes while wetland sites at higher altitudes, (with higher soil organic matter content), contain more endemic and other geographically-restricted taxa. The increase in endemism with increasing altitude is consistent with 84 A. Kamrani et al 17.5*** other wetland or terrestrial studies (Kessler 2000;Vetaas & Grytnes 2002;Hájek et al 2008;Noroozi et al 2008;Naqinezhad et al 2009). Many of wetland species, ca.…”