4.4 Applicability of hypotheses for elevational patterns
The results of the discrete mid-domain effect model revealed that the
alpha diversity of all the plant groups differed from those expected by
the mid-domain effect hypothesis (Figure 1). Furthermore, we found no
relationship between the elevational range and alpha diversity of all
the plant groups, and none of the plant groups had a wider elevational
range in the alpine area (Figure 4), which contradicted those expected
by Rapoport’s elevational rule.
The lack of applicability of the mid-domain effect and Rapoport’s rule
to elevational patterns is attributed to the simple assumptions of these
hypotheses; the former excludes any effects of gradients on expected
patterns (Colwell, Rahbek, & Gotelli, 2004), whereas the latter fails
when species distribution is affected by the interaction of several
factors including climate (Bhattarai & Vetaas, 2006; Grau, Grytnes, &
Birks, 2007). Specifically, in the study area, strong winds and heavy
snowfall at higher elevations increased the differences in climate
between lower and higher elevations. These differences can enhance the
influence of climate and the related plant-plant interactions on the
elevational patterns of plants.