Non-directional rescue effect
The rescue effect emphasizes that the proximity of the range margins of
potentially interacting species can impact species richness (Stevens,
1992). Our results detected a positive correlation between inflow
intensity and species richness along the elevational gradient (Figure
4a), which indicated that the richness “hump” in the middle elevation
of Lebu Valley should be “rescued” by the species from the lowland and
highland simultaneously (non-directional rescue effect). Furthermore,
the inflow intensity in the low elevations was higher than that in the
high elevations, which indicated that the left-skewed species richness
hump towards lower elevation in the Lebu Valley could be explained by
the stronger inflow intensity in the low elevations.
Studies have shown that the hump-shaped pattern is one of the most
common (about 50%) elevational species richness patterns (Rahbek,
1995). Particularly, most of the recent studies on terrestrial
vertebrates in the Himalayas have discovered a consistent hump-shaped
elevational richness pattern across taxa (e.g., Acharya, Sanders,
Vijayan, & Chettri, 2011; Ding et al., 2019; Hu et al., 2017; Pan et
al., 2016; Joshi & Bhatt, 2015).
However, studies are often
fascinated by the relationship between environments (e.g., climate and
productivity) and biodiversity, and few studies have explored another
form of explanation for species richness pattern, such as species range
size and the interaction between
species richness and species range size. To better understanding the
relationship between species richness and species range size, the rescue
effect should be tested in more regions.