The climate variability hypothesis
According to the climate variability hypothesis, the species range size
expands as the stability of climatic conditions decreases (Stevens,
1989, 1992). Many studies have found evidence to support the climate
variability hypothesis (latitude: Letcher & Harvey, 1994; Köckemann,
Buschmann, & Leuschner, 2009; Morin & Lechowicz, 2013; Pintor, Lin, &
Krockenberger, 2015; elevation: Pintor, Lin, & Krockenberger, 2015;
Chan et al., 2016; Liang et al., 2020). Studies argued that this
positive relationship was probably caused by the physiological tolerance
of species (Kevin J. Gaston & Spicer, 2001). Species with wider
physiological tolerances are generally considered to have a wider niche
breadth, so the species can adapt to more habitats and thus have a wide
range of distribution (Brown, 1984).
Our result was inconsistent with the prediction of the climate
variability hypothesis (the annual temperature range was
negatively correlated with species
mean elevational range size along the elevational gradient in Lebu
Vally). There are many indicators to measure climate variability and
using different indicators to access the climate variability hypothesis
may lead to changes in the results. For example, seasonal temperature
range was also considered as a good indicator of climate variability,
and studies have shown that species range size could be positive
correlated with seasonal temperature range (e.g., Köckemann, Buschmann,
& Leuschner, 2009; Whitton, Purvis, Orme, & Olallatarraga, 2012; Chan
et al., 2016; Liang et al., 2020). Hence, we correlated
seasonal temperature range
(additional to annual temperature range) with the species range size,
and we also found that seasonal temperature range was negative
correlated with species range size (standardized beta
coefficient=-0.661, R ²=0.436, P <0.01), which was also
inconsistent with the prediction of climate variability hypothesis.
Climate variability is closely related to many other environmental
factors (e.g., productivity, habitat). The influence of climate
variability on species range size may have different manifestations
under different situations (Letcher & Harvey, 1994). For example, the
impact of unfavorable climate could be mediated by high productivity or
resources. Moreover, climate
variability also influences species range size in an evolutionary time
(Kevin J Gaston, 1996). However, studies have struggled to take all
these factors into account. Therefore, whether the climate variability
hypothesis is applicable to explain the mean range size of species
pattern (particularly regarding its generality when considering
elevation) remains further tested in different regions and taxa.