Abstract
In their recent paper published in Science (2016, 351, 1437–1439), Chan et al. analysed 137 montane gradients, concluding that they found a novel pattern—a negative relationship between mean elevational range size of species and daily temperature variation, which was claimed as empirical evidence for a novel macrophysiological principle (Gilchrist's hypothesis). This intriguing possibility was their key conceptual contribution. Unfortunately, as we show, the empirical evidence was flawed because of errors in the analyses and substantial sampling bias in the data. First, we re-ran their analyses using their data, finding that their model should have been rejected. Second, we performed two additional re-analyses of their data, addressing biases and pseudoreplication in different ways, both times again rejecting the evidence claimed to support Gilchrist's hypothesis. These results overturn the key empirical findings of Chan et al.'s study. Therefore, the “macrophysiological principle” should be regarded as currently remaining unsupported by empirical evidence.
Highlights
Numbers: Number of words, number of cited references = 19; number of figures = 3
40°S or N) of 137 montane gradients to relate mean elevational range size of species to their measures of seasonal temperature range and diurnal temperature range simultaneously. They claimed that they found a novel pattern in their study: diurnal temperature range negatively affects mean elevational range size (Fig. 1B)
The diurnal temperature range and mean elevational range size variables are not correlated with each other (r = -0.039, P = 0.651; Fig. 1A)
Summary
The diurnal temperature range and mean elevational range size variables are not correlated with each other (r = -0.039, P = 0.651; Fig. 1A). Chan et al constructed 29 path models, selecting as ‘best’ one that generates a weak (R2 = 0.06; P = 0.012) direct effect of diurnal temperature range on mean elevational range size (Fig. 1C); note that the ‘R= -0.25’
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