It is a known fact among scientists that spatial distributions of fauna are sensitive to climate variabilities.  Classic ecological hypotheses have all suggested that greater seasonal climatic fluctuations will result in a wider geographic distribution for a species.  Proposed about a half century ago, these hypotheses have been heavily tested throughout the years.  However, scientists at NTU noted that animals experience not only seasonal climatic changes but diurnal meteorological dynamics as well; however, these daily variations are rarely addressed or investigated.

To address this subject, Prof. Cho-Ying Huang of the NTU Department of Geography recently participated in a collaborative study that spent over five years analyzing a global dataset studying the distribution of species.  Using new technologies to assess the influences that short-term physical environmental drivers have on a species’ elevational range size, the team was surprised to find that, in general, the size of a species’ elevational range is negatively correlated to the diurnal temperature range.  In other words, the greater the temperature variation, the narrower the species’ distribution range is recorded over different altitudes.  This result is the opposite of the effect of seasonal fluctuations.

The team, which includes Wei-Ping Chan, Sheng-Feng Shen, and Wei-Chung Liu of Academia Sinica, I-Ching Chen of National Cheng Kung University, and Robert Colwell of the University of Connecticut, had its results published in the prestigious international journal Science in March.

The climatic variability hypothesis states that organisms distributed across wider geographic ranges are associated with greater climatic variability.  Hence, tropical mountain species are recognized to be more susceptible to climate change than species in temperate regions because tropical species are inhabitants of stable climate regimes with narrower elevational range sizes.  However, this is inconsistent with what scientists have observed in the mountainous areas of tropical and near-tropical regions where daily temperature variability tends to be pronounced.

In order to investigate the comprehensiveness of this hypothesis, project leaders Shen and Chan organized a research team comprised of ecology theorists I-Ching Chen and Robert Colwell, statistician Liu, and spatial analyst Prof. Huang.  They applied structural equation modeling to investigate the relationships among climatic factors from high-resolution climatic spatial datasets and more than 16,000 species elevational range sizes on 180 montane gradients.  The study’s results reveal a novel macroecological rule: species elevational range sizes are influenced by diurnal and seasonal climatic variability in opposite ways.

In the past, assessments of the impact that climate change has on a species’ movements have focused mainly on long-term climatic trends, especially elevated temperatures.  By focusing on short-term daily variations, this study provides fresh insight that indicates a new direction for climate research.