Range size, the ‘fundamental unit’ of macroecology, is generally geographically limited, and few species are ubiquitously distributed, even for microorganisms (e.g., bacteria and diatoms). The systematic variation in range size along geographical gradients (i.e., elevation or latitude) represents an important underlying driver of species richness patterns. Species elevational range size has been theorized to increase towards higher elevations; this prediction has been known as the elevational Rapoport’s rule (Stevens, 1992) and represents an extension of the latitudinal Rapoport’s rule, which suggested that climate variability may be the underlying mechanism for range size.
In order to study how and why species range size is constrained, we examined patterns of range size of stream microbes (i.e., bacteria and diatoms) and macroorganisms (i.e., macroinvertebrates) along elevational gradients in Asia and Europe. There were six streams for bacteria and diatoms and four streams for macroinvertebrates along mountainsides in three regions (Wang et al 2017): (1) one stream in the Balggesvarri Mountain region, (2) one stream in the Pyrenees Mountains in Spain, and (3) four streams in the Hengduan Mountain region in China. Macroinvertebrates were sampled only in the Hengduan mountain region.
Our results highlight five main findings.
(1) Phylogeny cannot predict species elevational range in bacteria.
(2) There was a consistent and general relationship between niche breadth and species elevational range size across all taxonomic groups, and both local environmental and climatic variables contributed strongly to these relationships.
(3) We found that no taxon follows the elevational Rapoport’s rule, indicating that species elevational range size did not increase towards higher elevations.
(4) At the community level, climate variability was the most dominant factors for explaining mean elevational range size in microbes, whereas local environmental variables were more important than climatic variables for explaining range size in macroinvertebrates.
(5) Daily climate variation related positively with elevational range size for all taxa, while longer-term climatic variability scaled negative with range size, which is contrary to Chan et al’s (2016) major findings of the influences of climate variability with different temporal scales.
We discuss these main findings in detail in a recent Environmental Microbiology paper (Wang & Soininen, 2017).
References:
Chan W-P, Chen I-C, Colwell RK, Liu W-C, Huang C-y, Shen S-F (2016). Seasonal and daily climate variation have opposite effects on species elevational range size. Science 351: 1437-1439.
Stevens G (1992). The elevational gradient in altitudinal range: an extension of Rapoport's latitudinal rule to altitude. Am Nat 140: 893-911.
Wang J, Meier S, Soininen J, Casamayor E, Tang X, Yang X et al (2017). Regional and global elevational patterns of microbial species richness and evenness. Ecography 40: 393-402.
Wang J, Soininen J (2017). Thermal barriers constrain microbial elevational range size via climate variability. Environ Microbiol DOI: 10.1111/1462-2920.13823 On-Line