Contrasting diversity-temperature relationships between the three domains of life along extreme thermal gradients

Background/Question/Methods

 The observed increase in taxonomic richness in most major groups of plants and animals with increasing environmental temperature from the poles to the equator is one of the few recognized general patterns or laws in ecology. However, a clear understanding of the precise mechanisms underpinning the latitudinal diversity gradient and its concordant temperature-diversity relationship has remained elusive. Because temperature is one of the most basic abiotic variables underlying geographic, physiological, and ecological patterns in diversity, understanding the mechanisms underlying the temperature-diversity relationship is crucial to interpreting latitudinal and altitudinal diversity gradient studies. Here we ask the questions: (1) What is the relationship between diversity and temperature across a wide range of temperatures that extends to temperatures hotter than those in the tropics?  (2) How does the biodiversity of the three domains of life making up communities change along temperature gradients? We address these questions by investigating patterns of biodiversity in streamer and microbial mat communities comprised of comprised of bacteria, archaea, fungi, microscopic metazoa, and protists along the thermal gradients of Yellowstone Nation Park hot springs, from 30 °C to boiling temperatures. We used the 16S rRNA gene to quantify diversity. 

 

Results/Conclusions

We found contrasting taxonomic richness-diversity relationships. Whereas Bacteria and Eukaryota decreased continuously in richness along the thermal gradients, Archaea increased continuously in richness from 30 °C to near-boiling temperatures.  The Jaccard index of similarity for pairwise comparisons of the taxonomic composition of Bacteria communities decreased as heir difference in temperatures increased, suggesting the importance of species-sorting and thermal niches in structuring their communities. Eukaryota exhibited similar patterns of diversity. In contrast, for a given temperature difference between pairwise comparisons, Archaea communities were less similar in taxonomic composition and similarity was less strongly dependent on temperature difference. The width of the thermal niches of taxa were found to be similar in Bacteria and Archaea but smaller in Eukaryota. Overall, our results highlight the importance of niches in explaining diversity-temperature patterns and suggest that the diversity-temperature theory based solely on the chemical kinetic effects of temperature, such as the metabolic theory of ecology, may insufficient for explaining macroecological pattens of diversity.