Species richness patterns at the transition from the Tropics to the Subtropics: Studying environmental and historic effects
Evolution and Systematics of Plants and Fungi
Final Report Abstract
The main results of our study can be summarized in the following five points. First, overall latitudinal range size increased with increasing latitude. Second, range size decreased with elevation on the Atlantic slope but not on the Pacific slope. Third, range size decreased in areas with high humidity, low temperature seasonality and intermediate precipitation seasonality, as well as a constant cloud cover. Fourth, there was a strong difference in range size between the Pacific and Atlantic sides that was not captured by the climatic factors, with ranges on the Pacific side being much broader. Fifth, we found great variation between individual transects. Our results confirm our hypothesis that on average, latitudinal species ranges become wider at higher latitudes, presumably reflecting increasingly stressful and variable climatic conditions that require broader climatic tolerances of the species, resulting in larger ranges. This is a common pattern previously documented for animals, algae, and other plant groups mainly in the northern hemisphere, and while not fundamentally novel, it is confirmative for ferns and reflects the representativeness of our data. In contrast, our other hypothesis that range sizes should decrease with elevation was supported only on the Atlantic (Gulf of Mexico and Caribbean) side of Mexico, whereas on the drier Pacific side we detected no elevational trend. The decrease of range size with elevation has also been found in ferns in Costa Rica and Bolivia, and is likely linked to topographic complexity, leading to fragmented species ranges that foster allopatric speciation. This effect appears to be most pronounced in wet tropical climates or areas of favorable ocean currents that create refugia for endemics, as found on the Atlantic slope. In addition, formation of endemic species might also be related to past climatic fluctuations that led to successive periods of habitat connectivity and disruption, although this remains to be tested for the Mexican mountains.
Publications
- (2018). Additions to the pteridophyte flora of humid montane forests of Tabasco, Mexico. Acta Botanica Mexicana 124: 7–18
Carvajal-Hernández, C.I. Silva-Mijangos, L., Kessler, M. & Lehnert, M.
(See online at https://doi.org/10.21829/abm124.2018.1300)
