Abstract
Disentangling contributions from co-varying environmental variables is likely crucial for understanding the drivers of biodiversity patterns, including latitudinal diversity gradients. Here, we describe a novel use of wavelet power spectra to separate wavelength-dependent trends as a function of position on Earth’s surface. Spectra reveal scale- and location-dependent coherence between species richness and topography (E), mean annual precipitation (Pn), temperature (Tm) and annual temperature range (ΔT). Greater than 97% of species richness of carnivorans, bats, songbirds, hummingbirds and amphibians (which encompass ~ of terrestrial vertebrate species) are generated at large scales, i.e. wavelengths ≳ 103 km. 30–69% is generated at scales ≳ 104 km. At these scales, richness across the Americas, the longest transect examined, tends to be highly coherent and anti-phase with E and ΔT (i.e. one high, the other low), and in-phase with Pn and Tm (e.g. both high or both low). Coherence between carnivorans and ΔT is low across all scales, which suggests insensitivity to seasonal temperature variations. By contrast, amphibian richness is strongly anti-correlated with ΔT at large scales. At scales ≲ 103 km, examined taxa, except carnivorans, show highest richness within the tropics. Terrestrial plateaux (e.g. Colorado, Altiplano) are foci of high coherence between carnivorans and E at scales ~ 103 km, which is consistent with the notion that large-scale tectonic processes contribute to local biodiversity, even for carnivorans. These results are similar to those obtained from transects across Africa, Eurasia, Australia and average global latitudinal transects. They highlight scale-dependent sensitivities of mammal, bird and amphibian populations to local environments and global climate.
Significance Statement Understanding connections between environment and biodiversity is crucial for conservation, identifying causes of ecosystem stress, and predicting population responses to changing environments. Explaining biodiversity requires an understanding of how species richness and environment co-vary across different scales. Here, we apply wavelet power spectral analysis to terrestrial latitudinal transects, in order to identify scales and locations at which biodiversity is generated. Terrestrial species richness is found to be highly scale-dependent. Coherence with elevation, mean annual precipitation and temperature depends on scale and location. These results highlight the importance of global-scale climate for determining distributions of mammals, birds and amphibians. Smaller-scale climatic changes are increasingly important within the tropics, especially for groups such as bats, hummingbirds, and amphibians.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
C.O. and G.R. designed the project, developed code, interpreted results and wrote the manuscript with contributions from P.M., Y.W., J.H.; C.O performed the analyses and generated figures.
The authors declare no competing interests.