Abstract
Although we understand how species evolve, we do not appreciate how this process has filled an empty world to create current patterns of biodiversity. Here, we conduct a numerical experiment to determine why biodiversity varies spatially on our planet. We show that spatial patterns of biodiversity are mathematically constrained and arise from the interaction between the species’ ecological niches and environmental variability that propagates to the community level. Our results allow us to explain key biological observations such as (a) latitudinal biodiversity gradients (LBGs) and especially why oceanic LBGs primarily peak at midlatitudes while terrestrial LBGs generally exhibit a maximum at the equator, (b) the greater biodiversity on land even though life first evolved in the sea, (c) the greater species richness at the seabed than at the sea surface, and (d) the higher neritic (i.e., species occurring in areas with a bathymetry lower than 200 m) than oceanic (i.e., species occurring in areas with a bathymetry higher than 200 m) biodiversity. Our results suggest that a mathematical constraint originating from a fundamental ecological interaction, that is, the niche–environment interaction, fixes the number of species that can establish regionally by speciation or migration.
Highlights
One of the most fundamental curiosities in biology is to understand what influences biodiversity and its spatial and temporal distribution (Gaston, 2000; Lomolino, Riddle, & Brown, 2006)
Some models have been proposed as part of the MacroEcological Theory on the Arrangement of Life (METAL) theory (Beaugrand et al, 2013, 2014, 2015; Beaugrand & Kirby, 2018a)
The model was designed to implement a set of basic ecological/climatic principles to test whether latitudinal gradients in species diversity might arise from the interaction between the ecological niches of species and spatiotemporal fluctuations in temperature and/or precipitation related to climate variability
Summary
One of the most fundamental curiosities in biology is to understand what influences biodiversity and its spatial and temporal distribution (Gaston, 2000; Lomolino, Riddle, & Brown, 2006). On land and in the sea, many taxonomic groups exhibit a latitudinal increase in species richness from the poles to the midlatitudes or the equator (Gaston, 2000; Lomolino et al, 2006; Tittensor et al, 2010). What causes these latitudinal gradients in species richness has been a topic of study and debate for decades (Rosenzweig & Sandlin, 1997), and more than 25 hypotheses have been proposed (Gaston, 2000). Neither natural selection nor speciation alone can explain (a) why there are more species on land than in the sea, (b) why there are different latitudinal biodiversity gradients (LBGs) exhibited on land (narrow maximum at the equator) and in the ocean
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