Data and code from: Geologic history explains freshwater fish species richness across the conterminous USA

Aim: Freshwater fishes comprise over 20% of vertebrate biodiversity
despite occupying <1% of the Earth’s surface. However, species
richness differs substantially among river basins. Fundamentally, richness
patterns can be explained by spatial variation in diversification rates,
evolutionary time, and habitat capacities, which are in turn shaped by
landscape change over geologic timescales. To test how geologic
disturbances have influenced the accumulation of freshwater fish
biodiversity, we hypothesized species richness would be (1) ordered by
regional geologic history, (2) associated with high or intermediate river
capture rates, (3) higher in assemblages with older evolutionary origins,
and (4) positively associated with stream size. Time period: 2008-2019.
Location: Conterminous United States (USA). Major Taxa: Freshwater fishes.
Methods: We analyzed native species richness from a spatially
representative survey of 5,321 fish assemblages at 3,609 sites. Geologic
history was determined from surrogates of tectonic activity, glaciation,
sea levels, and river capture over the last 66 million years, which were
paired with previously published evolutionary time estimates. Hypotheses
were tested with spatial linear models. Results: All hypotheses were at
least partially supported. (1) Rank-order richness matched hypothesized
effects of geologic disturbances on evolutionary time and diversification
rates. (2) Richness peaked in lowlands with high putative river capture
rates. (3) Richness increased with evolutionary time at broad scales, but
this relationship was weak and influenced by non-teleost taxa. (4)
Richness largely increased with stream size. Overall, the tectonically
active western USA exhibited lower richness, weaker effects of stream
size, and a greater share of young lineages compared to the more
geologically stable eastern USA, especially unglaciated lowlands within
the Mississippi Basin. Main conclusions: We demonstrate that deep-time
processes leave a persistent mark on fish species richness. Thus,
accounting for geologic history can improve assessments of freshwater
biodiversity and biological condition in the USA and beyond.