Data for: Stronger niche than dispersal effects on α- and β-diversity of stream algae, insects, and fish across latitudes in the US

Aim: Niche and dispersal processes influence biodiversity, but their
relative importance along latitude is unclear. We predicted that: i) niche
processes would dominate at high latitudes due to increased climatic
stress, consistent with the physiological tolerance hypothesis and the
Dobzhansky-MacArthur hypothesis and ii) dispersal limitation would prevail
at low latitudes due to narrower niches and smaller range sizes, as
postulated by the dispersal-ecological specialization tradeoff hypothesis,
the latitude-niche breadth hypothesis, and Rapoport’s rule. 
Location: Central United States Time Period: 1993-2019 Major taxa studied:
Stream algae, insects, and fish Methods: We examined the relative effects
of environment (climate and physicochemistry) vs. space on stream
biodiversity in seven latitudinal zones, spanning 19 latitudinal degrees.
In each zone, species richness (α-diversity) was analyzed with multiple
regression and variance partitioning. Compositional dissimilarity
(β-diversity) within zones was assessed with distance-based RDA and
variance partitioning. Results: For α-diversity, latitudinal variability
of niche and dispersal processes conformed to our predictions in all three
groups, except for dispersal processes in insects. However, the drivers of
β-diversity did not follow our predictions. The latitude-niche breadth
hypothesis and Rapoport’s rule were weakly supported only in fish. Main
Conclusions: The importance of niche and dispersal processes varied
predictably along the latitudinal gradient only for α-diversity. However,
the niche effects were driven mostly by physicochemistry, and the
dispersal effects were not always linked with ecological specialization
and range size. This suggests that climate-based biodiversity theories do
not have particular relevance for the streams in our study. Niche
processes had a greater impact than dispersal processes across species
groups and diversity metrics, emphasizing the primary role of the
environment.