Methods
We assembled a niche model dataset of 72,372 American seed plants based
on digitized and georeferenced specimen records. We used this dataset to
quantify occupied abiotic niche space with regards to temperature,
precipitation, and elevation. This approach further permitted
differentiation of higher-elevation specialists (i.e., ranges centered
at high elevations) from generalists (i.e., ranges centered at lower
elevations but extending into mountain areas).