Data from: Large niche differences emerge at the recruitment stage to stabilize grassland coexistence

Niche differences and average fitness differences jointly determine
coexistence. However, little empirical information about the magnitude of
these two mechanisms is available. Using multispecies population models
fit to long-term demographic data for common, co-occurring species in five
grassland and shrubland plant communities in western North America, we
estimated the strength of stabilizing niche differences and average
fitness differences. In all five communities, both pairwise and full
community comparisons showed evidence for strong stabilizing mechanisms
and relatively small average fitness differences. For a total of 17
species pairs, a measure of niche differences based on simulations of
invasion growth rates ranged from 0.59 to 0.93 with a mean of 0.81, where
0 indicates complete niche overlap and 1 indicates zero niche overlap. A
corresponding measure of average fitness differences ranged from 1.02 to
2.54 with a mean of 1.53, where 1 indicates identical fitness and a value
of 2 indicates a four-fold difference in sensitivity to competition.
Comparisons of full communities displayed similar patterns: niche
differences ranged from 0.58 to 0.69 with a mean of 0.64, and the average
fitness differences ranged from 1.42 to 1.63 with a mean of 1.47. In
almost every case, the stabilizing mechanisms were much stronger than
minimally necessary to prevent competitive exclusion. Considering that all
but one of the species we studied are perennial grasses, which are often
grouped in the same functional type, the magnitude of these niche
differences is surprising. In all five communities, differences between
intra- and interspecific effects at the recruitment stage contributed far
more to stabilization than interactions affecting growth and survival. Our
results indicate that for these abundant, co-occurring species 1) dynamics
are far from neutral, with strong niche differences and weak fitness
differences combining to stabilize coexistence, and 2) processes operating
at early life stages account for a large proportion of the stabilizing
effect. Given the limitations of our inductive approach, both these
findings represent hypotheses in need of experimental testing.