Germination phenology alters species coexistence outcomes

Species-specific phenological responses to changing climate are reshuffling the timing of species interactions, however, we don’t fully understand the consequences of these changes for species’ population dynamics and community composition. In this study, we experimentally manipulated the timing of germination for five annual plant species from southern California and used pairwise competition experiments and coexistence theory to quantify how phenological shifts may impact species interactions and coexistence. We found that phenological shifts may help promote coexistence when they confer an advantage for competitively inferior species, but in other cases promote dominance by competitively superior species. Earlier germination generally increased species’ performance relative to competitors, but the relative changes in intra-and inter-specific interactions caused more complex effects on niche and fitness differences. Phenological differences tended to reduce stabilizing niche differenc..., We studied five study species: two non-native grasses, Bromus diandrus (BRDI) and Bromus rubens (BRRU), and three native forbs, Lasthenia gracilis (LAGR), Nemophila menziesii (NEME), and Plantago erecta (PLER). The native species are common members of the herbaceous community, and the two non-native grasses are both species that are well-known to become abundant at the expense of local native species diversity and abundance.
These data come from a common garden competition experiment at the University of California, Riverside’s Agricultural Operations facilities, in Riverside, CA. The experiment was designed to calculate pairwise interaction coefficients (including intra-specific interactions) for all combinations of the five species, yielding 10 unique species pairs. Each study species was sown into three plots (1m2) at low, medium and high densities, to form a competitive density gradient for each species. Into each plot we sowed focal individuals of each species, establishing all pai..., , # Germination phenology alters species coexistence outcomes

[https://doi.org/10.5061/dryad.7pvmcvf2c](https://doi.org/10.5061/dryad.7pvmcvf2c)

#### Description of the data and file structure.

The core dataset contains individual plant seed production as a function of the composition and density of neighbors.

 **Variable definitions (in dataset):**

Phenology: Experimental treatment:  In \"focal first\" plots, the focal seeds were sown, and then three weeks later the competitor species were sown (Figure S1). Similarly, \"background first\" plots were established by waiting three weeks after sowing competitor species to introduce the focal species. Finally, a \"same time\" treatment was established by sowing focal plants and competitors at the same time, mid-way between the first and last dates. 

background.spp:  Identity of the competitor species:  *Bromus diandrus* (BRDI), *Bromus rubens* (BRRU), *Lasthenia gracilis* (LAGR), *Nemophila* *menziesii* (NEME), and *Plantago erecta* (PLER)

f...