Fitness differences override variation-dependent coexistence mechanisms in California grasslands

While most studies of species coexistence focus on the mechanisms that maintain coexistence, it is equally important to understand the mechanisms that structure failed coexistence. For example, California annual grasslands are heavily invaded ecosystems, where non-native species have largely dominated and replaced native communities. These systems are also highly variable, with a high degree of rainfall seasonality and interannual rainfall variability – a quality implicated in the coexistence of functionally distinct species. Yet, despite the apparent strength of this variation, coexistence between native and non-native annuals in this system has faltered. It is therefore uncertain to what degree rainfall variation can offset average fitness differences between native and non-native annual plants in California grasslands to promote coexistence, nor what coexistence mechanisms are most relevant. To test these dynamics, we implemented a competition experiment between five annual species o..., Datasets contain plant phytometer and background competitor stem counts, biomass, and allometric fecundity estimates from a 6-species surface-response competition experiment in a California annual grassland. The six species were: Avena fatua (introduced annual grass), Bromus hordeaceus (introduced annual grass), Vulpia myuros (introduced annual grass), Trifolium hirtum (introduced annual, nitrogen-fixing forb), Lasthenia californica (native annual forb), and Eschscholzia californica (native annual forb). The competition experiment took place in year 3 (Fall 2016 - Spring 2017) of a 3-year (Fall 2014 - Spring 2017) seasonal drought manipulation study at Sierra Foothill Research and Extension Center (SFREC), Browns Valley, California (field coordinates: 39.25117507590813, -121.31116918773333). See Shaw et al. 2022 for details on the overarching 3-year seasonal drought experiment. Competition experiment and data processing abbreviated methods are described next. See Muehleisen et al. 2024 ..., , # Fitness differences override variation-dependent coexistence mechanisms in California grasslands

[https://doi.org/10.5061/dryad.j3tx95xqk](https://doi.org/10.5061/dryad.j3tx95xqk)

## Description of the data and file structure

This data was collected in a field experiment implemented 2016-2017 (Brown's Valley California), in which phytometers of each of six species were grown in a pairwise competitive background of one of the other competitors. They were grown under two treatments: rainfall exclusion and no rainfall exclusion over the growing season (October to April) and then harvested to measure growth and seed production.

### Files and variables

DATA-SPECIFIC INFORMATION FOR: Competition_allometric_clean.csv

Description: OLS linear regression intercept and beta estimate (slope) with associated statistics for each of 6 species allometric regressions. One regression run per species using form 'lm(seeds ~ 0 + biomass)'. Because we did not see strong significant differences in all...