Trade-offs are central to many topics in biology, from the evolution of life histories to ecological mechanisms of species coexistence. Trade-offs observed among species may reflect pervasive constraints on phenotypes that are achievable given biophysical and resource limitations. If so, then among-species trade-offs should be consistent with trade-offs within species. Alternatively, trait variation among co-occurring species may reflect historical contingencies during community assembly rather than within-species constraints. Here, we test whether a key trade-off between relative growth rate (RGR) and water-use efficiency (WUE) among Sonoran Desert winter annual plants is apparent within four species representing different strategies in the system. We grew progeny of maternal families from multiple populations in a greenhouse common garden. One species, Pectocarya recurvata, displayed the expected RGR – WUE trade-off among families within populations. For other species, although RGR and WUE often varied clinally among populations, among-family variation within populations was lacking, implicating a role for past selection on these traits. Our results suggest that a combination of limited genetic variation in single traits and negative trait correlations could pose constraints on the evolution of a high-RGR and high-WUE phenotype within species, providing a microevolutionary explanation for phenotypes that influence community-level patterns of abundance and coexistence.

Angert et al. Desert Annuals DataPhenotypic measurements of relative growth rate (RGR, measured based on change in leaf area per day) and water-use efficiency (as measured by carbon isotope discrimination, Delta, in ppm) for winter annual plants grown in a greenhouse common garden at Colorado State University. Note that Delta is negatively related to water-use efficiency. Design includes replicate individuals of up to 30 maternal families from each of 4-5 populations per each of 4 species. Species codes: STMI = Stylocline micropoides, PERE = Pectocarya recurvata, ERTE = Erodium texanum, ERLA = Eriophyllum lanosum. Population codes: TUMH = Tumamoc Hill, AZ; OPNM = Organ Pipe National Monument, AZ; SDNM = Sonoran Desert National Monument, AZ; SENT = Sentinel, AZ; RINC = Rincon Mountains, AZ; CALI = Californian populations (see manuscript for exact locations for each species). Climatic values for winter maximum temperature (Tmax_wt), winter minimum temperature (Tmin_wt), and winter precipitation (PPT_wt) were estimated based on latitude and longitude using the program ClimateWNA.AngertDAGreenhouseDryad.csv