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Data from: Trait responses to competition are mostly parallel among competitor plants but can cause convergence or divergence in key traits

Bebout, Julia1; Loaiza, Juliana1; Gillert, Alexander1; Cleland, Elsa1

Research facility: University of California San Diego
Published Jul 01, 2026 on Dryad. https://doi.org/10.5061/dryad.4qrfj6qqw

Data files

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Abstract

Plants competing for resources exhibit different traits than plants which are not. Phenotypic plasticity can shape competition by altering trait differences between competitors. Studies show that plastic traits may converge or diverge among competitors as competition intensifies. However, another possibility is that interacting species could exhibit similar trait shifts as competition intensifies (trait parallelism). We used a field experiment to assess trait responses and performance outcomes for six co-occurring native and invasive annual California grassland species when grown together at various densities. We grew one focal individual of each species in each plot and manipulated the identity and density of competitors, from bare ground to a dense lawn. Species displayed many trait responses to competitor density which depended on competitor identity more than focal species identity. Most trait responses were parallel among competing plants with no effect on trait differences between competitors. The exceptions were specific root length, which diverged among competitors with increased competitor density, root mass fraction and leaf dry matter content, which both converged among competitors with increased competitor density. Competitors’ effects on performance were not correlated with greater responses in any trait. A few traits displayed non-parallel responses among competing plants, altering trait differences between competitors. These traits may be of interest for future studies of plasticity's effects on competition or species coexistence.