(1) Environmental conditions experienced in the past may lead to intraspecific differences

in ecological and chemical traits of plants, which likely affect future responses to

altered or new environments. Whether competition by neighbors is such a trait-shaping

factor is not yet well-known. We aimed to understand how the level of ancestral plant

competition affects traits related to plant fitness and resource allocation, reproduction,

and (phyto-)toxin accumulation in offspring, and whether a potential differentiation in

these traits can be found in different geographic origins of which one belongs to the native

and one to the invaded range. (2) We compared differentiation of the following traits in

offspring plants of multiple populations in Erodium cicutarium (Geraniaceae): biomass,

seed production, seed traits related to dispersal and germination, and concentrations

of foliar mono- and sesquiterpenes. We tested the allelopatic potential of aqueous

extracts of the same E. cicutarium plants on seeds of five different plant families. (3)

In plants originating from populations that experienced high levels of competition, we

found twice as high monoterpene concentrations. These plants also produced more

biomass and a higher proportion of ripe to unripe seeds until harvesting. Seeds originating

from high competition sites were shorter. Aqueous E. cicutarium leaf extracts with

high terpenoid content reduced radicle length of Zea mays and radicle and hypocotyl

length of E. cicutarium seedlings. (4) The results of this study provide first evidence

that the surrounding vegetation may shape chemo-ecological plant traits that may be

fundamental for competitive ability. Our study calls for more research testing whether

competition experienced in the native range may lead to an enhanced capability of plants

to establish populations and spread in a new range.