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Establishing laws of plant and ecosystems functioning has been an overarching objective of functional and evolutionary ecology. However, most theories neglect the role of human activities in creating novel ecosystems characterized by species assemblages and environmental factors that are not observed in natural systems. We argue that agricultural weeds, as an emblematic case of such an 'ecological novelty', constitute an original and underutilized model for challenging current concepts in ecology and evolution. We highlight key aspects of weed ecology and evolutionary biology that can help to test and recast ecological and evolutionary laws in a changing world. We invite ecologists to seize upon weeds as a model system to improve our understanding of the short-term and long-term dynamics of ecological systems in the Anthropocene. Agricultural weeds constitute an original model to understand the impact of anthropogenic changes on ecological and evolutionary dynamics. A combination of environmental factors in cultivated fields has driven the selection of novel functional trait combinations in agricultural weeds. Therefore, agricultural weeds can be considered as rule breakers of ecological and evolutionary laws. Weeds in cropped fields are particularly valuable for assessing the consequences of out-of-equilibrium and transient dynamics on community assembly. Weed herbicide resistance and crop mimicry syndromes represent some of the best-documented examples of rapid evolution in plants and provide a promising context for the study of eco-evolutionary feedbacks. [ABSTRACT FROM AUTHOR]

Highlights • The magnitude of impact of an invasive plant depends on resident species traits. • Resident species that use a different temporal niche can coexist with the invader. • Trait values conferring high competitive ability allow coexistence with the invader. • Communities where the invader was removed recovered rapidly high species richness. • These communities still display different trait values than reference communities. Abstract It is well known that alien plant invasion modifies the composition and diversity of resident plant communities, yet our ability to predict patterns of vegetation responses to invasion is hampered by a poor understanding of which functional traits make some resident plants more or less vulnerable to invader impacts. For example, resident species may be more likely to persist and coexist with the invader if they display different strategies of resource use (i.e. high niche differences) or if they share similar highly competitive traits (i.e. competitive hierarchy). Here, we used a trait-based approach to 1) specifically test whether species changes in abundance following plant invasion is random or depends on specific functional trait values, 2) identify which functional strategies allow resident species to coexist with the invader and 3) assess to what extent communities where the invader has been removed return to a reference state. To do so, we applied a semi-experimental approach with the annual vine Humulus japonicus , an invasive species in riparian habitats of Southern France. We monitored plant communities seven times over two years in non-invaded reference plots, invaded plots and removal plots in which the invader had been removed at the seedling stage. We quantified species richness and functional richness as well as mean community trait values of seven traits. The comparison of invaded and removal plots highlighted a strong impact of Humulus japonicus on both species and functional richness of riparian communities. Resident species that had a distinct flowering onset from the invader faced less pronounced declines. Specifically, species that flowered before the invader reached high cover, and species that had a short flowering duration had lower risk of declining. In addition, species coexisting with the invader when it reached its maximum cover displayed high stature and high seed mass. These results suggest that both niche differentiation (in terms of flowering strategy) and competitive hierarchies (in terms of height and regeneration strategy) play a role in explaining plant community responses to plant invasion. Finally, while species richness recovered rapidly in removal plots, functional richness remained lower than in non-invaded plots, pointing to a state-shift that would otherwise go undetected. Overall, our study highlights that the analysis of the functional traits of both invaders and resident species, combined with regular monitoring over time of non-invaded reference plots, invaded and removal plots can greatly improve our understanding of the impact of plant invasion on resident communities. [ABSTRACT FROM AUTHOR]