Individual plant traits are often assumed to be linked in a straightforward manner to plant performance and processes such as population growth, competition and community dynamics. However, little is known on how effects of these traits differ (i) depending on the context of other traits (e.g. different identity of species), and (ii) depending on other species in the community. Thus, the magnitude and direction of correlation between values of any particular trait and performance may differ among these contexts. To examine this, we used a spatially explicit, individual-based model of clonal plant population dynamics that includes traits of growth, resource allocation, response to competition, and architectural traits that determine spatial spread. We parameterized this model for four co-occurring species of a species-poor mountain grassland using field measurements of plant growth and architecture; interference parameters were obtained by fitting model predictions to a fine-scale time series of field data. The parameterized model was then validated with a separate set of fine-scale time series of field data. In the virtual community composed of these four species, we changed values of individual traits of generative reproduction, vertical growth and architecture, and examined effects of these changes on (i) performance of the species with the trait changed, and (ii) performance of the co-occurring species.
First, effects of individual traits strongly differed; traits can thus be scored as to their effect on community structure and dynamics. Further, effects of each single trait examined on its bearer performance differed across species; the context of other traits thus interacts with the net trait effect. Comparison of trait effects in monoculture with the effect on the whole community showed that within community effect of the trait cannot be predicted from its monoculture effect. Correlation between the monoculture- and community-effect of a trait was stronger for traits of generative reproduction and/or of vertical growth, and weaker for architectural traits. Spatial pattern and abundances were affected by trait changes independently of each other. The results show that even in a simple herb community, trait values per se cannot be used to predict species performance and community dynamics in a straightforward manner.
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