Closely related species differ in their traits, but competition induces high intra-specific variability

Theories explaining community assembly assume that biotic and abiotic filters sort species into communities based on the values of their traits and are thus based on between-species trait variability (BTV). Nevertheless, these filters act on individuals rather than on species. Consequently, the selection is also influenced by intraspecific trait variability (ITV) and its drivers. These drivers may be abiotic (e.g., water availability) or biotic (e.g., competition). Although closely related species should have similar traits, many of them coexist.
We investigated the relative magnitudes of BTV and ITV in coexisting closely related species and how their individual traits differ under different drivers of ITV.
We manipulated conditions in a greenhouse pot experiment with four common Carex species, where individuals of each species originated from four source localities. Individuals were grown in factorial combinations of two moisture levels, with and without a competitor (grass species Hol..., Species and localities
For our greenhouse experiment, we chose four common Carex species (Table S1 in Appendix) able to co-occur although they differ especially in preference of soil moisture (Ellenberg-type indicator value for moisture is 4 for C. caryophyllea, 5 for C. pilulifera, 6 for C. pallescens and 8 for C. panicea; Chytrý et al., 2018). These species are all perennial herbs, hemicryptophytes, commonly distributed in the South Bohemia region, where they were recorded in all 12 × 11 km quadrats of grid mapping and in the majority of their 6 × 5.5 km sub-quadrats (Pladias – database of Czech flora and vegetation, www.pladias.cz, access June 13, 2024; Wild et al., 2019). These species are able to co-occur, although they also often occur separately, especially in the case of C. caryophyllea which prefers drier habitats. Although these Carex species frequently co-occur in relatively small plots (2x2 m, personal observation), they seldom achieve high cover, and the main competitor is ..., , # Closely related species differ in their traits, but competition induces high intra-specific variability

[https://doi.org/10.5061/dryad.69p8cz9bh](https://doi.org/10.5061/dryad.69p8cz9bh)

## Description of the data and file structure

We conducted a greenhouse experiment with four closely related *Carex* species, from four different populations each, and measured their functional traits under water availability and competition treatments. We were interested in the size of intraspecific differences caused both by experimental treatments (competition, water availability) and by the origin of individual transplants (source locality), as well as how ITV compares to BTV of these species. We also compared traits measured in a greenhouse with traits measured in the source localities to disentangle the effect of individual factors (genetic versus environmental) influencing ITV. We aimed to answer the following questions to guide our experiment: 1) How are the traits of individual species aff...,