Ecological gradients shape the evolution of plant functional traits through variation in climate, abiotic factors, and biological processes. While recent observations highlight elevation clines in functional trait variation, several traits vary independently of others and vary in species-specific manner thereby hindering community-level generalization. In this study, we examined whether whole plant communities at different elevations independently converge to elevation-specific trait values. Using a combination of field-derived trait quantification and a literature survey, we analysed eight functional traits relating to plant palatability (specific leaf area (SLA), leaf dry matter content, carbon to nitrogen ratio), and defenses (spines, trichomes, silica, and the relative importance of phenolic- or non-phenolic-based chemical defenses in plants) of plants growing along several mountain transects in Switzerland, and computed community-level means for each trait.
We observed a general decline of most defense traits in communities at high elevations. The individual traits’ patterns underlined a concerted decline of the physico-chemical defense syndrome at high elevation, and low SLA values at high elevation also indicate investment in the production of leaves with slow turnover rates. In addition, we found that high elevation plant trait values tend to converge, while at low elevation, to diverge.
Our data suggest that community-level defense syndromes along elevation gradients are influenced by ecological filtering. Lower herbivore pressures selects for reduced plant defenses, while harsh environmental conditions select for investment in tolerance-related traits. Secondly, since species are highly variable in their functional trait space within communities, niche-partitioning theory might explain which variabilities of the defense functional space are selected within communities, particularly at low elevation.