Integrated demographic strategies are more strongly associated with variation in conspecific density dependence than single traits in tropical tree seedlings

Abstract Conspecific negative density dependence (CNDD) is considered a key mechanism shaping species diversity in plant communities. However, species vary widely in CNDD strength, and the main ecological drivers of this variation remain unclear. We tested whether interspecific variation in CNDD is linked to (i) species' demographic strategies related to growth–survival and stature–recruitment trade‐offs, (ii) functional traits, including wood density, seed mass, maximum height and four leaf traits and (iii) species' relative abundance. Using 18 years of seedling mortality data (145,768 individuals, 260 tree species) from a tropical moist forest in Panama and a robust modelling framework that accounts for potential biases due to non‐linearities and variation in baseline mortality, we calculated species‐specific estimates of CNDD that quantify the effect of conspecific relative to heterospecific neighbours and tested for relationships between CNDD strength and demographic strategies, functional traits and relative abundance. CNDD strength varied widely across species and was significantly related to species location along both the growth–survival and stature–recruitment trade‐off axes. Fast‐growing species and tall, long‐lived pioneers exhibited stronger sensitivity to CNDD compared to slow‐growing and short‐lived species, respectively. With the exception of wood density, single functional traits were not significantly associated with CNDD strength. Rare species experienced stronger CNDD than common species. These findings underscore the importance of life‐history strategies over isolated traits in shaping density‐dependent effects, suggesting that CNDD variation could reinforce niche differences and influence community composition and species coexistence in tropical forests. Additionally, our results confirm that rare species experience stronger CNDD than common species at the seedling stage, suggesting that CNDD may constrain species abundances and shape tropical tree diversity. Synthesis . Our results show that, with the exception of wood density, single traits were weak predictors of CNDD strength, while integrated demographic strategies captured meaningful variation. CNDD is strongest in rare, fast‐growing and long‐lived pioneer species, suggesting that biotic interactions at early life stages align with key life‐history trade‐offs. Studies that assess and integrate links between CNDD and demographic trade‐offs across multiple life stages are needed to understand the combined impact of these mechanisms on tree communities.