Facilitation promotes changes in leaf economics traits of a perennial forb.

Optimal allocation of resources is crucial to maximize plant success. Plants modify their economic strategies by adjusting functional traits in response to shifts in environmental conditions. Facilitation has been recognized as a major biotic filter of trait distribution in communities, although the effect of facilitation on intraspecific variability has been scarcely explored. We evaluated intraspecific shifts in leaf functional traits of a perennial forb (Helleborus foetidus) in relation to the presence of a nurse plant (Juniperus sabina) in two sites with contrasting abiotic stress levels. The effects of abiotic (site) and biotic (juniper presence, microsite) environments on specific leaf area (SLA), leaf area (LA), lamina/petiole length ratio (LPR), intrinsic water use efficiency (iWUE) and leaf nutrient content (N, P and N:P) per mass were evaluated. Alleviation of drought stress associated with nurse plant presence was reflected in SLA, LA, LPR and iWUE at the high-stress site. Individuals growing in open areas showed more resource-conservative traits, supporting the argument that this strategy is advantageous in environments that limit opportunities for rapid carbon gain. Leaf nutrients were unrelated to other traits. The large amount of intraspecific variation in leaf functional traits related to facilitative processes highlights the importance of facilitation as a major source of plant trait variation. Both positive and negative biotic interactions, as well as intraspecific trait variability, should be considered in mechanistic models of plant communities' functional responses to environmental changes.

Continuous within-plant variation as a source of intraspecific functional diversity: Patterns, magnitude, and genetic correlates of leaf variability in Helleborus foetidus (Ranunculaceae).

PREMISE OF THE STUDY: Continuous within-plant variation in quantitative traits of reiterated, homologous structures is a component of intraspecific variation, but its contribution to functional diversity remains largely unexplored. For the perennial Helleborus foetidus, we measured functional leaf traits to quantify the contribution of within-plant variation to intraspecific functional variance and evaluate whether within-plant variability itself deserves separate consideration. METHODS: Within-individual variation in eight leaf traits was quantified for 138 plants sampled from 10 widely spaced locations in the Sierra de Cazorla, southeastern Spain. An amplified fragment length polymorphism (AFLP) technique was used to look for associations between within-plant variability and specific AFLP markers. KEY RESULTS: Leaflets from basal positions in ramets were longer, heavier, had greater surface area and larger stomata, and lower specific area, stomatal index, and stomatal density than those from distal positions. Continuous variation between leaves from the same ramet was the main source of population-wide variance for most traits. Within-plant variability differed among populations. Individuals differed in within-plant variability, which was largely independent of trait means and associated with genetic characteristics. Up to four AFLP markers were associated with the within-plant variability level of a given leaf trait. CONCLUSIONS: Subindividual variability in continuous leaf traits was independent of plant means and related to genetic features. The within-individual component generally exceeded the between-individual component of intraspecific variance. Within-plant variation may broaden the ecological breadth and enhance stability and persistence of plant populations and communities and may provide novel insights when incorporated in trait-based community ecology models.

Conflicting selection on diaspore traits limits the evolutionary potential of seed dispersal by ants.

Conflicts of selection on diaspore traits throughout the dispersal cycle can limit the evolutionary consequences of seed dispersal. However, these conflicts have never been investigated in directed dispersal systems. We explored conflicts of selection through life stages of dispersal in the myrmecochorous herb Helleborus foetidus. Seeds are subject to two contrasting partial selective scenarios. Undispersed seeds are subject to positive directional selection on seed size characters, whereas seeds dispersed are subject to stabilizing selection for size. In both scenarios, seedling establishment determined the magnitude and direction of selection. This does not reflect ant preferences for seed size. However, total selection still depends largely on ant activity, as ants control the relative importance of each selective scenario. We advocate the use of analytical approaches combining multiplicative fitness and microenvironment-specific selection to more realistically estimate the realized selection on traits functional during several life stages. This approach may be extended to any organism dispersing offspring to different environments.