Analyzing variability in nectar amino acids: composition is less variable than concentration.

Thirty species of flowering plants were analyzed for floral nectar amino acid composition. High-performance liquid chromatography (HPLC) was used in conjunction with AccQtag derivatization to produce accurate and precise data. For any one species, the total concentration of amino acids varies greatly (average coefficient of variation 0.65), but composition is much less variable (average correlation among samples from a single species 0.85). Absolute concentration of individual amino acids is much more variable than the relative abundance (coefficients of variation 0.98 and 0.77, respectively; N = 544, t = 16.98, P < 0.001). When amino acids that occur in only small relative abundance (<1%) are removed from the analysis, the difference is even more marked (0.78 and 0.51, respectively; N = 344, t = 15.13, P < 0.001). The results highlight the need for large sample sizes when making observations concerning the absolute amounts of amino acids in nectar and for sensitive analyses of the composition, as even small changes may be biologically significant.