Temporal, spatial and biotic variations in extrafloral nectar secretion byMacaranga tanarius

1. Many plants produce extrafloral nectar (EFN) to nourish ants and other a nimals which defend them against herbivores. We aimed to find reasons for t he high variability in amounts of EFN produced by most plant species. We in vestigated the influence of several biotic and abiotic factors (time of day , leaf age, nectar removal and leaf damage) on secretion rates of EFN in th e common south-east Asian pioneer tree species, Macaranga tanarius (L.) Mue ll. Arg. 2. In most experiments leaves were washed with pure water and bagged in net s to protect them against nectar-collecting insects, and nectar was collect ed and quantified 24 h later. Six soluble sugars and up to eight amino acid s were detected in nectar samples derived from untreated, field-grown plant s. Total amounts of soluble substances varied more than the relative compos ition of EFN. 3. Nectar secretion rates were highest on young, expanded leaves. A diurnal pattern with a secretion peak in the first 2 h after dusk was detected in the field. Nectar removal had a positive effect and its accumulation a nega tive effect on further EFN production. Artificial leaf damage (punching lea ves with a needle or removing parts of the leaf blade with scissors) led to a significant induction of EFN production for the next 3 days. 4. Extrafloral nectar of M. tanarius was secreted in complex patterns influ enced by different biotic and abiotic factors; its production appeared to b e adapted temporally and spatially in order to ensure optimal use of invest ed resources.