In this work we analyse the pollination community in a South American forest known as 'talar'. This is a vegetal woody community that inhabits fossil coastal banks characterized by seasonal temperate weather and calcareous soil, at the coast of the Río de la Plata, in the province of Buenos Aires, Argentina. We obtained data of the interactions between anthophylous insects and entomophylous flowering plants over an extensive period of time. We showed that pollination system parameters, such as partners' identity, system size, and connectance, fluctuated among months, when sampled year-long. Maximal network size occurred in early spring and early autumn, when both the number of mutualistic species and the number of interactions peaked, and this was also when network asymmetry was higher than average. Monthly connectance of the plant-flower visitor matrix decreased to its lowest values at these peaks. Available data suggest that cumulative traditional connectance (i.e. the connectance calculated as the whole number of interactions registered in the community divided by the full size system) underestimates actual connectance values by a factor of c. 3 ×. Monthly values of connectance decreased exponentially as system size increased, and the distribution of interactions per species followed powerlaw regimes for animals, and truncated power-law regimes for plants, in accordance with patterns previously deduced from among-network cumulative communities studies. We think that either within or and among pollination networks, systems that are organized as power-law regimes may be a basic property of these webs, and provide examples of the fact. Both seasonal changes and interactions between mutualists like competition, and some degree of facilitation, may be very important to understand the performance of the system as a whole, and the role and importance of different species in the community. We suggest that communities of plant -pollinators that exhibit extended activity, such as temperate or tropical seasonal ones, should be studied through consecutive plant-pollinator webs rather than cumulative ones. The partition of the system into smaller serial parts allows us to obtain outstanding information of every short period. This information is flattened by the average effect when we considered the combined analysis of the whole data.

We examined diurnal and nocturnal nectar secretion across sexual stages in protandrous Alstroemeria aurea, a bumble bee-pollinated herb with long-lived flowers native to the southern Andes. We found the following patterns: (1) most nectar was produced diurnally and (2) three times more sugar was secreted during the male than female phase, not only because the male phase lasted longer but also because the rate of nectar production was higher. This 3:1 ratio in nectar production matched the ratio of the minimum number of bumble bee visits required on average to saturate male (pollen removal) vs. female (seed set) functions. Standing crop of nectar, on the other hand, did not differ greatly between male- and female- stage flowers left open to visitors, because the high-production male-phase flowers were visited more frequently than female- phase flowers. In an experiment concurrent with the repeated nectar sampling of individual flowers over their life-span, we removed pollen from anthers or deposited pollen on stigmas by hand. Neither treatment, designed to mimic effects of visits by Alstroemeria's native bumble bee pollinator, affected nectar production. The absence of plasticity in nectar secretion in relation to pollination events may reflect a low cost of nectar production, or may result from developmental constraints related to the evolution of the synchronous protandry that characterizes A. aurea.

Although dichogamy is a prevailing feature of the angiosperms, the simultaneous change from male to female phases among hermaphrodite flowers within a plant (i.e., synchronous protandry) has been reported for only a few families (e.g., Araliaceae, Umbelliferae). Here we present an example of synchronous protandry at the ramet level in the Alstroemeriaceae. Dichogamy was analyzed in clonal Alstroemeria aurea at the flower, ramet, and at the whole flowering patch level. Alstroemeria aurea is self-compatible but totally dependent on biotic agents for pollen transfer. There was evidence of strong inbreeding depression expressed during seed development. Comparisons of seed set in open-pollinated flowers with those obtained after hand selfing and outcrossing resulted in a selfing rate of 0.3. At the flower level protandry was complete. The male phase lasted about 4 days and the female phase lasted about 3 days. Between the female and male phase, there was an approximately 1-day long "neuter" phase. Flowering ramets produce a terminal inflorescence bearing one or more whorls of flowers. Within a ramet, flowers of the same order opened within a period of 1–2 days, and male and female phases of different flowers did not overlap. When inflorescences held two whorls of flowers, the ramet went through two alternating non-overlapping male–female cycles. Using spatial autocorrelation techniques, we found little evidence for pairs of neighboring ramets expressing the same sexual phase beyond random expectations at any scale ranging between 0.25 to 15 m. By ensuring pollen interchange between flowering ramets, synchronized protandry at the ramet level could be an important feature in reducing selfing in A. aurea. Key words: Alstroemeria aurea, dichogamy, synchronous protandry, inbreeding depression.

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