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.

In this paper we summarize for the first time the effects of agriculture expansion and intensification on animal diversity in the Pampas of Argentina and discuss research needs for biodiversity conservation in the area. The Pampas experienced little human intervention until the last decades of the 19th century. Agriculture expanded quickly during the 20th century, transforming grasslands into cropland and pasture lands and converting the landscape into a mosaic of natural fragments, agricultural fields, and linear habitats. In the 1980s, agriculture intensification and replacement of cattle grazingcropping systems by continuous cropping promoted a renewed homogenisation of the most productive areas. Birds and carnivores were more strongly affected than rodents and insects, but responses varied within groups: (a) the geographic ranges and/or abundances of many native species were reduced, including those of carnivores, herbivores, and specialist species (grassland-adapted birds and rodents, and probably specialized pollinators), sometimes leading to regional extinction (birds and large carnivores), (b) other native species were unaffected (birds) or benefited (bird, rodent and possibly generalist pollinator and crop-associated insect species), (c) novel species were introduced, thus increasing species richness of most groups (26% of non-rodent mammals, 11.1% of rodents, 6.2% of birds, 0.8% of pollinators). Much taxonomic and ecological work is still needed to understand Pampean animal biodiversity, to understand how agriculturization is affecting it, and to identify appropriate conservation actions. Networks of Important Bird Areas and Valuable Grassland Areas harbor a balanced representation of Pampean biodiversity and, if adequately protected, may provide valuable research sites, but complementary work should be carried out on agriculturized areas.

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Oils are atypical floral rewards in Orchidaceae and are produced by epidermal glands called elaiophores. Flowers of many members of the subtribe Oncidiinae either produce oil or mimic oil-producing flowers of Malpighiaceae. We focus our research on 3 species of Gomesa, namely, G. flexuosa, G. riograndensis, and G. varicosa in order to investigate the presence of elaiophores, their micromorphology and internal structure, and the process of oil secretion. Elaiophores were located using Sudan III and their internal and external features examined using light and scanning electron microscopy, respectively. The presence of elaiophores was confirmed for regions of calli that are prominent and exposed. In all 3 species the secretory tissue comprised a single layer of epidermal cells, together with some parenchymatous, subsecretory cells. Epidermal cells were isodiametric or palisade-like, with dense cytoplasm, small vacuoles, and prominent nuclei. Gomesa flexuosa differs from the other species investigated in that it bears intermediate elaiophores (i.e. epithelial and possessing unicellular, secretory trichomes). Based on the absence of a distended cuticle, we propose that oil may pass through the wall and cuticle as small lipid moieties. In addition, some evolutionary trends in the elaiophores in the genus Gomesa are suggested.

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Temporal changes of flesh flies abundance were simultaneously recorded at monthly intervals during a year in a woodland and in a grassland at the "Reserva Ecológica Costanera Sur" (RECS), Buenos Aires city, Argentina. Samples were taken at monthly intervals (February 2004-January 2005). Hourly captures of adult flies (10:00 am-04:00 pm) were taken each sampling date with a hand net. Temperature was recorded at each hourly capture. The baits used were 200 g of rotten cow liver and 200 g of fresh dog faeces. Records of abundance included only species whose abundance was ≥30 individuals accumulated during the whole sampling period. Considering overall abundance, a non-parametric Chi-square test was used to estimate deviations of an expected habitat and bait preference ratios of 1:1. The same criterion was applied to include species in a contingency table to describe their seasonality. The final matrix included four species whose associations to seasons were analyzed by using a Correspondence Analysis. To normalize the data, a log 10 (n+1) transformation was applied prior to the analysis of correlation. Pearson product-moment correlations were used to examine the relationship between flesh-fly abundance with temperature and habitat preference. The entire sample accumulated 1 305 individuals and 18 species. The flies were more abundant in the grassland than in the woodland. Microcerella muehni, Oxysarcodexia paulistanensis, O. varia and Tricharaea (Sarcophagula) occidua exhibited the higher relative abundance, representing the remaining species less than 8 % of the entire sample. Most of the recorded species showed preference for faces as bait. Concerning the dominant species, all of them but M. muehni, a suggestively termophobic species, prevailed in late spring-summer. The observed species arrangement at both sites indicates low species diversity and equitability and high information per individual in the average. The referred community traits would indicate the possible effects of environmental disturbance due to the proximity of study sites to dense urban settlements.

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The elaiophores of G. bifolia are of the epithelial type. The general structure of the secretory cells resembles that described for other species of Oncidiinae, but some unique features were encountered for this species. The oil appears to pass through the outer tangential wall and the cuticle, covering the latter without forming cuticular blisters.