Norberto H. Montaldo

Effects of agriculture expansion and intensification on the vertebrate and invertebrate diversity in the Pampas of Argentina

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 grazing-cropping 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.

Exito reproductivo de plantas ornitócoras en un relicto de selva subtropical en Argentina

En un relicto de selva riberena situado en la region central de Argentina (Punta Lara, provincia de Buenos Aires) se estudio la fenologia reproductiva, y la produccion y dispersion de diasporas de cinco especies arboreas nativas y de dos malezas exoticas (Rubus ulmifolius y Ligustrum lucidum). Ademas se determino el poder germinativo de las semillas y la tasa de reclutamiento y caracteristicas de las plantulas. En el ultimo medio siglo las malezas invadieron la selva, amenazando actualmente con destruirla. El elenco de aves frugivoras del area es reducido y esta integrado por siete especies residentes y una migratoria. Hay plantas nativas que manifiestan limitaciones reproductivas por escasa produccion y/o dispersion de diasporas. Si bien las plantas exoticas no superan significativamente a las nativas en las relaciones fruto/ flor y frutos consumidos/ frutos disponibles, las primeras tienen ventajas en la cantidad de semillas que incorporan al medio por unidad (m2) de superficie de copa (ca. 1700 vs. 800 en la nativa que mas dispersa), y en su germinacion abundante (Ligustrum) o en la habilidad competitiva de sus plantulas (Rubus). El exito de las malezas se explicaria en gran parte por su agresividad intrinseca y por la situacion de marginalidad ecologica de esta comunidad selvatica, ya que muchas especies se encuentran en el extremo meridional de su distribucion