Enrique H. Bucher

Reliability of the in situ incubation methods used to assess nitrogen mineralization : a microbiological perspective

The reliability of in situ incubation methods to measure soil N mineralization was assessed by comparing the initial and final values for several soil parameters inside and outside the isolated soil containers laid in the ground for 2 weeks. We measured soil water content, ammonifying and nitrifying bacteria, soil respiration, and ammonium and nitrate content. Soil water content did not change inside the container, whereas in the surrounding soil significant differences were found, with varying magnitude and sign according to climatic conditions during the incubation period. Ammonifiers number and ammonium content did not change inside the container, whereas nitrifiers number, nitrate content, and soil respiration decreased significantly (49, 22 and 36%, respectively). When comparing container content and the surrounding soil, a similar pattern was found: ammonifiers number and ammonium content did not change, whereas nitrifiers and soil respiration were lower inside the container than in the outside soil (44 and 33%, respectively). At the end of the incubation period, nitrate contents inside the container correlated significantly with both number of nitrifying organisms and respiration rate. It suggests that aerobic processes inside the cylinder were affected, probably because of oxygen depletion due to microbial activity in a closed environment. We conclude that the in situ incubation methods underestimate the N mineralization rate in soils. Shortening the incubation period may minimize this source of error.

The Lizard Teius teyou (Squamata: Teiidae) as a Legitimate Seed Disperser in the Dry Chaco Forest of Argentina

We analyzed the occurrence and number of viable seeds in droppings of the lizard Teius teyou, and the influence of seed ingestion on the germination capacity of Ziziphus mistol seeds in dry Chaco forests of northwestern Argentina. Seeds were found in 59% of 607 droppings collected during the wet season, belonging to Ziziphus mistol (Rhamnaceae), Celtis pallida (Ulmaceae) and Capparis atamisquea (Capparaceae). Seeds of Z. mistol accounted for 98% of all seeds found in droppings. Seeds found in the droppings were viable, suggesting that lizards are legitimate seed dispersers. Passage through the lizards digestive tract did not enhance germination of Z. mistol seeds. Lizards appear to be efficient dispersers of Z. mistol given that they usually defecate in open areas, a favorable condition for the establishment of Z. mistol.

SEASONAL DIET OF THE PAMPAS FOX (LYCALOPEX GYMNOCERCUS) IN THE CHACO DRY WOODLAND, NORTHWESTERN ARGENTINA

Abstract The seasonal diet of Pampas foxes (Lycalopex gymnocercus) was examined from 431 scat samples collected during 1 year in the dry Chaco woodland of Salta Province, northwestern Argentina. Fleshy fruits dominated the diet during the dry and wet seasons, representing 69% of the total frequency and comprising 91% of the total volume. Most of the fruit diet was contributed by 5 woody plant species. Mistol (Ziziphus mistol, Rhamnaceae), was the most important fruit resource throughout the year. Arthropods (particularly beetles and scorpions) and small mammals (mainly rodents and marmosets) were the most frequently consumed animal prey. Seasonal shifts in the frequency of the main food items in the diet were not significant, but there was considerable seasonal variation in the frequency of fruit species. Diversity of prey in the diet was highest in the wet season. The Pampas fox is a generalist feeder that can alter its diet to changes in food availability. However, its diet in the Chaco, which is dominated by fruit, differs from its diet in Pampas grassland habitat, where it consumes mostly meat.

Critical environmental costs of the Paraguay-Parana waterway project in South America

Abstract The proposed Paraguay-Parana waterway project, know as “Hidrovia”, would improve and develop year-round navigation by large ships and barge trains from Caceres, Brazil, to the harbor of Nueva Palmira, Uruguay. Of particular environmental concern, the project would drastically alter the river system in the previously undeveloped reach from Caceres to Corumba, Brazil, and directly affect the Pantanal. The Pantanal is one of the worlds largest wetlands and is important both for the biodiversity it supports and for its regulatory impact on the downstream river system. This preliminary evaluation of the project establishes a critical value for the environmental costs that, if included in the evaluation of the project, would tip the scale in favor of preserving the Pantanal rather than developing the waterway through it. It is concluded that the environmental costs may exceed this critical value and that the waterway may be uneconomical in the Pantanal. The indication is that expenditures on further feasibility studies are likely best spent by investigating the feasibility of the project downstream from the Pantanal.

The importance of phyllosphere microbial populations in nitrogen cycling in the Chaco semi-arid woodland

In tropical rain forest, the interface between leaf surfaces and the atmosphere is a fundamental pathway for nutrient cycling (particulary nitrogen), possibly even more important than the soil–plant interface (Parker 1994, Silver et al . 1996). Most important nutrient exchanges in the phyllosphere–atmosphere interface are mediated by microbial populations. For example, some authors have considered that nitrogen fixation in the phyllosphere is the main mechanism for nitrogen gain in humid tropical ecosystems, because of the substantial nutrient demand resulting from a high plant productivity and the constraint imposed by the generally low nitrogen availability in soil (Ruinen 1974, Salati et al . 1982, Silver et al . 1996).

Genetic evidence of extra-pair paternity and intraspecific brood parasitism in the monk parakeet

IntroductionThe monk parakeet (Myiopsitta monachus) is a widespread invasive species native to southern South America that has become established in many regions of the world. Monk parakeets breed in a large, fully enclosed structure built from twigs, which consist of one to many individual brooding chambers. The species has been considered to be socially and genetically monogamous. However, genetic relatedness of adults to juveniles in the native area was found to be lower than expected for monogamy. To assess the significance of this discrepancy, we examined individual and population genetic patterns of microsatellite loci at two sites in Córdoba province, Argentina.ResultsWe sampled 154 nestlings and 42 adults in Córdoba, Argentina. Mean value of pairwise relatedness of nestlings within chambers was about 0.40. Contrarily, relatedness of nestlings between chambers was close to zero. We found a considerable degree of variation in nestling pairwise relatedness and parentage within chambers, including chambers with combinations of unrelated, half-sib, and full-sib nestlings. The proportion of sibling relatedness indicated monogamy in 47% and extra pair-paternity in 40% of the chambers. We also found intra-brood parasitism in 3% of the chambers.ConclusionsOur results indicate that the monk parakeet is sexually polygamous in its native range in Argentina, which is consistent with the observed mean value of relatedness of adults to juveniles of about 0.4. We also confirm the existence of intra-brood parasitism. High density of monk parakeets may favor occurrence of extra-pair paternity and intra-brood parasitism in the native sites.

Decline of the Tucumán parrot Amazona tucumana in Argentina: present status and conservation needs

The Tucuman parrot Amazona tucumana is a rare, Near Threatened species on CITES Appendix I with a restricted range in the tropical and subtropical montane forests of Argentina and Bolivia. We assessed the conservation status of the species in Argentina based on a detailed review of available information and an extensive survey throughout its range. A total of 6,015 individuals were detected in 14 sites, eight of which are new localities. The total number recorded in this study represents less than a third of the number exported from Argentina between 1985 and 1989 (18,641), indicating a significant reduction in population size. Research needs to be extended to additional sites, especially in Bolivia, to assess further the global status of the species, and high priority given to the creation of state and private reserves for the species.

The Near Threatened Tucumán parrot Amazona tucumana in Bolivia: insights for a global assessment

The Tucuman parrot Amazona tucumana is restricted to the southern Yungas mountains, from south-eastern Bolivia to north-western Argentina, and has undergone intense capture for the pet trade. We provide updated information on the status of the Bolivian population of the species and past capture levels for the international pet trade. We surveyed 18 sites during the non-breeding season in 2006 and 2007 and recorded a total of 1,643 individuals. In the 1980s 5,400 Tucuman parrots were captured for the international pet trade before the species was listed on CITES Appendix I. Capture of the Tucuman parrot for local trade appears to continue but at a reduced scale. Available evidence from this study and from Argentina indicates a need to change the categorization of the species on the IUCN Red List from Near Threatened to Vulnerable.

Litter quality and litter removal by the native fauna in the western Chaco woodland of Argentina

Most researchers assume litter decomposition to take place at the site where litterfall occurs, mostly by soil micro-organisms and microfauna of less than 1 mm in size. Accordingly, the litterbag method has become the standard technique for evaluating litter decomposition rates (Schlesinger 1985, Wedderburn & Carter 1999). However, there is evidence indicating that at least in tropical arid ecosystems litter can be removed from the site in substantial amounts by animals, including large vertebrates. For example, litter is removed for forage or as building material for nests by ants (particularly leaf-cutting ants) and termites (Bucher 1982, Scholes & Walker 1993). Moreover, ruminant species (including domestic cattle and goats) supplement their food intake by feeding on falling leaf litter during the dry season in African savannas (Owen-Smith & Cooper 1987) and in the Chaco savannas of Argentina (Morello & Saravia-Toledo 1959). These observations suggest that litter removal may be an important component of the decomposition process, particularly in tropical semi-arid environments where lack of soil moisture decreases microbial activity, increasing litter availability for herbivores.

Nesting habitat of the Tucuman Parrot Amazona tucumana in an old-growth cloud-forest of Argentina

Summary Tucuman Parrot Amazona tucumana breeds in the cloud-forest of south-eastern Bolivia and north-western Argentina (or Southern Yungas forest). We studied the nesting requirements of the Tucuman Parrot and assessed cavity availability, reuse, and spatial pattern of nests in El Rey National Park – one of the last mature, undisturbed areas of the Southern Yungas forest. We recorded 44 nesting attempts in seven tree species, with most nests (95%) being located in live canopy trees . 60 cm DBH. Most parrot nest-cavities occurred in Blepharocalix salicifolius (60%) and cavities in this species were selected significantly more than expected based on availability. Nests were shallower and higher than nests of other Amazona species. For all years combined, mean nest density of Tucuman Parrot was 0.24 6 0.04 nest ha -1 and the distance to the nearest active nest was significantly greater than the distance between all trees used as nests. Nesting pairs of Tucuman Parrot were separated by 144.1 6 152.8 m, while potential nest-trees were 66.0 6 55.4 m apart. Density of suitable cavities for nesting was 4.6 cavities ha -1 . Approximately 16 suitable cavities were available for each breeding pair (0.24 breeding pair ha -1 and four suitable cavities ha -1 ) and 5% of the suitable cavities available were occupied, suggesting that suitable cavities are not a limiting resource. However, due to the territorial behaviour of breeding pairs, some of these cavities are unavailable to other breeding pairs. The spatial requirements of Tucuman Parrot for nesting could limit management actions intended to increase the density of nesting pairs.