Descripción: We analyzed the effect of density-dependent habitat selection and interspecific competition on the use of space by small rodent species in agroecosystems. We studied rodent abundance in cropfields and their borders, weedy margins less disturbed by agricultural activities. We could distinguish two kind of species: those habitat intolerants, Akodon azarae and Oligoryzomys flavescens, which select the borders, and those habitat tolerants, Calomys laucha and Calomys musculinus. The two most abundant species in the community, A. azarae and C. Laucha, differ in their habitat use: while the first has a clear preference for borders, the other is more equally distributed between habitats, although it is more abundant in fields. Both species show a shift towards an increased use of fields via density-dependent habitat selection with increasing abundance at some moments of the year. C. musculinus does not show habitat preference in any season, overlaping with the other species in both habitats. There is an interspecific effect on habitat use between A. azarae and C. laucha : While the first species cause a shift in habitat preference of C. laucha towards fields, this latter species affects the density-dependent habitat use of A. azarae. It is concluded that the pattern of habitat use of the studied species is affected by their differential preferences as well as by intra and interspecific density-dependent processes that change seasonally.

Descripción: Landscape simulators are widely applied in landscape ecology for generating landscape patterns. These models can be divided into two categories: pattern-based models that generate spatial patterns irrespective of the processes that shape them, and process-based models that attempt to generate patterns based on the processes that shape them. The latter often tend toward complexity in an attempt to obtain high predictive precision, but are rarely used for generic or theoretical purposes. Here we show that a simple process-based simulator can generate a variety of spatial patterns including realistic ones, typifying landscapes fragmented by anthropogenic activities. The model "G-RaFFe" generates roads and fields to reproduce the processes in which forests are converted into arable lands. For a selected level of habitat cover, three factors dominate its outcomes: the number of roads (accessibility), maximum field size (accounting for land ownership patterns), and maximum field disconnection (which enables field to be detached from roads). We compared the performance of G-RaFFe to three other models: Simmap (neutral model), Qrule (fractal-based) and Dinamica EGO (with 4 model versions differing in complexity). A PCA-based analysis indicated G-RaFFe and Dinamica version 4 (most complex) to perform best in matching realistic spatial patterns, but an alternative analysis which considers model variability identified G-RaFFe and Qrule as performing best. We also found model performance to be affected by habitat cover and the actual land-uses, the latter reflecting on land ownership patterns. We suggest that simple process-based generators such as G-RaFFe can be used to generate spatial patterns as templates for theoretical analyses, as well as for gaining better understanding of the relation between spatial processes and patterns. We suggest caution in applying neutral or fractal-based approaches, since spatial patterns that typify anthropogenic landscapes are often non-fractal in nature. © 2013 Pe'er et al.

Descripción: 1. Leaf structural and physiological traits are associated with growth form and habitat, but little is known of the specific traits associated with hemiepiphytes, which are an important component of many tropical forests. Given their life history that includes a drought prone epiphytic stage, hemiepiphytes should be expected to have more drought tolerance-related traits than co-occurring terrestrial species. 2. The genus Ficus includes woody hemiepiphytes distributed in tropical areas throughout the world. Traits related to the flux of water through the leaf and to drought adaptations were studied in five hemiephiphytic (H) and five non-hemiepiphytic (NH) Ficus tree species grown in a common garden to determine genetically based differences. 3. Leaves of H and NH species differed substantially in structure and physiology; on average, H species had smaller leaves with higher leaf mass per unit area, thicker epidermis, smaller vessel lumen diameters in petioles and lower petiole hydraulic conductivity. Leaf traits also indicated stronger drought tolerance in H species, including lower epidermal conductance and turgor loss point and earlier stomatal closure with desiccation than NH species. Across H and NH species, traits related to water flux capacity were negatively correlated with traits related to drought tolerance. 4. The divergences in hydraulics and water relations between growth forms for these closely related species reflected specialization according to contrasting habitat and life form. Conservative water use and increased ability of leaves to persist under severe drought would provide an advantage for H species, especially during the epiphytic phase, while the higher potential water use of NH species would be associated with higher assimilation rates and competitiveness under high water supply. 5. The results indicate a trade-off between leaf water flux capacity and leaf drought tolerance across these hemiephiphytic and non-hemiepiphytic species. Species adaptation to habitats with contrasting demands on leaf function may lead to divergence along a leaf water-flux-drought-tolerance spectrum. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.

Descripción: The Marsh Seedeater Sporophila palustris is one of the most endangered and least known of the capuchino seedeaters. Breeding populations are patchy, occurring in north-east Argentina, southern Brazil, and Uruguay. We present data on the breeding biology of the species, and describe nests and eggs, behaviour (including courtship, nesting, incubation and parental care), breeding sites and food items. Marsh Seedeaters breed in well-preserved grasslands with wet soils and tall vegetation. In general, these habitats are used for extensive livestock ranching. Main threats are overgrazing, widespread use of fire, conversion of grasslands to pastures of exotic grasses and rice fields, afforestation, and illegal trapping. Most breeding sites are located in Important Bird Areas, but only one in Brazil and one in Argentina are protected. We propose a series of actions to promote the conservation of Marsh Seedeaters and other endangered birds that coexist in grassland habitats. Copyright © BirdLife International 2013 Â.

Descripción: Size distribution, sex ratio and use of burrows of the burrowing toad Rhinella fernandezae were studied in Buenos Aires province, Argentina. Two sites separated by approximately 300 m were studied: one was a road next to a swamp, and the other a garden of a country house located further from the swamp. We identified toad burrows, and individuals were sexed, measured and given an individual mark. Burrows were examined in subsequent months after the first sampling to assess the presence of toads. We found significant differences in the size distribution between areas, being the proportion of juveniles greater at the site next to the swamp where the reproduction of the species was observed. This result may suggest that the site located near to the swamp functions as a source habitat of individuals that migrate to the other site, where recruitment would be very scarce. Sex proportion of adults did not differ from 1:1 in neither the total population nor in each site, suggesting that there was not differential mortality by sex. Some toads changed burrows throughout the study period, but there were not differences in the frequency of change between adults and juveniles.

Descripción: We experimentally assessed the effect of controlling vegetation height along farm perimeters on the abundance of rodents in 2 broiler poultry farms in central Argentina. We carried out an experimental design based on the before-after-control-impact method. After vegetation treatments, there was a significant decrease in rodent abundance at the perimeter of the farm with control of vegetation height because of the reduction of the Pampean grassland mouse Akodon azarae. In poultry houses, there was a significant decrease in rodent abundance on nonaffected farms because of the reduction of the commensal house mouse Mus musculus domesticus, possibly because of a major collocation of rodenticide. Our results indicate that both the control of vegetation growth at the perimeters and the appropriate timing of rodenticide applications are effective measures for rodent control on broiler poultry farms when both control measures are applied simultaneously. We achieved effective rodent control through an understanding of the habitat use and population dynamics of the species involved and the characteristics of the area where the control program would be applied. © 2009 Poultry Science Association, Inc.

Descripción: The European Starling (Stumus vulgaris) was introduced in Argentina by 1987. Starlings are secondary cavity nesters and may constitute a threat to other cavity nesters. We estimated the density of starlings in Buenos Aires city urban parks and examined the relationships between some habitat characteristics and the presence and abundance of starlings. We also evaluated the interactions between starlings and native species, by observations during foraging and nesting. Because starlings may use Rufous Hornero (Fumarius rufus) dome-shaped nests, we also located and observed them. Starlings were recorded in 293 transects distributed in 20.8 km2 corresponding to 103 Buenos Aires public-access parks, in which 447 individuals were recorded. We found that the relative population density for starlings in parks of Buenos Aires (individuals/ha ± SD) was 2.21 ± 0.09. Starling presence was positively associated with the park area and number of palms and negatively with the number of trees. A positive significant association between starling density and number of tipu trees was also found. Neither the presence nor the abundance of starlings was associated with the park's avian species richness. Although starlings were found to feed in heterospecrfic flocks in 60.3% of the 58 observations (totally 464 min), only five interspecific interactions were recorded (the starling being always the losing species). Twenty-one starling nests were built in natural cavities and nine in cavities made by woodpeckers (Colaptes spp). None of the 26 Rufous Hornero nests found was occupied by starlings. However, the nestling cycle of the Golden-breasted Woodpecker (Colaptes melanolaimus) was recorded to be interrupted in three occasions due either to aggressive interactions or to the presence of starlings near the nests. These findings can be relevant in relation with the need of any action against starlings in Argentina. Accepted 21 September 2010. © The Neotropical Ornithological Society.