Understanding the factors underlying species coexistence is a major focus in community ecology. When dealing with competition between native and exotic species, the competitive exclusion of the ...'weaker' species can have consequences for biodiversity conservation. We examined interspecific interactions during foraging between black vultures Coragyps atratus and Andean condors Vultur gryphus in Southern Argentina. Previous studies suggest facilitatory interactions between them. However, in most parts of their distribution ranges, these species did not coexist until recently, when black vultures expanded their geographic range following human development. Thus, facilitatory processes or segregation patterns could not be fine-tuned enough to allow their coexistence. Our hypothesis is that black vultures and Andean condors compete for food resources, and that this competitive scenario can change depending on local species abundances and habitat humanization. We experimentally placed sheep carcasses in two habitats differing in degrees of humanization to study the foraging patterns in these species. Both species exploited carcasses with similar temporal patterns. However, the first to arrive and the dominant species were different in both habitats, according to their abundances. Although black vultures do not completely prevent the arrival of Andean condors to carcasses, they represent serious obstacles for feeding. Thus, while dominance hierarchy at carcasses could be related to body size, carcass consumption was determined by species abundance. Our results support the hypothesis that the expansion of a 'winning' species may trigger interspecific competition with other 'loser' species, with negative responses towards human activities when they became abundant. Although the results are not conclusive, invasion and extinction processes could be occurring and they can have serious consequences for the diversity (i.e. richness and evenness) of the New World scavenger guilds.
Small-game hunting plays an important economic role in central Spain and some game species are key food resources for threatened predators. Small carnivores may reduce numbers of important game ...species. To alleviate predation pressure on game populations, management is often focused on predator control. Control methods can be non-selective, and so could potentially have a negative impact on non-target carnivore species, affecting carnivore guild composition and diversity. Using data on carnivore diversity in 70 quadrants (5 × 5 km) in a large area of central Spain with two main land uses (small-game hunting and a mixture of big-game hunting and forestry), we assessed how game management was related to carnivore diversity. Carnivore species richness was significantly lower in those areas managed for small-game hunting than in areas where other land uses predominated. The apparently least affected species by predator control was the red fox (Vulpes vulpes), the main target species of predator control. Results suggested that low carnivore species richness was linked to small-game hunting activities, which was probably associated with non-selective predator control practices. Therefore, in order to reconcile carnivore conservation and economic goals it is imperative to develop and to evaluate selective predator control techniques.PUBLICATION ABSTRACT
We used path analysis to investigate the causal relationships between Iberian lynx and Egyptian mongoose track numbers, and to estimate the direct effect of the former on the latter in the Doñana ...area (2750 km²), south‐western Spain. Relative abundance of rabbits, shrub cover and protection level were also considered in the path analysis. An observational study consisting of a repeated track survey with a split‐plot design was also carried out between 1990 and 1996 to independently test the results obtained by path analysis. Maximum likelihood ratio tests of the goodness‐of‐fit of the model to the data and other indices used all indicated that the proposed theoretical model depicting the relationships among variables was adequate. Egyptian mongooses suffered a significant direct negative effect from lynx, and rabbits and protection level positively, and significantly affected lynx track abundance; rabbits were also significantly affected by shrub cover (all these standardized partial correlation coefficients ranged from 0.34 to 0.41). Shrub cover did not directly affect either lynx or mongoose tracks. Relatively important indirect effects were found between shrubs and lynx (0.12), and between rabbits and mongooses (−0.14), and protection and mongooses (−0.17). The two latter non‐intuitive indirect effects were through the lynx path, as a consequence of the negative direct influence of lynx on mongooses. The repeated track censuses confirmed that lynx presence significantly affects number of mongoose tracks. In areas without lynx, mean number of mongoose tracks were 3.6 times higher than in areas with lynx. It remains an interesting question which of several proposed hypotheses explains co‐existence of both species in south‐western Spain.
La gestión de la fauna silvestre debe basarse en sólida información de base. Ello incluye el seguimiento de poblaciones para ayudar a mantenerlas en tamaños próximos a aquellos previamente fijados. ...El desarrollo de programas de seguimiento requiere de una considerable planificación y evaluación estadística antes de su implementación. El objetivo de nuestro trabajo fue desarrollar un programa de seguimiento para dos especies de cánidos silvestres en Patagonia: el zorro colorado (Pseudalopex culpaeus) y el zorro gris (P. griseus). Tratamos de averiguar, utilizando el programa MONITOR, cual debería ser el esfuerzo de muestreo anual para detectar una disminución del 50% de la población actual en los próximos 5 años (esto es una tasa anual de –12,94%), o en los próximos 10 años (una tasa anual de –6.70%), satisfaciendo una potencia mínima del 80%. El trabajo de campo se realizó en el área protegida “Monumento Natural Bosques Petrificados”, Provincia de Santa Cruz, Argentina. Como estimador de la abundancia de los zorros se utilizaron las visitas a líneas de estaciones de cebado. El costo ambiental de cometer un error de Tipo II es mayor que el de cometer uno de Tipo I, por lo que utilizamosalternativamente tres niveles de α: 0.05, 0.10 y 0.15. Probamos también un esfuerzo de muestreo (número de líneas de estaciones de cebado) creciente, activándolas una, dos y hasta tres veces por año. Como valores iniciales para alimentar el programa MONITOR utilizamos la media y desviación estándar del índice de visita a cada una de las 20 líneas que se instalaron en el área de estudio. Para detectar una disminución del 50% en cinco años cualquier programa de seguimiento poblacional deberá basarse al menos en dos repeticiones anuales de las estaciones de cebado. Un programa de seguimiento accesible a las disponibilidades del área protegida sería aquel diseñado para detectar una disminución del 50% en diez años (-6.7% anual), con un α de 0.10 y un esfuerzo de 16 líneas, activadas una vez por año y revisadas durante dos o tres noches consecutivas. Se proponen alternativas para utilizar solo la primer noche de muestreo, de forma que los resultados sean luego comparables con los de experiencias de estaciones de olor en otras regiones de la Patagonia. La puesta en marcha de programas como el aquí presentado servirán para la toma de decisiones a organizaciones encargadas de la gestión de la fauna silvestre, autorizando o prohibiendo extracciones destinadas al mercado peletero. Servirían también para conocer a tiempo incrementos poblacionales, permitiendo así tomar medidas preventivas tendentes a disminuir conflictos con la actividad ganadera.
The habitat-related microgeographical body size variations in red foxes Vulpes vulpes living in two separated areas of Mediterranean Spain, the Central Ebro Valley (CEV) and Doaana National Park ...(DNP) are analysed. In both areas, samples taken from good and bad fox-habitats were compared regarding body weight and head and body length. In the Ebro Valley, foxes collected in the good habitat were heavier (14%, P < 0.001 for males; 9%, P < 0.01 for females) and larger (4%, P < 0.01 for males; 1%, P < 0.05 for females) than those collected in the bad habitat. In Doaana, males from the good habitat were 19% heavier (P < 0.01) and 3% longer (P < 0.05) than those from the poorer one. The average weight and size of DNP vixens did not show significant differences, although both are higher in the good habitat. It is shown that body size of adult foxes can vary, linked to habitat change even across short geographic distances. Some tentative explanations for these results are discussed.
The habitat-related microgeographical body size variations in red foxes Vulpes vulpes living in two separated areas of Mediterranean Spain, the Central Ebro Valley (CEV) and Doáana National Park ...(DNP) are analysed. In both areas, samples taken from good and bad fox-habitats were compared regarding body weight and head and body length. In the Ebro Valley, foxes collected in the good habitat were heavier (14%, P < 0.001 for males; 9%, P < 0.01 for females) and larger (4%, P < 0.01 for males; 1%, P < 0.05 for females) than those collected in the bad habitat. In Doáana, males from the good habitat were 19% heavier (P < 0.01) and 3% longer (P < 0.05) than those from the poorer one. The average weight and size of DNP vixens did not show significant differences, although both are higher in the good habitat. It is shown that body size of adult foxes can vary, linked to habitat change even across short geographic distances. Some tentative explanations for these results are discussed.
Abstract
A catalog containing details of the highest-energy cosmic rays recorded through the detection of extensive air showers at the Pierre Auger Observatory is presented with the aim of opening ...the data to detailed examination. Descriptions of the 100 showers created by the highest-energy particles recorded between 2004 January 1 and 2020 December 31 are given for cosmic rays that have energies in the range 78–166 EeV. Details are also given on a further nine very energetic events that have been used in the calibration procedure adopted to determine the energy of each primary. A sky plot of the arrival directions of the most energetic particles is shown. No interpretations of the data are offered.
Crested caracara (Caracara plancus) in Patagonia have a generalist diet, feeding mainly on mammalian carrion and arthropods. Vertebrate prey (mammals, birds and reptiles) are primarily captured to ...feed nestlings and marginally as food for breeding or immature adults. Immature birds are less selective in their diet than breeding adults, consuming mainly large carrion and arthropods. This may be caused by intraspecific hierarchical interactions where immature birds are displaced by adult breeding birds to less profitable prey. On the other hand, differences between breeding adults and nestlings fit central place foraging theory predictions. Adults consume smaller prey (mostly arthropods), and take larger prey (mostly vertebrates) to the nest.
Abstract
A search for time-directional coincidences of ultra-high-energy (UHE) photons above 10 EeV with gravitational wave (GW) events from the LIGO/Virgo runs O1 to O3 is conducted with the Pierre ...Auger Observatory. Due to the distinctive properties of photon interactions and to the background expected from hadronic showers, a subset of the most interesting GW events is selected based on their localization quality and distance. Time periods of 1000 s around and 1 day after the GW events are analyzed. No coincidences are observed. Upper limits on the UHE photon fluence from a GW event are derived that are typically at ∼7 MeV cm
−2
(time period 1000 s) and ∼35 MeV cm
−2
(time period 1 day). Due to the proximity of the binary neutron star merger GW170817, the energy of the source transferred into UHE photons above 40 EeV is constrained to be less than 20% of its total GW energy. These are the first limits on UHE photons from GW sources.
Abstract
Results of a search for ultra-high-energy neutrinos with the Pierre Auger Observatory from the direction of the blazar TXS 0506+056 are presented. They were obtained as part of the follow-up ...that stemmed from the detection of high-energy neutrinos and gamma rays with IceCube, Fermi-LAT, MAGIC, and other detectors of electromagnetic radiation in several bands. The Pierre Auger Observatory is sensitive to neutrinos in the energy range from 100 PeV to 100 EeV and in the zenith-angle range from
θ
= 60° to
θ
= 95°, where the zenith angle is measured from the vertical direction. No neutrinos from the direction of TXS 0506+056 have been found. The results were analyzed in three periods: one of 6 months around the detection of IceCube-170922 A, coinciding with a flare period of TXS 0506+056, a second one of 110 days during which the IceCube collaboration found an excess of 13 neutrinos from a direction compatible with TXS 0506+056, and a third one from 2004 January 1 up to 2018 August 31, over which the Pierre Auger Observatory has been taking data. The sensitivity of the Observatory is addressed for different spectral indices by considering the fluxes that would induce a single expected event during the observation period. For indices compatible with those measured by the IceCube collaboration the expected number of neutrinos at the Observatory is well below one. Spectral indices as hard as 1.5 would have to apply in this energy range to expect a single event to have been detected.
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