ABSTRACT
Apex predators are threatened globally, and their local extinctions are often driven by failures in sustaining prey acquisition under contexts of severe prey scarcity. The harpy eagle Harpia harpyja is Earth's largest eagle and the apex aerial predator of Amazonian forests, but no previous study has examined the impact of forest loss on their feeding ecology. We monitored 16 active harpy eagle nests embedded within landscapes that had experienced 0 to 85% of forest loss, and identified 306 captured prey items. Harpy eagles could not switch to open-habitat prey in deforested habitats, and retained a diet based on canopy vertebrates even in deforested landscapes. Feeding rates decreased with forest loss, with three fledged individuals dying of starvation in landscapes that succumbed to 50-70% deforestation. Because landscapes deforested by > 70% supported no nests, and eaglets could not be provisioned to independence within landscapes > 50% forest loss, we established a 50% forest cover threshold for the reproductive viability of harpy eagle pairs. Our scaling-up estimate indicates that 35% of the entire 428,800-km2 Amazonian 'Arc of Deforestation' study region cannot support breeding harpy eagle populations. Our results suggest that restoring harpy eagle population viability within highly fragmented forest landscapes critically depends on decisive forest conservation action.
ABSTRACT
Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, which are important subunits of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.
Subject(s)
Birds/anatomy & histology , Birds/physiology , Body Size , Feeding Behavior , Animals , Competitive Behavior , Ecosystem , Models, Biological , Social BehaviorABSTRACT
The author presents a vauable and authorized information about the Parque Naciona Manu (Dpto Madre de Dios-Perú), declared as a Reserve Biosphere for Unesco in 1977. He gives historical data the importance of the responsible and guided turism to this place that is the most natural park in the Amazonia. 95 reference of literature completes the information.
El autor expone una valiosa y muy autorizada información acerca del Parque Nacional Manu (Dpto Madre de Dios - Perú) que en 1977 fue declarada por la UNESCO como Reserva de la Biosfera. Incluye datos históricos, datos sobre la importancia en la investigación científica y los resultados de ella, que han aumentado cada vez más el interes de la comunidad científica internacional. Enfatiza la necesidad de un turismo guiado y responsable hacia este lugar más representativo de la Amazonía no intervenida por el hombre. 95 referencias bibliográficas completan la información.
