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Santa Cruz de la Sierra, Bolivia

Jahn A.E.,University of Florida | Levey D.J.,University of Florida | Hostetler J.A.,University of Florida | Mamani A.M.,Museo de Historia Natural Noel Kempff Mercado
Journal of Animal Ecology

1. Little is known about mechanisms that drive migration of birds at tropical latitudes. Because most migratory bird species in South America have populations that are present year-round, partial migration (in which only some individuals of a given population migrate at the end of the breeding season) is likely to be common, providing an opportunity to assess proximate mechanisms of migration. 2. Two non-mutually exclusive hypotheses explaining intraspecific variation in migratory behaviour were tested in a Tropical Kingbird Tyrannus melancholicus population in the southern Amazon Basin, where a dramatic dry season decrease in the abundance of insect food for kingbirds may promote migration of some individuals. 3. The Dominance hypothesis predicts sub-dominant individuals migrate at the end of the breeding season and dominant individuals do not, whereas the Body Size hypothesis predicts smaller individuals migrate and larger individuals do not. 4. Based on 4 years of data on individually-marked birds, strong support was found for occurrence of partial migration in the study population. 5. In the best model, the largest males (which are typically older and dominant to younger individuals) had the highest probability of migrating. Younger females (which are the smallest individuals in the population) were also more likely to migrate than other kingbirds, except the largest males. Thus, an individual's probability of migrating was associated with a more complex interaction of size, age and sex than predicted by current hypotheses. 6. These results suggest that determinants of migratory behaviour differ between North temperate and tropical latitudes. Most tests of partial migration theory have been conducted on granivores (e.g. emberizids) or omnivores (e.g. turdids and icterids) at North temperate latitudes, where seasonality is primarily defined by temperature cycles. In tropical South America, however, the most common long-distance migrants are primarily insectivorous (i.e. tyrannids), and seasonality is largely defined by rainfall cycles. 7. We propose a hypothesis based on seasonal food limitation to explain partial migration of primarily insectivorous species in seasonal tropical habitats. © 2010 The Authors. Journal compilation. Source

Piacentini L.N.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia | Avila Calero S.L.,Coleccion Boliviana de Fauna | Perez M.E.,Museo de Historia Natural Noel Kempff Mercado | Grismado C.J.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia

The araneomorph spider family Palpimanidae is reported from Bolivia for the first time. Two new species: Otiothops kath-iae and O. naokii are described and illustrated based on specimens recently collected in Santa Cruz Department. Addition-ally, Fernandezina pulchra Birabén, 1951 previously known only from Formosa, in northern Argentina, is newly recorded from Santa Cruz, and the female is described for the first time. Potential relationships with previously described species are also briefly discussed. Copyright © 2013 Magnolia Press. Source

Watling J.I.,University of Florida | Watling J.I.,John Carroll University | Braga L.,Museo de Historia Natural Noel Kempff Mercado
Landscape Ecology

Context: Although amphibian distributions are associated with environmental moisture at global and local scales, less is known about how desiccation tolerance influences landscape distributions of amphibians. Objectives: We evaluated two hypotheses linking amphibian distributions in a fragmented tropical forest landscape to desiccation risk. The patch quality hypothesis predicts that desiccation-prone species are absent on small forest patches, which are generally warmer and drier than large patches. Alternatively, the matrix effects hypothesis suggests that desiccation-prone species are absent on isolated forest patches surrounded by open savanna because they will be unable to traverse the matrix in which patches occur. Methods: We quantified interspecific variation in desiccation proneness using field-based desiccation trials, and tested for associations between desiccation proneness and distributions of amphibians in fragmented forest in northeastern Bolivia. Results: Rates of evaporative water loss were negatively associated with an index of dispersal limitation, but unrelated to species’ area requirements. Conclusions: By demonstrating that desiccation-prone species do not occur on isolated forest patches, we provide clear support for the matrix effects hypothesis. We suggest that desiccation proneness is a key trait that may determine amphibian responses to a range of global change drivers, including habitat loss and fragmentation, invasive species, and climate change. © 2015, Springer Science+Business Media Dordrecht. Source

Whitney B.S.,University of Edinburgh | Mayle F.E.,University of Edinburgh | Punyasena S.W.,University of Illinois at Urbana - Champaign | Fitzpatrick K.A.,University of Edinburgh | And 6 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology

We present a well-dated, high-resolution, ~45kyr lake sediment record reflecting regional temperature and precipitation change in the continental interior of the Southern Hemisphere (SH) tropics of South America. The study site is Laguna La Gaiba (LLG), a large lake (95km2) hydrologically-linked to the Pantanal, an immense, seasonally-flooded basin and the world's largest tropical wetland (135,000km2). Lake-level changes at LLG are therefore reflective of regional precipitation. We infer past fluctuations in precipitation at this site through changes in: i) pollen-inferred extent of flood-tolerant forest; ii) relative abundance of terra firme humid tropical forest versus seasonally-dry tropical forest pollen types; and iii) proportions of deep- versus shallow-water diatoms. A probabilistic model, based on plant family and genus climatic optima, was used to generate quantitative estimates of past temperature from the fossil pollen data. Our temperature reconstruction demonstrates rising temperature (by 4°C) at 19.5kyr BP, synchronous with the onset of deglacial warming in the central Andes, strengthening the evidence that climatic warming in the SH tropics preceded deglacial warming in the Northern Hemisphere (NH) by at least 5kyr. We provide unequivocal evidence that the climate at LLG was markedly drier during the last glacial period (45.0-12.2kyr BP) than during the Holocene, contrasting with SH tropical Andean and Atlantic records that demonstrate a strengthening of the South American summer monsoon during the global Last Glacial Maximum (~21kyr BP), in tune with the ~20kyr precession orbital cycle. Holocene climate conditions occurred as early as 12.8-12.2kyr BP, when increased precipitation in the Pantanal catchment caused heightened flooding and rising lake levels in LLG. In contrast to this strong geographic variation in LGM precipitation across the continent, expansion of tropical dry forest between 10 and 3kyr BP at LLG strengthens the body of evidence for widespread early-mid Holocene drought across tropical South America. © 2011 Elsevier B.V. Source

Jahn A.E.,University of Florida | Jahn A.E.,University of Buenos Aires | Levey D.J.,University of Florida | Levey D.J.,National Science Foundation | And 6 more authors.

Little is known about the timing of migration, migration routes, and migratory connectivity of most of the >230 species of birds that breed at south temperate latitudes of South America and then migrate toward the tropics to overwinter. We used light-level geolocators to track the migration of 3 male and 3 female Fork-tailed Flycatchers (Tyrannus savana) captured on their breeding territories in Argentina. All birds initiated fall migration between late January and late February, and migrated 45 to 66 km day-1 in a northwesterly direction through central South America to either one or two wintering areas. Five individuals first spent several weeks (in April and May) in western Amazonia (mainly Peru, northwestern Brazil, and southern Colombia) before moving east to spend the rest of the non-breeding season in central Venezuela and northern Brazil. One individual occupied primarily one wintering area in eastern Colombia, northwestern Brazil, and southwestern Venezuela. Fall migration took approximately 7-12 weeks to complete and covered a distance of 2,888-4,105 km. We did not analyze spring migration data because of broad overlap with the austral spring equinox. These results are the first data on wintering locations, migration timing, and routes of individual migrant passerine birds that breed in South America. Given the general lack of similar data for practically all migratory birds that breed in South America, geolocator technology has the potential to revolutionize our understanding of how birds migrate-and the threats they face-on South America's rapidly changing landscape. © 2013 by The American Ornithologists' Union. All rights reserved. Source

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