Tag Archives: tropical

Biogeography of Amazon birds: rivers limit species composition, but not areas of endemism

toucan.jpg

(Ubirajara Oliveira, Marcelo F. Vasconcelos & Adalberto J. Santos 7 June 2017)

 

Amazonian rivers are usually suggested as dispersal barriers, limiting biogeographic units. This is evident in a widely accepted Areas of Endemism (AoEs) hypothesis proposed for Amazonian birds. We empirically test this hypothesis based on quantitative analyses of species distribution. We compiled a database of bird species and subspecies distribution records, and used this dataset to identify AoEs through three different methods. Our results show that the currently accepted Amazonian AoEs are not consistent with areas identified, which were generally congruent among datasets and methods. Some Amazonian rivers represent limits of AoEs, but these areas are not congruent with those previously proposed. However, spatial variation in species composition is correlated with largest Amazonian rivers. Overall, the previously proposed Amazonian AoEs are not consistent with the evidence from bird distribution. However, the fact that major rivers coincide with breaks in species composition suggest they can act as dispersal barriers, though not necessarily for all bird taxa. This scenario indicates a more complex picture of the Amazonian bird distribution than previously imagined.


The impressive geographic vastness and biological diversity of the Amazon have stimulated attempts of geographic regionalization for more than two centuries.


The importance of Amazonian rivers as geographic barriers is supported by several lines of evidence, such as genetic differentiation between populations, and distribution patterns of passerine birds. However, these studies are restricted to a few rivers and taxa. Furthermore, rivers do not appear to be a major barrier for all taxa, suggesting that the Amazonian biota is the product of more complex evolutionary processes.


In this study we test whether the limits of the Interfluve AoEs can be recovered through quantitative analysis of bird distribution data, based on three methods of AoEs delimitation and through GIS and statistical methods applied to spatial variation in species and subspecies composition.


Results

Identification of areas of endemism

Our tests of the interfluve hypothesis were based on two datasets, one composed by distribution records of 612 Amazonian bird subspecies and another in which subspecies were merged within species, comprising records of 566 species. We built these two databases because the interfluve hypothesis was originally based on bird subspecies data. However, since bird subspecies delimitation can be controversial and are often based on geographic barriers, we decided to also analyse data classified only at species level. We delimited AoEs through three approaches that use different logical basis to identify co-occurrence patterns of species, in a way to perform a rigorous test of the interfluve AoEs hypothesis. The Geographical Interpolation of Endemism (GIE) interpolates species distribution through a kernel density function to estimate the degree of overlap in the species ranges in a spatially explicit way. The EnDemisM analysis (NDM) is based on spatial optimization of shared species between grid cells based on an endemism index, resulting in an estimate of species distribution overlap. Finally, the Parsimony Analysis of Endemicity (PAE), identifies AoEs based on a cladistic analysis of grid cells, with species as characters, to identify clusters of grid cells that are interpreted as AoEs.

Read the complete report here

Study reveals new insights into the dining habits of toucans

Study reveals new insights into the dining habits of toucans

(Brian Mcneill; 10 March 2017)

While Toucans’ diets consist primarily of fruit, new research co-authored by a Virginia Commonwealth University biology major suggests the bird species’ dining habits are actually more opportunistic than previously believed and include the eggs of ground-nesting birds.

Maria Vera, a student in the Department of Biology in the College of Humanities and Sciences, was part of a small team of undergraduate students and researchers who traveled to Costa Rica last summer for a nine-week National Science Foundation Research Experiences for Undergraduates program to conduct a nest predator study.

As part of the study, the team built artificial bird nests on the forest ground and monitored the fake nests with camera traps. The cameras picked up two species of toucan descending to the ground to consume the eggs, marking what the team believes may be the first report of the bird preying upon nests on the forest floor.

The findings suggest toucans may be more opportunistic eaters, particularly in disturbed or fragmented habitats where fruit trees are scarce.

The team’s study, “Toucans descend to the forest floor to consume the eggs of ground-nesting birds,” is published in the March edition of the journal Food Webs.

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Avian Gems of the Caribbean Foothills

(Patrick O’Donnell, 18 March 2017)

Want to know a good recipe for tons of different bird species? Mix high mountains with abundant water, add warm stable temperatures, throw in a pinch of dry areas, and blend it in a place where different evolutionary lineages meet. The end result is southern Central America and in terms of birds, we get a bonanza of literally hundreds of bird species in a pretty small place.

Whether volcanic, tectonic, or both, the mountains are a vital part of the species equation. The slopes catch or prevent water from falling and thus produce conditions for different habitats and continue with habitat generation by lifting land to different elevations with accompanying cooler temperatures. Microhabitats also come out of this situation for an extra dose of biodiversity, including transition zones that have their own suites of adapted birds. One of those transition areas is my favorite habitat in Costa Rica because it blends the richness of lowland avifauna with some aspects of the highlands along with a local set of restricted bird species. Although the prospect of rare and little known birds is always a draw, the slightly cooler temperatures and dripping mossy vegetation of foothill forests likewise make them an attractive place to visit, and in Costa Rica, another bonus comes into play for birding foothill forests. While steep slopes and heavy rains make these interesting transition areas tough to access in many other parts of the globe, the rare combination of good roads and protected areas makes them one of the easier places to access when visiting Costa Rica.

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Will climate change leave tropical birds hung out to dry?

(University of Ill College of Agricult., Consumer and Environm. Sci, January 3, 2017)

The future of the red-capped manakin and other tropical birds in Panama looks bleak. A research project spanning more than three decades and simulating another five decades analyzes how changes in rainfall will affect bird populations. The results show that for 19 of the 20 species included in the study, there may be significantly fewer birds if conditions become dryer.

The study took place in Panama’s Soberania National Park. It is approximately 100 square miles of protected rainforest in central Panama and home to well over 500 bird species. In the region, about 90 percent of the annual rainfall occurs in the wet season, typically from late April to early January. The key result of the study is that with longer dry seasons and more intense seasonal drought, there is an overall negative effect on bird populations. With climate change, there may be longer dry seasons. This is not good news for the birds.

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