Dispersal of forest birds and trees along the Uruguay River in southern South America

Abstract

The Uruguay River starts in Serra do Mar in Brazil, runs through the Paranense forest, and flows southward through grassland and savannas. It has a continuous gallery forest of 750 km from the southern border of the Paranense forest to the river mouth. The gallery forest extends for 100 km more along the Río de la Plata. 125 (68.7%) of the 182 species of forest birds recorded in the southern Paranense forest penetrate into the gallery forest of the Uruguay River and only 13 (7.1%) reach the end of the gallery forest (Punta Lara). The number of bird species is inversely correlated ( r 2 = 0.942) with distance and the slope of the regression is 58.10. This means a decline in diversity with 32% of species lost per unit distance. A hundred and eighty forest tree species were recorded in the southern Paranense forest, of which 113 (62.8%) penetrate into the gallery forest of the Uruguay River, and 28 (15.6%) reach Punta Lara. The number of tree species is inversely correlated ( r 2 = 0.976) with distance and the slope of the regression is − 45.62. This means a decline in diversity with 25% of species lost per unit distance. The Uruguay River enables the dispersal of many species of forest birds and trees from the rain forest, but species richness tends to decrease with increased distance from the source area. A clear association pattern was found for birds between size, diet, habitat use and distance reached into the gallery forest. Species of smaller body size, granivores, insectivores and those that use both the interior and exterior parts of the gallery forest advanced noticeably further along the river than larger species, carnivores, nectarivores or frugivores, and those that frequent only a part of the forest. Similarly, a clear association between dispersal mechanism, water dependence and distance reached into the gallery forest was found for trees. Species with vegetative reproduction, zoochorous species and riparian species advanced markedly longer distances along the river than, anemochorous species and non-riparian species.

Woody Plant Invasions in Pampa Grasslands: A Biogeographical and Community Assembly Perspective

“…This suggest that while aridity excludes cold-resistant trees from temperate steppes, low temperatures (and frost) may exclude subtropical trees (Bredenkamp et al 2002 ) . Such a causal scenario might explain why, when occurring at higher latitudes, trees originating in the subtropical Paranaense province remain con fi ned to mild riparian habitats, without invading adjacent Pampa grasslands (Cabrera 1958 ;Nores et al 2005 ) .…”

“…Turdus ru fi ventris , zorzal) fi nd perching sites along these corridors and in domestic woodlots, thus transporting the seeds of introduced woody plants across the landscape (Ghersa and León 1998 ). Riparian zones have also been invaded by frost-tolerant exotic trees such as G. triacanthos , L. lucidum , and M. alba (Ghersa et al 2002 ) , probably induced by directed, bird-mediated dispersal (Nores et al 2005 ) . Lastly, the modern Pampas landscape contains many human-disturbed areas of noncultivated or waste land, which are invaded by exotic trees like G. triacanthos and Ulmus pumila (olmo) forming dense forest patches (Facelli and León 1986 ;Mazía et al 2001 ) .…”

“…The Pampean phytogeographic province is surrounded by the Espinal province, a belt-shaped system of open woodlands and savannas (Cabrera 1958(Cabrera , 1976Cabrera and Willink 1980 ) . Native forests also occur along riparian corridors of the Uruguay and Paraná rivers, which extend from the subtropical Paranaense province into the northern part of the Pampas (Nores et al 2005 ) . Precipitation decreases from the north-east to the south-west of the region (1,000-500 mm/year).…”

“…frugivorous birds) can be critical for animal-dispersed species. Seed dispersers interact strongly with landscape structure in determining the spatial pattern of dispersal, both within and across biomes (Nores et al 2005 ) . Propagule "pressure" (i.e.…”

Four decades after Belton: a review of records and evidences on the avifauna of Rio Grande do Sul, Brazil

“…The former is suspected to be expanding in southern Brazil (Arzua et al, 2001;Ghizoni-Jr & Silva, 2006), while the latter is known from unconfirmed records in RGS (Bencke, 2001). However, both have been recorded in southern Misiones and eastern Corrientes close to the RGS border (Chebez, 1996;Capllonch et al, 2005;Nores et al, 2005), either historically or in recent times, and may simply have gone unnoticed until recently.…”