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South America

Article by: Salazar, Deborah A. Department of Geography, Oklahoma State University, Stillwater, Oklahoma. White, C. Langdon Formerly, Stanford University, Palo Alto, California. Publication year: 2014 DOI: http://dx.doi.org/10.1036/1097­8542.638200 (http://dx.doi.org/10.1036/1097­8542.638200)

Content

Regional characteristics Physiographic features Biotic features Deforestation and environmental contamination Bibliography Additional Readings

The southernmost of the New World or Western Hemisphere continents, with three­fourths of it lying within the tropics. South America is approximately 4500 mi (7200 km) long and at its greatest width 3000 mi (4800 km). Its area is estimated to be about 7,000,000 mi2 (18,000,000 km2). South America has many unique physical features, such as the Earth's longest north­south mountain range (the Andes), highest waterfall (Angel Falls), highest navigable freshwater lake (Lake Titicaca), and largest expanse of tropical rainforest (Amazonia). The western side of the continent has a deep subduction trench offshore, whereas the eastern continental shelf is more gently sloping and relatively shallow. See also: Continent (/content/continent/158900)

Regional characteristics

South America has three distinct regions: the relatively young Andes Mountains located parallel to the western coastline, the older Guiana and Brazilian Highlands located near the eastern margins of the continent, and an extensive lowland plains, which occupies the central portion of the continent. The regions have distinct physiographic and biotic features.

The Andes represent the highest and longest north­south mountain system on Earth. Altitudes often exceed 20,000 ft (6000 m) and perpetual snow tops many of the peaks, even along the Equator (Fig. 1). So high are the Andes in the northern half of the continent that few passes lie below 12,000 ft (3600 m). Over most of their length the Andes are not just a single range but two or three parallel ranges. Within the parallel peaks lie a vast series of intermontane basins and plateaus. Ecuador contains a string of 10 such basins. Bolivia has the Altiplano, an extensive basin about 400 mi (640 km) long and up to 200 mi (320 km) wide that is almost entirely surrounded by rugged and lofty peaks. The

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Altiplano is cold and high, averaging 12,000 ft (3600 m), and is mostly level. The Altiplano is distinctive in that it possesses the highest navigable freshwater body, Lake Titicaca, measuring approximately 3488 mi2 (8965 km2 ) at 12,497 ft (3750 m) elevation and approximately 918 ft (275 m) in depth.

Fig. 1 Andes Mountains, Chile. The Andes, which parallel the Pacific coast, constitute one of the Earth's most majestic features. Only the Himalayas exceed them in elevation and mass. (United Press International)

On the northeastern and eastern continental periphery lie the Guiana and the Brazilian Highlands. These vast areas of hilly uplands and low mountains are separated from each other by the Amazon River drainage (Fig. 2). Together these two plateaus form the geologically oldest part of South America. Rocks of ancient igneous and metamorphic origin are partially covered by younger sedimentary beds and sandstones. The vegetation and animal life associated with the flat­topped mesas of the highlands, called tepuis, show a high proportion of endemicity (in­situ speciation) resulting from long periods of isolation and ecosystem stability.

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Fig. 2 Representative view of the hilly uplands and low mountain country of the Guiana Highlands. One of five waterfalls on the Canaima River, Gran Sabana in southern Venezuela. (Venezuelan Information Service)

More than 65% of South America's total area is characterized by lowland plains under 1000 ft (300 m) in elevation. Some 40% of the continent is less than 650 ft (200 m) above sea level. The plains lie from about 8°N to 40°S between the lofty Andean backbone on the west coast and the Guiana and the Brazilian Highlands on the east coast, and between the Río Orinoco in the north and the Río Colorado in the south. Also in this region are the Llanos of Venezuela and Colombia, the Amazon plain of Brazil, the Paraguayan Chaco, and the Pampas of Argentina. Some of these areas are quite flat while others are undulating. Some, such as the Llanos and Chaco, are alternately flooded and baked.

Physiographic features

The three Andes regions, the lowlands, and the eastern highlands are composed and bounded by many physiographic features, including mountains, intermontane basins, extensive lowland plains, coastlines, and rivers.

M o u n t a i n s

Because of the vast extent of the Andes, a greater proportion of South America than of any other continent lies above 10,000 ft (3000 m). The young, rugged, folded Andean peaks stand in sharp contrast to the old, worn­down mountains of the eastern highlands. Although the Andes appear to be continuous, most geologists believe that they consist of several structural units, more or less joined. They are a single range in southern Chile, two ranges in Bolivia, and dominantly three ranges in Peru, Ecuador, and Colombia.

Except in Bolivia, where they attain their maximum width of 400 mi (640 km), the Andes are seldom more than 200 mi (320 km) wide. They do not equal the Himalayas in height, but have at least 30 peaks above 20,000 ft (6000 m). The average height of the Andes is estimated to be 13,000 ft (3900 m). However, it is only north of latitude 35°S that the mountains exceed elevations of 10,000 ft (3000 m) [see table].

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Table ­ Principal Andean peaks*

Peak Height, ft (m)

Aconcagua, Argentina 22,835 (6960)

Ampato, Peru 21,702 (6615)

Caca Aca, Bolivia 20,329 (6196)

Cachi, Argentina 21,326 (6500)

Chimborazo, Ecuador 20,577 (6272)

Cincel, Bolivia 20,102 (6127)

Condoriri, Bolivia 20,043 (6109)

Coropuna, Peru 22,802 (6950)

Cuzco (Ausangate), Peru 20,187 (6153)

Del Acay, Argentina 20,801 (6340)

Dos Conos, Argentina 22,507 (6860)

Falso Azufre, Argentina­Chile 22,277 (6790)

Huascaran, Peru 22,188 (6763)

Illampu, Bolivia 21,276 (6485)

Illimani, Bolivia 21,282 (6487)

Incahuasu, Argentina­Chile 21,720 (6620)

Llullaillaco, Argentina­Chile 22,015 (6710)

Mercedario, Argentina­Chile 21,884 (6670)

Ojos del Salado, Argentina­Chile 22,573 (6880)

Payachata, Bolivia 20,768 (6330)

Pissis, Argentina 22,245 (6780)

Porongos, Argentina­Chile 20,512 (6252)

Pular, Chile 20,342 (6200)

Sajama, Bolivia 21,390 (6520)

Sarmiento, Chile 20,670 (6300)

Socompa, Argentina­Chile 19,787 (6031)

Tocorpuri, Bolivia­Chile 22,163 (6755)

Tortolas, de las, Chile 20,018 (6101)

Tres Cruces, Chile 21,720 (6620)

Turpungato, Chile 21,490 (6550)

Valadero, Argentina 20,735 (6320)

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*The elevations are approximate and some are controversial. Data based mostly on tables in Goode's World Atlas, 12th ed., Rand McNally, 1964.

Both active and quiescent volcanic formations are common in southern Colombia, Ecuador, central and southern Peru, and western Bolivia. These volcanic peaks are the surface expression of the subduction of the Nazca tectonic plate beneath the South American plate, forming the offshore Peru­Chile Trench. The Andes were raised up by tectonic forces from 6560 ft (1970 m) to an average 13,120 ft (3940 m) during the Pliocene uplift approximately 5 million years ago, and they continue to rise incrementally each year. As a result of these powerful tectonic forces, there is a spectacular series of volcanic peaks in western Bolivia and on each side of the structural depression in Ecuador. See also: Plate tectonics (/content/plate­tectonics/527000)

Stratification of climate and vegetation with altitude can be readily observed in the Andes. At their eastern base is a zone with hot, humid lowland and foothills up to 3300 ft (1000 m), known as tierra caliente. Tierra templada, the zone from 3300 to 6600 ft (1000 to 2000 m), has a relatively mild, frost­free climate and was preferred for European settlement and the production of plantation crops such as coffee and coca. From 6600 to 13,200 ft (2000 to 4000 m) is tierra fria, a montane zone with occasional frosts. Tierra helada, at 13,200 to 19,800 ft (4000 to 6000 m), occupies the zone between the daily frost line and the final zone of permanent snow called tierra nevada.

Because of the great north­south extent of the Andes, the processes of their erosion and denudation have varied. Southward from about 40°S, and especially in the far south, the Andes were heavily glaciated during the Ice Age, and an extensive area north of the Strait of Magellan still has a broad mantle of permanent ice. Glaciers descend to the heads of many fiords on the Pacific coast or into lakes on the eastern side of the mountains.

Coastal features

From the southern tip of Cape Horn north to 41°S latitude, the western coastal zone consists of a broad chain of islands where a mountainous strip subsided and the ocean invaded its valleys. This is one of the world's finest examples of a fiorded coast. Nowhere along the Pacific coast is there a true coastal plain. South of Arica, Chile, the bold, precipitous coast is broken by only a few deep streams, the majority of which carry no water for years at a time. Between Arica and Caldera, Chile, there are no natural harbors and almost no protected anchorages. In fact, South America's coastline is the least indented of all the continents except Africa's. The only exceptions are the fiorded coast and the offshore archipelagoes of southern Chile, the Gulf of Venezuela including Lake Maracaibo in the north, the Gulf of Guayaquil in the west, and the estuaries of the Amazon and the Río de la Plata in the east. See also: Fiord (/content/fiord/257900)

Many raised beaches are seen along the coast (Fig. 3), supporting the premise that the Andes are of recent origin and that the forces that raised them are still at work. Nearly every port in coastal Peru is an open roadstead (less enclosed than a harbor). Coastal Ecuador, separated by mountain spurs and a narrow coastal plain east of the Gulf of Guayaquil, varies in width from 50 to 150 mi (80 to 240 km). Two important river systems cross it, the Esmeraldas in the north and the Guayas in the south. But the most important segment of the entire area is the Guayas Lowland, east and north of the Gulf of Guayaquil. Here are found one­quarter of Ecuador's total population, the most important commercial agricultural lands, and the principal port, Guayaquil. The climatic transition that occurs in coastal Ecuador

http://www.accessscience.com/content/south­america/638200 5/11 7/27/2015 South America ­ AccessScience from McGraw­Hill Education is one of the most pronounced in the world. Within a distance of only 425 mi (680 km), one passes from areas having a rainy tropical climate, to wet and dry tropical, to semiarid tropical, and finally to arid tropical—in short, from the world's rainiest to its driest climates.

Fig. 3 Uplifted beaches on desert coast, east side of San Juan Bay, Departmento de Ica, Peru. The sea cliff is about 100 ft (30 m) high. Each horizontal line represents a former beach. (Photograph by F. Atchley)

The Caribbean coast of Colombia is a lowland formed largely of alluvium, deposited by the Magdalena and Cauca rivers, and bounded by mountains on three sides. In Venezuela, the Central Highlands rise abruptly from the Caribbean, with lowlands around Lake Maracaibo, west of Puerto Cabello, and around the mouth of the Río Tuy of the Port of Guanta. The coastal region of Guyana, Suriname, and French Guiana is a low, swampy alluvial plain 10–30 mi (16–48 km) wide, and as much as 60 mi (96 km) wide along the larger rivers. This coastal plain is being built up by sediments carried by the Amazon to the Atlantic and then deflected westward by the equatorial current and cast upon the shore by the trade winds.

There is no broad coastal plain south of the Amazon and east of the Brazilian Highlands to afford easy access to the interior as is characteristic of North America's coast. The rise from the coastal strip to the interior is quite gradual in northeastern Brazil; but southward, between Bahia and Río Grande do Sul, the steep Serra do Mar is a formidable obstacle to transportation. Nonetheless, the first railroad was constructed here connecting São Paulo in the coffee region with the port of Santos. Though only 40 mi (64 km) long, it was a remarkable feat since the abrupt escarpment of the Serra do Mar behind Río de Janeiro posed difficult engineering problems and required the use of cog tracks and cables.

Along coastal Uruguay there is a transition between the hilly uplands and plateaus of Brazil and the flat Pampas of Argentina, whereas coastal Argentina as far south as the Río Colorado, in Patagonia, is an almost featureless plain. In Patagonia, steep cliffs rise from the water's edge. Behind these cliffs lies a succession of dry, flat­topped plateaus, surmounted occasionally by hilly land composed of resistant crystalline rocks. Separating southern Patagonia from Tierra del Fuego is the Strait of Magellan, which is 350 mi (560 km) long and 2–20 mi (3–32 km) wide. Threading through numerous islands, the strait is lined on each side with fiords and mountains.

Major rivers and river systems

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There are three great river systems in South America and a number of important rivers that are not a part of these systems. The largest river system is the Amazon which, with its many tributaries, drains a basin covering 2.7 million square miles (7 million square kilometers), or about 40% of the continent. The next largest is the system composed of the Paraguay, Paraná, and La Plata rivers, the last being a huge estuary. The third largest river system, located in southern Venezuela, is the Orinoco, which drains 365,000 mi2 (945,000 km2) of land, emptying into the Atlantic Ocean along the northeast edge of the continent.

Amazon River system. The Amazon River begins in the eastern Andean highlands and stretches across the north­ central part of the continent, draining the interior lowlands. Not only is it the longest, but it carries the largest volume of water and silt of any river in the world. It is also navigable for oceangoing vessels for a greater distance than any other river. The Amazon discharges 3.4 billion gallons/min 13 billion liters/min and has an average flow of 7.5 million cubic feet/s (210,000 cubic meters/s). Its discharge is about 18% of that of all rivers of the world. In places, for example, between Obidos, Brazil (500 mi or 800 km upstream) and the mouth, its depth exceeds 300 ft (90 m). It drains an area of 2.3 million square meters (6 million square kilometers), and its gradient averages only 0.2 in./mi (3 mm/km) or about 35 ft (11 m) for the last 2000 mi (3200 km) to the sea. Considering the enormous amount of silt, sand, and alluvial debris the Amazon carries to the Atlantic Ocean, it might be expected that a huge delta would have formed. But the Amazon has no delta because of the steady submergence of the land where the river reaches the sea. The Amazon is joined by some 500 tributaries descending the Andes and the Brazilian and Guiana Highlands.

Paraguay­Paraná­La Plata system. From its headwaters in southwestern Brazil, the Paraguay River courses southward 1300 mi (1780 km), discharging into the Paraná at the southern edge of Paraguay. The western bank of the Paraguay is low, and during the rainy season the western side of the entire basin becomes inundated, flooding thousands of square miles of low­lying country.

The Paraná ranks among the world's major rivers. It is longer and carries more water than the Mississippi River in the United States. Its source in the Brazilian Highlands is 2450 mi (3920 km) from its outlet in the Río de la Plata. The Paraná has cut a deep canyon in the flat­topped plateau of its upper course. As the river drops over the edge of the lava formation, famous waterfalls are found—La Guayra and Iguazú, the latter on the Iguazú, a tributary of the Paraná. However, from Corrientes, where the water of the Paraguay is added, the gradient is gentle. Since the Paraná rises in areas with characteristically heavy summer rainfall, its water volume fluctuates widely, the variation from high to low water reaching 15 ft (4.5 m) in the lower course. At the mouth of the Paraná is an enormous delta, shared with the emptying Uruguay River. The delta consists of numerous low, flat islands that are submerged for weeks at a time.

The largest indentation on the east coast of South America occurs from the head of the estuary of La Plata to the open Atlantic and is almost 200 mi (320 km) long. At Buenos Aires the estuary is about 25 mi (40 km) wide, at Montevideo 60 mi (96 km), and at its mouth 138 mi (221 km). The Paraná and the Uruguay transport huge quantities of silt into La Plata, some of which settles in navigation channels, necessitating costly dredging.

Navigation for vessels drafting 6–7 ft (1.8–2.1 m) is possible as far as Corumba, Brazil, some 1800 mi (88 km) upstream from Buenos Aires via the Paraná and Paraguay rivers. The remainder of the Paraná is rarely used for navigation, and its hydroelectric potential is as yet undeveloped because markets are too distant. The Paraguay,

http://www.accessscience.com/content/south­america/638200 7/11 7/27/2015 South America ­ AccessScience from McGraw­Hill Education however, serves the interior, and is considered the lifeline to the outside world for Paraguay.

Orinoco River system. The headwaters of the Orinoco River lie in southern Venezuela near the Brazilian border. Near Esmeraldas, in southern Venezuela, is a stretch of about 220 mi (350 km) known as the Casiquiare canal, joining the Orinoco with the Negro of the Amazon system.

The Orinoco, approximately 1600 mi (2560 km) long, is noted for its variability in volume from wet to dry season. It is a broad stream, and is a mile wide at Ciudad Bolivar, Venezuela, the “narrows.” Rainfall from June to October is so heavy that the Orinoco and its many tributaries are unable to handle all the water, and enormous areas become inundated. The river rises 39 ft (12 m) at Puerto Ordaz, Venezuela. From January to March, the dry season, the waters recede and only the larger rivers flow freely. The smaller rivers are gradually converted into chains of pools and swamps lying along the valley bottoms. Where the Orinoco flows into the Atlantic, it forms a low, wide delta consisting of small islands and swamps and an intricate maze of distributaries.

Biotic features

The plants and animals of the South American tropics are classified as Neotropical, defined by the separation of the South American and African continents during the Middle Cretaceous (95 million years ago). The Paraná basalt flow, which caps the Brazilian shield in southern Brazil and adjacent parts of Uruguay and Argentina, as well as western Africa, indicates the previous linkage between the South American and African continents. During the Middle Cretaceous Period, angiosperms (flowering plants) expanded in distribution across the Earth's landmasses, largely replacing the gymnosperms, which previously dominated the Gondwana landmass. While there are regions of important endemicity for plants and animals within South America, many evolved early enough to share significant similarities with North American, Eurasian, and African fauna and flora. South America has many biotic environments, including the constantly moist tropical rainforest, seasonally dry deciduous forests and savannas, and high­altitude tundra and glaciated environments.

Tropical rainforest

Amazonia contains the largest extent of tropical rainforest on Earth. It is estimated to encompass up to 20% of the Earth's higher plant species and is a critically important source of freshwater and oxygen. Structurally complex, the rainforest is composed of up to four distinct vertical layers of plants and their associated fauna. The layers often cluster at 10, 20, 98, and 164 ft (3, 6, 30, and 50 m) in height. The highest levels of canopy experience intense competition for light and water. Epiphytes and lianas are often found in the taller trees of this layer. The lower canopy and forest floor are usually open spaces because of the low intensity of light (around 1%) that reaches the forest floor. Over 75% of Amazonian soils are classified as infertile, acidic, or poorly drained, making them undesirable for agriculture because of nutrient deficiencies. Most of the nutrients in the tropical rainforest are quickly absorbed and stored in plant biomass because the high annual rainfall and associated leaching make it impossible to maintain nutrients in the soils. In addition to the high structural complexity of the tropical rainforest, there is considerable horizontal diversity or patchiness. As many as 300 separate species of trees can be found in a square mile (2.6 km2) sample tract of rainforest in Brazil. The high complexity and species diversity of the rainforest are the result of long

http://www.accessscience.com/content/south­america/638200 8/11 7/27/2015 South America ­ AccessScience from McGraw­Hill Education periods of relative stability in these regions. Many areas of Amazonia show unique concentrations of species that suggest these territories may have acted as Pleistocene refugia where plants and animals were able to survive the glacial advances of higher latitudes. See also: Pleistocene (/content/pleistocene/528200)

Deciduous and conifer forest

Deciduous forests are found in areas where there is seasonal drought and the trees lose their leaves in order to slow transpiration. The lower slopes of the Andes, central Venezuela, and central Brazil are areas where these formations are found. Conifer forests occur in the higher elevations of the Andes and the higher latitudes of Chile and Argentina. Many of the species of these formations derive from the Late Cretaceous Southern Gondwana flora, including the Araucaria (star pine), Podocarpus, and Dacrydium. See also: Deciduous plants (/content/deciduous­ plants/182300)

S a v a n n a

Tropical savannas occupy an extensive range in northern South America through southeastern Venezuela and eastern Colombia. Temperate savannas are found in Paraguay, Uruguay, the Pampas of Argentina, and to the south, Patagonia. Savannas are composed of a combination of grass and tree species. The climate in these areas is often quite hot with high rates of evapotranspiration and a pronounced dry season. Most of the plants and animals of these zones are drought­adapted and fire­adapted. Tall grasses up to 12 ft (3.5 m) are common as are thorny trees of the Acacia (Fabaceae) family. Many birds and mammals are found in these zones, including anteater, armadillo, capybara (the largest rodent on Earth), deer, jaguar, and numerous species of venomous snake, including rattlesnake and bushmaster (mapanare).

D e s e r t

South America is unique in having a west­coast desert that extends almost to the Equator, probably receiving less rain than any on Earth (the Atacama), and an east coast desert located poleward from latitude 40°S (the Patagonian).

The Atacama­Peruvian Desert dominates the Pacific coast for nearly 2000 mi (3200 km), lying between the ocean and the higher slopes of the Andean ranges. In many places, particularly in Chile, the land rises abruptly from the sea to an elevation of 2000–3000 ft (600–900 m). The driest stretch, one of the driest places in the world, is between Arica and Caldera, Chile (Fig. 4). Above the seaward scarp is a low range of hills and a desert trough, 30–50 mi (48–80 km) wide, from which nitrate deposits are extracted. The persistence of this desert through latitudes at which deserts are not found elsewhere is the result of the north­moving Humboldt Current (Peru Current), accompanied along the immediate shore by the upwelling of cold water from considerable depths, creating stable, high­pressure atmospheric conditions. Prevailing winds, blowing from the west, carry cold air onto the warmer land with a drying effect.

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Fig. 4 Port of Matarani on the desert coast of southern Peru. This oblique aerial view looks coastwise southward over one of the world's driest and most barren coastal zones. (Servicio Aerofotográfico Nacional)

South America's east­coast desert, the Patagonian, is found between the Río Colorado and the Strait of Magellan. This desert is partly located in the rain shadow of the Andes, and the meager annual rainfall is ordinarily 5–6 in. (13– 15 cm). Also contributing to the region's aridity and to the presence of the desert near to the shores of the Atlantic are the cold waters of the Falkland Current, moving northward off the eastern coast, and the ceaseless winds, which hasten evaporation. Wind velocities can exceed 70 mi/h (31 m/s). What precipitation there is occurs mostly in the winter. The region's very cold winter temperatures are the result of high latitude and high elevation.

T u n d r a

In Bolivia and Peru the zone from 10,000 to 13,000 ft (3000 to 3900 m), though occasionally to 15,000–16,000 ft (4500 to 4800 m), is known as the puna. Here the hot days contrast sharply with the cold nights. Above the puna, from timberline to snowline, is the paramo, a region of broadleaf herbs and grasses found in the highest elevations of Venezuela, Colombia, and Ecuador. Many of the plant species in these environments are similar to those found at lower elevations; however, they grow closer to the ground in order to conserve heat and moisture.

Deforestation and environmental contamination

The 1992 Quincentennial and the 1992 Earth Summit (United Nations Conference on Environment and Development) have drawn widespread attention to environmental policy and economic development in South American countries that have encouraged the destruction of natural vegetation. Intense political discourse has focused on the removal of tropical rainforest and the contamination of both lowland and highland environments across the continent. An estimated 20% of the Amazonian forest has already been destroyed, and more than 7700 mi2 (200,000 km2) are estimated to be replaced by agriculture, cattle ranching, and urbanization each year. The loss of tropical rainforest in particular has been widely publicized, although many other biotic environments, including deciduous forest, coastal mangrove, and tundra environments, are also being degraded by human use.

Deborah A. Salazar C. Langdon White

Bibliography

http://www.accessscience.com/content/south­america/638200 10/11 7/27/2015 South America ­ AccessScience from McGraw­Hill Education

B. Box, South American Handbook, 82d ed., 2006

C. Caviedes and G. Knapp, South America, 1995

B. Cox and B. Moore, Biogeography, 7th ed., 2005

A. Morris, South America, 3d ed., 1991

S. E. Place, Tropical Rainforests, rev. ed., 2001

A. H. Strahler and A. Strahler, Introducing Physical Geography, 4th ed., 2005

Additional Readings

C. B. Cox and P. D. Moore, Biogeography: An Ecological and Evolutionary Approach, 8th ed., John Wiley & Sons, Hoboken, NJ, 2010

T. C. Giannini et al., Interactions at large spatial scale: The case of Centris bees and floral oil producing plants in South America, Ecol. Model., 258:74–81, 2013 DOI: 10.1016/j.ecolmodel.2013.02.032 (http://dx.doi.org/10.1016/j.ecolmodel.2013.02.032)

A. Millington, M. Blumler, and U. Schickhoff (eds.), The SAGE Handbook of Biogeography, SAGE, London, UK, 2011

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