Tropical Biogeography Overview

Tropical Biogeography

• Biogeography is the study of how plant and animal species are distributed across the planet and how they got there.
• Alfred Russel Wallace helped establish the field of biogeography.
•  The tropics are the region between the Tropic of Cancer (23.5° N) and the Tropic of Capricorn (23.5° S).
•  Nearly every country in Africa is tropical.
• Palm trees are common in tropical regions.
• The Burj al Arab is an iconic hotel in the United Arab Emirates, a tropical country.
• The tropics have a wide range of ecosystems, including rainforest, savanna, and desert.

Types of Tropical Ecosystems

• Tropical Rain Forest: Precipitation is about 250 cm/year. Temperature variation is minimal, and moisture is abundant. Rainforests have greater species diversity than other biomes.

• Savanna: Precipitation ranges from 90 to 150 cm/year. It's characterized by open, widely spaced trees and seasonal rainfall. This biome is found in parts of Africa, South America, and Australia.

• Desert: Precipitation is about 20 cm/year. Vegetation is sparse and includes scattered grasses. Deserts are found in parts of Africa, Asia, Australia, and North America.

Biogeography of Tropical Regions

• Approximately 250 million years ago, almost all land was a single large continent known as Pangaea.
• Plants and animals were widely distributed across Pangaea with few geographical barriers.
• Plate tectonics is the theory that Earth's outer shell is divided into plates that move over the mantle, impacting biogeographic regions. Plate movement shapes continents and affects how species are distributed.
• The Earth's crust is composed of several distinct plates.

Biogeography of Tropical Regions (Continued)

• More than 200 million years ago, after the dinosaurs evolved, Pangaea broke into Laurasia and Gondwana.
• Laurasia became North America, Europe, Asia, Greenland, and Iceland.
• Gondwana became South America, Africa, Australia, Antarctica, and India.
• Fossil evidence (like Glossopteris and Mesosaurus) highlights how these continents were once connected.

Evidence of Plate Movement

• Clear folding in the Himalayan rock formations shows evidence of plate movement and tectonic forces.
• The rocks tilted towards higher snow-covered peaks in areas influenced by plate collisions.
• The geological study of rocks shows they were originally on the sea floor.

Gondwanaland

• Gondwanaland represents the southern part of the supercontinent Pangaea and encompassed present-day South America, Africa, Arabia, Madagascar, India, Australia, and Antarctica.
• It shows how these continents were once joined.

Biogeography in the Tropics

• Much evolution has occurred since Gondwanaland.
• South American and Australian midges are closely related to each other, yet not to New Zealand midges.
• The midges of all three key land masses (South America, Africa, and Australia) are more closely related than to those in the African landmass.
• Southeast Asia has many conifers whereas there are only two species in the New World tropics and only one in Africa.
• Dipterocarps are mostly found in Southeast Asia. The tropical regions exhibit the highest biodiversity of plants and animals on Earth.

Laurasia

• Laurasia was the northern part of the supercontinent Pangaea. Present-day North America, Europe, and Asia were incorporated in Laurasia.

Alfred Russel Wallace

• Alfred Russel Wallace was a naturalist who significantly contributed to the science of biogeography.
• He observed a distinct boundary (Wallace's Line) in Indonesia dividing the Asian and Australian regions, highlighting different species distribution patterns. The line distinguishes distinct fauna and flora.

Wallace's Line

• Wallace's line is a faunal boundary that separates the ecozones of Asia and Wallacea which, in turn, are a transitional zone between Asia and Australia.
• West of this line, mostly Asian species are found, and east of the line, the species are a mix of Asian and Australian.
• The line runs through Indonesia, between Borneo and Sulawesi, and through the Lombok Strait between Bali and Lombok.

Additional Information

• The diagrams and maps provide visual representations of the geographical distributions, plate tectonics and the distribution of species.