Biogeography and Tropical Ecosystems

Tropical Biogeography

• Biogeography is the study of how species are distributed across the planet and how they got there.
• Tropical regions are defined by the area between the Tropic of Cancer and the Tropic of Capricorn.
• Nearly every country in Africa is tropical.
• Palm trees are common in tropical regions.
• The Burj al Arab is an iconic hotel located in a tropical country, the United Arab Emirates.

Geographical Zones

• The tropics are located between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S).
• The equator is located at 0°.
• The arctic circle is located at 66.5°N.
• The Antarctic circle is located at 66.5°S.
• These lines indicate the different zones based on the amount of daylight received throughout the year.
• The length of daylight varies with latitude, from 24 hours of sunlight in the arctic circle to 0 hours in the Antarctic circle.

Types of Tropical Ecosystems

• Tropical Rain Forest: Precipitation is 250 cm/year; temperature variation is low; abundant moisture; contains more species than other biomes.
• Savanna: Precipitation is 90-150 cm/year; open, widely spaced trees; seasonal rainfall; found in parts of Africa, South America, and Australia.
• Desert: Precipitation is 20 cm/year; dry; sparse vegetation; scattered grasses; found in parts of Africa, Asia, Australia, and North America.

What is Biogeography?

• Biogeography is the study of the geographic distribution of species and how they got there.
• Alfred Russel Wallace played a significant role in developing this field.

Biogeography of Tropical Regions

• About 250 million years ago, almost all landmasses were part of a single continent called Pangaea.
• Plants and animals were widely distributed across Pangaea.
• Plate tectonics is the theory that Earth's outer shell is divided into several plates that move over the mantle.
• The plates' movement has shaped the distribution of biomes. The Earth's crust has been found to be composed of several distinct plates.

Biogeography of Tropical Regions: History

• More than 200 million years ago, this land mass broke up into two parts: Laurasia and Gondwanaland.
• Fossil evidence shows organisms were widespread across landmasses.
  • Land reptiles like Cynognathus and Lystrosaurus.
  • Freshwater reptiles, like Mesosaurus.
  • The fern Glossopteris.
• Continental drift has impacted the distribution and evolution of plants and animals.

Evidence of Plate Movement

• Evidence of plate movement can be seen in the Himalayan rocks, which demonstrate folding and tilting due to the plates' collision.
• These rocks are sedimentary, indicating they were once on the seabed.

Gondwanaland

• Gondwanaland was a supercontinent, the southern part of Pangea; it included present-day South America, Africa, Arabia, Madagascar, India, Australia, and Antarctica.

Biogeography in the Tropics

• Much evolution has happened since Gondwanaland.
• South American and Australian midges are more closely related to each other than to New Zealand species.
• Midges of all three land masses are more closely related to each other than to African species.
• Southeast Asia has many conifers compared to the New World tropics and Africa.
• Dipterocarps are mainly found in Southeast Asia
• Tropical regions have the highest diversity of plant and animal life on Earth.

Laurasia

• Laurasia was the northern part of the Pangaea supercontinent.
• Today, it would include North America, Europe, and Asia.

Alfred Russel Wallace

• Alfred Russel Wallace was a great naturalist who helped develop the science of biogeography.
• While exploring Indonesia, he observed a clear line of difference in animal species between the western and eastern parts.
• This became known as Wallace's Line.

Wallace's Line

• Wallace's Line is a faunal boundary line separating the Asian and Australian ecozones.
• West of the line are organisms related to Asiatic species, while east of the line shows a mixture of Asian and Australian species.
• The line includes Indonesia, between Borneo and Sulawesi (Celebes) and the Lombok Strait between Bali and Lombok.