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LECTURE OUTLINE 11 PLATE TECTONICS, CLIMATE CHANGE, SEA-LEVEL RISE AND THE GLOBAL DISTRIBUTION OF BIODIVERSITY. R. R. Thaman GE201: Introduction to Biogeography and Ethnobiology. HISTORICAL BIOGEOGRAPHY AND LARGE PATTERNS OF DISTRIBUTION (Chapter 8, 9 and 10).
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LECTURE OUTLINE 11 PLATE TECTONICS, CLIMATE CHANGE, SEA-LEVEL RISE AND THE GLOBAL DISTRIBUTION OF BIODIVERSITY R. R. Thaman GE201: Introduction to Biogeography and Ethnobiology
HISTORICAL BIOGEOGRAPHY AND LARGE PATTERNS OF DISTRIBUTION (Chapter 8, 9 and 10) • Ecological biogeography can explain the smaller-scale local patterns of distribution, but the major global faunal and floral regions and distributions must be explained using historical biogeography which focuses on longer-term events such as plate tectonics, climate change, sea-level rise. • Although few groups (e.g., mammals and angiosperms) have the similar distributions, there are some general zones that mark the limits of distributions of many groups.
HISTORICAL BIOGEOGRAPHY AND LARGE PATTERNS OF DISTRIBUTION • These zones are separated by areas or zones that are inhospitable that mark the limits of distribution of these major groups. • Barriers, which inhibit the dispersal and/or genetic interchange, include oceans, mountains, deserts and other areas of climatic extreme.
HISTORICAL BIOGEOGRAPHY AND LARGE PATTERNS OF DISTRIBUTION • Oceans completely surround Antarctica and Australia, separate the New World and Old World continents from each other, and virtually have isolated North America from South America. • Seas and extensive deserts of North Africa and the Middle East have isolated Africa from Eurasia and the Himalayas, Tibetan Plateau and deserts separate India and Southeast Asia from the rest of Asia. • The major causes of these barriers and the resulting patterns have been related to Plate Tectonics (formerly known as “continental drift”) Climate Change (including glacials and interglacials) and associated Eustatic Sea-level rise and.
PLATE TECTONICS Responsible for • Major long-term changes in the distribution of organisms through the splitting and collision of land masses and their movement across latitudinal bands of climate (very slow at only 5 to 10 cm/year). • The movement and collision and subduction of major tectonic plates and spreading from systems of mid-ocean spreading ridges/underwater mountain ranges. • Changing patterns of oceanic currents (water circulation)
PLATE TECTONICS Responsible for • The division of previously contiguous populations by new barriers (seas, mountains, deserts, isthmuses, etc.), causing vicariance events and speciation due to vicariance rather than dispersal • Connecting previously separated areas (e.g., India joining Laurasia and the Isthmus of Panama joining N. and S. America about 3 ma.)
PLATE TECTONICS Responsible for • Changes in ocean currents through the formation and separation of continents. • Altering the distance of places from the sea, which is the ultimate source of most rainfall. E.g., the interiors of most of the large continents are dry. • 180ma beginning of the formation of the Tethys Sea which brought moisture to the edges of the circumtropical Tethys Sea, which reached its fullest extent about 150ma, and led to the evolution of new plants and animals (Tethyian Flora and Fauna) and the separate evolution of the Laurasian and Gondwana flora and fauna.
PLATE TECTONICS Responsible for 180ma - Beginning of the formation of the Tethys Sea which brought moisture to the edges of the circumtropical Tethys Sea, which reached its fullest extent about 150ma, and led to the evolution of new plants and animals (Tethyian Flora and Fauna) and the separate evolution of the Laurasian and Gondwana flora and fauna.
PLATE TECTONICS • Africa, Madagascar and India split off from Gondwana about 180ma (forming the Atlantic Ocean between Africa and S. America), while S. America, Antarctica, Australia, New Zealand and New Caledonia still connected (Glossopterus and Nothofagus examples of Gondwanic fern and angiosperm flora) • According to new evidence, the New Zealand platform/island shelf, was totally submerged about 30ma and re-emerged about 6 – 5 ma and was recolonised by cross-ocean/sweepstakes dispersal. • S. America split off from Antarctica about 130ma
PLATE TECTONICS • Antarctica split from Australia about 50-80ma which allowed the establishment of the Circum-Antarctic Current and with its relocation over the South Pole. Build-up of ice started about 30ma which led to a fall in sea level of about 200 m Antarctica is now almost totally covered by ice (has about 90% of Earth’s ice). And led to global climate change and the drying out of Australia. New Caledonia also split off from Australia at about this time. • 60-70 ma Africa and Madagascar split.
CLIMATE CHANGE, GLACIATION AND SEA-LEVEL CHANGE • There have been many episodes of climate change that have affected the distribution and evolution of plants and animals.
CLIMATE CHANGE, GLACIATION AND SEA-LEVEL CHANGE • The KT-event and the KT boundary related to the collision with the Earth of a giant meteorite (bollide) 10 km across, which led to • A massive fireball, acid rain, killing of plants and animals, a ‘global night’, breakdown in the Earth’s ozone layer and increasing UV (ionizing radiation) • 75% of all species and 25% of all families of organisms, including the dinosaurs became extinct, and led to the rapid diversification of marsupial and placental mammals.
CLIMATE CHANGE, GLACIATION AND SEA-LEVEL CHANGE • Unprecedented cyclical climate change, with glacial (cold, generally dry) and interglacial (warm, generally moist) periods during the tertiary (last 65 million years), especially during the Holocene (last 10my) during the Pleistocene • Last major glacial at about 20 - 18,000 B.P. (sea level fell about 120 m below the current level) and the last great interglacial at about 130,000 –120,000 B.P. (sea level about + 6m) • Last minor glacial occurring about 10-12,000BP allowing humans to migrate across the Bering Straits.
CLIMATE CHANGE, GLACIATION AND SEA-LEVEL CHANGE • Cooling of Antarctica led to existence of major land bridges and island stepping stones. • It must be noted that the edges of continents and islands are marked, not by their coastlines, but by the edges of the continental or island shelf. At times, during major glacials, most of these continental plates would have been above water creating large epicontinental shelves, land bridges and islands and shallow reefs where there are none today.
CLIMATE CHANGE, GLACIATION AND SEA-LEVEL CHANGE • E.g., there used to be a large island between Australia and New Caledonia in the area now occupied by Chesterfield Reef. • During the interglacials the continents and islands would be smaller in area and some islands would have disappeared, land bridges would have been submerged, reefs and mangroves would have been drowned (if they couldn’t keep up!!), and shallow epicontinental seas would have covered large areas along the coastline or inland (e.g., the North Sea and Hudson’s Bay).
