BIO 303 — Biogeography and Soil Biology: Lecture Note

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This is the complete lecture note for BIO 303 Biogeography and Soil Biology. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.

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BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: BIO 303 Course title: Biogeography and Soil Biology Course credit load: 2 Units Series 1: Continental Drift and Gondwanaland • Part 1.1: The Theory of Continental Drift o Sub Part 1.1.1: Wegener and the continental drift hypothesis o Sub Part 1.1.2: Evidence for continental drift o Sub Part 1.1.3: Plate tectonics as the mechanism • Part 1.2: Gondwanaland and Laurasia o Sub Part 1.2.1: Pangaea, Gondwanaland, and Laurasia o Sub Part 1.2.2: The breakup of Gondwanaland o Sub Part 1.2.3: Biogeographic consequences of Gondwanaland • Part 1.3: Land Bridges o Sub Part 1.3.1: The theory of land bridges o Sub Part 1.3.2: Major land bridges and their biogeographic effects o Sub Part 1.3.3: Land bridges versus rafting • Part 1.4: Continental Drift and Biogeography o Sub Part 1.4.1: Vicariance and dispersal o Sub Part 1.4.2: Continental drift and disjunct distributions o Sub Part 1.4.3: Applying continental drift to interpreting distribution patterns

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Introduction Biogeography asks why organisms are distributed where they are across the surface of the Earth. The answers require understanding not only the biology of the organisms themselves but also the geological history of the planet, since the positions of continents, the presence or absence of land connections, and the opening and closing of ocean barriers have profoundly shaped which species could reach which parts of the world and when. Continental drift is the foundational geological process that biogeographers must understand. This Series introduces Alfred Wegener continental drift hypothesis, the evidence that supports it, and plate tectonics as the underlying mechanism; the history of the supercontinent Pangaea and its Gondwanaland and Laurasian components; the theory of land bridges and their role in facilitating or restricting faunal and floral exchange; and the key concepts of vicariance and dispersal through which continental drift shapes biogeographic distribution patterns. Series Learning Outcomes Upon completing this Series, you should be able to: • SLO 1.1 describe Wegener continental drift hypothesis, the evidence supporting it, and plate tectonics as its mechanism, • SLO 1.2 describe Pangaea, Gondwanaland, and Laurasia and explain the biogeographic consequences of their breakup, • SLO 1.3 explain the theory of land bridges and describe the biogeographic effects of major historical land bridges, and • SLO 1.4 distinguish vicariance from dispersal and explain how continental drift generates disjunct distribution patterns

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.1 The Theory of Continental Drift 1.1.1 Wegener and the continental drift hypothesis Alfred Wegener, a German meteorologist and geophysicist, proposed the continental drift hypothesis in 1912, suggesting that the continents were once joined in a single supercontinent he called Pangaea (meaning "all land") and have since moved apart to their current positions; Wegener was struck by the remarkable fit of the opposing coastlines of South America and Africa, which suggested they had once been joined, and he compiled evidence from geology, palaeontology, palaeoclimatology, and biology to support his hypothesis. Although Wegener assembled a compelling body of evidence, his hypothesis was initially rejected by most geologists because he could not propose a plausible physical mechanism capable of moving entire continents through solid oceanic crust; the missing mechanism was supplied decades later by the theory of plate tectonics, which provided the physical framework of seafloor spreading and convection in the mantle that drives continental movement; Wegener is now recognised as a visionary whose hypothesis, though initially controversial, fundamentally transformed understanding of Earth history. Fill in the blank: Alfred Wegener proposed that the continents were once joined in a single supercontinent called ________ , which has since broken apart and drifted to the current positions of the continents. 1.1.2 Evidence for continental drift The evidence Wegener assembled in support of continental drift includes: geometric fit of continents (the matching outlines of opposing continental shelves, particularly South America and Africa, suggesting a former connection); geological evidence (matching rock types, ages, and structural features such as fold mountain belts across the Atlantic, consistent with the continuation of the same geological formations before separation); palaeoclimatic evidence (glacial deposits and striated bedrock indicating past glaciation in regions now near the equator, such as India and southern Africa, consistent with their former position near the South Pole).

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Palaeontological evidence is among the most compelling: the freshwater reptile Mesosaurus, found only in South America and southern Africa, could not have crossed the open Atlantic Ocean, suggesting the two continents were once joined; the seed fern Glossopteris, a distinctive fossil plant found on all southern continents (South America, Africa, Antarctica, Australia, and India), demonstrates that these landmasses were once connected; similarly, the Lystrosaurus mammal-like reptile fossils found across Africa, Antarctica, and India support a common landmass. Fill in the blank: The fossil seed fern ________ , found on all southern continents, provides compelling palaeontological evidence that these landmasses were once joined in a single supercontinent. 1.1.3 Plate tectonics as the mechanism The theory of plate tectonics, developed in the 1960s, provided the physical mechanism that Wegener lacked; the Earth lithosphere (crust and upper mantle) is divided into a mosaic of rigid plates that move relative to one another, driven by convection currents in the underlying asthenosphere; at mid-ocean ridges (divergent plate boundaries), new oceanic crust is continuously created as magma rises and solidifies, pushing the plates apart in a process called seafloor spreading; at subduction zones (convergent boundaries), older oceanic crust is consumed back into the mantle. Continental drift is therefore a consequence of plate movement: continents are embedded in and carried along with the lithospheric plates; the rate of plate movement is typically a few centimetres per year, similar to the rate at which fingernails grow, but over geological timescales of tens to hundreds of millions of years this produces the vast movements documented in the geological and palaeontological record; palaeomagnetic evidence (the alternating bands of normal and reversed magnetic polarity symmetrically distributed on either side of mid-ocean ridges) provided decisive proof of seafloor spreading. Fill in the blank: Seafloor spreading at mid-ocean ________ creates new oceanic crust as magma rises and solidifies, pushing tectonic plates apart and driving continental drift.

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Figure 1.1: Continental drift theory and evidence Pilot questions 1.1 1. State the name and year of Wegener continental drift hypothesis and the supercontinent he proposed. 2. Name four types of evidence Wegener used to support continental drift. 3. Explain why Wegener hypothesis was initially rejected. 4. Explain what plate tectonics is and how it provides the mechanism for continental drift. 5. Explain what seafloor spreading is and where it occurs.

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.2 Gondwanaland and Laurasia 1.2.1 Pangaea, Gondwanaland, and Laurasia Approximately 335 to 175 million years ago, the Earth landmasses were assembled into a single supercontinent called Pangaea, which began to fragment during the Triassic and Jurassic periods; the initial fragmentation split Pangaea into two major landmasses: Laurasia in the north (comprising what are now North America, Europe, and most of Asia) and Gondwanaland (also called Gondwana) in the south (comprising what are now South America, Africa, Antarctica, Australia, and the Indian subcontinent). The two landmasses were initially separated by the Tethys Sea, a warm shallow tropical ocean; Gondwanaland itself began to fragment further during the Jurassic and Cretaceous periods, with different landmass fragments separating at different times and rates; the Indian subcontinent broke from Antarctica and drifted northward to collide with Eurasia approximately 50 million years ago, forming the Himalayan mountain range; Africa separated from South America during the Cretaceous, opening the South Atlantic Ocean. Fill in the blank: Pangaea first fragmented into ________ in the north (comprising North America, Europe, and Asia) and Gondwanaland in the south. 1.2.2 The breakup of Gondwanaland The sequence and timing of Gondwanaland breakup is reconstructed from geological, palaeomagnetic, and palaeontological evidence: Africa began separating from South America approximately 130 to 135 million years ago (Early Cretaceous), with the South Atlantic Ocean progressively widening; India separated from Antarctica-Australia around 130 million years ago and drifted rapidly northward; Australia and Antarctica remained joined until approximately 35 to 45 million years ago, when Australia separated and drifted northward, and Antarctica became isolated over the South Pole. The progressive isolation of each Gondwanaland fragment at a different time had profound biogeographic consequences: organisms present on the separating landmass were vicariated (split

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS apart by the opening ocean), and each isolated fragment subsequently underwent independent evolutionary diversification; the biota of Australia, South America, and Africa all bear the legacy of their Gondwanaland origin, with shared ancient lineages (such as the ratite birds and southern beeches Nothofagus) distributed across fragments that were

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