2.5 Biogeographical consequences of plate tectonics

Plate tectonics reshapes Earth's surface, driving species distribution and evolution. Continental drift, mountain formation, and ocean basin changes create barriers and corridors for organisms, influencing biodiversity patterns globally.

These geological processes impact climate, form new habitats, and isolate populations. Understanding tectonic biogeography helps explain current species distributions, predict future changes, and guides conservation efforts in a dynamic world.

Continental drift theory

• Explains the movement of Earth's continents over geological time scales, fundamentally reshaping our understanding of global biogeography
• Provides a framework for understanding the distribution of species and ecosystems across the planet, linking geological processes to biological patterns

Early evidence for drift

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• Matching coastlines of continents suggested they once fit together like puzzle pieces
• Similar fossil records found on now-separated continents indicated past connections (Glossopteris flora in South America, Africa, India, and Australia)
• Geological similarities across distant landmasses pointed to shared histories (mountain ranges, rock types)
• Paleoclimatic evidence showed tropical plant fossils in now-polar regions, suggesting continental movement

Wegener's hypothesis

• Alfred Wegener proposed the theory of continental drift in 1912, challenging prevailing views of static continents
• Wegener's "supercontinent" Pangaea explained the distribution of fossils and geological features across modern continents
• Proposed mechanisms for continental movement included centrifugal force and lunar tides, later proven incorrect
• Faced significant scientific skepticism due to lack of a plausible mechanism for continent movement

Modern plate tectonics

• Developed in the 1960s, integrating continental drift with seafloor spreading and subduction processes
• Explains continental movement through the interaction of rigid lithospheric plates floating on the asthenosphere
• Supported by multiple lines of evidence including paleomagnetism, seafloor magnetic anomalies, and earthquake distributions
• Provides a unifying theory for Earth's geological processes, including mountain building, volcanism, and earthquake activity

Plate boundaries and movements

• Describes the interactions between tectonic plates, driving global geological processes and shaping Earth's surface
• Influences the formation and evolution of habitats, creating barriers and corridors for species dispersal and evolution

Convergent vs divergent boundaries

• Convergent boundaries occur where plates move towards each other, resulting in:
  • Subduction zones where oceanic crust sinks beneath continental or oceanic plates (Pacific Ring of Fire)
  • Continental collision forming mountain ranges (Himalayas)
• Divergent boundaries form where plates move apart, creating:
  • Mid-ocean ridges where new oceanic crust is formed (Mid-Atlantic Ridge)
  • Rift valleys in continental settings (East African Rift)
• Impacts biogeography by creating or removing barriers to species movement and creating new habitats

Transform faults

• Occur where plates slide horizontally past each other, neither creating nor destroying crust
• Often result in earthquakes due to friction between moving plates (San Andreas Fault)
• Can create localized habitats and influence species distributions through landscape changes
• May act as barriers or corridors for species movement depending on their orientation and associated topography

Hot spots and mantle plumes

• Stationary areas of upwelling magma from deep within the Earth's mantle
• Create chains of volcanic islands as tectonic plates move over them (Hawaiian-Emperor seamount chain)
• Provide opportunities for speciation and adaptive radiation on newly formed islands
• Influence ocean currents and climate patterns, affecting marine and terrestrial ecosystems

Biogeographical impacts of tectonics

• Tectonic processes fundamentally shape the distribution and evolution of life on Earth
• Create and destroy land bridges, isolate populations, and form new habitats, driving biodiversity patterns

Vicariance vs dispersal

• Vicariance involves the separation of populations by geological events:
  • Formation of mountain ranges or ocean basins splitting previously continuous populations
  • Results in allopatric speciation as populations evolve independently (marsupials in Australia and South America)
• Dispersal occurs when organisms move across existing barriers:
  • Long-distance dispersal events (seeds carried by wind or birds)
  • Gradual range expansion along newly formed land bridges
• Both processes contribute to biogeographical patterns, with their relative importance debated in different scenarios

Allopatric speciation

• Occurs when populations become geographically isolated, leading to independent evolution
• Tectonic events often create barriers that promote allopatric speciation:
  • Formation of islands (Galápagos finches)
  • Mountain building (Andean cloud forests)
  • Continental breakup (placental vs marsupial mammals)
• Results in unique species assemblages in different regions, contributing to global biodiversity

Adaptive radiation

• Rapid diversification of species from a common ancestor to fill diverse ecological niches
• Often occurs following major tectonic events that create new habitats or isolate populations:
  • Hawaiian honeycreepers diversifying across different island habitats
  • Cichlid fish radiation in African rift lakes
• Drives the evolution of novel traits and adaptations, increasing biodiversity in newly available environments

Formation of major biomes

• Tectonic processes play a crucial role in shaping Earth's major biomes by influencing climate patterns and creating diverse landscapes
• Understanding biome formation helps explain global biodiversity distribution and ecosystem functioning

Tropical rainforests

• Develop in areas of consistent high rainfall and warm temperatures near the equator
• Tectonic uplift creates orographic rainfall patterns supporting rainforest development:
  • Andes mountains influence Amazon rainforest climate
  • Himalayan uplift affects Southeast Asian rainforests
• Continental drift has influenced rainforest distribution over geological time:
  • Breakup of Gondwana separated tropical forests on different continents
  • Collision of India with Asia created conditions for Asian rainforests

Deserts and arid regions

• Form in areas of low precipitation, often due to global circulation patterns or rain shadow effects
• Tectonic processes contribute to desert formation through:
  • Mountain building creating rain shadows (Atacama Desert)
  • Continental positioning affecting atmospheric circulation (Sahara Desert)
• Plate movements can shift continents into arid zones or create conditions for increased aridity over time

Mountain ranges

• Result from tectonic collision or uplift, creating diverse habitats along elevation gradients
• Influence regional and global climate patterns:
  • Orographic rainfall on windward slopes
  • Rain shadows on leeward sides
• Promote speciation and endemism through isolation and varied environmental conditions:
  • Altitudinal zonation of vegetation and animal life
  • Sky islands harboring unique species assemblages

Paleobiogeography

• Studies the distribution of ancient life forms and ecosystems in relation to past continental configurations
• Provides insights into the evolution and dispersal of species over geological time scales

Pangaea and early distributions

• Pangaea, the supercontinent existing from ~335 to 175 million years ago, allowed widespread distribution of terrestrial organisms
• Uniform climate and lack of major barriers facilitated:
  • Global distribution of early reptiles and amphibians
  • Widespread plant groups (Glossopteris flora across southern Pangaea)
• Set the stage for subsequent diversification as continents separated

Breakup of supercontinents

• Fragmentation of Pangaea into Laurasia (northern continents) and Gondwana (southern continents) began ~180 million years ago
• Resulted in:
  • Isolation and independent evolution of flora and fauna on separate landmasses
  • Formation of new ocean basins and marine ecosystems
• Gondwana breakup led to the distinctive biotas of Africa, South America, Australia, Antarctica, and India

Fossil evidence of past ranges

• Fossils provide crucial evidence for historical species distributions and past continental connections
• Key examples include:
  • Mesosaurus fossils in South America and Africa supporting continental drift theory
  • Fossil marsupials in South America and Australia indicating past connections
• Molecular clock analyses complement fossil data to reconstruct biogeographical histories and divergence times

Island biogeography and tectonics

• Explores how tectonic processes influence the formation, colonization, and evolution of island ecosystems
• Provides insights into fundamental ecological and evolutionary processes

Volcanic vs continental islands

• Volcanic islands form from oceanic hotspots or along plate boundaries:
  • Often younger and more isolated (Hawaiian Islands)
  • Colonized entirely by long-distance dispersal
• Continental islands result from flooding of continental margins or tectonic separation:
  • May have a history of connection to mainlands (British Isles)
  • Often retain relict species from past continental connections
• Island type influences biodiversity patterns and evolutionary trajectories of colonizing species

Colonization and endemism

• Islands are colonized through various dispersal mechanisms:
  • Wind dispersal of seeds and small organisms
  • Rafting of larger animals on floating vegetation
  • Bird-mediated dispersal of plants and small animals
• Isolation promotes endemism through:
  • Adaptive radiation of colonizing lineages (Darwin's finches)
  • Anagenetic evolution of single lineages (Cocos Island finch)
• Degree of isolation and island age influence rates of colonization and endemism

Island arc systems

• Form along convergent plate boundaries where oceanic plates subduct:
  • Create chains of volcanic islands (Mariana Islands)
  • Provide stepping stones for species dispersal across ocean basins
• Influence marine biodiversity through:
  • Creation of diverse shallow water habitats
  • Altering ocean currents and nutrient upwelling patterns
• Can eventually collide with continents, transferring unique island biotas to mainland environments

Climate changes due to tectonics

• Tectonic processes significantly influence global and regional climate patterns over geological time scales
• Climate changes driven by tectonics have profound impacts on species distributions and ecosystem structure

Mountain building and rain shadows

• Orographic uplift creates precipitation gradients:
  • Increased rainfall on windward slopes supports lush vegetation (Pacific Northwest forests)
  • Rain shadows on leeward sides create arid conditions (Great Basin Desert)
• Mountain ranges influence atmospheric circulation patterns:
  • Tibetan Plateau uplift intensified Asian monsoon systems
  • Andes formation altered South American climate and vegetation patterns

Ocean current alterations

• Tectonic changes in ocean basin configuration affect global ocean circulation:
  • Closure of the Central American Seaway ~3 million years ago strengthened the Gulf Stream
  • Opening of Drake Passage allowed circumpolar current development, isolating Antarctica
• Changes in ocean currents influence:
  • Heat and moisture distribution across the planet
  • Marine productivity and ecosystem structure
  • Continental climate patterns through ocean-atmosphere interactions

Global temperature shifts

• Long-term climate trends are influenced by tectonic processes:
  • Continental positions affect global heat distribution (polar continents promote ice sheet formation)
  • Mountain building increases weathering rates, drawing down atmospheric CO2
• Major tectonic events linked to global climate shifts:
  • Himalayan uplift associated with Cenozoic cooling trend
  • Breakup of Pangaea influenced transition from Mesozoic greenhouse to Cenozoic icehouse conditions

Biodiversity hotspots and tectonics

• Examines the relationship between areas of exceptional species richness and endemism and tectonic activity
• Highlights the importance of geological processes in creating and maintaining biodiversity

Centers of endemism

• Areas with high concentrations of species found nowhere else on Earth
• Often associated with tectonic activity:
  • Mountainous regions with complex topography (Tropical Andes)
  • Recently isolated islands or archipelagos (Madagascar)
• Tectonic processes promote endemism through:
  • Creation of diverse habitats and environmental gradients
  • Isolation of populations leading to allopatric speciation

Refugia during climate shifts

• Areas that maintain relatively stable conditions during periods of climate change
• Tectonic features often create or preserve refugia:
  • Mountain ranges providing elevational gradients for species to track climate (European Alps during ice ages)
  • Deep valleys or gorges maintaining microclimates (Pleistocene refugia in Amazon Basin)
• Refugia play crucial roles in:
  • Preserving biodiversity during unfavorable climatic periods
  • Serving as sources for post-disturbance recolonization

Tectonic collision zones

• Areas where tectonic plates converge, often resulting in complex landscapes and high biodiversity
• Examples of biodiversity hotspots in collision zones:
  • Wallacea in Indonesia, where Asian and Australian plates meet
  • Mediterranean Basin, at the intersection of African and Eurasian plates
• Promote biodiversity through:
  • Mixing of previously separate biotas
  • Creation of diverse habitats through mountain building and island formation
  • Dynamic landscapes maintaining non-equilibrium conditions favoring speciation

Human impacts and future changes

• Explores the intersection of human activities, tectonic processes, and biogeographical patterns
• Considers how ongoing tectonic activity and anthropogenic changes will shape future species distributions

Anthropogenic climate change

• Rapid warming due to human activities interacts with tectonic influences on climate:
  • Accelerated melting of glaciers in tectonically active mountain ranges
  • Changes in precipitation patterns affecting rain shadow deserts
• Species responses to climate change influenced by tectonic landscapes:
  • Upslope migration in mountainous areas (Andean cloud forest species)
  • Shifts in marine species distributions due to changing ocean currents

Conservation in tectonic regions

• Tectonic hotspots often coincide with areas of high biodiversity and endemism:
  • Challenges include natural hazards and human development pressures
  • Opportunities for protecting unique and diverse ecosystems
• Conservation strategies in tectonically active regions:
  • Designing protected areas to accommodate species range shifts
  • Maintaining connectivity across complex landscapes
  • Considering geological processes in long-term conservation planning

Predicting future distributions

• Integrating tectonic processes into species distribution models:
  • Incorporating long-term landscape evolution in predictions
  • Considering how tectonic activity might create future refugia or dispersal corridors
• Challenges in forecasting biogeographical changes:
  • Uncertainty in rates of tectonic processes and climate change
  • Complex interactions between geological, climatic, and biological systems
• Importance of understanding historical tectonic influences for accurate future predictions

Case studies in tectonic biogeography

• Examines specific examples illustrating the profound influence of tectonic processes on species distributions and evolution
• Provides concrete applications of biogeographical principles in understanding global biodiversity patterns

Wallaces line and Asian fauna

• Biogeographical boundary separating Asian and Australian fauna in Indonesia
• Resulted from complex tectonic history:
  • Collision of Australian and Southeast Asian plates
  • Formation of deep water channels between islands
• Influences faunal distributions:
  • Western islands (Borneo, Sumatra) with Asian fauna (tigers, rhinos)
  • Eastern islands (New Guinea) with Australian fauna (marsupials, birds of paradise)
• Demonstrates importance of geological history in shaping modern biodiversity patterns

South American mammal evolution

• Illustrates the impact of tectonic isolation and subsequent connections on evolutionary trajectories
• Key events in South American mammal evolution:
  • Isolation during much of the Cenozoic leading to unique fauna (giant ground sloths, glyptodonts)
  • Great American Biotic Interchange following formation of Panama Isthmus ~3 million years ago
• Resulted in complex patterns of extinction, adaptation, and diversification:
  • Extinction of many endemic South American mammals
  • Successful radiation of North American immigrants (jaguars, llamas)

African rift valley speciation

• Demonstrates how tectonic activity can drive rapid speciation and adaptive radiation
• East African Rift System created diverse aquatic and terrestrial habitats:
  • Formation of deep lakes (Lake Tanganyika, Lake Malawi)
  • Creation of isolated mountain ranges and valleys
• Notable examples of rift-driven speciation:
  • Cichlid fish radiation in African Great Lakes
  • Diversification of plants and animals in montane forests and grasslands
• Ongoing tectonic activity continues to shape African biodiversity patterns