Convection currents in the Earth's mantle push continental plates around.
Historical Context of Continental Drift
Pangaea
Approximately 250 million years ago, all continents were interconnected in a supercontinent known as Pangaea.
Breakup of Pangaea
Pangaea later split into two supercontinents about 200 million years ago:
Gondwana (southern supercontinent)
Laurasia (northern supercontinent)
Further Splitting of Supercontinents
Gondwana's Split
Gondwana fractured into present-day continents:
South America
Africa
Antarctica
Australia
India
Laurasia's Connecting Countries
Laurasia included modern Europe, Asia, and North America and maintained connections longer before eventually breaking up.
Modern Continental Arrangement
Through geological processes, continents shifted to their current locations creating the Atlantic Ocean Basin.
The movement of continents led to species populations becoming isolated, allowing independent evolution.
Mechanisms of Plate Movement
Current Movement
Continents are still moving:
Example: Nazca plate and Pacific plate are pulling apart.
Example: Filipino plate and North American plate are colliding.
Ring of Fire
A significant area of volcanic activity located around the Pacific plate boundaries.
Ecological Consequences of Continental Drift
Barriers to Dispersal
Separation of continents creates barriers, leading to isolated populations evolving independently.
Example: India and Madagascar separated from Africa about 100 million years ago.
Creating Ecological Exchanges
When continents reconnect, it breaks barriers and allows species exchange, leading to greater biodiversity.
Timeline of Continental Changes
Geological Timeline
Separation events:
Greenland separating from North America and Europe: 49 million years ago
Indonesia's connection: 15 million years ago
Creation of the Panamanian Isthmus: 6 million years ago
The Impact of Dispersal Barriers
Islands of Isolation
When landmasses split (e.g., Madagascar), populations can evolve into different species (biogeographic distributions).
Example lineage history comparisons reveal relatedness and contribute to diversification.
Recent Geographical Movements
Panamanian Isthmus and Ecological Impact
Completion of the isthmus allowed species to travel between North America and South America, causing an ecological exchange.
Example: Jaguars moved south as a result of connections and dispersal.
Changed Ocean Currents and Climate
Atlantic and Pacific waters were re-routed by the isthmus, impacting climates (Introduction of Gulf Stream).
Climatic Changes and Species Distribution
Historical Climate Conditions
Over the past 250 million years, plate movements significantly altered Earth's climate and biogeography.
Ice Age Cycles
Following the isthmus formation, glacial advances in the Northern Hemisphere forced many species to migrate southward.
Flora and Fauna Responses to Climate Changes
Response of Species
Example: Spruce trees were pushed south during glacial maximums and re-expanded as glaciers retreated.
Not all species reacted uniformly; some went extinct unable to adapt quickly to changes.
Biodiversity Patterns Around the World
Latitudinal Diversity Gradient
Biodiversity peaks at equatorial regions and declines towards polar regions, evident across various taxa (plants, birds, amphibians).
Notable Examples
A half-square kilometer of rainforest can contain as many tree species as a huge area of temperate forest in Europe and North America.
Theories Explaining Biodiversity Distribution
Solar Radiation Hypothesis
Regions closer to the equator receive more solar energy, which supports greater biodiversity by providing more resources.
Patterns show that increased energy correlates with species richness, but this relationship stabilizes at higher energies.
Longer Evolutionary History Hypothesis
The tropics have maintained persistent ecological zones over time, promoting higher diversity within those areas.
Climate Stability Hypothesis
Tropical regions provide less stressful conditions than temperate areas, allowing more species to thrive due to consistent resource availability.
Conclusion
Understanding the implications of continental drift and ecological exchanges is crucial for comprehending modern biodiversity patterns.
Researchers continue to study these patterns to unravel underlying ecological and evolutionary processes.
Final Exam Information
Review all discussed concepts and their implications for biodiversity, ecological exchanges, and patterns of species richness in relation to geological changes.