🌾World Biogeography
Historical biogeography examines how species distributions have changed over time. It combines ecology, evolution, geology, and climate science to understand why plants and animals live where they do today and how they got there.
Key concepts include plate tectonics, vicariance vs dispersal, and island biogeography. Scientists use fossil evidence, genetic data, and analytical methods to reconstruct past species movements and divergences, revealing Earth's complex biogeographical history.
Origins of historical biogeography
- Historical biogeography explores the distribution of plants and animals across space and time, providing insights into evolutionary processes and Earth's geological history
- Integrates concepts from ecology, evolution, geology, and climatology to understand species distributions and their changes over time
- Fundamental to understanding global biodiversity patterns and informing conservation strategies
Early biogeographical theories
Top images from around the web for Early biogeographical theories
Evidence for Evolution ‹ OpenCurriculum View original
Is this image relevant?
18.5I: Biogeography and the Distribution of Species - Biology LibreTexts View original
Is this image relevant?
Rates of Speciation | Biology for Majors II View original
Is this image relevant?
Evidence for Evolution ‹ OpenCurriculum View original
Is this image relevant?
18.5I: Biogeography and the Distribution of Species - Biology LibreTexts View original
Is this image relevant?
1 of 3
Top images from around the web for Early biogeographical theories
Evidence for Evolution ‹ OpenCurriculum View original
Is this image relevant?
18.5I: Biogeography and the Distribution of Species - Biology LibreTexts View original
Is this image relevant?
Rates of Speciation | Biology for Majors II View original
Is this image relevant?
Evidence for Evolution ‹ OpenCurriculum View original
Is this image relevant?
18.5I: Biogeography and the Distribution of Species - Biology LibreTexts View original
Is this image relevant?
1 of 3
- Developed in the 18th and 19th centuries as naturalists observed global species distribution patterns
- Georges-Louis Leclerc, Comte de Buffon proposed "Buffon's Law" stating that geographically isolated regions have distinct species
- Karl Willdenow introduced the concept of "floristic regions" based on plant distributions
- Alexander von Humboldt pioneered biogeography by linking species distributions to environmental factors
- Centers of origin theory suggested species originated in specific locations and spread outward
Contributions of Darwin and Wallace
- Charles Darwin's voyage on the HMS Beagle (1831-1836) provided crucial observations for his theory of evolution
- Darwin noted unique species on the Galápagos Islands, inspiring ideas about speciation and adaptation
- Alfred Russel Wallace independently developed similar ideas while exploring the Malay Archipelago
- Wallace Line identified a sharp biogeographical boundary between Asian and Australian fauna
- Their joint publication in 1858 presented the theory of evolution by natural selection
- Darwin's "On the Origin of Species" (1859) further elaborated on biogeographical patterns as evidence for evolution
Plate tectonics and biogeography
- Plate tectonics revolutionized understanding of species distributions and evolutionary history in biogeography
- Provides a mechanism for long-term changes in land configurations and connections between continents
- Explains similarities in flora and fauna between now-separated landmasses
Continental drift theory
- Proposed by Alfred Wegener in 1912 based on matching coastlines and similar fossils across continents
- Initially rejected by scientific community due to lack of a plausible mechanism
- Seafloor spreading discovery in the 1960s provided evidence for continental movement
- Pangaea supercontinent existed approximately 300-200 million years ago
- Breakup of Pangaea into Laurasia and Gondwana led to isolation and divergence of species
Impact on species distribution
- Explains disjunct distributions of related species on different continents (vicariance)
- Gondwanan distribution patterns observed in Southern Hemisphere flora and fauna (marsupials)
- Laurasian patterns seen in Northern Hemisphere taxa (bears)
- Influences endemism rates on different continents based on isolation time
- Affects dispersal routes and barriers for species movement
- Explains relict distributions of ancient lineages (Ginkgo biloba)
Vicariance vs dispersal
- Two primary mechanisms explaining disjunct distributions of related species
- Vicariance involves population separation by a physical barrier
- Dispersal occurs when organisms move across existing barriers
Allopatric speciation
- Occurs when populations become geographically isolated
- Genetic drift and adaptation to different environments lead to divergence
- Vicariance events often trigger allopatric speciation
- Formation of isthmuses (Panama Isthmus)
- Mountain range uplifts (Andes)
- Continental drift (marsupial evolution)
- Reproductive isolation develops over time, preventing gene flow between populations
- Can result in sister species on different landmasses
Long-distance dispersal events
- Involves movement of organisms across significant barriers
- Can lead to colonization of new areas and subsequent speciation
- Mechanisms include:
- Wind dispersal (plant seeds, small insects)
- Ocean currents (coconuts, marine iguanas)
- Animal-mediated transport (bird-dispersed seeds)
- Rafting on floating vegetation (lizards, small mammals)
- Explains unexpected distributions not explained by vicariance
- Molecular clock studies often support more recent dispersal events than vicariance alone
Phylogeography
- Integrates phylogenetics and biogeography to study geographical distributions of genetic lineages
- Provides insights into historical processes shaping current species distributions
- Utilizes molecular data to reconstruct past population movements and divergences
Molecular clock techniques
- Estimate timing of evolutionary events based on genetic differences between species
- Assumes relatively constant mutation rates over time
- Calibrated using fossil evidence or known geological events
- Relaxed clock models account for rate variation among lineages
- Bayesian methods incorporate uncertainty in rate estimates
- Helps distinguish between vicariance and dispersal explanations for distributions
Genetic evidence for migrations
- DNA sequencing reveals patterns of genetic diversity within and between populations
- Mitochondrial DNA often used for animal studies due to maternal inheritance
- Chloroplast DNA utilized for plant phylogeography
- Genetic markers indicate:
- Population bottlenecks during migrations
- Founder effects in newly colonized areas
- Gene flow between populations
- Coalescent theory used to infer demographic history from genetic data
- Reveals complex migration patterns (humans out of Africa)
Paleobiogeography
- Studies the distribution of fossil organisms to understand ancient biogeographical patterns
- Provides direct evidence of past species ranges and environmental conditions
- Crucial for understanding long-term changes in biodiversity and ecosystems
Fossil record interpretation
- Requires consideration of preservation biases and incomplete nature of fossil record
- Taphonomy studies factors affecting fossilization and preservation
- Index fossils used to date and correlate rock layers across regions
- Trace fossils provide evidence of organism behavior and paleoecology
- Microfossils (pollen, foraminifera) offer insights into past climates and environments
- Fossil assemblages indicate past community compositions and ecological interactions
Ancient distribution patterns
- Reveal historical ranges of extinct species and ancestral forms of modern taxa
- Gondwanan fossil distributions support continental drift theory
- Lazarus taxa show discontinuous fossil records due to preservation gaps
- Ghost lineages inferred from phylogenetic analyses to explain missing fossil evidence
- Fossil evidence of intercontinental dispersal events (North American-Asian mammal exchanges)
- Paleoendemism indicates species restricted to a particular area in the past
Island biogeography
- Focuses on factors influencing species richness and composition on islands
- Islands serve as natural laboratories for studying ecological and evolutionary processes
- Principles apply to other isolated habitats (lakes, mountain tops, habitat fragments)
Colonization and extinction rates
- Species richness on islands results from balance between colonization and extinction
- Colonization rate decreases as more species occupy available niches
- Extinction rate increases with more species due to competition and limited resources
- Factors affecting colonization:
- Distance from mainland (source populations)
- Island size (target effect)
- Dispersal abilities of organisms
- Factors influencing extinction:
- Island size (habitat availability, population sizes)
- Habitat diversity
- Presence of predators or competitors
Equilibrium theory
- Proposed by MacArthur and Wilson in 1967
- Predicts species richness reaches equilibrium when colonization and extinction rates balance
- Larger islands have higher equilibrium species numbers
- Islands closer to mainland have higher species richness
- Turnover in species composition occurs even at equilibrium
- Criticisms include oversimplification and neglect of speciation processes
- Extensions incorporate evolutionary processes and habitat heterogeneity
Refugia and glaciations
- Refugia are areas where species survive during periods of unfavorable climate conditions
- Glaciations have profoundly influenced species distributions and evolution over geological time
- Understanding refugia crucial for predicting responses to current climate change
Pleistocene ice ages
- Series of glacial-interglacial cycles over past 2.6 million years
- Caused by variations in Earth's orbit (Milankovitch cycles)
- Major ice sheets covered large portions of North America and Eurasia
- Sea levels dropped up to 120 meters, exposing continental shelves
- Dramatic shifts in climate zones and vegetation patterns
- Beringia land bridge allowed migrations between Asia and North America
Species range shifts
- Many species experienced latitudinal and altitudinal range shifts during glacial cycles
- Temperate species retreated to southern refugia during glacial maxima
- Recolonization of northern areas during interglacial periods
- Genetic evidence reveals:
- Multiple refugia for many species (cryptic refugia)
- Rapid postglacial expansions (leading edge effect)
- Hybridization between divergent lineages in contact zones
- Refugial populations often show high genetic diversity
- Glacial cycles contributed to speciation events in some taxa
Biogeographical regions
- Major divisions of Earth's terrestrial areas based on distinctive assemblages of plants and animals
- Reflect long-term evolutionary history and geological processes
- Important for understanding global biodiversity patterns and conservation planning
Wallace's realms
- Proposed by Alfred Russel Wallace in 1876
- Six major biogeographical realms:
- Nearctic (North America)
- Neotropical (Central and South America)
- Palearctic (Eurasia and North Africa)
- Ethiopian/Afrotropical (Sub-Saharan Africa)
- Oriental/Indomalayan (South and Southeast Asia)
- Australian (Australia, New Guinea, and nearby islands)
- Based on distribution patterns of animal families and genera
- Reflect both historical connections and long-term isolation of regions
- Later additions include Antarctic and Oceanic realms
Transition zones and boundaries
- Areas where biogeographical regions meet and overlap
- Often have high biodiversity due to mixing of different biotas
- Wallace Line marks boundary between Oriental and Australian realms
- Wallacea transition zone includes islands between Wallace and Lydekker lines
- Mexican transition zone between Nearctic and Neotropical realms
- Sahel transition zone between Palearctic and Afrotropical realms
- Boundaries can shift over time due to climate change and tectonic activity
Methods in historical biogeography
- Analytical approaches to reconstruct historical biogeographical patterns and processes
- Integrate phylogenetic, distributional, and geological data
- Aim to test hypotheses about historical events shaping current distributions
Cladistic biogeography
- Uses phylogenetic relationships of organisms to infer area relationships
- Assumes vicariance as primary mechanism for disjunct distributions
- Steps include:
- Construct taxon cladograms for multiple groups
- Replace taxa with their areas of distribution
- Search for congruent patterns across area cladograms
- General area cladogram represents shared history of regions
- Limitations include difficulty in accounting for dispersal and extinction events
Parsimony analysis of endemicity
- Focuses on distributions of endemic taxa rather than phylogenetic relationships
- Creates presence-absence matrix of taxa across areas
- Uses parsimony algorithms to find most parsimonious area cladogram
- Assumes minimal dispersal and treats each taxon as independent character
- Useful when phylogenetic information is limited or unavailable
- Can identify areas of endemism and potential vicariance events
- Limitations include sensitivity to sampling biases and homoplasy
Human impact on biogeography
- Anthropogenic activities have dramatically altered species distributions and biogeographical patterns
- Humans act as both dispersal vectors and creators of barriers
- Understanding human impacts crucial for conservation and management of biodiversity
Anthropogenic species introductions
- Intentional and accidental transport of species to new areas
- Causes include:
- Agriculture and horticulture (crop plants, ornamentals)
- Pet trade and zoos (escaped exotic animals)
- Ballast water in ships (aquatic organisms)
- Cargo transport (insects, plants)
- Invasive species can disrupt native ecosystems and cause economic damage
- Homogenization of biotas across regions (Anthropocene mixing)
- Some introductions lead to successful naturalizations and range expansions
Habitat fragmentation effects
- Breaking up of continuous habitats into smaller, isolated patches
- Causes include deforestation, urbanization, and agricultural expansion
- Impacts on biogeography:
- Reduced gene flow between populations
- Increased edge effects and vulnerability to disturbances
- Changes in species composition and community structure
- Altered dispersal patterns and migration routes
- Island biogeography theory applied to habitat fragments
- Metapopulation dynamics become important for species persistence
- Conservation strategies include creating corridors and maintaining habitat connectivity