2.6 Vicariance and geodispersal
6 min read•august 21, 2024
and are key processes shaping global biodiversity. Vicariance occurs when populations are separated by physical barriers, leading to . Geodispersal involves range expansion as barriers disappear, allowing species to spread to new areas.
These processes are driven by geological events like , sea level changes, and mountain formation. Understanding vicariance and geodispersal helps explain current species distributions, evolutionary patterns, and how biodiversity may respond to future environmental changes.
Definition of vicariance
- Vicariance describes the geographic separation of populations due to physical barriers leading to speciation
- Plays a crucial role in shaping global biodiversity patterns and species distributions
- Fundamental concept in world biogeography explaining how similar species occur in different parts of the world
Types of vicariant events
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- Tectonic events split continents and create new physical barriers (formation of the Isthmus of Panama)
- Climate changes cause and isolate populations (glacial periods)
- Mountain range formation divides previously continuous habitats (uplift of the Andes)
- Sea level fluctuations create or remove land bridges between regions ()
Importance in biogeography
- Explains disjunct distributions of related species across different continents
- Provides a mechanism for allopatric speciation and evolution of
- Helps reconstruct historical biogeography and past continental configurations
- Influences current biodiversity patterns and species richness in different regions
Geodispersal concept
- Refers to the expansion of species ranges due to the removal of geographic barriers
- Contrasts with vicariance by focusing on the joining of previously separated areas
- Significant in understanding species distributions and biogeographic patterns over geological time
Mechanisms of geodispersal
- Formation of land bridges connects previously isolated landmasses (Isthmus of Panama)
- Sea level drops expose continental shelves and create new dispersal routes
- Tectonic collisions join separate landmasses and their biotas (India-Asia collision)
- Climate changes create corridors through previously inhospitable regions (greening of the Sahara)
Geodispersal vs vicariance
- Geodispersal results in range expansion while vicariance leads to range fragmentation
- Both processes can occur cyclically as barriers form and disappear over geological time
- Geodispersal often increases species richness in an area while vicariance may lead to speciation
- Understanding the interplay between these processes helps explain complex biogeographic patterns
Geological processes
- Fundamental drivers of both vicariance and geodispersal events in world biogeography
- Operate over long time scales shaping the Earth's surface and influencing species distributions
Plate tectonics and vicariance
- Continental drift separates landmasses and creates vicariant events (breakup of Gondwana)
- Seafloor spreading forms new oceanic barriers between populations
- Subduction and mountain building create topographic barriers (Andes formation)
- Island arc formation leads to stepping-stone dispersal and subsequent isolation
Sea level changes
- Glacial-interglacial cycles cause global sea level fluctuations
- Low sea levels expose land bridges facilitating geodispersal (Bering land bridge)
- High sea levels isolate populations on islands or high elevation areas
- Influences coastal habitat availability and marine species distributions
Biological implications
- Vicariance and geodispersal significantly impact evolutionary processes and biodiversity patterns
- Understanding these processes helps explain current species distributions and predict future changes
Allopatric speciation
- Geographic isolation leads to independent evolution of separated populations
- Genetic drift and adaptation to local conditions drive divergence
- Reproductive isolation develops over time preventing gene flow if populations reconnect
- Results in sister species on different sides of a barrier (Darwin's finches on Galápagos Islands)
Genetic divergence
- Vicariance events initiate genetic differentiation between isolated populations
- Mutation rates and selection pressures influence the speed of divergence
- Genetic markers used to estimate divergence times and reconstruct biogeographic history
- Phylogeographic studies reveal population structure and historical demographic changes
Case studies
- Specific examples illustrate the principles of vicariance and geodispersal in world biogeography
- Provide evidence for the impact of geological and climatic events on species distributions
Gondwanan vicariance
- Breakup of the supercontinent Gondwana led to vicariant speciation events
- Ratite birds (ostriches, emus, kiwis) evolved on different southern continents
- Marsupial mammals diversified in Australia and South America
- Plant families show disjunct distributions across former Gondwanan landmasses (Nothofagus trees)
Marine organism dispersal
- Ocean currents facilitate long-distance dispersal of marine species
- Periodic land bridge formation allows exchange between ocean basins (Great American Biotic Interchange)
- Vicariance occurs when ocean basins become isolated (closure of the Tethys Sea)
- Larval dispersal patterns influence genetic connectivity of marine populations
Methods of analysis
- Various analytical techniques help researchers study vicariance and geodispersal patterns
- Combining multiple methods provides a more comprehensive understanding of biogeographic history
Phylogenetic approaches
- Construct evolutionary trees to infer relationships between species
- Compare phylogenies with geological events to identify potential vicariance or dispersal events
- Biogeographic methods like Dispersal-Vicariance Analysis (DIVA) optimize ancestral distributions
- Parsimony and maximum likelihood methods used to reconstruct biogeographic scenarios
Molecular clock techniques
- Estimate divergence times between lineages using genetic data
- Calibrate molecular clocks with fossil evidence or geological events
- Help distinguish between ancient vicariance and more recent long-distance dispersal
- Relaxed clock models account for rate variation across lineages and through time
Vicariance biogeography
- Theoretical framework emphasizing the role of geological events in shaping species distributions
- Developed as an alternative to dispersalist explanations for biogeographic patterns
Historical development
- Emerged in the 1970s with the acceptance of plate tectonic theory
- Pioneered by researchers like Léon Croizat and Gareth Nelson
- Emphasized pattern-based approaches to biogeography
- Led to the development of cladistic biogeography methods
Criticisms and limitations
- Overemphasis on vicariance at the expense of dispersal explanations
- Difficulty in distinguishing between vicariance and geodispersal in some cases
- Challenges in dating divergence events accurately
- Neglect of ecological factors influencing species distributions
Dispersal-vicariance analysis
- Analytical method combining elements of both dispersalist and vicariance approaches
- Aims to reconstruct ancestral distributions and biogeographic events
DIVA method
- Optimizes ancestral distributions on phylogenetic trees
- Assigns costs to different biogeographic events (vicariance, dispersal, extinction)
- Finds the most parsimonious explanation for current distributions
- Implemented in software packages like RASP (Reconstruct Ancestral State in Phylogenies)
Applications in research
- Used to study historical biogeography of various plant and animal groups
- Helps identify major biogeographic events and dispersal routes
- Combines with molecular dating to test hypotheses about timing of events
- Informs conservation strategies by revealing historical connectivity between populations
Biogeographic patterns
- Observable distribution patterns of species and higher taxa across the globe
- Result from complex interactions of historical and ecological processes
Disjunct distributions
- Discontinuous ranges of closely related taxa separated by large geographic distances
- Often explained by vicariance events or long-distance dispersal
- Amphi-Atlantic distributions in plants suggest former land connections
- Circum-Antarctic distributions in marine organisms reflect ancient vicariance and dispersal
Endemism and vicariance
- High levels of endemism often associated with long-term isolation due to vicariance
- Biodiversity hotspots frequently result from vicariant events (, New Caledonia)
- Relict species represent remnants of formerly widespread groups isolated by vicariance
- Island archipelagos showcase endemism patterns related to vicariance and dispersal (Hawaiian honeycreepers)
Conservation implications
- Understanding vicariance and geodispersal processes informs conservation strategies
- Historical biogeography provides context for current biodiversity patterns and future changes
Habitat fragmentation
- Anthropogenic fragmentation mimics natural vicariance processes
- Disrupts gene flow between populations leading to genetic isolation
- May accelerate speciation in some cases but often threatens population viability
- Conservation corridors attempt to mitigate fragmentation effects
Climate change effects
- Alters species distributions and creates new opportunities for dispersal or isolation
- May lead to novel combinations of species as ranges shift
- Threatens species adapted to specific climatic conditions or with limited dispersal abilities
- Understanding past responses to climate change helps predict future biodiversity patterns
Key Terms to Review (18)
Adaptive radiation: Adaptive radiation is the evolutionary process where organisms diversify rapidly into a variety of forms to adapt to different environments or niches. This phenomenon often occurs when a species colonizes a new area with diverse habitats, leading to the emergence of new species that are adapted to those varying conditions.
Bering Land Bridge: The Bering Land Bridge, also known as Beringia, was a land connection between Asia and North America that existed during the last Ice Age, allowing for the migration of people and animals across what is now the Bering Strait. This bridge played a critical role in the dispersal of species and human populations, highlighting how geographic barriers can shape the distribution of life through vicariance and geodispersal events.
Continental drift: Continental drift is the theory that the Earth's continents have moved over geological time, shifting positions relative to one another. This movement is primarily due to the processes associated with plate tectonics, leading to significant changes in climate, sea levels, and the distribution of species across the globe.
David M. Raup: David M. Raup was a prominent paleontologist known for his work in evolutionary biology and biogeography, particularly in understanding patterns of biodiversity and extinction. His contributions helped shape the field of biogeography by emphasizing the significance of both vicariance and geodispersal in the distribution of species over time, ultimately influencing how scientists study the historical relationships between organisms and their environments.
Disjunct distribution: Disjunct distribution refers to a pattern where populations of the same species are geographically separated by large distances, often with gaps that prevent continuous distribution. This can occur due to historical events like continental drift or climate change, leading to isolated populations that may evolve independently. Understanding disjunct distribution is crucial for studying how species adapt to different environments and how historical biogeographical processes shape current biodiversity.
Dispersal limitation: Dispersal limitation refers to the restrictions on the movement of organisms that can prevent species from reaching suitable habitats or colonizing new areas. This concept is crucial in understanding patterns of biodiversity, especially in the context of geographic barriers and habitat fragmentation, as well as the dynamics of species distributions over time. Dispersal limitations can occur due to physical barriers like mountains and rivers or biotic factors such as predation or competition, influencing both vicariance events and the colonization processes observed in island ecosystems.
Endemic species: Endemic species are organisms that are native to and restricted to a specific geographical area. These species have evolved over time in isolation, making them unique to their environment and often vulnerable to changes such as habitat loss or climate change.
Geodispersal: Geodispersal refers to the movement of organisms across geographical barriers, leading to the spread and diversification of species. This process can occur through various mechanisms such as wind, water, or animal movement, enabling organisms to establish new populations in different locations. It is an important concept in understanding how species distribution patterns change over time, especially in relation to vicariance events where physical barriers arise, separating populations.
Habitat fragmentation: Habitat fragmentation refers to the process in which larger habitats are divided into smaller, isolated patches, often due to human activities like urban development, agriculture, and infrastructure projects. This division can significantly affect biodiversity, species interactions, and ecosystem functions, as it alters the landscape and limits the movement of organisms between habitat patches.
Himalayan uplift: Himalayan uplift refers to the geological process that led to the formation and elevation of the Himalayan mountain range, which began around 50 million years ago due to the collision between the Indian Plate and the Eurasian Plate. This monumental event not only shaped the landscape of South Asia but also had significant ecological and biogeographical implications, including influencing climate patterns and species distribution in the region.
Madagascar: Madagascar is the fourth largest island in the world, located off the southeastern coast of Africa, and is renowned for its unique biodiversity and rich ecosystems. The island's isolation has led to a high number of endemic species, making it a significant area for studying evolutionary processes, biogeography, and conservation efforts.
Neutral Theory of Biogeography: The neutral theory of biogeography proposes that the diversity and distribution of species are primarily driven by random processes of colonization, extinction, and dispersal rather than deterministic factors like natural selection. This perspective highlights how geographic isolation and environmental changes can affect species distribution, emphasizing the role of chance events in shaping biodiversity over time.
Panbiogeography: Panbiogeography is an approach in biogeography that focuses on the distribution of organisms across geographical space, emphasizing the relationships between their locations and geological events. It analyzes patterns of biotic distribution through the lens of historical geography, particularly looking at how vicariance and geodispersal have influenced species distribution over time. This perspective aids in understanding how past environmental changes shape the current biodiversity we see today.
Robert J. Whittaker: Robert J. Whittaker was an influential American ecologist known for his work on plant ecology and biogeography, particularly the development of the concept of 'plant community types' and the significance of environmental gradients in determining species distribution. His contributions to biogeography are particularly relevant in understanding patterns of vicariance and geodispersal, emphasizing how geographical and environmental changes shape biodiversity.
Speciation: Speciation is the evolutionary process through which new biological species arise, driven by factors such as genetic divergence and reproductive isolation. This process plays a critical role in biodiversity, as it leads to the formation of distinct species that adapt to various environmental conditions and ecological niches.
Sundaland: Sundaland is a biogeographical region that encompasses the Malay Peninsula, Borneo, Sumatra, Java, and surrounding islands. It is significant for its unique biodiversity and geological history, shaped by past sea level changes that created land bridges and separated species. This region plays a crucial role in understanding the processes of vicariance and geodispersal, as well as being part of the Indomalayan realm which is characterized by rich flora and fauna, and is also recognized as a biodiversity hotspot due to its high levels of endemism and threats from human activities.
Tectonic plate movement: Tectonic plate movement refers to the shifting of the Earth's lithosphere, which is divided into several large and small plates that float on the semi-fluid asthenosphere beneath. This movement can lead to significant geological events, such as earthquakes and volcanic activity, and plays a crucial role in shaping the distribution of biodiversity and biogeographic patterns across the planet.
Vicariance: Vicariance refers to the process by which a population is split into separate groups due to geographical barriers, leading to the development of distinct lineages. This concept is crucial for understanding how species distributions are affected by historical events such as continental drift and the formation of physical barriers that isolate populations.