Glossary

4.4 Disjunct distributions

5 min read•august 21, 2024

Disjunct distributions occur when species inhabit separate areas with no current connectivity. These patterns result from various factors like , long-distance , and climate change. Understanding disjunct distributions is crucial for unraveling biogeographical histories and evolutionary processes.

Studying disjunct distributions involves methods like phylogenetic analysis and fossil record examination. These patterns have significant implications for speciation, genetic diversity, and conservation. As climate change progresses, existing disjunctions may shift, creating new challenges for species survival and biodiversity preservation.

Definition of disjunct distributions

  • Disjunct distributions describe populations of organisms separated by significant geographical barriers
  • Occur when species inhabit two or more distinct areas with no current connectivity
  • Play a crucial role in understanding historical biogeography and evolutionary processes

Types of disjunct distributions

Continental disjunctions

Top images from around the web for Continental disjunctions

1 of 3

Top images from around the web for Continental disjunctions

1 of 3
  • Occur when populations are separated across different continents
  • Often result from continental drift or long-distance dispersal events
  • Include classic examples like southern beech trees (Nothofagus) found in South America, Australia, and New Zealand

Oceanic disjunctions

  • Involve populations separated by large bodies of water
  • Can result from island hopping or long-distance dispersal mechanisms
  • Exemplified by plant species found on both sides of the Atlantic Ocean (amphiatlantic disjunctions)

Altitudinal disjunctions

  • Describe populations separated by elevation differences
  • Often occur in mountainous regions with distinct ecological zones
  • Include species found at high elevations in separate mountain ranges (sky islands)

Causes of disjunct distributions

Vicariance events

  • Occur when a previously continuous population is divided by a physical barrier
  • Include geological events like mountain formation or continental separation
  • Result in isolated populations that may evolve independently over time

Long-distance dispersal

  • Involves movement of organisms or propagules across significant barriers
  • Can occur through various mechanisms (wind, water, animal vectors)
  • Explains some unexpected disjunctions across large distances (transoceanic dispersal)

Habitat fragmentation

  • Results from the breaking up of continuous habitats into smaller, isolated patches
  • Often caused by natural processes or human activities
  • Creates disjunct populations within formerly continuous ranges

Climate change

  • Alters species distributions over time as environmental conditions shift
  • Can lead to range contractions and fragmentation of populations
  • Explains some disjunctions as remnants of formerly widespread distributions during different climatic periods

Examples of disjunct distributions

Plant disjunctions

  • Ginkgo biloba native to China, with relict populations in Japan and Korea
  • Sequoia sempervirens (coast redwood) restricted to California and Oregon coasts
  • Araucaria species found in South America and Australasia

Animal disjunctions

  • Tapirs found in Southeast Asia and Central/South America
  • Camels native to Central Asia and South America (llamas, alpacas)
  • Alligators occurring in southeastern United States and eastern China

Microbial disjunctions

  • Thermophilic bacteria found in geothermal areas across different continents
  • Halophilic archaea inhabiting hypersaline environments worldwide
  • Extremophiles in deep-sea hydrothermal vents with similar species in geographically distant locations

Biogeographical implications

Speciation and endemism

  • Disjunct populations may evolve into distinct species over time
  • Leads to high levels of in isolated areas
  • Contributes to unique biodiversity patterns in different regions

Genetic diversity patterns

  • Disjunct populations often show reduced genetic diversity compared to continuous populations
  • May exhibit genetic drift and founder effects
  • Can lead to local adaptations and divergence between isolated populations

Conservation significance

  • Disjunct populations often represent unique genetic lineages
  • May serve as refugia for species during environmental changes
  • Require special conservation attention due to their isolation and vulnerability

Methods for studying disjunctions

Phylogenetic analysis

  • Uses genetic data to reconstruct evolutionary relationships between populations
  • Helps determine the timing and direction of dispersal events
  • Reveals patterns of diversification and speciation in disjunct populations

Molecular clock techniques

  • Estimate the timing of divergence between disjunct populations
  • Utilize genetic mutation rates to calculate time since separation
  • Help distinguish between ancient events and recent long-distance dispersal

Fossil record examination

  • Provides historical evidence of species distributions
  • Reveals past connections between now-disjunct populations
  • Helps reconstruct biogeographic histories and paleoenvironments

Disjunctions vs continuous distributions

  • Disjunct distributions characterized by geographical gaps between populations
  • Continuous distributions show uninterrupted ranges without significant barriers
  • Disjunctions often indicate complex biogeographical histories or unique dispersal events
  • Continuous distributions typically reflect more recent or ongoing range expansions

Historical biogeography perspectives

Continental drift theory

  • Explains some disjunctions as results of tectonic plate movements
  • Accounts for similarities in flora and fauna between now-distant landmasses
  • Supports the concept of Gondwanan and Laurasian distributions in many taxa

Land bridge hypotheses

  • Propose temporary connections between landmasses as dispersal routes
  • Include well-known examples like the Bering Land Bridge
  • Explain some disjunctions between continents or islands that were once connected

Ecological factors influencing disjunctions

Niche requirements

  • Specific environmental conditions needed for species survival
  • Can limit distribution to areas with suitable habitats
  • Explain some disjunctions where intervening areas lack appropriate conditions

Dispersal barriers

  • Physical or ecological obstacles that prevent species movement
  • Include oceans, mountain ranges, deserts, or unfavorable climatic zones
  • Maintain separation between disjunct populations over time

Competition and predation

  • Biotic interactions that can limit species distributions
  • May prevent establishment in areas between disjunct populations
  • Contribute to the maintenance of disjunct patterns over ecological time scales

Human-induced disjunctions

Introduced species

  • Result from human-mediated transport of organisms to new areas
  • Create artificial disjunctions between native and introduced populations
  • Can lead to rapid evolution and adaptation in new environments

Habitat destruction effects

  • Fragment previously continuous populations
  • Create human-induced disjunctions in formerly widespread species
  • Often result in isolated populations with reduced gene flow and increased vulnerability

Future of disjunct distributions

Climate change impacts

  • Alter existing disjunct patterns as species ranges shift
  • May create new disjunctions as populations become isolated by changing conditions
  • Potentially lead to local extinctions in areas that become unsuitable

Conservation strategies

  • Focus on preserving genetic diversity within disjunct populations
  • Include corridor creation to reconnect fragmented habitats
  • Involve assisted migration for species threatened by rapid environmental changes

Key Terms to Review (18)

Alfred Wallace: Alfred Wallace was a British naturalist, explorer, and biogeographer known for independently proposing the theory of evolution through natural selection alongside Charles Darwin. His observations of species distributions in the Amazon and the Malay Archipelago led to important insights regarding biogeography and the concept of disjunct distributions, which refer to the presence of related species in geographically separated areas.
Allopatric distribution: Allopatric distribution refers to the geographical separation of populations, leading to the evolution of distinct species due to this isolation. This process often occurs when a physical barrier, such as a mountain range or body of water, divides a population, preventing gene flow and fostering genetic divergence over time. Allopatric distribution is a critical concept in understanding how speciation occurs in different environments.
Biogeographic barriers: Biogeographic barriers are physical or biological obstacles that restrict the movement and distribution of species across geographical areas. These barriers can include mountains, rivers, oceans, and even climate factors that limit how organisms disperse and colonize new habitats. Understanding these barriers is crucial in explaining disjunct distributions of species and the distinct characteristics of various biogeographic realms.
Climate zones: Climate zones are regions of the Earth that share similar climatic conditions, including temperature, precipitation, and seasonal patterns. These zones are essential for understanding the distribution of ecosystems, plant and animal species, and human activities across different geographical areas. Climate zones can significantly influence biodiversity and ecological processes, contributing to patterns like disjunct distributions and affecting realms such as the Palearctic.
Competitive exclusion: Competitive exclusion is a principle stating that two species competing for the same limited resource cannot coexist indefinitely. When two species compete, one will ultimately outcompete the other, leading to its local extinction or exclusion from that niche. This concept is significant in understanding how species distributions and community structures are formed and maintained, particularly in relation to spatial distributions and community assembly processes.
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.
Dispersal: Dispersal is the movement of organisms from one place to another, which plays a crucial role in shaping biodiversity and influencing species distributions. This process is linked to ecological dynamics, evolutionary patterns, and biogeographical phenomena, as it determines how species spread across landscapes, adapt to new environments, and establish populations in various habitats.
Endemism: Endemism refers to the ecological state where a species is native to and restricted to a specific geographic area. This concept is important for understanding biodiversity, as endemic species often evolve unique adaptations due to their isolation, making them key indicators of the ecological health of their environments.
Extinction Events: Extinction events refer to significant and widespread occurrences in Earth's history where a substantial number of species die out in a relatively short period of time. These events can drastically reshape ecosystems, leading to shifts in biodiversity and the evolution of new species. Understanding extinction events helps reveal patterns in species survival and adaptation across different temporal scales, influencing the distribution of organisms and the interpretation of fossil records.
Glaciation: Glaciation refers to the processes and effects associated with the formation and movement of glaciers, significantly altering landscapes and ecosystems over time. This phenomenon has played a crucial role in shaping biogeographical patterns, influencing species distributions, and facilitating speciation events due to environmental changes. Glaciation can lead to disjunct distributions of flora and fauna, affecting genetic diversity and habitat availability, particularly in polar regions like Antarctica.
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.
Island biogeography: Island biogeography is the study of the distribution of species and ecosystems in oceanic islands and the processes that affect these distributions, focusing on how the size and distance of islands influence biodiversity. It connects ecological and evolutionary principles, showing how isolation impacts species richness, extinction rates, and colonization dynamics.
Mutualism: Mutualism is a type of interaction between two species where both parties benefit from the relationship. This ecological partnership is essential for many organisms, influencing community structure and biodiversity. It can involve various forms, such as pollination, seed dispersal, and nutrient exchange, playing a critical role in ecosystem functioning and resilience.
Niche Differentiation: Niche differentiation refers to the process by which competing species adapt to utilize different resources or habitats, reducing competition and allowing for coexistence. This concept highlights how species evolve distinct ecological roles, leading to more efficient use of resources and enhancing biodiversity within ecosystems.
Robert MacArthur: Robert MacArthur was a prominent ecologist known for his groundbreaking contributions to the field of biogeography, particularly through his development of the theory of island biogeography. His work emphasized the relationships between species richness, habitat area, and isolation, fundamentally shaping how we understand ecological patterns and processes across different spatial scales.
Species richness: Species richness refers to the number of different species present in a given area or ecosystem. This concept is crucial for understanding biodiversity, as it highlights how many unique species contribute to the ecological community, which can be influenced by various factors such as environmental conditions and historical events.
Sympatric distribution: Sympatric distribution refers to the occurrence of different species or populations in the same geographic area, where they coexist and interact without being separated by physical barriers. This can lead to complex ecological relationships and evolutionary processes, such as resource competition, niche differentiation, and speciation through mechanisms like adaptive radiation and character displacement.
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.
© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Back
Practice QuizGlossary
Practice QuizGlossary
Next guide