13.3 Island biogeography in the fossil record
3 min read•august 7, 2024
in the fossil record reveals how species diversity and evolution unfold on isolated landmasses. It explores the relationships between island size, species richness, and evolutionary adaptations like body size changes and .
Fossil evidence helps scientists understand past events, development, and extinction patterns on islands. This knowledge is crucial for interpreting modern island ecosystems and predicting their responses to environmental changes.
Island Biogeography Concepts
Island Size and Species Diversity
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Top images from around the web for Island Size and Species Diversity
Frontiers | Functional Paleoecology and the Pollen-Plant Functional Trait Linkage View original
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Frontiers | The island rule with multiple islands and its application to the Indonesian Throughflow View original
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Frontiers | Diversity of Fagaceae on Hainan Island of South China During the Middle Eocene ... View original
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Frontiers | Functional Paleoecology and the Pollen-Plant Functional Trait Linkage View original
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- Island rule explains the body size changes that occur in island populations compared to their mainland counterparts
- Larger islands tend to have more species than smaller islands due to increased habitat diversity and resources
- describes the positive correlation between island size and number of species, represented by the equation , where is the number of species, is the area, and and are constants
- Larger islands have lower extinction rates because they can support larger populations and have more diverse habitats (tropical rainforests)
Equilibrium Theory and Species Turnover
- proposes that the number of species on an island is determined by a balance between immigration and extinction rates
- Immigration rates decrease as an island becomes more populated, while extinction rates increase
- refer to the rate at which species are replaced by new species through immigration and extinction
- Higher turnover rates are associated with smaller islands that are farther from the mainland (Galápagos Islands)
Island Evolutionary Processes
Body Size Changes on Islands
- is the evolutionary process where large animals evolve to become smaller on islands due to limited resources and reduced predation pressure (dwarf elephants on Mediterranean islands)
- is the opposite process, where small animals evolve to become larger on islands due to reduced competition and predation (giant tortoises on the Galápagos Islands)
- These body size changes are adaptations to the unique ecological conditions found on islands
Adaptive Radiation on Islands
- Adaptive radiation is the rapid diversification of a single ancestral species into multiple descendant species, each adapted to different ecological niches
- Islands provide opportunities for adaptive radiation due to the presence of unoccupied niches and reduced competition
- Classic examples of adaptive radiation on islands include Darwin's finches in the Galápagos and Hawaiian honeycreepers
Island Colonization and Endemism
Colonization and Dispersal
- Colonization is the process by which species reach and establish populations on islands
- Successful colonization depends on factors such as ability, island size, and distance from the mainland
- Species with high dispersal abilities (birds, bats) are more likely to colonize islands than those with limited dispersal (land mammals)
- can facilitate the colonization of more distant islands by providing intermediate habitats
Relict Species and Endemism
- are remnant populations of once-widespread species that have become restricted to islands due to extinction on the mainland (tuatara in New Zealand)
- Endemic species are those that are unique to a particular island or archipelago and are found nowhere else in the world
- Islands often have high levels of endemism due to their isolation and unique evolutionary histories (lemurs in Madagascar)
- Endemic species are particularly vulnerable to extinction because of their limited range and small population sizes
Key Terms to Review (12)
Adaptive radiation: Adaptive radiation is the rapid diversification of a single ancestral lineage into a wide variety of forms, each adapted to different ecological niches. This process often occurs in response to new environmental opportunities or after mass extinction events, leading to the emergence of distinct species with unique adaptations.
Colonization: Colonization is the process through which a species establishes a new population in a previously unoccupied or sparsely populated area. This concept plays a crucial role in understanding how organisms spread and adapt to new environments, which can be observed through the fossil record in island biogeography. The dynamics of colonization help explain patterns of biodiversity, species interactions, and ecological changes over time.
Dispersal: Dispersal refers to the movement of organisms from their original habitat to new areas, which can occur through various mechanisms such as wind, water, or animal transport. This process plays a critical role in shaping biodiversity and influencing ecological dynamics, as it determines how species colonize new environments, survive changes in their habitats, and contribute to evolutionary processes over time.
Endemic species: Endemic species are organisms that are native to and found exclusively in a specific geographic area. This limited distribution often makes them particularly vulnerable to environmental changes and extinction. Understanding endemic species is crucial for studying biodiversity, ecosystem health, and the impacts of habitat fragmentation.
Equilibrium Theory: Equilibrium theory refers to the concept that ecosystems, including island biogeographic systems, tend to reach a state of balance where species diversity and abundance stabilize over time. This theory highlights the dynamic relationship between species immigration, extinction rates, and the size and isolation of habitats, allowing researchers to understand how species distributions change over time in response to environmental factors.
Insular dwarfism: Insular dwarfism is a biological phenomenon where species that live on islands evolve to become smaller in size compared to their mainland relatives. This adaptation often occurs due to limited resources, reduced competition, and specific environmental pressures found in island ecosystems, leading to changes in body size as a survival strategy.
Insular gigantism: Insular gigantism is a biological phenomenon where species on islands grow to larger sizes than their mainland relatives. This occurs due to factors like limited resources, reduced predation, and the unique environmental conditions of islands, which often lead to distinct evolutionary pressures.
Island biogeography: Island biogeography is the study of the ecological relationships and species diversity on islands, focusing on how island size, distance from the mainland, and environmental factors influence the number of species that can inhabit a given island. This concept highlights the dynamic interactions between species and their environments, emphasizing the balance of immigration and extinction rates that affect biodiversity. It provides insights into how geographic isolation impacts evolutionary processes and community composition.
Relict species: Relict species are organisms that have persisted in a specific area or habitat, despite significant environmental changes or the extinction of related species. These species often provide critical insights into past ecological conditions and evolutionary processes, as they represent remnants of earlier biological communities and contribute to our understanding of biodiversity in changing environments.
Species-area relationship: The species-area relationship is a fundamental ecological principle that describes the positive correlation between the area of a habitat and the number of species it can support. This concept suggests that larger areas tend to harbor more species due to increased habitat diversity and availability of resources, leading to higher rates of colonization and lower extinction probabilities. It is particularly relevant in understanding biodiversity patterns on islands and fragmented habitats.
Stepping Stone Islands: Stepping stone islands are small land masses that serve as critical points for species migration, providing necessary habitats that connect larger land areas. They play an important role in island biogeography, facilitating the movement of organisms between isolated ecosystems, thus promoting genetic diversity and species dispersion over time.
Turnover Rates: Turnover rates refer to the rate at which species within a community are replaced over time due to various ecological and evolutionary factors. This concept is vital in understanding the dynamics of biodiversity and ecosystem resilience, revealing how communities respond to disturbances, habitat changes, and extinction events. The rates can influence both the richness and composition of species in an area, making them crucial for studying patterns of biodiversity across different geological periods and in isolated environments.