10.3 Stability and change in ecological communities over geological time scales
3 min read•august 7, 2024
Ecological communities change over vast timescales, influenced by factors like stability, resilience, and . Long-term dynamics reveal patterns of , where communities remain stable for millions of years before rapid shifts occur.
suggests evolution happens in bursts, challenging gradual change ideas. drastically reshape biodiversity, followed by recovery periods where surviving species diversify and fill empty niches.
Community Stability and Resilience
Factors Influencing Community Stability
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- refers to the ability of an ecological community to maintain its structure and function over time despite disturbances or perturbations
- is the capacity of a community to absorb disturbances and reorganize while maintaining its essential functions, structure, and feedbacks
- Communities with high resilience can bounce back to their original state after a disturbance (coral reefs recovering after a hurricane)
- Turnover rates describe the rate at which species composition changes within a community over time
- High turnover rates indicate frequent changes in species composition, while low turnover rates suggest more stable communities (tropical rainforests have lower turnover rates than temperate forests)
Long-term Ecological Dynamics and Coordinated Stasis
- refer to the patterns and processes of community change over extended geological time scales (millions of years)
- Coordinated stasis is a pattern observed in the fossil record where communities remain relatively stable for long periods, punctuated by rapid turnover events
- During periods of coordinated stasis, species within a community evolve together and maintain their ecological relationships (Paleozoic marine communities)
- Coordinated stasis suggests that communities can persist in stable configurations for millions of years before undergoing significant changes
Punctuated Equilibrium and Mass Extinctions
Punctuated Equilibrium Theory
- Punctuated equilibrium is a theory proposed by Niles Eldredge and Stephen Jay Gould, suggesting that evolutionary change occurs in rapid bursts followed by long periods of stasis
- According to this theory, species remain relatively unchanged for most of their evolutionary history, with brief periods of rapid speciation and morphological change ()
- Punctuated equilibrium challenges the gradual, continuous view of evolution and suggests that the fossil record reflects long periods of stability interrupted by short intervals of rapid change
Mass Extinctions and Recovery
- Mass extinctions are events characterized by the rapid, global loss of a significant proportion of Earth's biodiversity
- The fossil record reveals five major mass extinction events (, , )
- follow mass extinctions, during which surviving species diversify and recolonize vacant ecological niches
- The duration and patterns of recovery can vary depending on the severity of the extinction and the environmental conditions (recovery after the End-Cretaceous extinction took millions of years)
- are species that disappear from the fossil record during a mass extinction but reappear later, suggesting they survived in refugia or were simply not preserved
- The reappearance of Lazarus taxa highlights the incompleteness of the fossil record and the resilience of some species (coelacanths, believed extinct, were rediscovered in the 20th century)
Environmental Perturbations and Extinction
- , such as , , and , can trigger mass extinctions by altering habitats and disrupting ecological relationships
- The End-Cretaceous mass extinction, which wiped out the non-avian dinosaurs, is linked to the Chicxulub asteroid impact (resulting in global cooling and disruption of food webs)
- The severity and selectivity of extinctions can vary depending on the nature and duration of the environmental perturbation
- Some groups may be more vulnerable to extinction due to their ecological specialization or limited geographic range (ammonites were particularly hard hit during the End-Cretaceous extinction)
Key Terms to Review (17)
Asteroid impacts: Asteroid impacts refer to the collision of asteroids with Earth, which can lead to significant changes in the planet's environment and biological communities. These events can cause mass extinctions and dramatic shifts in ecological dynamics, fundamentally altering stability and biodiversity over geological time scales.
Cambrian Explosion: The Cambrian Explosion refers to a remarkable period of rapid diversification of life that occurred around 541 million years ago, marking the beginning of the Paleozoic Era. This event is characterized by the sudden appearance of many major groups of marine invertebrates in the fossil record, establishing a foundation for modern ecosystems and evolutionary processes.
Climate Change: Climate change refers to significant and lasting alterations in temperature, precipitation, wind patterns, and other elements of the Earth's climate system over extended periods. This concept is pivotal in understanding historical ecological shifts, adaptations, and the dynamics of biodiversity across different geological epochs.
Community Stability: Community stability refers to the ability of an ecological community to maintain its structure, composition, and function over time, despite external disturbances or changes. This concept is crucial for understanding how ecological systems respond to environmental shifts and stresses, including climate changes and human impacts. Stable communities can resist changes or recover quickly from disturbances, while unstable communities may undergo significant shifts in species composition or function.
Coordinated stasis: Coordinated stasis refers to a period in evolutionary history where multiple species within an ecological community remain relatively stable in their forms and functions over significant geological time scales, showing little morphological change despite environmental shifts. This concept highlights how certain communities can exhibit remarkable resilience, maintaining biodiversity and ecological integrity even during periods of climatic or geological upheaval.
Ecological resilience: Ecological resilience refers to the capacity of an ecosystem to absorb disturbances and still maintain its basic structure and function. This concept emphasizes that ecosystems can recover from disruptions such as natural disasters or human-induced changes while sustaining their biodiversity and ecological processes. Understanding ecological resilience helps in examining the impacts of major mass extinction events, predicting how ecosystems will respond to ongoing environmental changes, and analyzing the stability and adaptability of ecological communities over geological time scales.
End-cretaceous: The end-cretaceous refers to the boundary between the Cretaceous and Paleogene periods, approximately 66 million years ago, marked by a significant mass extinction event that led to the disappearance of about 75% of Earth's species, including the dinosaurs. This event reshaped ecological communities and altered evolutionary pathways, highlighting how drastic environmental changes can impact biodiversity and community structure over geological time scales.
End-Permian: The End-Permian refers to the mass extinction event that occurred around 252 million years ago at the boundary between the Permian and Triassic geological periods, marking the most severe biodiversity loss in Earth's history. This event had profound effects on ecological communities, leading to the extinction of about 90% of marine species and 70% of terrestrial vertebrate species, drastically reshaping ecosystems and paving the way for the dominance of dinosaurs in the following era.
End-Triassic: The End-Triassic refers to a major geological event that occurred approximately 201 million years ago, marking the boundary between the Triassic and Jurassic periods. This event is significant due to the mass extinction it caused, leading to the loss of many marine and terrestrial species and dramatically reshaping ecological communities. The end-Triassic event illustrates how catastrophic changes can disrupt ecosystems and pave the way for new groups of organisms to dominate in the aftermath.
Environmental Perturbations: Environmental perturbations refer to disturbances in ecological systems caused by various factors, such as climate change, natural disasters, or human activities, which can alter the structure and dynamics of communities. These disruptions can lead to shifts in species composition, changes in population dynamics, and affect the overall stability of ecosystems over geological time scales.
Lazarus Taxa: Lazarus taxa are species or groups of organisms that disappear from the fossil record for a significant period, only to reappear later, suggesting they survived in isolated or undiscovered habitats. This phenomenon is significant as it highlights the complexities of extinction and survival in ecological communities over geological time. Understanding Lazarus taxa helps scientists grasp patterns of stability and change in biodiversity and the resilience of certain species amidst environmental shifts.
Long-term ecological dynamics: Long-term ecological dynamics refers to the patterns of change and stability in ecosystems over extended geological time scales, emphasizing how communities and their interactions evolve in response to environmental shifts. This concept helps us understand that ecosystems are not static but instead undergo continuous transformations influenced by factors such as climate change, species interactions, and geological events. It encompasses both the resilience of ecosystems in maintaining structure and function and the potential for significant alterations that can lead to new community configurations.
Mass extinctions: Mass extinctions are significant and rapid decreases in biodiversity, characterized by the widespread loss of species across multiple taxa. These events have played a crucial role in shaping the history of life on Earth, influencing evolutionary processes and ecological communities, and often leading to the emergence of new species and ecosystems in their aftermath.
Punctuated equilibrium theory: Punctuated equilibrium theory is an evolutionary concept that suggests species remain relatively stable for long periods, interrupted by brief, rapid changes during which new species arise. This theory contrasts with the idea of gradual evolution and emphasizes the role of environmental changes and speciation events in shaping biodiversity over geological time scales.
Recovery Intervals: Recovery intervals refer to the periods of time during which ecological communities regain stability and functionality after experiencing disturbances, such as natural disasters or human-induced changes. These intervals are crucial for understanding how ecosystems respond to stressors and can vary significantly in duration and intensity, reflecting the resilience and adaptability of different ecological communities over geological time scales.
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.
Volcanic eruptions: Volcanic eruptions are geological events where magma from beneath the Earth's crust is expelled through the surface, resulting in explosive activity that can release ash, gases, and lava. These eruptions can have profound impacts on ecological communities, altering habitats and influencing biodiversity through both immediate and long-term changes in the environment.