7.5 Niche theory

Niche theory explores how species interact with their environment and each other. It explains why certain organisms thrive in specific habitats and how they coexist. This concept is crucial for understanding biodiversity patterns and species distributions across the globe.

The theory encompasses fundamental ideas like niche breadth, overlap, and partitioning. It also delves into niche construction, competitive exclusion, and conservation. These concepts help scientists predict how species might respond to environmental changes and inform conservation strategies.

Definition of ecological niche

• Ecological niche describes the role and position of a species within its environment
• Encompasses the range of environmental conditions and resources a species requires to survive and reproduce
• Fundamental to understanding species interactions, distribution patterns, and ecosystem dynamics in World Biogeography

Fundamental vs realized niche

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• Fundamental niche represents the full range of environmental conditions in which a species can theoretically survive and reproduce
• Realized niche constitutes the actual space occupied by a species due to biotic interactions and competition
• Fundamental niche typically larger than realized niche due to factors like predation, competition, and resource availability
• Realized niche can vary across different geographic regions and time periods

Hutchinson's n-dimensional hypervolume

• Conceptual model proposed by G. Evelyn Hutchinson to represent ecological niches mathematically
• Describes niche as a multi-dimensional space where each dimension represents an environmental variable
• Dimensions include abiotic factors (temperature, humidity, pH) and biotic factors (prey availability, predator presence)
• Allows for quantitative analysis and comparison of niches between species
• Hypervolume concept helps visualize niche overlap and differentiation in complex ecosystems

Components of niche

Habitat niche

• Refers to the physical space and environmental conditions a species occupies
• Includes abiotic factors such as temperature range, soil type, and water availability
• Biotic factors like vegetation structure and presence of other species also influence habitat niche
• Can vary in scale from microhabitats (tree bark for insects) to broad geographic regions (tropical rainforests for primates)
• Understanding habitat niches crucial for predicting species distributions and responses to environmental changes

Trophic niche

• Describes a species' role in the food web and its feeding relationships
• Encompasses diet composition, feeding strategies, and energy transfer within ecosystems
• Includes factors such as prey selection, foraging behavior, and competitive interactions
• Trophic niches can be classified into broad categories (herbivores, carnivores, omnivores)
• Specialization within trophic niches can lead to unique adaptations (nectar-feeding birds, filter-feeding whales)

Temporal niche

• Refers to the timing of species activities and resource use within a 24-hour cycle or seasonal patterns
• Includes diurnal, nocturnal, or crepuscular activity patterns
• Encompasses seasonal behaviors such as migration, hibernation, or breeding cycles
• Temporal niche partitioning allows species to coexist by utilizing resources at different times
• Influences species interactions, resource availability, and adaptation to environmental rhythms

Niche breadth and overlap

Generalists vs specialists

• Niche breadth describes the range of resources or environmental conditions a species can utilize
• Generalists have broad niches, able to thrive in various environments and use diverse resources
• Specialists have narrow niches, adapted to specific environmental conditions or resource types
• Generalist examples include raccoons (adaptable diet and habitat) and coyotes (varied ecosystems)
• Specialist examples include koalas (eucalyptus diet) and snow leopards (high-altitude habitats)
• Trade-offs exist between generalist and specialist strategies in terms of competitive ability and environmental tolerance

Niche partitioning

• Process by which species reduce competition by utilizing different resources or habitats
• Allows coexistence of similar species within the same ecosystem
• Can occur along various niche dimensions (spatial, temporal, trophic)
• Spatial partitioning examples include different bird species nesting at various heights in a forest
• Temporal partitioning examples include nocturnal and diurnal predators hunting the same prey species
• Trophic partitioning examples include grazing animals feeding on different parts of the same plant species

Niche construction theory

Ecosystem engineering

• Process by which organisms modify their environment, creating or altering niches
• Beavers constructing dams, altering hydrology and creating new habitats for other species
• Earthworms changing soil structure and nutrient cycling, impacting plant communities
• Coral reefs building complex structures that provide habitat for numerous marine species
• Ecosystem engineers can have far-reaching effects on biodiversity and ecosystem functioning

Feedback loops

• Niche construction creates feedback mechanisms between organisms and their environment
• Positive feedback loops can amplify environmental changes and niche modifications
• Negative feedback loops can stabilize ecosystems and maintain niche characteristics
• Example of positive feedback: increased plant growth leading to more soil organic matter, further enhancing plant growth
• Example of negative feedback: predator population growth limited by prey availability, preventing overexploitation

Competitive exclusion principle

Gause's experiment

• Classical study conducted by Georgy Gause using Paramecium species in laboratory conditions
• Demonstrated that two species competing for the same limiting resource cannot coexist indefinitely
• When grown separately, both species thrived, but when combined, one species always outcompeted the other
• Supported the concept that complete competitors cannot coexist in a stable environment
• Led to the formulation of the competitive exclusion principle, a fundamental concept in ecology

Resource partitioning

• Mechanism by which species avoid competitive exclusion by utilizing resources differently
• Allows similar species to coexist by reducing direct competition for limiting resources
• Can occur through differences in diet, habitat use, or temporal activity patterns
• Darwin's finches on the Galápagos Islands exemplify resource partitioning through beak adaptations
• Enables higher biodiversity in ecosystems by creating more ecological niches

Niche conservatism

Phylogenetic niche conservatism

• Tendency of species to retain ancestral ecological characteristics over evolutionary time
• Closely related species often occupy similar niches due to shared evolutionary history
• Influences patterns of species distribution and community assembly across geographic regions
• Can lead to the clustering of related species in similar environments (niche clustering)
• Challenges arise when environmental conditions change faster than species can adapt

Niche evolution

• Process by which species adapt to new environmental conditions, potentially expanding or shifting their niche
• Can occur through genetic changes, phenotypic plasticity, or behavioral adaptations
• Niche evolution may be driven by environmental changes, competition, or new ecological opportunities
• Examples include the evolution of C4 photosynthesis in plants adapting to low CO2 environments
• Balances with niche conservatism in shaping species distributions and biodiversity patterns

Niche modeling

Species distribution models

• Statistical tools used to predict species' geographic distributions based on environmental variables
• Incorporate occurrence data and environmental layers to create probability maps of species presence
• Useful for understanding current distributions and projecting potential range shifts
• Applications include identifying suitable habitats for reintroduction programs and assessing invasion risks
• Limitations include data quality, model assumptions, and the challenge of capturing biotic interactions

Climate envelope models

• Subset of species distribution models focusing on climatic variables to predict species ranges
• Assume that climate primarily determines species distributions at broad spatial scales
• Used to assess potential impacts of climate change on species distributions and biodiversity
• Can project future range shifts based on different climate change scenarios
• Limitations include oversimplification of species-environment relationships and neglect of non-climatic factors

Applications of niche theory

Conservation biology

• Niche theory informs habitat protection strategies and species management plans
• Helps identify critical habitats and environmental conditions for endangered species
• Guides restoration efforts by understanding species requirements and ecosystem functions
• Assists in designing protected areas and corridors to maintain ecological niches
• Supports ex-situ conservation by replicating niche conditions in captive breeding programs

Invasive species management

• Niche theory aids in predicting potential spread and impact of invasive species
• Helps identify vulnerable ecosystems and native species at risk of displacement
• Informs management strategies by understanding niche differences between native and invasive species
• Supports risk assessment for intentional species introductions (biological control agents)
• Guides habitat manipulation techniques to reduce invasive species' competitive advantage

Climate change predictions

• Niche models project potential range shifts and extinctions under different climate scenarios
• Identifies species and ecosystems most vulnerable to climate change impacts
• Informs assisted migration strategies for species unable to naturally track shifting climates
• Helps predict changes in community composition and ecosystem functions
• Supports adaptive management strategies in conservation planning and policy-making

Criticisms and limitations

Niche concept ambiguity

• Lack of consensus on precise definition and measurement of ecological niches
• Challenges in distinguishing between fundamental and realized niches in natural systems
• Difficulty in accounting for all relevant niche dimensions and their interactions
• Niche concept may oversimplify complex ecological relationships and species interactions
• Debate over the relative importance of niche-based vs. neutral processes in community assembly

Empirical challenges

• Practical difficulties in measuring and quantifying all aspects of a species' niche
• Limited data availability for many species, especially in understudied or remote ecosystems
• Temporal and spatial scale mismatches between niche measurements and ecological processes
• Challenges in separating niche effects from other factors influencing species distributions
• Limitations of controlled experiments in capturing the complexity of natural ecosystems