1.2 Ecological biogeography

Ecological biogeography examines how species and ecosystems are distributed across geographical areas. It integrates principles from ecology, geography, and evolution to understand present-day patterns and processes shaping biodiversity at various scales.

This field provides crucial insights for conservation efforts and predicting responses to environmental changes. By studying factors like climate, topography, and species interactions, ecological biogeography helps explain current distribution patterns and informs strategies for managing ecosystems.

Fundamentals of ecological biogeography

• Ecological biogeography examines the distribution of species and ecosystems across geographical areas, focusing on present-day patterns and processes
• Integrates principles from ecology, geography, and evolutionary biology to understand how organisms interact with their environment and each other
• Provides crucial insights for conservation efforts, ecosystem management, and predicting responses to global environmental changes

Definition and scope

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• Study of spatial patterns of biological diversity and the processes that shape these patterns
• Encompasses various scales from local habitats to global ecosystems
• Investigates factors influencing species distributions (climate, topography, biotic interactions)
• Examines community structure, ecosystem functioning, and biogeochemical cycles across landscapes

Historical development

• Emerged as a distinct field in the mid-20th century, building on earlier works in biogeography and ecology
• Influenced by pioneering studies of Alexander von Humboldt on plant geography in the early 19th century
• Shaped by island biogeography theory developed by MacArthur and Wilson in the 1960s
• Evolved with advancements in technology (GIS, remote sensing) and statistical methods (species distribution modeling)

Relationship to other disciplines

• Integrates concepts from ecology, evolutionary biology, and physical geography
• Connects with paleontology to understand historical distributions and extinctions
• Incorporates elements of climatology and geology to analyze environmental factors
• Contributes to conservation biology and ecosystem management strategies
• Utilizes tools from computer science and statistics for data analysis and modeling

Ecological factors influencing distribution

• Ecological factors play a crucial role in shaping species distributions and community compositions across landscapes
• Understanding these factors helps explain current biogeographic patterns and predict future changes in response to environmental shifts
• Interactions between abiotic and biotic factors create complex networks that influence species' ranges and abundances

Climate and microclimate

• Macroclimatic factors (temperature, precipitation) determine broad distribution patterns
• Microclimatic conditions (local temperature, humidity) influence species at smaller scales
• Climate envelopes define the range of conditions suitable for species survival
• Seasonal variations in climate affect species' life cycles and migration patterns
• Climate change alters species distributions, leading to range shifts and potential extinctions

Soil composition and topography

• Soil pH, texture, and nutrient content influence plant distributions and associated fauna
• Topographic features (elevation, slope, aspect) create diverse microclimates and habitats
• Edaphic factors determine vegetation types and plant community compositions
• Soil moisture retention capacity affects water availability for organisms
• Geomorphological processes shape landscape features and habitat heterogeneity

Water availability and quality

• Precipitation patterns and hydrological cycles influence species distributions
• Freshwater ecosystems (rivers, lakes) support unique aquatic and riparian communities
• Groundwater availability affects vegetation in arid and semi-arid regions
• Water chemistry (salinity, dissolved oxygen) determines aquatic species compositions
• Drought tolerance and flood resistance shape plant adaptations and distributions

Biotic interactions

• Competition for resources influences species coexistence and niche partitioning
• Predator-prey relationships affect population dynamics and trophic cascades
• Mutualistic interactions (pollination, seed dispersal) shape plant distributions
• Parasitism and disease can limit species ranges and abundances
• Facilitation between species enables survival in harsh environments

Species distribution patterns

• Species distribution patterns reflect the complex interplay of ecological, historical, and evolutionary factors
• Understanding these patterns helps identify biodiversity hotspots, predict range shifts, and inform conservation strategies
• Biogeographers use various metrics and models to analyze and describe species distributions across space and time

Range size and shape

• Geographic range defines the area where a species naturally occurs
• Range sizes vary greatly among species, from narrow endemics to cosmopolitan taxa
• Factors influencing range size include dispersal ability, habitat specificity, and evolutionary history
• Range shapes can be continuous, fragmented, or disjunct depending on environmental conditions and barriers
• Species with larger ranges often show greater genetic diversity and resilience to environmental changes

Abundance gradients

• Species abundances often vary across their geographic ranges
• Abundant-center hypothesis suggests higher abundances in the center of a species' range
• Latitudinal gradients in abundance observed for many taxa, with peaks in tropical regions
• Elevation gradients affect species abundances in mountainous areas
• Edge populations may show lower abundances due to suboptimal conditions

Endemism vs cosmopolitanism

• Endemic species restricted to a particular geographic area (islands, mountain ranges)
• Cosmopolitan species widely distributed across multiple continents or oceans
• Endemism often results from long-term isolation, unique adaptations, or limited dispersal ability
• Cosmopolitanism facilitated by broad environmental tolerances or efficient dispersal mechanisms
• Understanding endemism patterns crucial for identifying biodiversity hotspots and conservation priorities

Disjunct distributions

• Populations of a species separated by significant geographic barriers or distances
• Can result from vicariance events (continental drift, mountain uplift) or long-distance dispersal
• Relict populations represent remnants of formerly wider distributions
• Disjunctions provide insights into historical biogeography and species' evolutionary histories
• Genetic divergence between disjunct populations may lead to speciation over time

Community composition and structure

• Community composition and structure describe the organization of species assemblages within ecosystems
• These patterns reflect the interplay of ecological processes, environmental filters, and historical factors
• Analyzing community structure helps understand ecosystem functioning, resilience, and responses to environmental changes

Species richness patterns

• Total number of species in a given area or community
• Latitudinal gradient in species richness, with peaks in tropical regions
• Elevational gradients in species richness, often showing mid-elevation peaks
• Area effects on species richness, described by species-area relationships
• Habitat heterogeneity positively correlates with species richness

Diversity indices

• Quantitative measures of biodiversity within communities
• Shannon-Wiener index incorporates species richness and evenness
• Simpson's index emphasizes dominance and evenness of species
• Whittaker's beta diversity measures turnover between communities
• Phylogenetic diversity indices account for evolutionary relationships among species

Functional diversity

• Diversity of ecological functions performed by species in a community
• Functional traits reflect species' adaptations and ecological roles
• Functional redundancy occurs when multiple species perform similar roles
• Functional complementarity enhances ecosystem stability and resilience
• Measuring functional diversity helps predict ecosystem responses to disturbances

Trophic interactions

• Food web structure describes energy flow and nutrient cycling in ecosystems
• Trophic levels include primary producers, herbivores, carnivores, and decomposers
• Top-down vs bottom-up control influences community structure and dynamics
• Keystone species exert disproportionate effects on community composition
• Trophic cascades can result from changes in predator or prey populations

Ecological niches

• Ecological niches describe the multidimensional space of resources and environmental conditions a species can occupy
• Niche concepts help explain species coexistence, community assembly, and adaptive radiation
• Understanding niches crucial for predicting species responses to environmental changes and invasive species impacts

Niche concept and theory

• Hutchinsonian niche defines the n-dimensional hypervolume of environmental conditions and resources
• Grinnellian niche focuses on abiotic factors determining species distributions
• Eltonian niche emphasizes species' functional roles and interactions within communities
• Niche differentiation enables species coexistence through resource partitioning
• Niche construction theory explores how organisms modify their environment and create new niches

Fundamental vs realized niches

• Fundamental niche represents the full range of conditions where a species can potentially survive and reproduce
• Realized niche describes the actual space occupied by a species due to biotic interactions and dispersal limitations
• Competitive exclusion can restrict species to a subset of their fundamental niche
• Realized niches may expand or contract in response to changes in community composition or environmental conditions
• Niche shifts can occur during species invasions or in novel environments

Niche breadth and overlap

• Niche breadth measures the range of resources or conditions utilized by a species
• Specialists have narrow niches, while generalists have broad niches
• Niche overlap quantifies the degree of similarity in resource use between species
• High niche overlap may lead to competitive interactions or facilitation
• Niche partitioning reduces overlap and promotes species coexistence

Niche conservatism

• Tendency of species to retain ancestral ecological characteristics over evolutionary time
• Influences patterns of species distributions and community assembly
• Can limit adaptive responses to environmental changes
• Phylogenetic niche conservatism observed in many taxa across various niche dimensions
• Implications for predicting species responses to climate change and habitat alterations

Biogeographic processes

• Biogeographic processes shape the distribution of species and communities across space and time
• These dynamic processes involve movement, establishment, and local extinctions of populations
• Understanding these mechanisms helps explain current distribution patterns and predict future changes

Dispersal mechanisms

• Active dispersal involves self-propelled movement of organisms
• Passive dispersal relies on external forces (wind, water, other organisms)
• Long-distance dispersal events can lead to colonization of new areas
• Dispersal barriers (mountains, oceans) limit species movements
• Human-mediated dispersal increasingly influences species distributions

Colonization and establishment

• Successful dispersal followed by population growth in a new area
• Founder effects may occur when new populations establish from few individuals
• Ecological fitting allows species to persist in novel environments
• Propagule pressure influences the likelihood of successful establishment
• Adaptive radiations can result from colonization of isolated areas (Galápagos finches)

Local extinction

• Disappearance of a species from a particular area while persisting elsewhere
• Caused by factors such as habitat loss, competition, or environmental changes
• Metapopulation dynamics involve balance between local extinctions and recolonizations
• Extinction debt refers to delayed extinctions following habitat fragmentation
• Rescue effects can prevent local extinctions through immigration from nearby populations

Range shifts

• Changes in species' geographic distributions over time
• Often driven by climate change or habitat alterations
• Poleward and upslope shifts observed in response to global warming
• Range expansions may lead to novel species interactions and community reorganization
• Assisted migration proposed as a conservation strategy for species threatened by rapid environmental changes

Habitat fragmentation and connectivity

• Habitat fragmentation divides continuous landscapes into smaller, isolated patches
• Connectivity between habitat fragments crucial for maintaining population viability and biodiversity
• Understanding fragmentation effects and connectivity patterns essential for conservation planning and landscape management

Patch dynamics

• Describes the changes in composition and structure of habitat patches over time
• Patch size influences species richness and population persistence
• Patch isolation affects colonization and extinction rates
• Matrix quality between patches impacts species movement and survival
• Patch dynamics models help predict community changes in fragmented landscapes

Metapopulation theory

• Describes spatially structured populations consisting of local subpopulations
• Extinction and recolonization processes maintain overall metapopulation persistence
• Source-sink dynamics involve net emigration from high-quality to low-quality patches
• Rescue effects prevent local extinctions through immigration
• Metapopulation models used to assess species viability in fragmented habitats

Corridors and stepping stones

• Corridors provide continuous habitat connections between patches
• Stepping stones consist of small habitat patches facilitating movement between larger areas
• Enhance functional connectivity for species in fragmented landscapes
• Design considerations include width, length, and habitat quality of corridors
• Effectiveness varies among species depending on dispersal abilities and habitat requirements

Edge effects

• Ecological changes occurring at boundaries between habitat types
• Influence microclimate, species composition, and ecological processes near patch edges
• Edge-to-interior ratio increases with habitat fragmentation
• Some species benefit from edge habitats (edge specialists)
• Others avoid edges due to increased predation risk or altered environmental conditions

Disturbance and succession

• Disturbances disrupt ecosystem structure and function, initiating successional processes
• Succession describes the sequential changes in community composition following disturbances
• Understanding disturbance regimes and successional dynamics crucial for ecosystem management and restoration

Types of ecological disturbances

• Natural disturbances include fires, storms, floods, and volcanic eruptions
• Anthropogenic disturbances involve human activities (logging, agriculture, urbanization)
• Disturbance characteristics include frequency, intensity, and spatial extent
• Intermediate disturbance hypothesis suggests maximum diversity at moderate disturbance levels
• Disturbance regimes shape ecosystem structure and species adaptations

Succession models

• Primary succession occurs on newly exposed substrates (lava flows, glacial retreat areas)
• Secondary succession follows disturbances in areas with existing soil and seed banks
• Clementsian model proposes a predictable, linear progression towards a climax community
• Gleasonian model emphasizes individualistic responses of species to environmental gradients
• Alternative stable states theory suggests multiple possible endpoints for succession

Community assembly rules

• Describe the processes governing species coexistence and community formation
• Environmental filtering selects species based on abiotic conditions
• Limiting similarity prevents coexistence of species with highly overlapping niches
• Priority effects influence community composition based on arrival order of species
• Neutral theory proposes community assembly driven by random processes and dispersal

Climax communities

• Theoretically stable endpoint of succession in the absence of disturbances
• Characterized by self-perpetuating species compositions
• Influenced by regional species pools and environmental conditions
• Debate over the existence and stability of true climax communities
• Dynamic equilibrium concept recognizes ongoing changes even in mature ecosystems

Island biogeography

• Island biogeography studies species diversity and distribution patterns on islands
• Provides insights into fundamental ecological and evolutionary processes
• Concepts apply to both true islands and habitat islands (lakes, mountaintops)

Island biogeography theory

• Developed by MacArthur and Wilson in the 1960s
• Predicts species richness on islands based on island size and isolation
• Equilibrium between immigration and extinction rates determines species richness
• Larger islands support more species due to greater habitat diversity and resources
• Closer islands have higher immigration rates and species richness

Species-area relationships

• Describes the increase in species number with increasing island or habitat area
• Often expressed as a power function: S = cA^z (S = species number, A = area)
• Z-values typically range from 0.2 to 0.35 for islands
• Nested subset pattern observed on archipelagos
• Species-area relationships used to estimate extinction rates from habitat loss

Isolation effects

• Greater isolation leads to lower immigration rates and species richness
• Isolation measured by distance to mainland or other source populations
• Influences genetic diversity and endemism levels on islands
• Affects species composition through selective colonization
• Isolation-by-distance patterns observed in genetic and community similarity

Equilibrium vs non-equilibrium models

• Equilibrium models assume balance between immigration and extinction rates
• Non-equilibrium models recognize historical factors and ongoing changes
• Habitat diversity and environmental heterogeneity influence species richness
• Evolutionary processes (adaptive radiation, anagenesis) shape island biotas over time
• Consideration of non-equilibrium dynamics important for conservation of island ecosystems

Anthropogenic impacts

• Human activities significantly alter global ecosystems and species distributions
• Anthropogenic impacts often occur at faster rates than natural processes
• Understanding these impacts crucial for developing effective conservation and management strategies

Habitat loss and degradation

• Leading cause of biodiversity loss worldwide
• Results from land-use changes (deforestation, urbanization, agriculture)
• Reduces available habitat area and quality for native species
• Increases edge effects and habitat fragmentation
• Disrupts ecosystem functions and services

Climate change effects

• Alters temperature and precipitation patterns globally
• Causes range shifts, phenological changes, and mismatches in species interactions
• Threatens species with limited dispersal abilities or specific habitat requirements
• Affects ecosystem processes (carbon cycling, nutrient dynamics)
• Interacts with other stressors, amplifying impacts on biodiversity

Invasive species

• Non-native species that spread and cause ecological or economic harm
• Often introduced through human activities (trade, transportation, horticulture)
• Compete with native species for resources and alter ecosystem processes
• Can lead to biotic homogenization of communities
• Management strategies include prevention, early detection, and control measures

Conservation implications

• Requires understanding of species distributions, ecological processes, and human impacts
• Protected area design based on biogeographic principles (size, connectivity, representativeness)
• Restoration ecology aims to recover degraded ecosystems and reintroduce lost species
• Assisted migration considered for species threatened by rapid environmental changes
• Ecosystem-based management approaches integrate ecological and socio-economic factors

Methods in ecological biogeography

• Diverse methods used to study species distributions and ecological patterns across landscapes
• Integration of traditional field techniques with advanced technologies and analytical approaches
• Continuous development of new methods to address complex biogeographic questions

Field surveys and sampling

• Transect and quadrat methods for vegetation and animal surveys
• Mark-recapture techniques for estimating population sizes and movements
• Camera traps and acoustic monitoring for detecting elusive species
• Soil and water sampling to assess environmental conditions
• Citizen science projects to collect large-scale distribution data

Remote sensing techniques

• Satellite imagery used to map land cover and vegetation types
• LiDAR technology for measuring forest structure and biomass
• Hyperspectral imaging to assess plant health and species composition
• Drone-based surveys for high-resolution mapping of small areas
• Integration of remote sensing data with field observations to improve accuracy

Species distribution modeling

• Statistical techniques to predict species occurrences based on environmental variables
• Commonly used algorithms include MaxEnt, GARP, and generalized linear models
• Bioclimatic envelope models to project potential ranges under climate change scenarios
• Ensemble modeling approaches to reduce uncertainty in predictions
• Challenges include accounting for biotic interactions and dispersal limitations

Multivariate statistical analyses

• Ordination techniques (PCA, NMDS) to visualize community patterns
• Cluster analysis for identifying groups of similar sites or species
• Canonical correspondence analysis to relate community composition to environmental gradients
• Mantel tests to assess correlations between distance matrices
• Structural equation modeling to explore complex relationships in ecological data