Chapter 9: Ecosystem

Learning Objectives

By the end of this chapter, you should be able to:

Differentiate between biotic and abiotic components of ecosystems
Understand community interactions and their ecological significance
Analyze population dynamics and growth patterns
Explain energy flow and nutrient cycling in ecosystems
Evaluate factors affecting ecosystem stability and resilience

Overview

Ecosystems represent the fundamental units of life on Earth, where living organisms interact with each other and their physical environment. From the smallest pond to the largest ocean, every ecosystem functions through complex networks of energy flow and nutrient cycling. Understanding ecosystem dynamics is crucial for comprehending how life persists, how communities change over time, and how human activities impact the natural world. This chapter explores the intricate web of interactions that sustain life across Earth's diverse habitats.

Ecosystem Components

Biotic Components

Living Organisms in Ecosystems:

Trophic Level	Description	Function	Examples
Producers (Autotrophs)	Self-feeding organisms	Convert inorganic to organic matter	Plants, algae, cyanobacteria
Primary Consumers (Herbivores)	Plant-eating organisms	Consume producers	Rabbits, deer, grasshoppers
Secondary Consumers (Carnivores)	Meat-eating organisms	Consume primary consumers	Foxes, frogs, spiders
Tertiary Consumers	Top carnivores	Consume secondary consumers	Eagles, sharks, lions
Omnivores	Both plant and meat eaters	Multiple feeding levels	Bears, humans, raccoons
Decomposers	Saprophytic organisms	Break down dead matter	Fungi, bacteria, earthworms
Detritivores	Organic matter feeders	Fragment dead material	Millipedes, dung beetles

Niche Concepts:

Aspect	Description	Importance	Examples
Fundamental Niche	All conditions where organism can survive	Ecological potential	Desert plant water range
Realized Niche	Actual conditions where organism exists	Competition effects	Desert plant actual range
Resource Partitioning	Division of resources	Reduces competition	Warbler feeding zones
Competitive Exclusion	One species dominates	Niche differentiation	Paramecium species competition

Abiotic Components

Non-living Environmental Factors:

Factor	Description	Ecological Impact	Examples
Temperature	Heat energy measurement	Affects metabolism, reproduction	Arctic adaptations, desert adaptations
Light	Solar radiation intensity	Photosynthesis, behavior	Plant growth patterns, animal activity
Water	$H_2$ O availability and quality	Essential for all life	Aquatic vs. terrestrial adaptations
Soil	Mineral matter and organic content	Plant growth, nutrient cycling	Soil pH, texture, fertility
Air	Atmospheric composition	Respiration, gas exchange	Altitude adaptations, pollution effects
pH	Acid-base measurement	Chemical reactions, toxicity	Acid rain effects, ocean acidification

Climate Factors:

Climate Factor	Description	Ecological Influence	Examples
Precipitation	Waterfall distribution	Water availability	Rainforest vs. desert adaptations
Seasonality	Periodic climate changes	Life cycle timing	Migration, hibernation, flowering
Wind	Air movement patterns	Dispersal, erosion	Seed dispersal, sand dune formation
Fire	Combustion events	Succession, nutrient release	Forest fires, grassland fires

Community Interactions

Species Interaction Types

Positive Interactions:

Interaction Type	Description	Effects	Examples
Mutualism	Both species benefit	Enhanced survival, reproduction	Bees and flowers, mycorrhizae
Commensalism	One benefits, other unaffected	Increased opportunities for one	Barnacles on whales, epiphytes
Protocooperation	Mutualistic but not obligatory	Temporary benefits	Herons and cattle, fish and shrimp

Negative Interactions:

Interaction Type	Description	Effects	Examples
Competition	Both species harmed	Reduced fitness for both	Plant root competition
Predation	One benefits, other harmed	Population control	Wolves and deer, spiders
Parasitism	Parasite benefits, host harmed	Host weakening, parasite spread	Ticks and mammals, tapeworms
Herbivory	Herbivore benefits, plant harmed	Plant damage, herbivore nutrition	Deer and trees, insects

Neutral Interactions:

Interaction Type	Description	Ecological Role	Examples
Amensalism	One harmed, other unaffected	Population regulation	Large trees suppressing small plants
Neutralism	No effect on either species	Independent survival	Species in different habitats

Ecological Succession

Primary Succession:

Stage	Characteristics	Dominant Organisms	Ecological Process
Pioneer Stage	Bare rock, extreme conditions	Lichens, mosses, algae	Weathering, soil formation
Nudation	Dispersal, establishment	Pioneer species	Colonization
Competition	Resource competition	Early succession plants	Niche differentiation
Inhibition	Established species control	Early dominants	Limitation of later species
Facilitation	Early species help later ones	Soil improvers	Environmental modification

Secondary Succession:

Stage	Characteristics	Dominant Organisms	Time Frame
Disturbance	Partial destruction	Pioneer species	Immediate
Early Succession	Rapid colonization	Grasses, herbs	1-5 years
Mid Succession	Shrub establishment	Shrubs, small trees	5-20 years
Late Succession	Climax community	Mature forest	100+ years

Succession Patterns:

Pattern	Description	Examples	Ecological Significance
Climax Community	Stable, self-perpetuating	Temperate forests, coral reefs	Long-term stability
Sere Types	Different starting conditions	Sand dunes, abandoned fields	Comparative studies
Inhibition Models	Resistance to change	Some coral reefs	Stability maintenance
Facilitation Models	Progressive improvement	Old field succession	Recovery and adaptation

Population Ecology

Population Characteristics

Demographic Properties:

Characteristic	Description	Measurement Methods	Ecological Significance
Population Size	Number of individuals	Direct count, sampling	Conservation status
Population Density	Individuals per unit area	Quadrats, transects	Habitat carrying capacity
Distribution Pattern	Spatial arrangement	Clumped, uniform, random	Resource availability
Age Structure	Age distribution	Size classes, demographic pyramid	Growth potential

Population Growth Models:

Model Type	Equation	Characteristics	Applications
Exponential Growth	dN/dt = rN	Unlimited resources, J-shaped curve	Population explosions, invasive species
Logistic Growth	dN/dt = rN(1-N/K)	Limited resources, S-shaped curve	Most natural populations, resource management
Boom and Bust	Cyclic fluctuations	Predator-prey cycles, seasonal changes	Population control strategies

Population Regulation Factors:

Factor Type	Description	Examples	Impact on Growth
Density-Dependent	Effects increase with population size	Disease, competition, predation	Limits carrying capacity
Density-Independent	Effects not related to population size	Natural disasters, climate	Reduces population size
Biotic Factors	Living organism interactions	Predation, competition, disease	Variable impact
Abiotic Factors	Environmental conditions	Weather, disasters, pollution	Immediate impact

Population Dynamics

Life History Strategies:

Strategy	Description	Characteristics	Examples
r-strategists	High reproductive rate	Early maturity, many offspring, low parental care	Insects, weeds, bacteria
K-strategists	Low reproductive rate	Late maturity, few offspring, high parental care	Humans, elephants, whales
Intermediate	Balanced approach	Moderate reproduction and investment	Most birds, mammals

Population Interactions:

Interaction	Effect on Populations	Mathematical Models	Examples
Predator-Prey	Oscillating populations	Lotka-Volterra equations	Wolves-moose, lynx-hare
Competition	Reduced growth rates	Lotka-Volterra competition	Plant species competition
Mutualism	Enhanced growth rates	Cooperative models	Pollinator-plant systems

Energy Flow and Nutrient Cycling

Energy Flow Patterns

Trophic Structure:

Trophic Level	Energy Transfer	Efficiency	Biomass
Producers	Solar to chemical	1-2% efficiency	Highest biomass
Primary Consumers	10% transfer efficiency	~10% efficiency	Lower biomass
Secondary Consumers	10% transfer efficiency	~10% efficiency	Lower biomass
Tertiary Consumers	10% transfer efficiency	~10% efficiency	Lowest biomass

Food Chains and Webs:

Type	Structure	Characteristics	Examples
Grazing Food Chain	Plants → herbivores → carnivores	Based on living organisms	Forest food chain
Detritus Food Chain	Dead matter → decomposers → predators	Based on dead matter	Decomposer food chain
Food Web	Interconnected food chains	Complex, realistic interactions	Ecosystem food web

Energy Transfer Efficiency:

Process	Efficiency Range	Factors Affecting	Ecological Significance
Photosynthesis	1-3% (terrestrial), 0.1-1% (aquatic)	Light, C $O_2$ , temperature	Primary production
Consumption	10-20% assimilation efficiency	Food quality, digestion	Energy transfer
Production Efficiency	30-40% (herbivores), 10-20% (carnivores)	Body size, metabolism	Growth efficiency
Ecological Efficiency	5-20% per trophic level	Multiple losses	Energy pyramid

Nutrient Cycling

Biogeochemical Cycles:

Carbon Cycle:

Process	Description	Microbial Involvement	Ecological Impact
Photosynthesis	C $O_2$ → organic matter	Cyanobacteria, plants	Carbon fixation
Respiration	Organic matter → C $O_2$	All organisms	Carbon release
Decomposition	Dead matter → C $O_2$	Decomposers	Carbon recycling
Fossilization	Organic matter → fossil fuels	Limited microbial activity	Carbon sequestration
Combustion	Organic matter → C $O_2$	Fire, incomplete decomposition	Rapid carbon release

Nitrogen Cycle:

Process	Description	Key Organisms	Products
Nitrogen Fixation	$N_2$ → N $H_3$	Rhizobia, Azotobacter	Ammonia
Nitrification	N $H_3$ → N $O_3$ ⁻	Nitrosomonas, Nitrobacter	Nitrates
Denitrification	N $O_3$ ⁻ → $N_2$	Pseudomonas, Bacillus	Nitrogen gas
Ammonification	Organic N → N $H_3$	Decomposers	Ammonia

Phosphorus Cycle:

Process	Description	Environmental Factors	Ecological Impact
Weathering	Rock → phosphate ions	Physical, chemical breakdown	Primary source
Assimilation	Plants → organic phosphorus	Plant uptake	Integration into biomass
Mineralization	Organic P → inorganic P	Decomposers	Recycling
Sedimentation	Phosphate → sediment	Water movement	Long-term storage

Water Cycle:

Process	Description	Ecological Role	Factors Affecting
Evaporation	Liquid → water vapor	Atmospheric moisture	Temperature, wind
Transpiration	Plant water loss	Plant cooling	Leaf area, stomata
Precipitation	Water vapor → liquid	Water distribution	Cloud formation
Infiltration	Water → soil	Groundwater recharge	Soil permeability
Runoff	Surface water flow	Stream formation	Topography, vegetation

Ecosystem Stability and Resilience

Succession and Community Development

Ecological Succession Process:

Early vs. Late Succession:

Aspect	Early Succession	Late Succession	Ecological Significance
Species Diversity	Low, r-strategists	High, K-strategists	Stability increases
Biomass	Low	High	Energy storage increases
Nutrient Cycling	Rapid, open	Slow, closed	Conservation improves
Food Web Complexity	Simple chains	Complex webs	Interactions increase

Climax Communities:

Type	Characteristics	Examples	Stability Factors
Climax Community	Stable, self-sustaining	Temperate forests, coral reefs	Complex interactions
Plagioclimax	Disturbance-maintained	Grasslands, heathlands	Human or natural disturbance
Subclimax	Short of full development	Early successional stages	Environmental limitation

Ecosystem Resilience

Resilience Factors:

Factor	Description	Effect on Resilience	Examples
Species Diversity	Number of species	Higher diversity → higher resilience	Coral reefs, tropical forests
Functional Redundancy	Multiple species for same function	Backup for ecosystem functions	Multiple pollinator species
Genetic Diversity	Variation within species	Adaptation to change	Disease-resistant crops
Connectivity	Linkages between areas	Migration, gene flow	Wildlife corridors
Disturbance History	Past disturbance experience	Adapted to disturbance	Fire-adapted ecosystems

Threats to Ecosystem Stability:

Threat	Description	Ecological Impact	Examples
Habitat Loss	Destruction of habitats	Species extinction, fragmentation	Deforestation, urbanization
Climate Change	Altered climate patterns	Range shifts, phenological changes	Global warming, altered precipitation
Invasive Species	Non-native species introduction	Competition, predation	Zebra mussels, kudzu
Pollution	Contaminant introduction	Toxicity, ecosystem disruption	Chemical spills, plastic waste

Laboratory Investigations

Ecosystem Analysis Techniques

Field Sampling Methods:

Method	Application	Equipment	Data Collected
Quadrat Sampling	Plant community structure	Quadrats, identification guide	Species abundance, coverage
Transect Sampling	Environmental gradients	Tape measure, sampling tools	Species distribution patterns
Pitfall Traps	Ground-dwelling arthropods	Traps, preservative, containers	Invertebrate diversity
Light Traps	Night-flying insects	Light source, collection bags	Moth, beetle surveys

Population Studies:

Technique	Purpose	Method	Applications
Mark-Recapture	Population estimation	Capture, mark, release, recapture	Animal population monitoring
Population Censuses	Direct counting	Visual surveys, photography	Endangered species monitoring
Track and Sign Surveys	Indirect evidence	Footprints, scat, nests	Elusive species monitoring

Energy Flow and Nutrient Analysis

Productivity Measurements:

Method	Purpose	Equipment	Applications
Oxygen Production	Photosynthesis rate	Oxygen electrodes, light chambers	Primary production
C $O_2$ Assimilation	Carbon fixation	Infrared gas analyzers	Photosynthetic efficiency
Biomass Assessment	Energy storage	Drying ovens, balances	Energy content analysis

Nutrient Analysis:

Element	Measurement Method	Equipment	Ecological Importance
Nitrogen	Kjeldahl method, N $O_3$ ⁻ test kits	Digestion apparatus, spectrophotometers	Primary production limitation
Phosphorus	Colorimetric tests, atomic absorption	Spectrophotometers	Eutrophication indicator
Carbon	Combustion analysis, titration	Carbon analyzers	Soil organic matter

Practice Tips for SPM Students

Key Concepts to Master

Ecosystem components and their interactions
Succession stages and community development
Population dynamics and growth patterns
Energy flow through trophic levels
Nutrient cycling and biogeochemical processes

Experimental Skills

Ecosystem sampling using appropriate methods
Population estimation using mark-recapture and other techniques
Energy transfer calculation and analysis
Succession observation in different environments

Problem-Solving Strategies

Food web analysis: Tracing energy and nutrient pathways
Population regulation: Identifying limiting factors and growth curves
Ecosystem stability: Assessing resilience and disturbance responses
Succession prediction: Understanding community development patterns

Environmental and Health Connections

Conservation Applications

Ecosystem restoration: Using succession principles for recovery
Habitat protection: Maintaining biodiversity and ecosystem function
Invasive species management: Understanding ecosystem impacts
Climate change adaptation: Building resilience to environmental changes

Agricultural and Forestry

Sustainable agriculture: Maintaining soil fertility and ecosystem health
Integrated pest management: Understanding predator-prey relationships
Agroforestry: Combining agriculture with forest ecosystems
Soil conservation: Maintaining nutrient cycles and soil health

Public Health and Medicine

Disease ecology: Understanding host-pathogen-environment interactions
Vector control: Managing ecosystem-based disease transmission
Water quality: Maintaining clean water through ecosystem processes
Food security: Sustainable ecosystem-based food production

Summary

Ecosystems function through interactions between biotic and abiotic components
Community interactions (mutualism, competition, predation) shape ecosystem structure
Population dynamics follow growth patterns influenced by various factors
Energy flows through trophic levels with decreasing efficiency
Nutrients cycle through ecosystems with specific biogeochemical processes
Ecosystem stability depends on diversity, connectivity, and disturbance history