Ecosystems and Biodiversity

Ecosystem Fundamentals

1. Ecosystem Definition and Structure

Ecosystem Components:

• Biotic: Living organisms (plants, animals, microorganisms)
• Abiotic: Non-living factors (climate, soil, water, light)
• Interactions: Relationships between organisms and environment
• Boundaries: Can be arbitrary (watershed, forest, lake)
• Dynamic and changing systems

Biodiversity Levels:

• Genetic diversity: Variation within species
• Species diversity: Number of species
• Ecosystem diversity: Variety of habitat types
• All levels important for ecosystem function

2. Energy Flow

Primary Production:

• Photosynthesis: Plants convert sunlight to chemical energy (glucose)
• Gross Primary Production (GPP): Total energy fixed
• Net Primary Production (NPP): GPP minus plant respiration
• Available for consumers

Trophic Levels:

• Producers: Plants and photosynthetic organisms
• Primary consumers: Herbivores (eat plants)
• Secondary consumers: Carnivores (eat primary consumers)
• Tertiary consumers: Top carnivores (eat secondary consumers)
• Decomposers: Break down dead organic matter

Energy Transfer:

• Only ~10% energy passes to next trophic level
• 90% lost as heat and respiration
• Shorter food chains more efficient
• Biomass pyramids typically narrow at top

3. Nutrient Cycling

Carbon Cycle:

• Photosynthesis: CO₂ → organic carbon
• Respiration: Carbon released back to atmosphere
• Decomposition: Dead material breaks down
• Fossil fuels: Carbon locked away (geological timescale)
• Combustion: Releases stored carbon
• Oceans: Major carbon reservoir

Nitrogen Cycle:

• Atmospheric N₂ unavailable to most organisms
• Nitrogen fixation: Converts N₂ → ammonia (bacteria)
• Nitrification: Ammonia → nitrate (bacteria)
• Assimilation: Plants use nitrate
• Denitrification: Nitrate → N₂ (bacteria)
• Human modifications: Artificial fertilizers

Phosphorus Cycle:

• Rock weathering: Releases phosphate
• Plant uptake: Phosphorus incorporated
• Animal consumption: Transfers via food chains
• Decomposition: Returns to soil
• Marine sedimentation: Long-term storage
• Limited (no atmospheric phase)

Sulphur Cycle:

• Weathering and volcanism: Release sulphur
• Microbial transformations
• Plant uptake
• Return through decomposition
• Anthropogenic: Fossil fuel emission

Ecological Relationships and Food Webs

1. Feeding Relationships

Food Chains:

• Linear pathway: Producer → Primary consumer → Secondary consumer
• Simple models
• Reality more complex

Food Webs:

• Multiple interconnected food chains
• Organisms feed at multiple levels
• Complex energy pathways
• Illustrate ecosystem interdependence

Types of Consumers:

• Herbivores: Plant eaters (cows, grasshoppers, rabbits)
• Carnivores: Meat eaters (lions, hawks, snakes)
• Omnivores: Both plants and meat (bears, humans, pigs)
• Detritivores: Dead organic matter (earthworms, crustaceans)
• Scavengers: Carrion feeders (vultures, hyenas)

2. Organism Relationships

Feeding Interactions:

• Predation: Predator kills prey
• Parasitism: Parasite benefits, host harmed
• Herbivory: Herbivore eats plants (subtype of predation)

Mutualistic Relationships:

• Both organisms benefit
• Flower-pollinator: Nectar for pollination
• Nitrogen-fixing bacteria: Nutrients for legumes
• Cleaner fish: Food and parasite removal
• Mycorrhizal fungi: Nutrients for plants

Competitive Relationships:

• Both organisms disadvantaged
• Intraspecific: Within same species (most intense)
• Interspecific: Between species
• Resource competition: Food, space, light
• Niche partitioning: Avoiding direct competition

Commensalism:

• One organism benefits, other unaffected
• Epiphytes on trees: Nutrients without harm
• Remoras on sharks: Transportation without harm
• Oxpeckers on large animals: Food without harm

Biomes and Biogeographic Zones

1. Tropical Rainforests

Characteristics:

• High temperature (20-25°C+), high precipitation (>200 cm/year)
• Year-round growing season
• Highest biodiversity (50% of species)
• Complex interactions and specialization
• Rapid nutrient cycling

Structure:

• Canopy: Upper tree layer (blocking light)
• Understory: Shrubs and smaller trees
• Forest floor: Rapid decomposition, minimal humus
• Epiphytes: Plants on trees

Threats:

• Deforestation: Logging, agriculture, development
• Habitat loss: Biodiversity extinction
• Climate vulnerability: Drought stress increasing
• Indigenous peoples: Displaced by development

2. Savanna and Grasslands

Characteristics:

• Seasonal rainfall (1 wet, 1 dry season)
• Grassland with scattered trees
• Fire-adapted vegetation
• Large herbivore herds
• Lower biodiversity than rainforest

Ecological Role:

• Grazing: Large herbivore herds shape vegetation
• Fire ecology: Natural fires prevent tree invasion
• Nutrient cycling: Grasslands capture and cycle nutrients
• Carbon: Grasslands store carbon

Human Impacts:

• Overgrazing: Degradation to desert
• Fire suppression: Woody encroachment
• Agriculture: Conversion to croplands
• Conservation: Protected areas for wildlife

3. Deserts

Characteristics:

• Low precipitation (less than 250 mm/year)
• High diurnal temperature range
• Sparse vegetation, high-stress adapted
• Low biodiversity but specialized species
• Limited water availability

Adaptations:

• Plant: Deep roots, small leaves, xerophytic
• Animals: Nocturnal, water conservation, dormancy
• Survival strategies: Extreme specialization
• Population stability: Low productivity limits

Types:

• Hot deserts: Sahara, Arabian, Kalahari
• Cold deserts: Gobi, Great Basin
• Coastal deserts: Peru, Namibia
• Polar regions: Antarctica (extreme desert)

4. Temperate Forests

Deciduous Forests:

• Moderate precipitation, distinct seasons
• Leaves drop in winter
• Rich soil from leaf litter
• Moderate biodiversity
• Found on eastern coasts (30-50° latitude)

Coniferous Forests (Boreal/Taiga):

• Cold winters, limited precipitation
• Evergreen (conifers)
• Acidic soil, slow decomposition
• Lower diversity
• Northern hemisphere at high latitude

Temperate Rainforests:

• High precipitation, mild winters
• Evergreen and deciduous mix
• Extremely productive and biodiverse
• Found at high latitudes (New Zealand, Scandinavia, Pacific Coast)

5. Wetlands

Characteristics:

• Water-saturated soils
• Anaerobic conditions
• Specialized (aquatic) vegetation
• High productivity
• Diverse habitats

Types:

• Freshwater marshes: Non-woody plants
• Swamps: Forested wetlands
• Mangroves: Tropical salty wetlands
• Bogs: Peat accumulation, acidic
• Fens: Peat accumulation, neutral pH

Ecological Importance:

• Water storage and flood control
• Nutrient filtering (water purification)
• Biodiversity hotspots
• Nurseries for fish and waterfowl
• Carbon storage (peat)

6. Aquatic Ecosystems

Freshwater:

• Lakes: Still water, varying depth/size
• Rivers: Flowing water, dynamic
• Groundwater: Underground aquifers
• Limited by salinity tolerance

Marine:

• Oceans: High salinity, vast
• Coral reefs: Shallow tropical, extreme biodiversity
• Kelp forests: Cold currents, high productivity
• Deep sea: Pressure and cold, hydrothermal vents

Global Biodiversity Patterns

1. Biodiversity Distribution

Biodiversity Hotspots:

• High species diversity
• High endemism (found nowhere else)
• Threatened habitat
• Conservation priority
• Examples: Madagascar, Amazon, Coral Triangle

Latitude Patterns:

• Tropical regions: Maximum biodiversity
• Temperate: Moderate
• Polar: Minimum
• Correlation with temperature and productivity

Altitude Patterns:

• Mountains: Diversity decreases with elevation
• Vertical zones (similar to latitude belts)
• Specialized alpine species
• Vulnerable to climate change

Endemism:

• Species found in limited area only
• Islands: Often high endemism
• Mountain ranges: Isolated populations
• Conservation significance

2. Biodiversity Loss

Extinction Rates:

• Background extinction: Natural, slow rate
• Current rate: 100-1000x background (anthropocene)
• Sixth mass extinction: Currently underway
• Threatened species: Thousands identified

Causes:

• Habitat loss: Primary driver (85%)
• Climate change: Increasing importance
• Pollution: Chemical, plastic, light
• Overexploitation: Overhunting, fishing
• Invasive species: Outcompete natives

Examples:

• Dodo: Hunted to extinction (1600s)
• Passenger pigeon: Overhunted (1900)
• California condor: Nearly extinct (captive breeding)
• Giant panda: Endangered habitat loss (recovery possible)

3. Conservation Strategies

Protected Areas:

• National parks: Multiple-use conservation
• Nature reserves: Protection focus
• Marine protected areas: Ocean conservation
• Coverage: less than 15% of land, less for ocean

Species-Specific:

• Captive breeding: Genetic rescue
• Habitat restoration: Restore degraded areas
• Reintroduction programs: Release into wild
• Legal protection: Trade restrictions, hunting bans

Ecosystem-Based:

• Corridor creation: Connect protected areas
• Landscape management: Buffer zones
• Sustainable use: Traditional practices
• Indigenous land management: Often effective

Summary

Ecosystems and biodiversity include:

• Ecosystem Structure: Components, energy flow, nutrient cycling
• Ecological Relationships: Food webs, predation, competition, mutualism
• Biomes: Tropical, temperate, desert, aquatic ecosystems
• Biodiversity Patterns: Distribution, hotspots, latitude patterns
• Biodiversity Loss: Causes, extinction rates, conservation strategies

Understanding ecosystems is crucial for environmental management and conservation of biological diversity.