Ecosystems and Biodiversity
Ecosystem Basics
1. What is an Ecosystem?
Definition:
- Community of organisms + physical environment
- Interdependent living and non-living things
- Energy flowing through system
- Nutrient cycling
- Self-sustaining unit
Key Components:
- Biotic factors: All living organisms
- Abiotic factors: Non-living physical elements
- Interactions: Relationships between components
- Boundaries: Sometimes distinct, often overlapping
- Scale: From small (pond) to global (biosphere)
2. Biotic Components
Producers (Autotrophs):
- Plants using photosynthesis
- Algae and cyanobacteria
- Chemosynthetic bacteria (deep sea)
- Foundation of food chain
- Convert solar energy to chemical energy
Consumers (Heterotrophs):
- Primary consumers: Herbivores eating plants
- Secondary consumers: Carnivores eating herbivores
- Tertiary consumers: Large predators
- Omnivores: Eating both plants and meat
- Detritivores: Feeding on dead organic matter
Decomposers:
- Bacteria and fungi
- Breaking down dead organisms
- Releasing nutrients back to soil
- Essential recycling role
- Completing nutrient cycles
3. Abiotic Factors
Climate Elements:
- Temperature: Affects metabolism and distribution
- Precipitation: Water availability
- Wind: Dispersal and erosion
- Light intensity: For photosynthesis
- Humidity: Water availability in air
Chemical Factors:
- Oxygen levels: For respiration
- Carbon dioxide: For photosynthesis
- Soil pH: Affecting nutrient availability
- Nutrient availability: Nitrogen, phosphorus, potassium
- Salinity: In aquatic ecosystems
Physical Factors:
- Soil type and structure
- Topography and elevation
- Water flow and currents
- Atmospheric pressure
- Season and day length
Food Chains and Webs
1. Energy Flow
Food Chains:
- Linear sequence of energy transfer
- Producer → Consumer → Consumer → ...
- Each arrow = energy transfer
- Example: Grass → Rabbit → Fox
- Simple but unrealistic
Food Webs:
- Multiple interconnected chains
- Organisms eating variety of food
- Alternative energy pathways
- More realistic representation
- Showing complexity
2. Trophic Levels
Energy Transfer:
- ~10% transferred to next level
- 90% lost as heat through respiration
- Limited energy at higher levels
- Fewer large predators than prey
- Few trophic levels (usually 3-4)
Pyramid of Energy:
- Producers: Base of pyramid
- Primary consumers: Smaller section
- Secondary consumers: Smaller still
- Tertiary consumers: Tiny apex
- Biomass decreases upward
Biomass:
- Total mass of organisms at each level
- Decreases with each level
- Pyramid of biomass is inverted in some aquatic systems
- Energy fuels biomass
3. Feeding Strategies
Feeding Levels:
- Grazing: Herbivores eating living plants
- Predation: Carnivores hunting prey
- Parasitism: Feeding on host without killing
- Detritus feeding: Eating dead material
- Filter feeding: Straining food from water
Biodiversity
1. Types of Biodiversity
Genetic Diversity:
- Variation within species
- Different alleles
- Adaptation to environments
- Evolution potential
- Health of populations
Species Diversity:
- Number of different species
- Variety in ecosystem
- Measured by richness and evenness
- Indicator of ecosystem health
- Related to stability
Ecosystem Diversity:
- Variety of habitats and ecosystems
- Different environmental conditions
- Global scale variation
- Landscape diversity
- Habitat mosaic
2. Biodiversity Hotspots
Characteristics:
- High species concentration
- Unique or endemic species
- High threat level
- Limited area
- High conservation priority
Global Examples:
- Tropical rainforests (Amazon, Congo, Southeast Asia)
- Coral reefs (extremely high diversity)
- Mediterranean regions
- Madagascar
- East African mountains
Conservation Importance:
- Protect majority of species
- Limited area makes protection feasible
- Cost-effective conservation
- Ecological and cultural value
- Scientific resources
3. Measuring Biodiversity
Species Richness:
- Number of different species
- Simple count
- Not accounting for abundance
- Basic measure
Species Evenness:
- Distribution of individuals among species
- Equal numbers = high evenness
- Unequal = low evenness
- Important for stability
Diversity Indices:
- Shannon diversity index
- Simpson diversity index
- Considering richness and evenness
- Comparative measure
- Numerical assessment
Habitats and Niches
1. Habitat Concept
Definition:
- Physical location where organism lives
- Specific environmental conditions
- Must meet organism needs
- Provides shelter, food, water, mates
- Can be small or large scale
Habitat Types:
- Terrestrial: Forest, grassland, desert
- Aquatic: Ocean, river, lake
- Mixed: Wetland, mangrove, estuary
- Specialized: Cave, hot spring, deep sea
2. Ecological Niche
Definition:
- Role organisms play in ecosystem
- How organisms interact with environment
- Resources used
- Space occupied
- Functional position
Niche Components:
- Food eaten
- Space required
- Time active
- Environmental preferences
- Interactions with other species
Competitive Exclusion:
- Two species cannot occupy identical niche
- One will exclude other
- Resource competition results
- Niche differentiation or extinction
- Species separation concept
3. Habitat Loss
Causes:
- Deforestation
- Agricultural expansion
- Urban development
- Mining and extraction
- Infrastructure development
Consequences:
- Species extinction
- Biodiversity loss
- Ecosystem degradation
- Reduced ecosystem services
- Human impact greatest threat
Ecological Interactions
1. Positive Interactions
Mutualism:
- Both organisms benefit
- Example: Bee and flower (pollination + nectar)
- Nitrogen-fixing bacteria and legumes
- Often obligate (essential)
- Co-evolution likely
Commensalism:
- One organism benefits, other unaffected
- Example: Remora fish on shark
- Clownfish in anemone
- One-way benefit
- Parasitic is opposite (harm)
2. Negative Interactions
Predation:
- Predator kills prey for food
- Population control
- Selective pressure on prey
- Predator-prey cycles
- Example: Wolf and elk
Competition:
- Both organisms harmed
- Fighting for shared resources
- Can reduce both populations
- Leads to niche differentiation
- Interspecific vs. intraspecific
Parasitism:
- Parasite benefits, host harmed
- Doesn't kill host (typically)
- Examples: Tapeworm, mosquito, louse
- Can affect host health
- Can control populations
3. Population Interactions
Predator-Prey Cycles:
- Prey increase → predator increase
- Predator overexploitation → prey decrease
- Predator starvation → predators decline
- Prey recover without predators
- Cyclical pattern
Symbiosis:
- Close long-term living together
- Can be mutual beneficial or parasitic
- Example: Lichen (fungus + algae)
- Chemical communication
- Coevolution
Ecological Succession
1. Primary Succession
Definition:
- Colonization of bare rock or soil
- No previous community
- Very slow (centuries)
- Eventually climax community
Stages:
- Pioneer species: Lichens and mosses weathering rock
- Early colonizers: Grasses and small shrubs establishing
- Intermediate: Taller plants and trees arriving
- Climax: Stable mature community established
2. Secondary Succession
Definition:
- Reestablishment after disturbance
- Soil and seed source present
- Faster than primary (~decades)
- Often back to similar community
Examples:
- Forest after fire
- Field after abandoned agriculture
- Pond after storm
- Faster recovery than primary succession
3. Climax Community
Characteristics:
- Stable and self-sustaining
- Diverse species composition
- No further change (theoretically)
- Equilibrium reached
- Specific to conditions
Factors:
- Climate determines ultimate community
- Not static—small changes continue
- Disturbance can restart succession
- Different climax in different environments
Summary
Ecosystem and biodiversity concepts include:
- Structure: Biotic and abiotic components
- Energy: Flow through trophic levels
- Biodiversity: Genetic, species, and ecosystem variation
- Habitats: Locations with specific conditions
- Niches: Functional roles in ecosystem
- Interactions: Relationships between organisms
- Succession: Change over time
Understanding ecosystems is fundamental to environmental management, conservation, and sustainability planning.