4. Ecology

4.1 Ecosystem Ecology

Concept of Ecology

Ecology is the scientific study of interactions between organisms and their environment. It is divided into:

• Autecology: Study of individual species or populations in relation to their environment.
• Synecology: Study of groups of organisms (communities) and their interactions with the environment.

Biotic Factors

Living components of an ecosystem include:

• Producers (autotrophs): Organisms that synthesize their own food via photosynthesis (e.g., phytoplankton, terrestrial plants).
• Consumers (heterotrophs): Organisms that obtain energy by feeding on other organisms.
  • Primary consumers (herbivores): Feed directly on producers (e.g., zooplankton, deer).
  • Secondary consumers (carnivores/omnivores): Feed on primary consumers (e.g., small fish, foxes).
  • Tertiary consumers: Feed on secondary consumers (e.g., large fish, tigers).
• Decomposers: Break down dead organic matter, returning nutrients to the soil (e.g., fungi, bacteria).

Biotic Interactions

• Predation: One organism (predator) kills and eats another (prey). Example: Lion‑zebra.
• Competition: Organisms vie for limited resources.
  • Interspecific: Between different species (e.g., two bird species competing for insects).
  • Intraspecific: Within the same species (e.g., seedlings competing for light).
• Mutualism: Both partners benefit. Example: Pollination by bees.
• Commensalism: One benefits, the other is unaffected. Example: Barnacles on whales.
• Parasitism: One benefits at the expense of the host. Example: Ticks on mammals.

Abiotic Factors

Non‑living components that influence life:

• Light: Drives photosynthesis; intensity and duration affect plant growth.
• Temperature: Regulates metabolic rates; extremes limit distribution.
• Water: Essential for biochemical reactions; availability shapes habitats.
• Soil: Provides anchorage, nutrients, and water retention.
• Minerals: Essential elements (N, P, K, Ca, etc.) required for growth.

Species Interactions (Summary)

Concept of Ecosystem

An ecosystem comprises a biotic community (all living organisms) interacting with their abiotic components (physical and chemical factors).

Structural Aspects

• Biotic community: Producers, consumers, decomposers.
• Abiotic components: Light, temperature, water, soil, minerals.
• Stratification: Vertical layering of habitats (e.g., forest canopy, understory, shrub layer, ground layer).

Functional Aspects

• Energy flow: Unidirectional transfer from producers → consumers → decomposers; governed by the 10% rule (only about 10% of energy is transferred between trophic levels).
• Nutrient cycling: Recycling of elements (C, N, P, S) through biogeochemical cycles.

Pond Ecosystem

Stratification zones:

1. Littoral zone: Shallow, light‑penetrated area near shore; rooted macrophytes, snails, insects.
2. Limnetic zone: Open, well‑lit surface water; dominated by phytoplankton and zooplankton.
3. Profundal zone: Deep, dark, low‑oxygen region; benthic organisms and detritus.

Typical food chain: Phytoplankton → Zooplankton → Small fish → Large fish → Bird (e.g., kingfisher).

Forest Ecosystem

Canopy layers:

• Emergent layer: Tallest trees (e.g., kapok) receiving full sunlight.
• Canopy layer: Dense leafy roof; habitat for birds, insects, mammals.
• Understory layer: Shade‑tolerant shrubs and young trees.
• Forest floor: Leaf litter, fungi, decomposers, detritivores.

Energy flows from producers (trees, understory plants) through herbivores (insects, deer) to carnivores (birds, big cats). Nutrient cycling is rapid due to prolific litter decomposition.

Food Chain and Food Web

Food chain: Linear sequence showing who eats whom.

Food web: Network of interconnected food chains illustrating the complexity of feeding relationships.

Trophic Levels

1. Level 1: Producers (autotrophs).
2. Level 2: Primary consumers (herbivores).
3. Level 3: Secondary consumers (carnivores/omnivores).
4. Level 4: Tertiary consumers (top carnivores).

Ecological Pyramids

Graphical representations of trophic structure.

Productivity

Primary productivity: Rate at which producers convert solar energy into chemical energy.

• Gross Primary Productivity (GPP): Total energy fixed by photosynthesis.
• Net Primary Productivity (NPP): Energy available for growth after respiration: NPP = GPP – R where R is plant respiration.

Secondary productivity: Rate of energy storage at consumer levels.

Factors affecting productivity: light intensity, temperature, water/nutrient availability, CO₂ concentration, species composition.

Biogeochemical Cycles

Carbon Cycle

Key processes:

• Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
• Decomposition: Breakdown of dead organic matter releasing CO₂.
• Combustion: Burning of fossil fuels and biomass adds CO₂ to atmosphere.
• Ocean absorption: CO₂ dissolves forming carbonic acid; marine organisms use it for shells.

Nitrogen Cycle

Key processes:

• Nitrogen fixation: Conversion of atmospheric N₂ to ammonia (NH₃) by bacteria (e.g., Rhizobium) or lightning.
• Nitrification: Oxidation of ammonia to nitrite (NO₂⁻) then nitrate (NO₃⁻) by nitrifying bacteria.
• Assimilation: Uptake of nitrate/ammonia by plants to synthesize amino acids.
• Ammonification: Decomposition of organic nitrogen returns ammonia.
• Denitrification: Reduction of nitrate back to N₂ gas by anaerobic bacteria, completing the cycle.

Concept of Succession

Ecological succession is the orderly process of community change over time.

• Primary succession: Begins on barren substrate with no soil (e.g., lava flow, glacial retreat). Pioneer species (lichens, mosses) initiate soil formation.
• Secondary succession: Occurs after disturbance that removes vegetation but leaves soil intact (e.g., fire, logging). Faster recovery due to existing soil and seed bank.
• Pioneer community: First colonizers, typically r‑selected, fast‑growing, tolerant of harsh conditions.
• Climax community: Stable, self‑perpetuating community characteristic of the climate (e.g., deciduous forest).
• Seral stages: Intermediate communities between pioneer and climax.

4.2 Ecological Adaptation

Concept of Adaptation

Adaptations are inherited traits that enhance an organism’s fitness in a specific environment. They can be:

• Structural: Morphological features (e.g., thick cuticle).
• Physiological: Internal functional adjustments (e.g., CAM photosynthesis).
• Behavioral: Actions that improve survival (e.g., nocturnal activity).

Hydrophytes (Aquatic Plants)

Adaptations to life in water:

• Aerenchyma: Large intercellular air spaces facilitating buoyancy and oxygen transport to roots.
• Thin cuticle: Reduces barrier to gas exchange; water is abundant.
• Flexible stems and leaves: Allow movement with water currents, reducing mechanical damage.
• Reduced or absent roots: Nutrients absorbed directly from water.

Examples: Lotus (Nelumbo nucifera), Water lily (Nymphaea spp.), Duckweed (Lemna spp.).

Xerophytes (Drought‑Resistant Plants)

Adaptations to arid conditions:

• Thick cuticle: Minimizes water loss.
• Sunken stomata: Stomata located in pits, reducing transpiration.
• Reduced leaf surface area: Leaves may be spines, needles, or shed during drought.
• Succulent tissues: Store water (e.g., cactus stems).
• CAM photosynthesis: Stomata open at night to fix CO₂, minimizing daytime water loss.
• Deep or extensive root systems: Access groundwater.

Examples: Cactus (Opuntia spp.), Acacia (Acacia spp.), Olive (Olea europaea), Sagebrush (Artemisia tridentata).

4.3 Ecological Imbalances

Greenhouse Effect and Climate Change

Certain gases trap infrared radiation, warming the Earth.

• Main greenhouse gases (GHGs): Carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), water vapor.
• Anthropogenic sources: Fossil fuel combustion, deforestation, agriculture (rice paddies, livestock), industrial processes.
• Global warming impacts: Rising sea levels, increased frequency of extreme weather, shifts in species ranges, coral bleaching, altered phenology.

Mitigation: Renewable energy, reforestation, carbon capture, sustainable agriculture.

Depletion of Ozone Layer

The stratospheric ozone layer absorbs harmful UV‑B radiation.

• Cause: Release of chlorofluorocarbons (CFCs), halons, and other ozone‑depleting substances (ODS).
• Chemical process: UV radiation breaks CFCs releasing chlorine atoms that catalytically destroy ozone (O₃).
• Observed effect: Seasonal ozone hole over Antarctica; increased UV‑B reaching Earth’s surface.
• Consequences: Higher incidence of skin cancer, cataracts, immune suppression, damage to phytoplankton and crops.

Response: Montreal Protocol (1987) phased out ODS; ozone layer showing signs of recovery.

Acid Rain

Precipitation with pH < 5.6 caused by atmospheric oxidation of SO₂ and NOₓ.

• Sources: Burning of sulfur‑containing coal, oil; vehicle emissions; industrial processes.
• Chemical reactions:
  • SO₂ + OH· → H₂SO₄ (sulfuric acid)
  • NO₂ + OH· → HNO₃ (nitric acid)
• Effects:
  • Corrosion of buildings, monuments, and infrastructure.
  • Leaching of nutrients from soil, release of toxic aluminum.
  • Acidification of lakes and streams → fish kills, loss of biodiversity.
  • Damage to foliage and forest decline.

Remediation: Flue‑gas desulfurization, catalytic converters, low‑sulfur fuels, emission caps.

Biological Invasion

Introduction of non‑native species that spread rapidly and harm native ecosystems.

• Examples:
  • Lantana camara: Forms dense thickets, outcompetes native shrubs.
  • Mikania micrantha (“mile‑a‑minute vine”): Smothers trees and crops.
  • Other notable invaders: Water hyacinth (Eichhornia crassipes), Zebra mussel (Dreissena polymorpha).
• Impacts:
  • Reduced native biodiversity through competition, predation, or disease.
  • Altered fire regimes, nutrient cycling, and hydrology.
  • Economic losses in agriculture, forestry, and fisheries.
• Management: Prevention (quarantine, ballast water control), early detection, mechanical/chemical removal, biological control agents.

Note: Diagrams referenced in the text (e.g., pond stratification, forest canopy layers, ecological pyramids, biogeochemical cycles) should be illustrated alongside the corresponding sections for optimal comprehension.