Ecology is the study of interactions between organisms and their environment, including both biotic (living) and abiotic (non-living) components.
Levels of Ecological Organization
Organism: A single living entity.
Population: A group of organisms of the same species in a specific area.
Community: All populations of different species living and interacting in an area.
Ecosystem: A community of organisms interacting with their physical environment.
Biome: A large geographical area with similar climate and ecosystems (e.g., rainforest, desert).
Biosphere: The global sum of all ecosystems, where life exists.
Ecosystem
Ecosystem is a biological community of interacting organisms and their physical environment.
It includes both living (biotic) and non-living (abiotic) components.
Components of an Ecosystem
Biotic Components:
Producers (autotrophs): Convert sunlight into energy (e.g., plants, algae).
Consumers (heterotrophs): Depend on producers for energy (e.g., herbivores, carnivores, omnivores).
Decomposers: Break down dead organic matter (e.g., fungi, bacteria).
Abiotic Components:
Non-living factors like sunlight, temperature, water, soil, and air.
Energy Flow in Ecosystems
Energy flows through ecosystems in a one-way direction:
Sunlight is the primary energy source.
Producers capture sunlight and convert it into chemical energy (photosynthesis).
Consumers obtain energy by eating producers or other consumers.
Decomposers recycle nutrients by breaking down dead organisms.
Food Chains and Food Webs illustrate energy transfer between trophic levels.
Food Chain: Linear flow of energy (e.g., Grass → Deer → Lion).
Food Web: Interconnected food chains.
Trophic Levels
Trophic Levels: Different levels in a food chain (Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers).
Producers: Base of the food chain (e.g., plants).
Primary Consumers: Herbivores that eat producers.
Secondary Consumers: Carnivores that eat herbivores.
Tertiary Consumers: Top predators that eat secondary consumers.
Energy Loss: Only about 10% of energy is transferred between trophic levels (10% rule).
Biogeochemical Cycles
Water Cycle: Evaporation, condensation, precipitation, and runoff.
Carbon Cycle: Photosynthesis, respiration, decomposition, and combustion.
Nitrogen Cycle: Nitrogen movement through nitrogen fixation, nitrification, assimilation, and denitrification.
Phosphorus Cycle: Movement of phosphorus from rocks to living organisms and back to the soil. It involves weathering of rocks, absorption by plants, and recycling through decomposition.
Sulphur Cycle: Nutrients are primarily stored in the Earth’s crust and move through soil, water, and living organisms through weathering, volcanic activity, and decomposition.
Ecological Interactions
Mutualism: A relationship where both species benefit. Example: Bees pollinating flowers (bees get nectar, flowers get pollinated).
Commensalism: A relationship where one species benefits, and the other is unaffected. Example: Birds nesting in trees (birds get shelter, trees are unaffected).
Amensalism: One species is harmed while the other is unaffected. Example: A large tree shading smaller plants, which reduces their growth.
Parasitism: A relationship where one species benefits at the expense of the other. Example: Ticks feeding on a host animal (ticks get blood, the host may suffer irritation or disease).
Predation: One organism (predator) kills and eats another (prey). Example: A lion hunting and eating a zebra.
Competition: Two species compete for the same resources, harming both to some extent. Example: Lions and hyenas competing for prey in the savannah.
Ecological Succession
Primary Succession: Development of ecosystems in previously uninhabited areas (e.g., bare rock). Starts with pioneer species like lichens and mosses.
Secondary Succession: Recovery of ecosystems after disturbances (e.g., forest fire). Soil is already present, so succession occurs faster than primary succession.
Hydrarch Succession: Starts in wet areas or water bodies, leading to land ecosystem (Hydrosere).
Xerarch Succession: Starts in dry areas like deserts and rocks (Xerosere).
Stages of Succession
Pioneer Stage: First organisms (lichens, mosses) colonize barren land.
Intermediate Stage: More complex plants like grasses, shrubs, and small trees grow.
Climax Community: A stable, mature ecosystem with large trees and diverse species.
The entire sequence of communities that successively change in a given area are called sere(s).
The individual transitional communities are termed seral stages or seral communities.
Ecological Pyramids
Pyramid of Numbers: Number of organisms at each trophic level. Can be Upright (grassland ecosystem) and Inverted (tree ecosystem).
Pyramid of Biomass: Total mass of organisms at each trophic level. Can be Upright (terrestrial ecosystems) and Inverted (aquatic ecosystem).
Pyramid of Energy: Shows energy flow (always upright). It demonstrates the 10% energy rule. Sun → Grass (10,000 kcal) → Grasshopper (1,000 kcal) → Frog (100 kcal) → Snake (10 kcal).
Ecological Productivity
The rate of biomass production is called Productivity.
The rate of generation of biomass in an ecosystem is called Ecological Productivity.
The energy or biomass produced by autotrophs (producers or plants) through photosynthesis or chemosynthesis is called Primary Productivity.
The energy or biomass produced by consumers (herbivores, carnivores, omnivores) is called Secondary Productivity.
The total productivity of an entire ecological community, including producers, consumers, and decomposers is called Community Productivity.
Primary Productivity can be divided into Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).
The total amount of energy captured and converted into chemical energy by producer is called Gross Primary Productivity (GPP).
GPP is expressed as energy per unit area per unit time (e.g., kcal/m²/year).
GPP=NPP+R (R is the energy used for respiration)
Net primary productivity is the energy or biomass available to for the consumption to heterotrophs (herbiviores and decomposers).
NPP=GPP-R
Biomes
Terrestrial part of the biosphere is divisible into enormous regions called biomes.
