BIO101 – Topic 31: Ecology and Ecosystems
© Lesuyai Organic Guides 2025
31.1 Introduction to Ecology
Ecology is the scientific study of interactions among organisms and between organisms and their
physical environment. It seeks to understand the patterns and processes that determine the
distribution, abundance, and diversity of life on Earth.
31.2 Levels of Ecological Organization
Level Description Example
Organism Individual living entity A lion (Panthera leo)
Population Group of same species in one area Lions in Maasai Mara
Community All populations in an area Lions, zebras, and acacia trees
Ecosystem Community plus abiotic environment Savanna ecosystem
Biome Large ecological region with uniform climate Tropical rainforest
Biosphere Global sum of all ecosystems Earth’s living zone
31.3 Components of an Ecosystem
Biotic components include producers, consumers, and decomposers. Abiotic components are
sunlight, temperature, soil, water, and minerals. These interact through energy flow and nutrient
cycling.
31.4 Energy Flow in Ecosystems
Energy enters ecosystems via photosynthesis and flows through trophic levels. Energy decreases
with each transfer due to the 10% rule.
31.5 Biogeochemical Cycles
Includes carbon, nitrogen, water, and phosphorus cycles essential for ecosystem stability.
31.6 Ecosystem Productivity
Gross Primary Productivity (GPP) is total energy fixed; Net Primary Productivity (NPP) is energy
available to consumers.
31.7 Ecological Succession
Primary succession starts on bare surfaces; secondary follows disturbances. Ends in a climax
community.
31.8 Population Ecology
Population size changes depend on birth, death, immigration, and emigration. Growth can be
exponential or logistic.
31.9 Human Impacts on Ecosystems
© Lesuyai Organic Guides 2025
31.1 Introduction to Ecology
Ecology is the scientific study of interactions among organisms and between organisms and their
physical environment. It seeks to understand the patterns and processes that determine the
distribution, abundance, and diversity of life on Earth.
31.2 Levels of Ecological Organization
Level Description Example
Organism Individual living entity A lion (Panthera leo)
Population Group of same species in one area Lions in Maasai Mara
Community All populations in an area Lions, zebras, and acacia trees
Ecosystem Community plus abiotic environment Savanna ecosystem
Biome Large ecological region with uniform climate Tropical rainforest
Biosphere Global sum of all ecosystems Earth’s living zone
31.3 Components of an Ecosystem
Biotic components include producers, consumers, and decomposers. Abiotic components are
sunlight, temperature, soil, water, and minerals. These interact through energy flow and nutrient
cycling.
31.4 Energy Flow in Ecosystems
Energy enters ecosystems via photosynthesis and flows through trophic levels. Energy decreases
with each transfer due to the 10% rule.
31.5 Biogeochemical Cycles
Includes carbon, nitrogen, water, and phosphorus cycles essential for ecosystem stability.
31.6 Ecosystem Productivity
Gross Primary Productivity (GPP) is total energy fixed; Net Primary Productivity (NPP) is energy
available to consumers.
31.7 Ecological Succession
Primary succession starts on bare surfaces; secondary follows disturbances. Ends in a climax
community.
31.8 Population Ecology
Population size changes depend on birth, death, immigration, and emigration. Growth can be
exponential or logistic.
31.9 Human Impacts on Ecosystems
