ENVS200-wk3.1-trophic
Ecology and Ecosystems Overview
Course: ENVS 200 at Cuesta College
Student Learning Objectives
By the end of this class, students will be able to:
Define an ecosystem and its main components.
Explain the photosynthesis equation and its importance to ecosystems.
Assign a trophic level to an organism within a food chain/web.
Explain how energy flows through an ecosystem.
Energy in an Ecosystem: Photosynthesis
Certain organisms convert solar energy into chemical energy.
Energy created via photosynthesis enters ecosystems continuously.
Energy can be transferred from one organism to another.
Production of Plant Matter in an Ecosystem
Primary Production: Creation of new organic matter via photosynthesis.
Autotrophs: Organisms that create their own nutrition (e.g., plants).
Primary Productivity: Rate of primary production.
Gross Primary Productivity (GPP): The rate at which producers convert energy into biomass (total production).
Net Primary Productivity (NPP)
Net Primary Productivity: The rate of photosynthesis minus the rate of aerobic respiration.
Represents the energy available for consumers.
Terrestrial and aquatic ecosystems differ in their NPP rates.
NPP in Oceans vs. Terrestrial Ecosystems
Despite lower NPP, oceans produce most of the world's biomass due to the massive amount of life.
Tropical rainforests have high NPP; however, much is lost through natural capital degradation.
Ecosystem Components
Ecosystems include both biotic and abiotic components.
Producers (Autotrophs): Organisms that produce their own food.
Consumers (Heterotrophs): Organisms that consume other organisms.
Herbivores: Plant eaters
Carnivores: Meat eaters
Omnivores: Eat both plants and meat
Decomposers (Heterotrophs): Break down dead organic matter.
Energy in an Ecosystem: Respiration
Aerobic Respiration: Uses oxygen to convert glucose into carbon dioxide and water.
Ecological balance is maintained between plants and animals through respiration.
Trophic Levels
Organisms are assigned a trophic level based on their feeding relationships.
Tertiary Consumers: Top-level carnivores.
Secondary Consumers: Consume other consumers (carnivores or omnivores).
Primary Consumers: Herbivores that eat producers.
Producers: Base of the food web (autotrophs).
Energy Flow in Ecosystems
Energy flows through ecosystems via food chains and food webs.
The amount and quality of energy decrease with each trophic level due to energy loss (heat).
Approximately 90% of energy is lost with each transfer between trophic levels (The 10% Rule).
Food Chains and Food Webs
Food Chain: A linear sequence of organisms where each serves as a nutritional source for the next.
Food Web: A complex network of interconnected food chains, illustrating multiple feeding relationships.
Pyramid of Energy Flow
Trophic levels organized into a pyramid, showing the energy available at each level:
Tertiary Consumers (top level)
Secondary Consumers
Primary Consumers
Producers (base level)
Practical Example: Eating at Lower Trophic Levels
Examples of how a farmer receives nutrition:
From hens
From grasshoppers
From soy