Constructing Food Chains
Definition
Food chain
A food chain is a linear sequence of organisms, each feeding on the previous one, illustrating the flow of energy and nutrients in an ecosystem.
- A food chain begins with a producer, usually a photoautotrophlike a plant or algae, which converts sunlight into chemical energy through photosynthesis.
- This energy is stored in organic molecules, such as carbohydrates.
Definition
Food web
A food web is a complex network of interconnected food chains, representing all the feeding relationships within a community.
Example: A Simple Forest Food Chain
- Producer: Oak tree (Quercus robur)-produces acorns.
- Primary Consumer: Squirrel (Sciurus vulgaris)-eats acorns.
- Secondary Consumer: Red fox (Vulpes vulpes)-preys on squirrels.
- Tertiary Consumer: Eurasian eagle-owl (Bubo bubo)-preys on red foxes.
Example
- In this food chain, energy flows from the oak tree to the squirrel, then to the red fox, and finally to the eagle-owl.
- The arrows indicate the direction of energy transfer.
Exam technique
When drawing a food chain, always ensure the arrows point in the direction of energy flow, from the organism being eaten to the organism doing the eating.
Constructing Food Webs
- Food webs provide a more realistic representation of feeding relationships in a community.
- They illustrate how multiple food chains intersect, highlighting the interconnectedness of organisms.
Example: Aquatic Food Web
- Producers: Cyanobacteria and Phytoplankton as primary producers of the ocean.
- Primary Consumers: Zooplankton and smaller fish whose diet mainly consists of small producer organisms.
- Secondary Consumers: Small carnivorous fish such as Yellowfin Tuna and Blue Sharks.
- Tertiary Consumers: Large carnivorous predators like the Great White Shark are the apex predators.
Example
- In this web, producers like phytoplankton and cyanobacteria supply energy to all other organisms.
- Primary consumers—Zooplankton—convert this energy into biomass for predators.
- Secondary consumers include Yellowfin Tuna and Blue Sharks, which hunt organisms that feed on producers.
- At the top, tertiary consumers like Great White Sharks prey on smaller carnivorous fish as well as other consumers.
Analogy
Food webs are like an interconnected highway rather than a straight road (which a food chain represents)
Constructing a Food Web: Step-by-Step
- Identify Key Species: List the producers, consumers, and decomposers in the ecosystem.
- Determine Feeding Relationships: Identify who eats whom. Use research tools like field observations or databases to gather information.
- Draw the Web: Start with producers at the bottom and work upwards. Use arrows to indicate energy flow.
- Include Decomposers: Show how decomposers recycle nutrients from dead organisms back to the environment.
Self review
Can you construct a food web for a local ecosystem, such as a pond or grassland? Identify at least three producers, three consumers, and one decomposer.
