Energy & Nutrients Food Web Dynamics
Energy & Nutrients Objectives:
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Describe how energy flows and nutrients cycle within a food web.
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Provide examples of different forms of fruit and seed dispersal.
A garden is the perfect place to explore how energy flows and nutrients cycle within a food web.
Energy Flows
Photosynthesis is carried out by most producers, and respiration is carried out in some form by all organisms (producers, consumers, and decomposers).
Producers convert sunlight energy into sugar molecular energy. When producers, consumers, and decomposers break down these sugars, the energy is converted to heat.
Energy is flowing through the system: entering as sunlight, traveling as sugar, and being lost as heat.
Although we typically think of plants when we think of photosynthesis, algae and photosynthetic bacteria play a significant role in sugar and oxygen production.
Nutrients Cycle
We continually need sunlight energy to replace the energy being lost as heat.
Nutrients are a different story.
Molecules are broken down into simpler forms by decomposers and recycled back to producers where they travel through the trophic levels over and over again.
In this video the concepts on this webpage get put together into a basic food web.
An additional group of organisms mentioned are the “detritivore” consumers that eat “detritus” (dead leaves, scat/fecal material, etc.). These include earthworms, some beetles, sowbugs, and more.
Masting year
In some years, fruit trees produce an abundant number of fruit, called a “masting” year. This was a masting year for our cherry trees.
The birds and fox left cherry pits in their scat. The next time you are out hiking, look for evidence of what animals are eating along the trail.
Why may it be important for seeds to be dispersed far from a parent plant?
Fruit & Seed Dispersal
Fruits often have modifications that enable seeds to disperse far from the parent plant, reducing potential competition.
Six types of fruit (and seed) dispersal
Wind
Animals: Burrs and Stickseeds
Animals: Fleshy Fruit
Animals: Stored Nuts
Propulsion: Twisting
Propulsion: Ballisitics
This video uses specimens to demonstrate fruits dispersing seeds.
Himalayan blackberries are invasive species in many parts of the northern hemisphere, including the willamette valley. You can see both the flowers and developing fruit in this video.
How are these fruits likely dispersed?
Maple trees produce dry samara fruits. This video shows the fruit in action, aiding in seed dispersal.
Many people are planting milkweed seeds because some of the species play a critical role in butterfly life cycles. This video shows how they can spread through a field.
The next section focuses in on the decomposition process, including the role of fungi and bacteria.
Check your knowledge. Can you:
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Describe how energy flows and nutrients cycle within a food web?
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Provide examples of different forms of fruit and seed dispersal?
Go back to the Biomass Page
Go forward to the Decomposers Page
Food Webs Lecture Guide Contents
This guide and lecture material are assessed on the weekly quiz.
Back to Module 4
This week’s overview
This Guide
Food Webs
