Chapter 28 - Chapter 28 How do ecosystems work Case Study...

Chapter 28: How do ecosystems work?
• Case Study: When the Salmon Return:
o Salmon flow from streams to the oceans as babies, but for some mysterious reason
they swim along the stream and swim upstream to return to their birth place and lay
their eggs.
• 28.1: What are the pathways of energy and nutrients?
o Ecosystems functions based on two laws:
 Energy moves through the community in a continuous one-way flow, needing
constant replenishment from an outside source, the sun.
 Nutrients constantly cycle and recycle within and among ecosystems.
• 28.2: How does energy flow through communities?
o Energy enter communities through photosynthesis
 Energy from the sun reaches earth as electromagnetic waves—of which only 1%
is absorbed as heat by the earth and plants only get 3% of that meaning—life on
this planet is thus supported by less than .03% if the energy reaching earth from
the sun.
o Energy is passed from one trophic level to another
 Tropic levels:
• 1 st —producer
• 2 nd —primary consumer--herbivores
• 3 rd — secondary consumer--carnivores
• 4 th —tertiary consumers—carnivores who eat other carnivores
 Food chains and food webs describe the feeding relationships within
communities:
• Food chain=a linear feeding relationship
• A food web shows the interconnecting food chains and more accurately
describes the actual feeding relationships within a given community.

• Humans, as well as others, are Omnivores which means that they act as
primary, secondary, and tertiary consumers.
 Detritus feeders and decomposers release nutrients for reuse:
• The most important strands of a food web are the decomposers and detritus
feeders:
o Detritus feeders—are an army mostly small and often unnoticed animals
that live on the refuse of life—rotten or dead stuff.
o Decomposers are primarily bacteria and fungi that digest food outside of
their bodies by secreting digestive enzymes into the environment.