Download Trophic Levels in Food Chains and Webs (Chap. 46)

Communities, Food Chains/Webs
and Succession (Chap. 46)
Communities
• interacting plants and animals forming a
identifiable group (doesn’t include abiotic
environment)
– Open communities gradually blend into
others
• forests
– Closed communities have more definite
borders and therefore few organisms pass
between communities
• pond, caves
Succession – species or groups in a community
give way to the next
• Autogenic succession
– the change is because of the current species
involved
• aspen and cherry create shady conditions that
are unfavorable to themselves but good for
maple and oak seedlings
• Allogenic succession
– external forces cause the change
• ponds become nutrient rich because of runoff
and plants begin to proliferate
• Primary succession
– the establishment of a community where no
community previously existed
– takes a very long time
• rocky ground  lichens, moss, plants
field  forest
• Secondary succession
– the establishment of a new community where
a previous community had been
– more rapid than 1º succession
• fields  small plants, shrubs  forests
Ecosystems
• consists of all the species AND components of
the physical environment (abiotic factors) of a
particular site
• components of an ecosystem
– Ecologists categorize organisms into three
categories/trophic levels based on their
metabolism and role within the community
1. Autotrophs (Producers)
– convert energy from sunlight or inorganic
molecules into organic molecules
– producers start all food chains
2. Heterotrophs (Consumers)
– organisms that use energy in organic matter
obtained from other organisms
– can be subdivided into
• primary, secondary, tertiary, quaternary
consumers
• ex. rabbit, snake, hawk, lion
3. Detritivores (Decomposers)
• feed off dead organic matter by ingesting it. ex.
worms, dung beetles, bacteria
4. Saprotrophs (Decomposers)
• feed off dead organic matter by secreting
digestive enzymes into it and absorbing the
products of digestion. ex. bread mold,
mushrooms
Both are very important to break down nutrients
in complex organic compounds that otherwise
would be permanently locked up in dead
organic matter
Food Chain
• a sequential path of food consumption
• the table below gives one example of a food
chain and the trophic levels represented in it.
Grass
→
Autotro
phs
(Produc
ers)
→
Grasshopper
→
Herbivores
(Primary
Consumers)
→
Toad
→
Snake
→
Hawk
→
Bacteria
of decay
In general,
Carnivores
(Secondary, tertiary, etc.
consumers)
→
Decompo
sers
Food Web
• a diagram that shows all the feeding relationships
in a community
• more realistic than a food chain and much more
complicated