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TROPHIC
LEVELS |
PRODUCERS - autotrophs
on land usually plants, in aquatic
ecosystems usually algae
use light to make carbohydrates as
sources of energy for all organisms in food chains
99% of all organic matter is made
up of plants and algae
all heterotrophs combined make up
only 1% of organic matter
key factors influencing productivity
are
duration
and intensity of sunlight
temperature
precipitation
availability of essential mineral elements (esp. in aquatic
ecosystems)
gross productivity - measure of the rate at which energy is
assimilated by the organisms in a particular trophic level
net productivity = gross productivity - cost of all the metabolic
processes/activities of those organisms
the increase in biomass (grams or tonnes in a
particular time)
biomass = total dry weight of all the organisms
measured at any one time
measure of the rate at which organisms store
energy
energy available to organisms of the next
trophic level
increase in mass of individuals and the mass of
offspring
net primary production is the increase in the
amount of plant or algal material between the beginning and end of a
specified time period e.g. agricultural ecosystem - the standing crop for a
season
primary production is very variable
CONSUMERS
Primary Consumers - herbivores
eat plants and/or algae
each ecosystem has its characteristic
herbivores
much of what is consumed is eliminated undigested
only a fraction of the chemical energy
consumed by the herbivore is converted into animal biomass (a very rough
guide is 10%)
most of what is consumed is used to maintain
metabolic processes and to provide energy for activities e.g.:
searching for food
eating and digesting food
mating
caring for young
fleeing predators
Secondary Consumers - carnivores
animals that eat other animals
only a small amount of the organic
material of the herbivore is incorporated into the body of the carnivore
some food chains have 4th or 5th
levels (i.e. 3rd and 4th consumer levels)
there are usually only 3 links (4 levels) in a food
chain
plant a herbivore a carnivore
a carnivore
the limit is usually 5 links regardless of the
ecosystem
at each level there is a decrease in the
total amount of energy stored as biomass
Detritovores
scavengers and decomposers (fungi and
bacteria)
live on the refuse or detritus of a community
scavengers - feed on dead organisms
(carrion)
decomposers - break down cellulose and
nitrogenous waste products as well as dead organisms
more than 90% of net primary
production is consumed by detritovores rather than herbivores
some of this energy is fed through the
food web by consumers of the detritovores
usually short because the
transfer of energy from one level to the next is rather inefficient
approx 10% at each level (1% - 20%
depending on the species involved)
1% - 3% of sunlight falling on
vegetation is used in photosynthesis
depict relationships at each
level of a food chain in quantitative form
energy
biomass
numbers of organisms
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Copyright © Jennie Walters: 1998 ~
2004
Last changed: May 10, 2003