Transcript OCEN1067N - Slideshow - Trophic Relationships

Trophic*
Relationships
This way to define organisms within
an ecosystem is based, simply put, on
what they eat and who eats them.
* Greek for nourishment
With respect to trophic levels,
marine organisms can be grouped
into 3 categories:
1. Primary producers form the basis of life by
producing food using energy from the sun
or chemical substrates. Primary producers
comprise the lowest, or first, trophic level.
The sun fuels photosynthesis—
This type of primary production is accomplished by
algae (tiny aquatic plants, such as the diatom pictured here)
macroalgae (big aquatic plants, such as kelp)
and
photosynthesizing bacteria
Chemical substrates fuel
chemosynthesis—
This type of primary production is accomplished by,
for example,
bacteria found at deep-sea hydrothermal vents
(hydrothermal vents are a type of underwater volcano).
University of Victoria
Canada
With respect to trophic levels,
marine organisms can be grouped
into 3 categories:
1. Primary producers form the basis of life. These organisms
produce food using energy from the sun or chemical substrates.
Primary producers comprise the lowest, or first, trophic level.
2. Consumers, as you can guess, eat other
organisms. Consumers comprise the second
and higher trophic levels.
Consumers can be divided into two
groups:
1. Herbivores
eat primary producers, such as algae, and occupy
the second trophic level. Common marine
herbivores are copepods, small crustaceans that
are usually a few millimeters long and very
abundant in coastal waters. This copepod is
about 5 mm long.
Consumers can be divided into two
groups:
2. Carnivores
eat herbivores and other carnivores, thus
occupying the higher trophic levels.
Common marine carnivores are fish,
although some copepods are also
carnivorous.
With respect to trophic levels,
marine organisms can be grouped
into 3 categories:
1. Primary producers form the basis of life. These organisms
produce food using energy from the sun or chemical substrates.
Primary producers comprise the lowest, or first, trophic level.
2. Consumers, as you can guess, eat other organisms. Consumers
comprise the second and higher trophic levels.
3. Decomposers are non-photosynthetic bacteria
and fungi; they derive energy from taking
up detritus (pieces of dead cells) and waste
products from other organisms.
Decomposers
Bacteria are the most abundant living organisms in the ocean
and
are key components of ecosystems with respect to
energy and carbon cycling.
Marine fungi are less studied than marine bacteria.
This photomicrograph is terrestrial fungi.
These relationships can be represented graphically as a
food chain.
Food chain
herbivores and carnivores eat organisms in trophic levels below them;
Decomposers take up detritus and waste from all trophic levels.
Consumer (carnivore)
Consumer (herbivore)
*
(This fresh-water
ostracod resembles
marine ostracods;
they are small
crustaceans.)
Decomposer
Primary producer
* The photo of the grouper is from VersAquatics Co. USA © 2004.
Energy Transfer within food chain
Energy transfer between trophic levels is quite
inefficient, on the order of 6-20%, with 10%
commonly used in calculations. Thus, the number
of trophic levels in a given ecosystem tends to be
small.
Furthermore, the food chain is a model, an
oversimplification of interactions occurring in the
real world. Most marine ecosystems are more
complex than a simple chain. For example, most
organisms eat more than one type of food, and some
organisms occupy different trophic levels at different
life stages.
Food web
Antarctic food web
Thus, food chains are
often more correctly
described as
food webs,
which have many
interactions.
http://octopus.gma.org/surfing/human/foodweb.gif