Download IB food webs

Marine food web
Figure 12 shows a simplified food web from the open ocean in southern hemisphere. The
arrows indicate the direction of energy
flow.
1) State the trophic level of
nanophytoplankton. (1)
2) Identify two primary consumers in
the food web. (2)
3) Identify in the food web:
a) The shortest food chain (1)
b) The longest food chain (1)
c) The species with the most predators
(1)
d) The species with the greatest
number of different types of prey (1)
4) Discuss the trophic level to which
emperor's penguin's should be
assigned. (3)
Fishing down marine food
webs
Tropic levels can be represented
by a number indicating the
position of the species within an
ecosystem. By definition, produces
occupy the first trophic level and
so have a TL of one. For primary
consumers TL equals two, and so
on. The larger the number, the
more energy transfer steps
between the organism and the initial fixing of the suns energy. Trophic levels are not always
stated as whole numbers. Fish and other animals that feed at more than one level often have
estimated mean trophic levels.
One effect of commercial overfishing is the reduction in the number of fish that feed at higher
trophic levels, such as long lived fish. The phrase "fishing down the marine food webs" refers to
the increased tendency for marine landings to consist of animals that feed at lower trophic
levels.
1) Suggest a method that might be used to deduce the tropic level of the fish once it is
captured. (2)
2a) Compare the changes and mean trophic level of landed fish from Marine and freshwater
fisheries since 1970. (3)
2b) Suggests why there is a difference in the two trends.
3) Explain why the mean trophic level might increase with the age of an individual fish. (2)
4) Deduce the change in age of captured fish over the period shown. (2)
5) Explain two advantages of humans catching and consuming fish at a lower mean trophic
level. (4)