Download 1. Producers = Phytoplankton, Seaweed

Pond Water Webs: Worksheet Answers
1. Producers = phytoplankton, seaweed
2. Carnivore = fish, gull, lobster, prawn, crab, whelk
Omnivore = mussels
Herbivore = zooplankton, limpets
3. (a) We would expect the limpet population to decrease since the organisms that eat mussels would have to eat
more limpets.
(b) We would expect the zooplankton population to increase, since the increased fish population would cause a
decrease in the prawn population.
(c) The whelk population would likely increase since there would be more mussels and limpets available due to
the decrease in crabs. However, the gulls and lobsters may eat more whelk than before because of the decrease
in crabs, resulting in a decrease of the whelk population.
4. Various Answers (depends on the food chains your group made)
5. Various Answers (depends on the food web your group made)
6. Various Answers (depends on the food web your group made) …but here are some basic ideas:
(a) If your only producers were aquatic plants, then the loss of aquatic plants would have a devastating affect on
your food web; without a producer the entire food web would eventually die (or need to relocate to a region
with producers). If your food web had other producers then their populations would decrease due to the
increased predation upon them. There may also be further impacts on the rest of the food chain (specifically
decreases in population size) because the remaining producers may not be able to provide enough food to
support the entire food chain.
In general, losing a producer will greatly harm the rest of the organisms in
the food chain.
(b) Again it depends on the organisms you included in your food web, but in general the population size of the
prey of the blue heron will increase due to a lack of predation, which will then result in a decrease in the
population size of the organisms that the blue heron’s prey eat. For example, for the food chain below we
would see an increase in the fish population, a decrease in the prawn population, an increase in the
zooplankton population and a decrease in the phytoplankton population.
We may also see an increase in
the population size of the blue heron’s competitors due to the lack of competition.
phytoplankton

zooplankton

prawn

fish

blue heron
(c) In general the introduction of Asian carp into your food web would cause a decrease in the fish population
because many of the juvenile fish would not be able to get enough food and therefore die. In extreme
cases the introduction of Asian carp could result in the extinction of fish populations. In either case (a
decrease in the fish population or extinction) other parts of the food web will be affected. In general, the
fish predator populations will decrease, and the fish prey populations would increase. For example in the
food chain below the blue heron population would decrease, the fish population would decrease (or go
extinct), the prawn population would increase, the zooplankton population would decrease, and the
phytoplankton population would increase.
Or alternatively, you could argue that the decrease or extinction
of fish populations would have little impact on the food web because the Asian carp would replace the role
that the other fish population had in the food web.
phytoplankton

zooplankton

prawn

fish

blue heron