Lab 7: Trophic Interactions 183 (8) Gambusia has been introduced throughout much

Question

Lab 7: Trophic Interactions 183 (8) Gambusia has been introduced throughout much of the United States. In some locations Gambusia mosquito larvae as you observed in lab. However, in other places, Gambusia behaves as a true feeds on generalist predator. It is not always clear on which trophic level it will start to feed. It can eat mosquito larvae and other tiny aquatic herbivores, as well as invertebrate predators on the native fishes, Use the generalized food web for this system, shown in Figure 7-12, to answer the three herbivores and small questions below. Predatory fish Invertebrate Tiny aquatic herbivores including mosquito larvae A general model of a freshwater food web that includes mosquito larvae Single-celled algae Figure 7-12 (a) When the introduction of Gambusia results in the sudden abundance of algae, called an algal bloom, on which food source is Gambusia likely to be concentrating? (% point) (b) When the introduction of Gambusia results in a sudden increase in the abundance of mosqui on which food source is Gambusia likely to be concentrating? (1 point) (e) How might the introduction of Gambusia lead to the extinction of native fish populations? (1 point)

Explanation / Answer

a. The Gambusia is likely to be eating mainly the tiny aquatic herbivores including mosquito larvae. By eating this group, the Gambusia limit the predation of the larvae on the algae. Consequently lead to an increase in the amount of algae (ie. an algal bloom)

b.If sudden increase in the mosquito population, the Gambusia is most likely to be eating the invertebrate predators that feed on mosquito larvae. By doing this, they allow the mosquito larvae as well as aquatic herbivores to survive and eventually reproduce.

c.The introduction of Gambusia, will decrease the number of prey available to the other fish in the population. The Gambusia and native fish populations will compete with each other. By decreasing one of the groups in the trophic levels will inevitably affect the higher trophic levels as well. By decreasing the number of prey, fish and other predators have no food for a resource. Thereby, leaving them with little to no source of food, which leads to the extinction of native fish populations.

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