Question

zebra mussels were first discovered in north america in the great lakes in 1988. this invasive species eats phytoplankton and other microscopic organisms in fresh water. what would be the most likely effect if zebra mussels are introduced into a local fresh water lake?
the ecosystem would benefit from the increased competition for food and increased diversity.
the ecosystem would be harmed as other phytoplankton - eating organisms would have less to eat.
the zebra mussels would only affect the lake if it already contained another species of mussels.
the zebra mussels would benefit the lake, especially species higher up on the food chain.
question 2(multiple choice worth 4 points)
(04.03 mc)
which of the following best explains how a biotic factor can control the population of a species in an ecosystem?
a sudden drop in temperature may cause many individuals in a population to die.
competition between two species may force one of them to migrate to survive.
a natural disaster may lead to a decline in the reproductive rate of the species main predator.
lack of water during a drought may cause many of the individuals in a population to die.

Explanation:

For the first question: Zebra mussels are invasive and eat phytoplankton. This would reduce the food available for other phytoplankton - eating organisms, harming the ecosystem.
For the second question: Biotic factors are living components. Competition between two species (a biotic interaction) can force one to migrate (control its population). Temperature, natural disasters, and lack of water (drought) are abiotic factors.

Answer:

First question: The ecosystem would be harmed as other phytoplankton - eating organisms would have less to eat.
Second question: Competition between two species may force one of them to migrate to survive.