Question

In a forest ecosystem, a species of bird was introduced. The birds had few predators, and for a period of time its population rose steadily and then roughly leveled off. Which of the following conclusions provides the best explanation for this phenomenon?
A predator of the birds entered the ecosystem, causing the bird population to level off.
Another species of bird was introduced, and the two species competed for nesting sites and food.
Migration of birds into the ecosystem began to decline, and emigration began to increase.
The ecosystem reached its carrying capacity, and was not able

Answer 1

Can you eliminate any of the choices?

Answer 2

no): im awful in bio

Answer 3

OK, then let's examine each choice. If a predator entered the system, would you expect the bird population to level off, increase, or decrease?

Answer 4

Decrease?

Answer 5

Yes. Similarly, a competitor would most likely cause the bird population to decrease. So that leaves migration/emigration and carrying capacity. There is no reason given that rates of immigration and emigration should change, and that doesn't account for rate of births and deaths, so that can't really explain population leveling off. For the remaining choice, look up logistic growth curve or carrying capacity - logistic growth curves level off when populations reach K, the carrying capacity.

Answer 6

I Am confused what is the answer ?