Question

Which group of organisms is an example of a population?

Answer 1

> leopard frogs in a stream.
Population means that the number of people or animals in a particular place.

The first one matches. 
The 2nd one is not specific. There is a lot of birds and a lot of space in Colorado.
The 3rd one is like the second one. Again there is a lot of types of reptiles in the Sahara and Sahara is BIG!!!
The 4th one is close, except int's not an animal.

Get it?

Answer 2

Answer: > leopard frogs in a stream

Explanation:

A population can be defined as members of the same species which exhibit similar morphological characteristics. These members are capable of inbreeding among themselves and producing viable fertile offsprings.

Among the given examples, leopard frogs in a stream is the correct option because the leopard frogs represents the members of the same species which can be taken as an example of a population.