Wildlife can be scarce in many large, densely populated cities. A few plants and animals can be found in these areas. For example, rats, mice, pigeons, cockroaches, and other insects are common in cities. Trees can grow by sidewalks or in local parks. Some cities even have small populations of coyotes within city limits.

Do you think these cities meet the definition of an ecosystem? Explain your reasoning.

the answer for PLATO is:

"Yes, because these organisms likely depend on each other for survival. For example, plants and grasses can make food for insects and other small animals, such as rats. Carnivores can eat the small animals and obtain energy from them. Humans are also living things, sk they contribute to the ecosystems of these organisms. They can provide food for rats and insects. Humans can also water the plants"

Paraphrase that as you will.

Hypothesis: the smell of decomposing apples may attract fruit flies more than the smell of decomposing bananas.

Experiment: two separated fruit fly populations with a sample size statistically significant (N: 500 or higher) must be grown in clean boxes. Subsequently, the fruit fly populations should be simultaneously released in a tube that connects the two boxes with other two boxes containing: -Box 1: apples in decomposition and -Box 2: bananas in decomposition. After one hour, the fruit boxes must be simultaneously closed and the fruit flies must be counted. Finally, it is necessary to apply a statistical index in order to calculate the significance between groups (i.e., fruit flies closed in both fruit boxes).

Positive control: fruit flies released and counted in boxes containing apples and bananas in normal conditions.  

Negative control: fruit flies released and counted in clean boxes.