Identify the interactions as positive, negative, or both.
a mudslide wipes out the side of a thriving hill:
a volcano erupts, covering the nearby land with lava:
a forest is rapidly growing new plant life:
humans remove wolves from a national park to protect surrounding homes:
a dam is built in the middle of a river ecosystem to supply water to a nearby town:

Option (4)

Explanation:

Positive aspects of dam-

Dams are the barriers that obstructs the flow of water. This dams are natural as well as man-made. The dams are often constructed across a river at its narrow valley. It is widely used to produce electricity that is required by humans at various places. In addition to this, it also stores water in the reservoirs in order to supply water and also to control flood.

Negative aspects of dam-

A dam also has some negative impacts such as the river ecosystem is affected. The fishes in the river dies. Also, during the storage of water, high amount of water is evaporated into the atmosphere. It also affects the soil and vegetation cover in the nearby areas.

Thus, a dam constructing in the middle of a river ecosystem in order to supply water to nearby town describes both positive as well as negative interactions.

Hence, the correct answer is option (4).

Other symbiotic interactions, called commensalism (+ 0), are beneficial for one organism, but do not affect the other in a positive or a negative way.