The amount of food available to organisms in an ecosystem is affected by biotic (living) and abiotic (nonliving) factors.
An ecosystem is a self supporting unit which is composed of living and nonliving parts. The living parts are called biotic factors while the nonliving parts are called the abiotic factors.
A heron is a fish eating bird. This means that its food depends on the availability of fish population in water.
The population of fish in water may decrease when there is an unprecedented increase in the heron population. This means that there will be fewer prey available to the herons thereby decreasing the food caught by each heron. This is a biotic factor.
On the other hand, if the amount of dissolved oxygen in the water drops due to pollution, many fishes in the water body will either migrate or die. This is an example of an abiotic factor which decreases the amount of food caught by a heron.
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