Answer;
A) a decrease in rainfall
Step-by-step explanation;
-An ecosystem depends on the interactions of the living and nonliving elements in the system. The living things in an ecosystem are called biotic factors. Living things include plants, animals, bacteria, fungi and more.
-The non living parts of an ecosystem are called abiotic factors. In an ecosystem some abiotic factors are sunlight, temperature atmospheric gases water and soil.
-A major difference between biotic and abiotic factors is that a change in any of the abiotic factors impacts the biotic factors, but changes in the biotic factors don't necessarily result in changes to the abiotic factors. For example, a decrease in rainfall would affect the mice population of an area by making it decrease.