If want a direct answer it would be the decrease in mice, but if you want to get technical the decrease in grain spills caused mice to leave so that would be the indirect cause
The answer is light dependent
MRNA is needed in the cells because it directs the synthesis of proteins which is found in the cytoplasm. It is a molecule that carries the message contained within DNA to the ribosome. The Proteins are assembled on the ribosomes using the mRNA nucleotide sequence as a guide.