The complementary strand of the DNA strand AATTGC would be UUAACG.
The complementary nucleotide for Guanine [G] will be Cytosine [C] and applies to both DNA and RNA. But the complementary nucleotide for Adenine [A] will be Thymine [T] in DNA and Uracil [U] in RNA.
A codon is a triplet of nucleotides, so it could be any three nucleotides in the strand. Example: AAT, ATT, TTG or TGC.
The Acacia tree's and other small plants the elephants eat would begin to grow in terms of population. Similar to if the elaphants grew in population, the Acacia tree's would decrease in population.