In the hills of north carolina, several different species of wrens live in one large pine tree. this is possible because the wrens
a) must have the resource competition from the other wren species.
b) eat different foods found in and on the tree.
c) have different natural enemies.
d) breed at different times.

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.