A cycle is made of two primary components: reservoirs and pathways. A reservoir is a holding place, a part of a cycle where something stays temporarily. It will stay in one reservoir before it is moved to another part of the cycle (another reservoir). Pathways are the processes or mechanisms that cause something to move from one reservoir to another.

The images show two species of tree frogs in a particular region. the gray tree frogs are adapted to the trees of the woodlands, while the green tree frogs can survive in woodlands or grasslands. the gray frog was abundant in the woodlands. because of climatic changes, most of the trees in the region died, and the woodlands changed to grasslands. in such a case, the . the gray tree frog is closely related to the green tree frog genetically, but they have different mating calls. this suggests that speciation occurred because of .

Darwin’s studies of finches on the galápagos islands suggest that the finches’ differences in beak structure were most likely directly due to:

Aspecies of butterfly has alleles for wing color that are either blue or orange. when a blue butterfly and an orange butterfly mate, their offspring have wings that are both blue and orange. explain the process through which wing color is expressed.