A biologist studying alpine wildflowers notices that two populations of similar species are able to occupy the same niches. However, species A is mostly found at lower altitudes, while species B is mostly found at higher altitudes. What has most likely caused the realized niches of these two wildflower populations to be smaller than their fundamental niches?
A.
Species B requires fewer resources than species A.
B.
The species are involved in a mutualistic relationship.
C.
Species A is capable of growing faster than species B.
D.
Competition has restricted the ranges of both species.