How Does an Ecologist Determine the Presence of an Ecotone

How does an ecologist determine the presence of an ecotone?

A) measure the abundance of plant species over space and abrupt changes in species composition
B) perform controlled crosses among all plant species within a community to determine the extent to which the species are reproductively isolated
C) measure microclimate and soil variables for abrupt changes
D) measure elevation, since many environmental and ecological variables change with elevation