How do you know that the original finch population and the reintroduced finch population are separate species rather thankist two variation within the same species

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.

loss of sensation to pressure and touch

the dorsal column–medial lemniscus pathway (dcml) (also known as the posterior column-medial lemniscus pathway (pcml)) is a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints.