You are doing biology field work studying two species of lizards on a small volcanic island. although quite hostile to each other when they accidentally meet, the two species usually remain in separate parts of the island. species a seems to live and hunt insects only in the lower grassland part of the island. species b seems to live and hunt only in the upper rocky areas. species a has a short tongue but has longer legs and is a faster runner. species b is short, squat, runs slower, but has a long tongue. you observe species a chasing down some pretty large, fast- moving insects, while species b meanders from rock to rock, using its long tongue to get insects hiding between rocks and in cracks. what principle of ecology do your two lizard species demonstrate?

Allopatric speciation , by geographical  isolation

Explanation:

Allopatric speciation   occurs  when two populations are separated  by geographical barrier from one another.

The differences in their traits as new species, is due to  influence  of  selective pressures in their individual  new environments on the morphological, physiological and behavioural features leading to the formation of a new  species..

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.