Tigers and lions are different species because their offspring (the liger) is infertile they are geographically separated in asia and africa the tiger has stripes, the lion does not. they have a type of pre-mating isolation

The answer is their offspring (the liger) is infertile. The male liger is usually sterile and cannot breed. This shows that the two are different species (different species cannot produce viable offsprings). However, the two species share a common ancestor since the female liger (though abnormally large) can still reproduce with the lion or tiger population.   

the organisms are not adapted to live in some communities or habitats.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".