Within each species, each population of those organisms will likely be affected differently. And within those populations, each age class, gender, life stage or even morph might have a different impact if they are removed. For instance, saving hatchling turtles on a beach does nearly nothing to their populations- even if you save thousands... if you want to conserve the species it's MUCH more important to save the adults- specifically the breeding females- for there to be any impact. Information like that is only available on a tiny fraction of animals (ie. commercial fish species)- and in a lot of cases we really don't know what will happen.
However, when it comes to amphibians, we do know some things. 30% of amphibians are already threatened with extinction. As soon as you remove an animal from the wild- it is essentially dead.