A deer eats certain plants, but if there is variation, it may like certain plants more than others. The deer may be causing extinction to those certain plants because of eating to much of it. The variation effects the survival of a species because of its unique characteristics called adaptations within the species. If there was a change in an environment, you have a greater chance of survival. Take the deer example. If they had stayed the same, all of that species could have survived because the deer did not eat it, or all of it could have not survived if a new organism changed the environment and ate it. However, with variation only a few of that species may die.