It seems that you are assuming that the pressure to survive is lower in places where there is abundant resouces, i.e. water, sunlight, temperature.
Even in a rich and highly diverse environment such as a rainforest the pressure to survive is enormous, yet it doesn't arise due to a lack of resources. The pressure comes from predation and competition for those resources.
Predation pressures favor those individuals with characteristics which give them an advantage in avoiding predation, for example, camouflage or poisonous skin in a frog, or toxins in a plants leaves or fruit.
Competition pressures favor those individuals with characteristics which give them an advantage in obtaining resources in a highly competive environment. For example, the camouflage in a snake to help it catch prey, or the ability to tolerate plant toxins in an insect or herbivore.