The man vs. nature conflict that Rainsford experiences starts from almost the very beginning. In order to battle nature, man must have both physical and mental stamina.
This is first seen in the events unfolding after the inciting incident in which Rainsford falls off the boat in the dark. With little ability to see, Rainsford uses his mental senses to hear gunshots and determine which direction to swim. Then, he exercises his physical stamina in order to swim for what seems like eternity. Although he eventually lands on an island in complete exhaustion, his battle has only just begun. He has no idea what awaits him.
Later, when Zaroff is hunting Rainsford, Rainsford must use his understanding of nature in order to outsmart Zaroff. Readers watch Rainsford use his trail, a couple of traps, and the environment of cliffs and water to elude Zaroff.
In terms of survival and growth, it is as if the more Rainsford fought, the greater his chances for survival became. Man has an uncanny will that seems to get stronger when more stressed. Rainsford experienced this. His senses sharpened and his intellect grew until the moment he completely outsmarted Zaroff and slept restfully in Zaroff's bed.