How does an animals level fitness relate to its chance of survival and reproduction

I'm not entirely sure what you mean, but a fit animal is one that is able to out-compete with other animals in its ecosystem. It possesses some kind of advantage, which makes it easier to compete with others for food, water, shelter, and mates. Due to these qualities, the animal is obviously able to live for a good deal of time and have a greater chance of producing viable offspring. 

Very minute and important evidence needs to be collected in order together detail and figure out what had happened