Dangers and unpredictable changes of living conditions lead to fear and stress in wild animals. In this paper, I will present adaptations of animals to such situations and their impact on the individual, the population, and even the entire ecosystem. These adaptations include evolutionarily conserved physiological response and behavioral changes. The main indicators of stress in animals are levels of glucocorticoids in the body and heart rate variability caused by the release of catecholamines (adrenaline and noradrenaline). These are also the main mediators of stress that enable the body better reaction and recovery. I will discuss the reactions of wild animals to dangerous situations with an emphasis on lack of food and predation. Marine iguanas in the Galapagos and emperor penguins will serve as examples of dealing with food shortages. Predation is the relationship in which the vast majority of animals in the wild find themselves, either in the role of predator, prey, or both. A food web often includes all animals in a certain area, and the role of the apex predator in such ecosystem is extremely important, as will be shown by the example of wolves impact on the environment in Yellowstone National Park. The growing impact of humans on the environment causes the appearance of chronic stress in wild animals, which is why research into the impact of stress on animals is becoming more and more important every day