How do factors independent of their density affect the population size?

Factors independent of population density change the number of populations in one direction, regardless of the number of individuals in them. Thus, severe winters reduce the number of populations of poikilothermic animals (snakes, frogs, lizards). The thick layer of ice and the lack of sufficient oxygen under the ice reduce the number of fish populations in winter. Dry summers and autumn, followed by frosty winters, reduce the population of the Colorado potato beetle