What restricts the growth of a small population in a favorable environment?

The physiological ability of a species to reproduce is a significant factor that can restrict the growth of a small population even in a favorable environment. This concept relates to the species' reproductive strategies, which include various aspects such as gestation period, frequency of reproduction, and reproductive maturity age.

If a species has a slow reproductive rate or if the physiological conditions are not optimal for reproduction (for example, if individuals are unable to find mates, or if there are health factors affecting reproductive success), the population may not grow as quickly as one would expect despite the surrounding conditions being favorable, such as abundant food, shelter, or other resources.

In contrast, factors like access to nutrients, presence of predators, or environmental pollutants may affect survival and growth potential, but if there are no physiological limitations on reproduction, these factors could lead to different population dynamics rather than a fundamental restriction on growth. Therefore, physiological ability to reproduce directly impacts population expansion and can ultimately limit the size of small populations in the best of environments.