Limiting factors are environmental factors that limit population sizes in a particular ecosystem.
Food and nutrients are a major limiting factor in ecosystems. If an ecosystem is not able to produce enough food, a percentage of the animals and organisms living in that ecosystem will not survive.
Temperature limits the types of organisms and animals that can survive in a particular ecosystem, and can affect their overall numbers.
Living organisms require water. If water is limited, the ability of an ecosystem to support life is limited.
Natural resources are a limiting factor for most human populations in ecosystems. If natural resources such as wood for cooking and heat are more limited, a particular ecosystem will be less able to support larger populations of humans.
Predators limit the growth of some populations. For example, lions limit the growth of gazelle populations by hunting.