Shelter is a density-dependent factor because too many individuals in an area is not conducive to living.
Food is a density-dependent factor because when too many individuals compete over food, weaker individuals will have a higher chance to be neglected.
A nutrient is a density-dependent factor because if there are too many plants competing for nutrients in the ground, there will be plants that will have stunted growth.
Floods are NOT a density-dependent factor because natural phenomena are not consumables and happen regardless if there are many individuals or few individuals living in an area.
ANSWER: Floods