Answer:
Limiting factor.
Step-by-step explanation:
If the resource is necessary to the survival of a population and is needed to sustain it and allow the population to grow, it is a limiting factor. Simply put, limiting factors are defined as anything that constrains a population's size and slows or stops it from growing. Over use of resources can cause the species that need it to survive to die out and possibly become extinct if they can only be found in that ecosystem.
It is not a Biotic factor because biotic factors are described as a living organism that shapes its environment. These can include plants like algae.
An abiotic factor is a non-living part of an ecosystem that shapes its environment.
Both of these are defined as factors in an ecosystem and are important. HOWEVER, the question is asking about resources in an ecosystem. Therefore Limiting factor is correct.