The possible answers are
1)Abiotic factors in their habitat only
2)Abiotic factors in their habitat and surrounding habitats
3)Biotic factors such as possible predators only
4)Both abiotic and biotic factors in their ecosystem
The correct answer is 4.
When a population of an organism is showing a decline, we should investigate both abiotic and biotic factors that could contribute to the decline.
Abiotic factors can be temperature, different level of nutrients etc. and the biotic factors include trophic interactions in the ecosystem.