Abiotic: prevent populations from overgrowing, either reducing their reproductive capacity or dying. These abiotic conditions can be very intense, and are considered natural disasters because they can have drastic effects on populations. Some examples include: fires, hurricanes, earthquakes, floods, landslides, ice, among others.
Biotic: there are factors that regulate the size of populations allowing population growth when population density is low and limiting it when it is high; this type is called density-dependent factors.