Answer :

1. Climate and natural disasters. There are certain seasons in each year that resources and the environment aren’t friendly or rather callous with living organisms, climates that include winter, most especially. Or natural disasters like storms, hurricanes, earthquakes and tidal waves that prohibit living organism to limit its food intake and due to scarcity.
2.
 Obtaining the resource or food. It may be very rare or in certain occasion only for the organism to acquire such exquisite resource to become its food.