Answer:
Changes in abiotic factors, or Lack of available mates after the flood. If one answer had to be chosen, choose "lack of available mates"
Step-by-step explanation:
New competition by displaced animals can not be an answer due to the possibility that there is little to no food left, and floods do not have the ability to displace animals. A decrease in predators would usually lead to a greater population, so this answer does not work. An increase in living space would also lead to an increase in population, so this answer is incorrect. A lack of available mates work as an answer because populations depend on genetic diversity and a large selection of mates in order to grow their population. Changes in abiotic factors can mean a lack of certain resources that could be shelter.