Answer: emigration or increase in death rate
Step-by-step explanation:
Many factors can modify the animal population in a specific area.
Amphibian populations are affected mostly by changes in temperatures, altered dry season rainfall, and modified leaf litter depth.
Considering the options provided, only emigration and an increase in death rate could explain the decrease of the frog population.
Immigration and an increased birth rate would result in the population growing, not decreasing.