Usually, when mutations cause major changes in the external appearance of a population, the selection mode is how well that new color blends in with its environment. It it blends well, the animal will be hidden better from predators and survive.
This happens because of the mode of inheritance, which would mask the dominant trait, during a cross. Therefore, this would lead to all offspring not expressing the dominant phenotype
Decline in the global population of amphibians is due to multiple reasons which include:
A moist ecosystem is necessary for amphibians especially for the purpose of their reproduction. The drainage of the wetlands deprives them of their habitat.
Pollutants adversely affects the survival of the gametes, tadpoles or the adult amphibians by acting as toxic agents and inhibiting their normal metabolic function.
Infectious diseases often cause their death resulting their population to decline.
Global climate warming affects their normal metabolic growth and development and hence causes their population to decline.
