They questioned whether an increased exposure to UV-B radiation in nature could have an adverse impact on amphibian development. Since the typical method of thymine dimer repair is photoenzymatic repair, the observed amount of DNA damage at any time of day is the net result of damage rates and repair rates. An understanding of this diel cycle of damage and repair is essential for the correct interpretation of relationships between solar irradiance and levels of DNA damage in field samples. Biotic factors, such as jelly capsules around eggs, melanin pigmentation of eggs, and color of larvae and metamorphosed forms, further reduce the effectiveness of UV-B penetration. Most amphibian population declines are probably due to habitat destruction or habitat alteration.
Some declines are probably the result of natural population fluctuations.
Other explanations for the population declines and reductions in range include disease, pollution, atmospheric changes and introduced competitors and predators. UV-B radiation is one agent that may act in conjunction with other stresses to adversely affect amphibian populations.