It seems that the effect is not manifested only on populations, but on individuals as well. Many of the subtropical environments with high moisture levels have significantly different foliages, some being heavily covered with forests while others have almost no wood at all. Johanna Delgado-Acevedo and Carla Restrepo from the University of Puerto Rico have shown recently that two Puerto Rican frog species collected from various locations in the north end of the island differ in size according to the foliage coverage.

X-ray investigations revealed that frogs living in environments with a forest coverage of less than 20 percent are 5 to 10 percent smaller than frog populations living in locations with more than 70 percent foliage coverage. Additionally, frogs living in areas that have been significantly altered by man have a greater chance of growing asymmetrical bodies.

"It has been reported before that amphibian body size decreases when the animals are exposed to large numbers of predators. But discovering this in response to human environmental disruption is really surprising", says Delgado-Acevedo.

The shrinking process is triggered by the lack of resources in the deforested environments, as smaller frogs have a much higher chance of success. Furthermore, the lack of the required foliage exposes frogs to dangers that are not regularly encountered, thus affecting them in the early development. However, it is not yet certain whether or not the decrease in the size of some frog populations is a good thing or a bad one.

"Being smaller has some advantages, but these species are not small because of natural causes, they are small in response to habitat disturbance, which we think is a bad thing. We think that body size combined with measurements of symmetrical traits could be used as a tool to evaluate the health of natural populations", says Delgado-Acevedo.

"They have uncovered some interesting trends that need further investigation. What I really wonder is whether pollutants, pathogens, or competition are causing the morphological changes in the fragmented forest dwelling frogs", says Rachel Santymire from the Lincoln Park Zoo in Chicago.