If you build it they will come: Frogs flourish in humanmade ponds

"When we first started this project our expectation was to find fewer frogs but also frogs of poor condition," said Brett Scheffers, lead researcher and assistant professor in the Department of Wildlife Ecology and Conservation at UF/IFAS. "This is because urban wetlands tend to have high levels of chemical run-off, siltation and introduced predatory fish -- conditions that are harmful to the health and survival of frogs."

In the past year almost 4 billion tons of cement was poured over the Earth and at least 25 million kilometres of new roads are anticipated by 2050. This is enough to encircle the Earth more than 600 times. This staggering amount of cement means that an equivalent area of Earth can no longer absorb, filter and clean water.

To make matters worse, as these cities are built many of the existing wetlands that do store water are filled and destroyed. In essence, cities replaced their 'sponges' with cement blocks and discovered a dilemma -- what do they do with all the excess water from run-off?

The answer: create artificial wetlands, often called stormwater ponds, to replace those that were destroyed. But surprisingly human are not the only animals to have benefited from creating wetlands -- frogs have moved into city ponds and have a knack for city living.

Scheffers and his co-author, Cindy Paszkowkdi, from University of Alberta, found that these expectations weren't entirely met. "To our surprise we did find frogs at urban ponds and their offspring were noticeably larger than those in more natural settings," Scheffers said.

But the story isn't entirely positive. The researchers believe the reason for large body size is because there are fewer frogs living in urban ponds compared to natural ponds.

In this case, "more isn't merrier" Paszkowski said. "We observed that fewer tadpoles existed in the urban wetlands and so there was likely less competition." Some frog species lay thousands of eggs at a single time and this means there is a lot of competition for resources. "But instead of splitting their resources a thousand ways, tadpoles in urban wetlands just had a few individuals to compete with," Paszkowski said.

This means that urban frogs may have an advantage by living in areas that tend to be hot and dry -- conditions that are usually not frog-friendly, Scheffers. Nevertheless, for frogs to truly benefit from these benefits gained while living inside the wetlands, they will need somewhere to live once they leave, he said.

Frogs require both a wetland for breeding but also land for living during their adult phase, Scheffers explained. Therefore, without building weltands surrounded by equally good habitat on land, the benefits from large body size will likely be lost, he said.

"The city life of giant frogs offers hope that humans may offset some losses in nature by creating animal-friendly habitats," Scheffers said. "To do this, we suggest that urban parks and recreational areas should try to maximize the amount of natural vegetation in parks and in areas surrounding urban stormwater ponds."