Frog use of urban and agricultural landscapes in lowland Vietnam

Background/Question/Methods

Most natural ecosystems are decreasing on the landscape while agricultural and urban land-use types are rapidly growing; these novel ecosystems have the potential to destroy existing habitat or to provide landscapes where wildlife can coexist with humans. Human-dominated landscapes are disproportionately impacting lowland wetlands where many amphibians breed because people tend to settle in flat areas with fresh water. These impacts are especially acute in understudied Southeast Asia where high biodiversity is paired with rapid population growth. This study represents the first comprehensive study of the impact of urbanization on amphibians in Southeast Asia. We surveyed amphibians in water bodies in and around the three largest cities in Vietnam and examined habitat features associated with successful breeding. For each city we surveyed three land-use types: urban, suburban, and rural. The last type was comprised almost exclusively by rice paddies as there are virtually no remaining pristine lowland wetlands in the country. For the urban and suburban water bodies we collected information on the following habitat variables to determine which factors best explain coexistence with humans: size of water body, edge type (natural vs. constructed), presence of aquatic vegetation, edge slope, presence of shallows, and amount of surrounding upland habitat.

Results/Conclusions

We found a total of thirteen species of frogs breeding in and around the largest cities in Vietnam. There were differences in species compositions among cities, but not among land-use types: all thirteen species were found breeding in rice paddies, suburban, and urban areas. We did find trends of decreasing pond occupancy and average species richness per water body with increasing urbanization level. The habitat variables most associated with species richness in cities were: natural edges, amount of upland habitat, and presence of shallows. For water bodies with constructed edges, aquatic vegetation increased frog species richness, even when plants were potted ornamentals. This study demonstrates that a variety of frogs breed in Vietnamese cities, and that they will likely benefit from: maintenance of natural edges where possible, adding aquatic vegetation when a constructed edge is desired, providing shallow areas to allow tadpoles to bask, and retaining and connecting upland habitat as much as possible. In general this study is inconsistent with current urban ecology theories describing urban avoiders and exploiters. This is likely because the surrounding matrix is already altered, and because these amphibians have specific aquatic habitat needs, do not utilize anthropogenic food, and have relatively low vagilities.