Frogs: The Animal Answer Guide

5. Frog Ecology

47 Which geographic regions have the most species of frogs? With few exceptions, frogs and toads are found worldwide, and at least one species lives in nearly every region and frogs live on all but one continent . Most species live in the Tropics, and none occur in Antarctica, Greenland, or Iceland. Because they cannot tolerate salt water, no frogs are found in marine habitats except for a species that lives close to marine habitats . This is the crab-eating frog (Fejervarya cancrivora) of Malaysia that lives near and lays its eggs in brackish water. In Temperate Zone regions, the numbers of frog species are highest in warm, humid areas, such as the southeastern United States, and are lower in arid regions, at high altitudes, and at high latitudes where temperatures are colder. What types of frogs live in rain forests? Tropical rain forests have more species of frogs than any other habitat in the world, and many of them are arboreal. Among the most common families found in rain forests are the Hylidae, Leptodactylidae, and Centrolenidae (glass frogs) in the Western Hemisphere and Australia and the Rhacophoridae in Asia and Africa. Some rain forest frogs are burrowing species, such as narrowmouth toads (genus Gastrophryne; family Microhylidae ) and species that live in the leaf litter. The Dendrobatidae (poison frogs) have approximately 180 species in the American Tropics. Toads (family Bufonidae) and true frogs (family Ranidae) occur in many tropical areas. Glass frogs and poison frogs are endemic to rain forests, but most Chapter 5 Frog Ecology 48 Frogs: The Animal Answer Guide other groups have species found in the Temperate Zones. Other frog families found entirely or almost exclusively in rain forests are the Allophrynidae with one species, Ruthven’s frog (Allophryne ruthveni), and Pseudidae in South America. What types of frogs live in deserts? Many frogs have adapted to living in dry areas and have different mechanisms for doing so. Some, such as the American spadefoot toads (genera Spea and Scaphiopus), live in arid or true desert conditions, stay underground for much of the year, and only emerge in large numbers during heavy rains for breeding. Thus, they survive the harsh conditions by coming to the surface only opportunistically and for relatively short periods. Spadefoots have been documented to remain underground for months or more than a year and possibly can do so for several years. Many frog species deal with drought or arid conditions by going underground and forming a cocoon that covers almost the entire body surface, including mouth, eyes, and cloaca. Only the nostril openings are not covered, allowing the animal to breathe while surrounded by the cocoon. The cocoon consists of an accumulation of multiple layers of single-cell-thick sheets of outer epidermal cells produced when the animal is exposed to dry conditions. Cocoons are common in many Australian desert species. Some frogs that live in deserts have special characteristics such as the ability to store water. The water-holding frog (Cyclorana platycephala; famSome frogs, such as the Southeast Asian toad (Bufo melanostictus), have extensive geographic ranges. The species is found from eastern China through India to Sri Lanka. Courtesy Cris Hagen 49 Frog Ecology ily Hylidae) and the desert spadefoot toad (Notaden nichollsi; family Myobatrachidae ) of Australia burrow as much as 3 feet beneath the ground during dry periods but are able to store enough water in their urinary bladder to increase their body weight by 50 percent. The aboriginal people of Australia have even been reported to capture water-holding frogs during periods of drought and squeeze them until they release water they can drink, similar to how a desert traveler might rely on a canteen. Toads in the family Bufonidae that live in the desert are able to combat dehydration by having a mostly impermeable skin so that water can be retained and not lost through the skin. These abilities allow these species to go for long periods without requiring water from external sources. Another factor that can affect the success of frogs living in deserts is the frequency and limited number of available breeding sites, which can result in a competitive advantage of one species over another. Gage H. Dayton and Lee A. Fitzgerald studied four species of desert toads at Big Bend National Park, Texas, and found that Couch’s spadefoot (Scaphiopus couchii) was dominant over three other species (western narrowmouth toad, Gastrophryne olivacea; Texas toad, Bufo speciosus...