Amphibians are ectothermic vertebrates that, in the adult stage, breathe through their porous skin and lungs.
The only amphibians in southern Africa fall under the order Anura (meaning ‘without tail’). Characteristics of this order are:
- No tail;
- breathes through the skin and lungs;
- legs are designed for jumping;
- webbed/partially webbed feet;
- no toe nails;
- three chambered heart;
- smooth , soft skin with glands below the epidermis to keep the skin moist;
- poison glands in the dermal layer.
Feeding And Ecology
Frogs belong to the order Anura. They are herbivores in the tadpole stage and as adults they become carnivorous vertebrates. Most frogs spend a portion of their lives in water whilst others remain totally independent of the aquatic life. This requires a total change in the structure of the stomach and mouthparts before the froglet can leave the water.
Most frogs feed on invertebrates but reptiles, fledgling birds and rodents are also taken. Cannibalism is common. Large prey is ingested through biting and swallowing. Smaller prey is caught by flicking out the short sticky tongue and retrieving it into the mouth. Prey is swallowed whole.
Although frogs are predators, they are a large part of the diet of many predatory species especially snakes and birds. They are primary consumers as tadpoles and secondary consumers as frogs.
The banded rubber frog produces a lethal toxin that affects the heart. Extended handling of one of these frogs that has exuded the toxin can cause nasty symptoms. The aposematic colouration is a warning to all predators not to eat. Any animal eating the banded rubber frog will result in death.
Our typical toads (genus Amietophrynus) produce a toxin from the parotid glands on the neck that contains epinephrine. The toxin is strong enough to kill small animals and cause severe symptoms in larger animals. Most animals that try eat toads spit out the foul tasting amphibian immediately and never try again! Some animals however learn that it is safe to eat only the rear end of these toads.
Frogs, such as the painted reed frog, have bright red skin on the hidden parts of the legs. When sitting, these frogs are camouflaged; if they are disturbed will leap to another perch flashing bright red legs…
Despite the Red Data listings that relate to South Africa the conservation status for all below species is common/abundant.
Giant Bullfrog (L3 Family Pyxicephalidae: African Common Frog Family)
Red data listing: near threatened
- These massive frogs can grow to more than 1 kg. As the name implies, the giant bull frog is larger than the African bull frog.
- L3 (The African bullfrog has broken bands on the upper jaw and a white, elliptic crescent on the tympanic membrane. These features are diagnostic when separating these two species;
- the dorsal area is normally an olive green and the flanks of the adult are yellow;
- raised ridges run down the length of the back.
Habitat and distribution
- Bullfrogs are widely distributed: occurring across most of southern Africa but absent from the coast and true desert areas;
- they favour grassland and savanna areas;
- they breed in temporary pools or pans;
- bullfrogs prefer to live in areas with sandy soils.
- bullfrogs breed after the first heavy summer rains;
- the call is a deep and long WHOOOOP made by both the giant bullfrog and the African bullfrog;
- males display in a lek and attack one another with open jaws. Occasionally the large teeth-like structures odontoids are used to inflict wounds.
- ominant males will mate with females and eggs hatch within 2 day after laying;
- depending on the temperature, it takes 18-33 days for tadpoles to metamorphose into froglets;
- bullfrogs are unique amongst the frogs in southern Africa in providing parental care. If the temporary pool the tadpoles are in begins to dry up, the male will dig a trench to a deeper pool (if one is available);
- it takes less than five weeks from an egg being laid to a metamorphosed bullfrog;
- bullfrogs will bury themselves up to 1m underground after breeding;
- they will release a thick slimy substance from their skin when safely buried. This substance hardens into a cocoon-like parchment that is waterproof preventing a loss of water through the skin. Only the nostrils remain open;
- the frog goes into a state of torpor where breathing and the heart rate drop to almost nothing. The bull frog may remain like this for several years until the next suitably heavy rains.
- camouflage: their olive green back blends with the surrounding grass;
- posture: when threatened, the adult opens its mouth in a threatening gesture and the body inflated to appear larger;
- the tadpoles live in temporary water where there are fewer aquatic predators than there are in permanent water;
- remaining underground in a cocoon until the next heavy rains, the adults
- reduce the chances of predation and
- are less vulnerable to drought conditions