In the past couple of weeks I have been going out photographing one of my favorite subjects, frogs! Ranomafana has one of the highest amphibian diversities of any national park in the country with only Andasibe offering any competition. Of the 300+ described species of frog in Madagascar all except two are endemic and at least 120 of those have been found in Ranomafana including 8 potential species endemic to the park.
According to the Global Amphibian Assessment (GAA) in 2004, Madagascar ranks as the country with the 12th highest amphibian species richness however it probably should be higher than this as over 200 candidate species have been identified since. This would make the estimated total number of frog species over 500 and would mean Madagascar is home to roughly 4.3% of the world’s amphibians whilst occupying less than 0.5% of the worlds land area.
The largest family of frogs in Madagascar is the Mantellidae which is very diverse and is estimated to have colonised Madagascar around 58 million years ago. Some species of the Mantella genus share convergent features with neotropical dendrobatids (poison dart frogs) with their sharply contrasting aposematic (warning) colouration being associated with toxic skin.
Boophis is another endemic genus of frogs belonging to the family Mantellidae. This genus is known for its brightly coloured eyes which it has been hypothesised act as an anti-predator startle response. The brightly coloured sections usually remain hidden during the day when the frog is resting but suddenly become visible when the frog opens its eyes.
Almost all Malagasy rainforest frogs are either terrestrial and diurnal or arboreal and nocturnal. This is probably because of alternating predation pressure from birds in trees during the day and snakes, tenrecs and other predators on the ground at night.
As with amphibians elsewhere in the world Malagasy frogs face numerous threats. Ongoing habitat destruction has already led to destruction of 90% of the original vegetation and threatens most species to some extent.
There are recent reports of the arrival of Asian common toads (Duttaphrynus melanostictus) in Madagascar, most likely arriving inside shipping containers from Asia. This species’ relative, the cane toad (Rhinella marina), has caused widespread ecological destruction in Australia, and there is now concern that an invasion in Madagascar will have disastrous impacts. One positive aspect is that so far this species has never been recorded as a carrier of the Chytrid fungus, Batrachochytrium dendrobatidis (Bd).
Unlike the majority of the world’s amphibian populations Madagascar has so far escaped the catastrophic declines associated with Bd. However Between 2010 and 2014, Bd was recorded in five different areas of the country, including Ranomafana, although the virulence of the strain is as yet unknown and no die-offs have been reported.