African rain frogs – priorities for conservation
Dry and hot savannah environments appear hostile to amphibian species, which are normally associated with damp and cool conditions. However, African rain frogs of the genus Breviceps exhibit amazing and unusual ecological adaptations to deal with the harsh, dry and hot conditions found across Central and South Africa. There are currently 15 recognised species of African rain frog, all of which are entirely terrestrial, globous in form, fossorial and endemic to sub-Saharan Africa. They occupy a range of terrestrial habitats from grassland savannah through open and closed woodland to coastal sand dunes. Very little is known of their ecology since they spend the majority of the year underground, only appearing when it rains. During dry periods, the frogs will use their spade-like feet to burrow backwards into the soil. There they remain, enclosed in a mucous cocoon until the first rains. After this period of aestivation, which may last many months, the frogs appear after rain to feed on a range of invertebrates. Males will call for females and perform amplexus, as in many frog species. Each species has its own unique call, which is used to identify species. The female lays small clutches of eggs, approximately 20-56 in number, in an underground chamber. The larvae hatch and create a white froth, in which they develop into tiny froglets. No additional water is required which is a remarkable adaptation for such dry and harsh conditions.
Unfortunately, like one third of amphibian species, many African rain frog species are under pressure from human activities and are becoming increasingly threatened. In 2003, a new species of rain frog was identified, Bilbo’s Rain Frog (Breviceps bagginsi). As with many of these secretive species, little is known of its behavioural and population ecology. This recently described rain frog occurs in the Kwazulu-Natal midlands of south-eastern South Africa. The area it occupies is declining and it is currently only known from 7 locations. The main threat to this species is the ongoing loss of grassland habitat due to afforestation and fragmentation of habitats due to roads and other human developments. Protection of Bilbo’s Rain Frog, which is classified as Vulnerable by the IUCN, is difficult due to the lack of knowledge of its population size and general ecology. Further research is required to determine these so effective conservation measures may be developed.
Another species of conservation concern is the Desert Rain Frog, Breviceps macrops (Fig. 1). This unusual looking species lives in sand dunes vegetated with low, succulent shrubs and other vegetation adapted to desert conditions in the regions close to Namibia. It is threatened by loss of its habitat as a result of coastal opencast diamond mining, development of roads, increasing pressure from human settlement and changing land-use.
The Giant Rain Frog (B. gibbosus) is declining in many parts of its natural range in the south-western Western Cape Province of South Africa. Unlike the Desert Rain Frog which inhabits sand dunes, this species occupies pine plantations and gardens where it breeds in subterranean nests (Fig. 2). Although it appears to be an adaptable species, much of its habitat is severely reduced and fragmented by agricultural expansion. It may be particularly impacted by the use of pesticides and herbicides which are used widely across the habitats where it occurs. Unfortunately, no research or conservation actions are currently in place for this species. However, it would be important to discover the influence of pollution from pesticides on this and other species in the genus. Further, population estimates are required in order to conduct monitoring, especially in areas of land transformation.
African rain frogs are unique with complex ecology and behaviour, much of which is still poorly understood. Conservation actions for the threatened species within this genus are limited due to this lack of understanding. Further research into the basic ecology of these species will be valuable in prioritising conservation action and will enable protection in an increasingly threatened landscape.
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